CA2219103A1 - Method and apparatus for automatic shock electrode enabling - Google Patents
Method and apparatus for automatic shock electrode enabling Download PDFInfo
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- CA2219103A1 CA2219103A1 CA002219103A CA2219103A CA2219103A1 CA 2219103 A1 CA2219103 A1 CA 2219103A1 CA 002219103 A CA002219103 A CA 002219103A CA 2219103 A CA2219103 A CA 2219103A CA 2219103 A1 CA2219103 A1 CA 2219103A1
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/362—Heart stimulators
- A61N1/37—Monitoring; Protecting
- A61N1/3706—Pacemaker parameters
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
- A61N1/39—Heart defibrillators
- A61N1/3925—Monitoring; Protecting
- A61N1/3931—Protecting, e.g. back-up systems
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/362—Heart stimulators
- A61N1/37—Monitoring; Protecting
- A61N1/3718—Monitoring of or protection against external electromagnetic fields or currents
Abstract
Methods, circuits and devices useful for maximizing the likelihood of successful defibrillation or cardioversion using an automatic implantable cardioverter/defibrillator ("AICD") system are provided which are capable of monitoring the impedance of AICDs for purposes of detecting lead malfunctions. After detection of a lead malfunction, the methods, circuits and devices are capable of connecting or disconnecting leads and electrodes to maximize the likelihood of effective cardioversion and defibrillation.
Description
, CA 02219103 1997-10-23 27~ PCT
-1- ' ~
Description Apparatus for Automatic Shock Electrode Enablin~
Technical Field The present invention relates to an apparatus for assuring that an automatic implantable cardioverter/defibrillator ("AICD") provides the necessary shock energy through a preselected combination of electrodes.
Background Art AICDs deliver shock energy through a combination of electrodes. For example, AICD
housings (cans) have been developed which allow an external programmer to enable or disabl.e these electrodes. At implant, the physician may select a combination of electrodes which produces the lowest defibrillation threshold (DFT) or which is the most expedient and least traumatic to the patient. If after implant, one of the electrodes breaks, dislodges or shows a rise in impedance, the likelihood of successful defibrillation or cardioversion procedure may decrease significantly.
In prior art approaches, in order to restore the likelihood of defibrillation orcardioversion, the physician had to diagnose the electrode impedance problem and either implant a new electrode or externally reprogram the AICD to use the rem:lining functional electrodes.
The delay between onset of the impedance problem and the corrective action posed a severe hazard to the patient if arrhythmias occurred during this period. Such a situation might occu:r, for example, in the use of a device such as that described in Kuehn, U.S. Patent 5,201,865.
Although Kuehn describes a pacemaker/cardioverter/defibrillator with impedance sensing to detect lead defects, there is no provision whereby the device would select a set of electrodes from amoung a plurality of electrodes to m~inr~in an adequate field to defibrillate the heart.
Lead related problems are not uncommon in AICDs. See, Magney et al., PACE 16:445-457 (1993). These failures may arise due to anatomical m~r.h~ni~m~ such as failure of centra.l venous catheters adjacent to the sterno-clavicular joint. Problems with AICD leads, such as lead fracture or loose connections, may result in sudden death if ventricular arrhythmias are not detected or not terminated by the AICD. See, Feldman et al., "I-lentific:~tit n of An Implantable Defibrillator Lead Fracture With a New Holter System," PACE 16:1342-1344 (1993).In one study, one hundred and fourteen patients undergoing successful implantation of an AICD were monitored. See, "Lead-Related Morbidity in Patients With Cardioverder-Defibrillators Utilizing Non-Thoracotomy Lead Systems, " Nallamothu, N. et al., PACE Vol. 17 No. 4, Part 2, page 761 (NASPE 1994 Abstracts). Twenty-two patients (19%) experienced after implantation lead-associated events which led to re-operation, re-hospitalization, andior~
ITM-271PCT '~
.
-1- ' ~
Description Apparatus for Automatic Shock Electrode Enablin~
Technical Field The present invention relates to an apparatus for assuring that an automatic implantable cardioverter/defibrillator ("AICD") provides the necessary shock energy through a preselected combination of electrodes.
Background Art AICDs deliver shock energy through a combination of electrodes. For example, AICD
housings (cans) have been developed which allow an external programmer to enable or disabl.e these electrodes. At implant, the physician may select a combination of electrodes which produces the lowest defibrillation threshold (DFT) or which is the most expedient and least traumatic to the patient. If after implant, one of the electrodes breaks, dislodges or shows a rise in impedance, the likelihood of successful defibrillation or cardioversion procedure may decrease significantly.
In prior art approaches, in order to restore the likelihood of defibrillation orcardioversion, the physician had to diagnose the electrode impedance problem and either implant a new electrode or externally reprogram the AICD to use the rem:lining functional electrodes.
The delay between onset of the impedance problem and the corrective action posed a severe hazard to the patient if arrhythmias occurred during this period. Such a situation might occu:r, for example, in the use of a device such as that described in Kuehn, U.S. Patent 5,201,865.
Although Kuehn describes a pacemaker/cardioverter/defibrillator with impedance sensing to detect lead defects, there is no provision whereby the device would select a set of electrodes from amoung a plurality of electrodes to m~inr~in an adequate field to defibrillate the heart.
Lead related problems are not uncommon in AICDs. See, Magney et al., PACE 16:445-457 (1993). These failures may arise due to anatomical m~r.h~ni~m~ such as failure of centra.l venous catheters adjacent to the sterno-clavicular joint. Problems with AICD leads, such as lead fracture or loose connections, may result in sudden death if ventricular arrhythmias are not detected or not terminated by the AICD. See, Feldman et al., "I-lentific:~tit n of An Implantable Defibrillator Lead Fracture With a New Holter System," PACE 16:1342-1344 (1993).In one study, one hundred and fourteen patients undergoing successful implantation of an AICD were monitored. See, "Lead-Related Morbidity in Patients With Cardioverder-Defibrillators Utilizing Non-Thoracotomy Lead Systems, " Nallamothu, N. et al., PACE Vol. 17 No. 4, Part 2, page 761 (NASPE 1994 Abstracts). Twenty-two patients (19%) experienced after implantation lead-associated events which led to re-operation, re-hospitalization, andior~
ITM-271PCT '~
.
prolongation of implant hospital stay for alteration of anti-arrkythmic drug therapy~ The causation of the lead associated events which led to the alternative therapies included lead dislodgement, lead fracture/malfunction, unacceptable DFT in the followup, and subclavian thrombosis The study proposed that the calculated incident of failure might be an underestimate, as some devices do not yield information on the lead integrity in routine followup and it is not routine to repeat defibrillation efficacy testing on a long term basis~ See also, Troop, P~J., "Implantable Cardioverters and Defibrillators," in Current Problems in Cardiology. Yearbook Medical Publishers, pp~ 673-815 (1989)~
It is known that monitoring impedance of AICD systems is one means for ~etPcting lead failures See, "Troubleshooting Implantable Cardioverter Defibrillator System Malfunctions:
The Role of Impedance Measurements," r-r~d-l~(i, L et ah, ~, Vol 17 1456-1461 (199~,).
This study found that external high impedance measurements may be used to troubleshoot A[CD
system malfunctions due to: lead fractures, faulty adapter connections, and loose set screw connections However, prior art approaches such as the ones suggested by this study require relatively immediate re-operation to replace the damaged lead.
Routine posterior-anterior and lateral chest x-rays can identify lead fractures prior to any clinical observation However, other of the cases demonstrate that not all lead or connector problems can be detected by routine chest x-rays.
Certain implantable pacing devices possess a mt-~h:~ni~m for switching from a bipolar lead configuration to a unipolar lead configuration when a fault is detected in the bipolar leacl ring See, U~S. Patent No. 4,964,407. In certain of these devices, a series of high impedance test signals are actively generated (not merely sensed) by a microprocessor in a p~cem~3ker to determine whether a bipolar or unipolar lead is attached. If no operational bipolar lead is detected, the programming of the p~Prn~k~r is altered to a unipolar pacing mode~ However, similar systems are not available for AICDs.
Methods, circuits and devices are needed which are capable of monitoring the impedance of AICDs for purposes of detecting lead malfunctions Such systems will avoid the tliMelllti( s associated with prior art approaches which require frequent x-raying, inefficient discovery of' lead malfunctions using x-raying, or other external monitoring devices. Methods, circuits and de vices are also needed which, after det~-ction of a lead malfunction, are capable of connecting or disconnecting leads and electrodes to m~ximi7P the likelihood of effective cardioversion and defibrillation. Preferably, such systems will be fully implantable and will not require imme~ tP
invasive surgical techniques or frequent x-irradiation in order to correct the problems.
l~isclosure of rnvention Systems useful for m~ximi7:ing the likelihood of successful defibrillation or cardioversion .
using an automatic implantable cardioverter/defibrillator system are provided by the present ~E~O S~
ITM-271PCT ,,, , -2a --invention. The system is capable of monitoring the impedance of AICDs for purposes of detecting lead malfunctions. After detection of a lead malfunction, the system of the presemt invention is capable of connecting or disconnecting leads and electrodes to m~ximi7e the ~ S~
W 096/37258 PCTrUS96/07770 likelihood of effective cardioversion and defibrillation. These systems are fully implantable and do not require immediate invasive surgical techniques or frequent x-irr~ tir/n.
Various methodologies may be used to implement the present invention. If a method i~i desired which can simply connect an electrode in response to a too-high impedance measurement, then the impedance of the AICD system is measured initially. This may occur, for example, during a first shock phase. The measured impedance then is compared to a high impedance threshold value. If the measured inlL edance exceeds the threshold value, then at least one electrode is electrically connected to the system prior to the next .~hocking cycle.
Likewise, if a method is desired which can simply electrically disconnect an electrode in response to a too-low impedance measurement, then the impefl~nre of the AICD system is initially measured, for example, during a first shock phase. The measured impedance is then compared to a low impedance threshold. Where the ~..easù-ed impedance drops below the lower threshold, at least one electrode is electrically disconnected from the system, as for example prior to the next shocking cycle.
A combined method for m~ximi7ing likelihood of snccr~fill defibrillation or cardioversion using an ~lf~ . implantable cardioverter/defibrillator system, will be preferred in certain in~t~nres. Such a method will comprise a two-stage impedance co..~a.ibon.
First, an impedance measu,cment of the system, as for example resulting from a first shock is taken. This value is co---~al~d to a high impedance threshold. Where the cu~ ibon demol~L.dles that the impedance meabll,c.. ~nl is above the upper threshold, one or more electrode is activated into the grid, as for example prior to the next shock. If this occurs, then the method calls for making a second impedance culll~ualibon of the system.
If the impedance meabulc---~--L is below the upper irnpedance threshold, then the method calls for comparing that impedance meabu-c~ --l to the lower impedance threshold. Where the impedance measurement is below the lower impedance threshold, one or more electrodes are discnnnrctt~.l from the system grid, as for example prior to the next shock in the cycle.
If the impedance ...easu-ement is neither above the upper limit nor below the lower limit, the method simply allows the next shock to occur and repeats itself. In this manner, the two-stage method coll~ lly monitors and adjusts for disc~c~al1cies in the system impedance.
,~ 30 There are a number of reasons why an AICD system will exhibit impedance ~lisclel)allcies above or below pre-set thresholds. Among them are lead dislodgement and lead malfunction. Lead dislodgement may occur where the lead shifts due to loss of anchoring in the tissue. In some in~t~nrec, the dislodgement is temporary and the lead will subsequently return to a position capable of gc:,~e,~li,,g the proper impedance. In other cases, the dislodgement is perm~nrnt Other lead m~l~lnrtions include lead fracture, or loose set screws at the point of ~tt~hm~nt of the electrode tip to the lead. It is also common imm~di~te]y post-transpl~nt~tiQn o~
~TM-271PCT ''~
: ': ; ' '"
4 ~ ~ ,t an AICD to detect impedance discrepancies due to acute phase tissue stabilization. This is a temporary condition which usually corrects itself with passage of time and infiltration of tissue into the lead and tip.
The invention may be used with electrodes implanted in a variety of locations surrounding the heart. Typically, such an electrode will include one implanted in or near the superior vena cava or one implanted in or near the patient's coronary sinus. Another typical location for an electrode is in or near the right ventricle. Auxiliary electrodes may also be present such as those which are implanted subcutaneously.
In many modern AICDs, another electrode available for selection is the irnplantable cardioverter/defibrillator can itself. These are typically referred to as "hot" cans. Such can electrodes are routinely implanted pectorally. However, they may also be irnplanted abdominally.
Thus, the invention monitors shock electrode impedance after each defibrillation or cardioversion shock. If the impedance exceeds a preset threshold, this invention will enable a preset combination of electrodes to be int~ (led in the subsequent shocks in an attempt to reduce the shock electrode impedance. This will provide increased safety for the patient in the case of shock electrode malfunction. For example, a physician may implant an RV-to-SVC+can sy,tem but choose to disable the can electrode due to patient discomfort during low energy cardiove:rsion shock. If at a later time, the SVC lead were to break, in one embodiment of this invention, i:t would be possible to detect the increase in impedance and include the can electrode in all subsequent shocks.
One method of calculating the impedance is by using the formula:
t R= V
C ln ( V ) where R=impedance; t=duration of delivered shock; Vj=pre-shock voltage reading; Vf=post-shock voltage reading; and C=capacitance.
Using this formula, an initial reading (Vj) is taken at the high voltage capacitor of the AICD just prior to delivery of the high voltage shock (typically 600 or more volts). After the delivery of a shock of duration (t) typically of approximately 10 milliseconds, a second reading (Vf)iS taken at the same capacitor. The capacitance (C) of the high voltage capacitor is a constant for each such device. The irnpedance (R) is then c~ d by taking the natural log of the ratio of the initial voltage reading to the final voltage reading, multiplying the result by the capacitance constant for the device, and dividing the result into the value for the duration of the delivered shock. While this is a means of measuring and calculating the system impedance found .~ ., r) CA 02219103 1997-10-23 rTM-271PCT . ;,' .. '.
by the inventor to be applicable to many types of AICD systems, it is but one such method.
Other methods for measuring and calculating system impedance will be known to those of skill in the art and will work equally well.
The invention may measure impedance at a capacitor prior to shock and following shock.
it a preferred mode, the measurement of impedance will be accomplished at the high voltage (HV) capacitor of the AICD. Again, while this position is one for measuring and calculating the system impedance found by the inventor to be applicable to many types of AICD systems, other positions for measuring and calculating system impedance will be known to those of skill in t.he art and will work equally well.
The impedance thresholds, both high and low are a function of both the particular AICD
system and the particular tissue environment. Thus, each patient's impedance thresholds will be unique to at least some degree. This is especially true where immediately post-implantation, acute phase tissue responses alter the system impedance for at least some time. However, it is possible to approximate certain high impedance thresholds to generally lie approximately between 50 and 100 Ohms. In other embodiments, the high impedance threshold will be approximate:ly between 60 and 80 Ohms. In a preferred mode of practicing the invention, the high impedance threshold will be approximately 70 Ohms. Thus, for example using the preferred mode, should the measured impedance exceed 70 Ohms, at least one electrode, for instance a hot can elect:rode will be switched on in order to lower the impedance to a level at or below 70 Oh ns.
Similarly, it is possible to approximate certain low impedance thresholds to generally lie approximately between 20 and 60 Ohms. In other embodiments, the low impedance thresho].d will be approximately between 30 and 40 Ohms. In a preferred mode of practicing the invention, the low impedance threshold will be approximately 40 Ohrns. Again for example using the preferred mode, should the measured impedance fall below 40 Ohms, the additional electrode added to bring the impedance to a level under the high impedance threshold, for instance the hot can electrode, will be switched off in order to raise the impedance to a level at or above 40 Ohms. Other electrodes can be switched off in lieu of the newly connected electrode, as well.
The invention is utilized with an AICD system which may take a number of configurations. In one of the most common, the system will comprise a hot can electrode, a superior vena cava (SVC) implanted electrode, and a right ventricle (RV) implanted electrode.
As initially implanted, the system may have all three electrodes activated (switched on). In t.his instance, the methods of the invention will monitor for too low impedance and, as necessary, switch one or more electrodes out of the system (typically, either the hot can or the SVC).
Alternatively, the physician may activate only the SVC and RV electrodes, leaving the can electrode as an optional electrode to switch on or off as needed using the methods of the invention. p~E~lo~9 S~
;; CA 02219103 1997-10-23 ITM-271PCT ~ : ;
Other configurations of the system are also possible. The system may comprise a hot can electrode, a superior vena cava implanted electrode, a right ventricle implanted electrode, and a subcutaneously implanted electrode. Or, the system may comprise only a hot can electrode, a right ventricle implanted electrode, and a subcutaneously implanted electrode.
The position of implantation of the electrodes of the invention is at the studied discrc tion of the surgeon. Thus, the invention will work equally well where the can electrode is implanted pectorally or where it is implanted abdominally. Similarly, the superiorly placed electrode rnay be implanted in the superior vena cava or equally as well in the coronary sinus. The implantation of the subcutaneous electrode or patch can be in any number of positions so long as the proper circuits can be established.
The invention also provides for circuits useful in maximizing the likelihood of successful defibrillation or cardioversion from an automatic implantable cardioverter/defibrillator system.
The circuits may be circuits for simply switching on a preselected electrode, or for simply switching off a preselected electrode.
Alternatively, the circuits of the invention may combine the capacity to both switch on and to switch off preselected electrodes. In each such circuit, means for measuring the impedance of the system as a result of a first shock em~n:lting from the AICD are required. As described generally above, these means may take the form of a measurement of the pre-shoc:k and post-shock impedance at the high voltage capacitor of the AICD. Where it is desired to monitor and adjust for too high impedance, means for comparing the measured impedance to a high impedance threshold are required.
In those instances where too high an impedance is found (when compared to the high impedance threshold), the circuits of the invention will provide means for connecting at least one electrode to the system prior to the next shock to emanate from the AICD. Where low impedance is of particular concern, the circuits of the invention will provide means for comparing the measured impedance to a low impedance threshold, and means for disconnecting at least one electrode from the system prior to the next shock, when that impedance is approximately below the low irnpedance threshold. Combined systems will have all means recited above in order to both connect or disconnect the preselected electrode or electrodes as nl~CP~s~ry when levels fall above or below the impedance thresholds.
The particular device found by the inventor to provide the advantages of the invention will be described in more detail by reference to the following figures and detailed descriptions of the preferred embodiments.
Brief l~)escription of ~rawin~s Figure 1. Shows an operational flow chart illustrating a method of measuring impedance and selecting electrodes.
AMENDF~
I~U-271PCT . ;-Figure ~. A. Heart assisted by a pectoral AICD with electrodes activated in the right ventricle and the superior vena cava. B. Heart assisted by a pectoral AICD with electrodes activated in the right ventricle, the superior vena cava, and subcutaneously. C. Heart assisted by a pectoral AICD with electrodes activated in the right ventricle and subcutaneously D.
Heart assisted by a pectoral AICD with electrodes activated in the right ventricle, the superior vena cava, and at the can. E. Heart assisted by a pectoral AICD with electrodes activated in the right ventricle, the superior vena cava, subcutaneously, and at the can. F. Heart assisted by a pectoral AICD with electrodes activated in the right ventricle, subcutaneously, and at the can. G.
Heart assisted by a pectoral AICD with electrodes activated in the right ventricle and at the c:an.
H. Heart assisted by an abdominal AICD with electrodes activated in the right ventricle and the superior vena cava. I. Heart assisted by an abdominal AICD with electrodes activated at the can and the superior vena cava.
Figure 3. Heart assisted by an AICD with electrodes which may be activated in the right ventricle, the superior vena cava, and at the can, including a block diagram of the AICD capable of switching leads.
Best Mode for Carrying Out the Invention Referring now to FIG. 1, the invention is generally demonstrated in a flow diagram of the decision process. The procedure depicted is that for a combined process of comparing both high and low impedance thresholds. However, each decision junction along with resulting actions may easily be segregated into single decision loops.
In each such method, the impedance of the shock electrode system is measured as previously described. Once that value has been determined, it is compared to an upper limit or high impedance threshold valve. If the measured impedance is above the upper limit, a preselected electrode is electrically connected to the system and is used to establish the shock field for the next shock. In association with that next shock, the system impedance is again measured. If the measured impedance is not greater than the upper limit, the method calls for a second decision. This decision is accomplished by comparing the measured impedance to a lower limit or low impedance threshold valve. If the measured impedance is below the lower limit, the electrode that was previously added to the system in order to compensate for too high of an impedance (or some other pre-selected electrode), is electrically removed or disconnected from the system. Where the electrode is removed prior to the next shock, the method calls for another measurement of system impedance. Where it is not necessary to add or remove an electrode by virtue of system impedance falling within the acceptable range both high and low, the apparatus of the invention awaits the next shock and repeats the decision-making matrix in contimnlm h~,',~''.~'9 S'r~
-8- .. ;
Referring generally to FIG. 2 A-I, it can be seen that a variety of configurations may be used with the system of the invention. While these configurations are those most typically encountered in implantable automatic cardioverter/defibrillators, other configurations, other types of electrodes, and other electrode implantation sites may be used similarly in conjunction with the circuits of the invention.
In FIG. 2A, heart 1 is assisted by an AICD system S by application of shocks capable of cardioverting or defibrillating heart inside tissue. AICD can 2 contains the circuitry and po~;ver supply for system S in a metal housing which may be used as an electrode itself, i.e. a "hot" can.
Issuing from and electrically connected or connectable to can 2 are leads 8 and 10 which are, in turn, electrically connected to electrodes 4 and 6, respectively. Electrode 4 is depicted as being implanted in a superior position relative to heart 1 such as in the superior vena cava (SVC).
Electrode 6 is depicted as being irnplanted in an inferior position in heart 1 such as in the right ventricle (RV). When a sufficient charge is developed a~ the high voltage capacitor of the AICD
(not shown), and at a regulated interval, a shock typically comprising 600 or more volts, is electrically transferred from can 2 through lead 10 to the RV electrode 6. The current passes from RV electrode 6, into the surrounding tissue of heart 1 through the current path 12. The circuit is completed by passage of the current to SVC electrode 4 and back to can 2 via lead 8.
Where the invention is employed, it is possible in one embodiment to add an electrode if the impedance of the system rises above an acceptable impedance range. In FIG. 2D, system S
is shown to have can 2 connected as an electrode. This results in the generation of an additional current path 20 by which the current arising from RV electrode 6 passes through heart 1 along both the original current path 12 and the new current path 20. Alternatively, where it is desired to remove an electrode from the system shown in FIG. 2A, it is possible to redirect the current path altogether along path 20 as shown in FIG. 2G. In this mode of operation, impedance measurement resulted in a value below the lower threshold, which in turn resulted in the disconnection of SVC electrode 4 and lead 8 while m~int~ining the electrical connection to the hot can electrode 2.
In a similar configuration, the AICD system S may have a can implanted in an abdorninal position such as shown in FIGS. 2H and 2I. System S of FIG. 2H generates current path 12 in a manner consistent with that described for FIG. 2A, above. Where comparison of the measured impedance to the high impedance threshold results in a decision to add an electrode, hot can electrode 22 is connected into system S resulting in current path 24. This may result in dual current paths 12 and 24 (not shown). However, as shown in FIG. 2I, RV electrode 6 and lead A~END~ S~Er :
-W 096/372~,8 PCTrUS96/07770 g 10 have been electrically disconnected from system S resulting in the single vector 24 through heart 1, as would be n~cPc~ " y where RV lead dislodgement of lead 10 or electrode failure of ~'V
electrode 6 occurred.
In more complicated configurations, more all~llldliv~s exist for switching electrodes into or out of connection to the AICD system. Thus, in FIGS. 2B, C, E, and F, AICD systems are depicted with subcutaneously implanted electrode 14 in electrical cormection with, or connectable through, lead 18 to can 2. Typieally, such systems will initially be configured with dual current paths c"~n~li"g from RV electrode 6--one vectoring to SVC electrode 4 along current path 12 and the other veetoring through heart 1 along eurrent path 16 to ~,ub~u~ eous electrode 14.
Alternatively, as shown in FIG. 2C, SVC electrode 4 and lead 8 have been electrically diseonneeted from system S resulting in the single vector 16 from RV electrode 6 to subcutaneous electrode 14.
FIG. 2E depicts the resulting vectors (12, 16, and 20) operating .ciml-lt~n~-ously when can 2 is connected into system S which system has bùbcuL~lleous electrode 14 in addition to standarcl electrodes 4 and 6 implanted in or around the tissue of heart 1. When the methods and systems of the ir,~vention are used to switch off selected electrodes, the resulting vectors ~,~llelal~ current paths such as those shown in FIG. 2F (current paths 16 and 20) and that shown in FIG. 2C
(current path 16). In each instance, one or more of the electrodes which were electrically connected to system S are disconnected in order to raise the impedance above the low impedance threshold.
In FIG. 3, a general block diagram of the ~,wiL~ illg circuit block is shown. FIG. 3 is analogous to FIGS. 2A, 2D and 2G (can electrode 2 disconn~ct~d, can electrode 2 connPctetl, and SVC eleetrode 4 diseo}-n~cte~i respectively). Can 2 houses the cil~:uiLly of the AICD
capable of switching among electrodes. Can 2 has a housing 26 which is electrically connPcted through eleetrical connection 36 to lead selection switehes 28. Similarly, leads 8 and 10 connec~
respectively to SVC electrode 4 and RV electrode 10, and also are electrically connected to lead selection switches 28. The lead selection switches 28 comprise a plurality of switches which can be opened or shut, as desired, to electrically connect or disconnect electrodes 4, 6 and housing 2,6 to the energy source 34. Selection of switch position, either conn~cting or disconnPcring each electrode/lead as n~ocPc.c~ry, is regulated by signals tr~ncmirt~d through the data bus 38. The data bus 38 interconnects lead selection switches 28 with memo;y 30 and microprocessor 32.
Memory 30 preferably encodes predetermined high and low impedance threshold values.
Microprocessor 32 includes logic to conduct the algoliLlllllic comparison of the memorized threshold values stored in memory with the measured impedance values obtained from impe-l~nce measurement circuit 40. Microprocessor 32 also controls the AICD circuits in manners known to W O 96/37258 PCTrUS96/07770 those of skill in the art in order to produce defibrillation/cardioversion shocks from the c-~nt~in~od energy source 34. Polarity output terminals 46 and 48 (minus and plus, respectively) of the defibrillation/cardioversion energy source 34 are electrically connected through the lead selection switches 28 to the ap~ iat~ leads and electrodes.
Thus, for example, the configuration of FIG. 2A would require that the lead selection switches 28 be configured to connect the positive polarity output terminal 48 to RV electrode 6 through lead 10. Current applied to electrode 6 then is tr~ncmitted across vector 12 (FIG. 2A) to SVC electrode 4, and back to terminal 46 via return lead 8 to complete the circuit. Where the metal housing 26 of can 2 is c- nnPcted into system S, lead switches 28 are configured by suitable signals from memory 20 and microprocessor 32 to cause housing 26 to accept current via current path 20 (FIG. 2D). This result is achieved by disconnPcting electrode 4 from negative output terminal 46 of the energy source 34, and connPcting lead 36 to the negative output terminal. As a result, housing 26 of can 2 functions as the ground electrode for energy source 34 by ap~ iat~ configuration of the selection switches 28. Where SVC electrode 4 and lead 8 are sensed by memory 30 and microprocessor 32 to be causing the measured impedance to drop below the low impedance threshold, lead selection switches 28 are configured to electrically disconnect lead 8 and SVC electrode 4 from the negative output terminal 46, and to connect lead 36 thereto, resulting in the current path 20 between electrode 6 and can 2 (FIG. 2G). The impedance is measured by the impedance mea~u~ circuit 40 which monitors the defibrillation/cardioversion energy source 34 via connection 42 and c-""""l"ic~l~s the measurement to the microprocessor 32 via data bus 38.
The present invention has been described in terms of particular embodiments found or proposed to comprise preferred modes for the practice of the invention. It will be appreciated by those of skill in the art that, in light of the present disclosure, llUlllt~l~JUS modifications and changes can be made in the particular embodiments exemplified without departing from the inten~d scope of the invention. For example, while the inventor has described the practice of his invention in a best mode of operation as a fully ~ntom~tic, implantable system, at least certain functions carried out in fully ?l.t.-m~tic mode may be conducted in a semi~ u"",li~ or strictly manual mode. Likewise, certain of the steps may be conducted telemetrically or otherwise external to the AICD itself. Thus, for instance, where a subcutaneous electrode is used, a simple out-patient operation may be conducted to connect or disconnect that electrode from the system.
Similarly, while the invention described is designed to make one or a few connect/disconnect operations, fully dynamic systems capable of constantly ~ccPccing and modifying the electrode configuration necessary for long-term cardioversion/ defibrillation management are possible. All such modifications are in~Pn~led to be inrlncled within the scope of the appended claims.
It is known that monitoring impedance of AICD systems is one means for ~etPcting lead failures See, "Troubleshooting Implantable Cardioverter Defibrillator System Malfunctions:
The Role of Impedance Measurements," r-r~d-l~(i, L et ah, ~, Vol 17 1456-1461 (199~,).
This study found that external high impedance measurements may be used to troubleshoot A[CD
system malfunctions due to: lead fractures, faulty adapter connections, and loose set screw connections However, prior art approaches such as the ones suggested by this study require relatively immediate re-operation to replace the damaged lead.
Routine posterior-anterior and lateral chest x-rays can identify lead fractures prior to any clinical observation However, other of the cases demonstrate that not all lead or connector problems can be detected by routine chest x-rays.
Certain implantable pacing devices possess a mt-~h:~ni~m for switching from a bipolar lead configuration to a unipolar lead configuration when a fault is detected in the bipolar leacl ring See, U~S. Patent No. 4,964,407. In certain of these devices, a series of high impedance test signals are actively generated (not merely sensed) by a microprocessor in a p~cem~3ker to determine whether a bipolar or unipolar lead is attached. If no operational bipolar lead is detected, the programming of the p~Prn~k~r is altered to a unipolar pacing mode~ However, similar systems are not available for AICDs.
Methods, circuits and devices are needed which are capable of monitoring the impedance of AICDs for purposes of detecting lead malfunctions Such systems will avoid the tliMelllti( s associated with prior art approaches which require frequent x-raying, inefficient discovery of' lead malfunctions using x-raying, or other external monitoring devices. Methods, circuits and de vices are also needed which, after det~-ction of a lead malfunction, are capable of connecting or disconnecting leads and electrodes to m~ximi7P the likelihood of effective cardioversion and defibrillation. Preferably, such systems will be fully implantable and will not require imme~ tP
invasive surgical techniques or frequent x-irradiation in order to correct the problems.
l~isclosure of rnvention Systems useful for m~ximi7:ing the likelihood of successful defibrillation or cardioversion .
using an automatic implantable cardioverter/defibrillator system are provided by the present ~E~O S~
ITM-271PCT ,,, , -2a --invention. The system is capable of monitoring the impedance of AICDs for purposes of detecting lead malfunctions. After detection of a lead malfunction, the system of the presemt invention is capable of connecting or disconnecting leads and electrodes to m~ximi7e the ~ S~
W 096/37258 PCTrUS96/07770 likelihood of effective cardioversion and defibrillation. These systems are fully implantable and do not require immediate invasive surgical techniques or frequent x-irr~ tir/n.
Various methodologies may be used to implement the present invention. If a method i~i desired which can simply connect an electrode in response to a too-high impedance measurement, then the impedance of the AICD system is measured initially. This may occur, for example, during a first shock phase. The measured impedance then is compared to a high impedance threshold value. If the measured inlL edance exceeds the threshold value, then at least one electrode is electrically connected to the system prior to the next .~hocking cycle.
Likewise, if a method is desired which can simply electrically disconnect an electrode in response to a too-low impedance measurement, then the impefl~nre of the AICD system is initially measured, for example, during a first shock phase. The measured impedance is then compared to a low impedance threshold. Where the ~..easù-ed impedance drops below the lower threshold, at least one electrode is electrically disconnected from the system, as for example prior to the next shocking cycle.
A combined method for m~ximi7ing likelihood of snccr~fill defibrillation or cardioversion using an ~lf~ . implantable cardioverter/defibrillator system, will be preferred in certain in~t~nres. Such a method will comprise a two-stage impedance co..~a.ibon.
First, an impedance measu,cment of the system, as for example resulting from a first shock is taken. This value is co---~al~d to a high impedance threshold. Where the cu~ ibon demol~L.dles that the impedance meabll,c.. ~nl is above the upper threshold, one or more electrode is activated into the grid, as for example prior to the next shock. If this occurs, then the method calls for making a second impedance culll~ualibon of the system.
If the impedance meabulc---~--L is below the upper irnpedance threshold, then the method calls for comparing that impedance meabu-c~ --l to the lower impedance threshold. Where the impedance measurement is below the lower impedance threshold, one or more electrodes are discnnnrctt~.l from the system grid, as for example prior to the next shock in the cycle.
If the impedance ...easu-ement is neither above the upper limit nor below the lower limit, the method simply allows the next shock to occur and repeats itself. In this manner, the two-stage method coll~ lly monitors and adjusts for disc~c~al1cies in the system impedance.
,~ 30 There are a number of reasons why an AICD system will exhibit impedance ~lisclel)allcies above or below pre-set thresholds. Among them are lead dislodgement and lead malfunction. Lead dislodgement may occur where the lead shifts due to loss of anchoring in the tissue. In some in~t~nrec, the dislodgement is temporary and the lead will subsequently return to a position capable of gc:,~e,~li,,g the proper impedance. In other cases, the dislodgement is perm~nrnt Other lead m~l~lnrtions include lead fracture, or loose set screws at the point of ~tt~hm~nt of the electrode tip to the lead. It is also common imm~di~te]y post-transpl~nt~tiQn o~
~TM-271PCT ''~
: ': ; ' '"
4 ~ ~ ,t an AICD to detect impedance discrepancies due to acute phase tissue stabilization. This is a temporary condition which usually corrects itself with passage of time and infiltration of tissue into the lead and tip.
The invention may be used with electrodes implanted in a variety of locations surrounding the heart. Typically, such an electrode will include one implanted in or near the superior vena cava or one implanted in or near the patient's coronary sinus. Another typical location for an electrode is in or near the right ventricle. Auxiliary electrodes may also be present such as those which are implanted subcutaneously.
In many modern AICDs, another electrode available for selection is the irnplantable cardioverter/defibrillator can itself. These are typically referred to as "hot" cans. Such can electrodes are routinely implanted pectorally. However, they may also be irnplanted abdominally.
Thus, the invention monitors shock electrode impedance after each defibrillation or cardioversion shock. If the impedance exceeds a preset threshold, this invention will enable a preset combination of electrodes to be int~ (led in the subsequent shocks in an attempt to reduce the shock electrode impedance. This will provide increased safety for the patient in the case of shock electrode malfunction. For example, a physician may implant an RV-to-SVC+can sy,tem but choose to disable the can electrode due to patient discomfort during low energy cardiove:rsion shock. If at a later time, the SVC lead were to break, in one embodiment of this invention, i:t would be possible to detect the increase in impedance and include the can electrode in all subsequent shocks.
One method of calculating the impedance is by using the formula:
t R= V
C ln ( V ) where R=impedance; t=duration of delivered shock; Vj=pre-shock voltage reading; Vf=post-shock voltage reading; and C=capacitance.
Using this formula, an initial reading (Vj) is taken at the high voltage capacitor of the AICD just prior to delivery of the high voltage shock (typically 600 or more volts). After the delivery of a shock of duration (t) typically of approximately 10 milliseconds, a second reading (Vf)iS taken at the same capacitor. The capacitance (C) of the high voltage capacitor is a constant for each such device. The irnpedance (R) is then c~ d by taking the natural log of the ratio of the initial voltage reading to the final voltage reading, multiplying the result by the capacitance constant for the device, and dividing the result into the value for the duration of the delivered shock. While this is a means of measuring and calculating the system impedance found .~ ., r) CA 02219103 1997-10-23 rTM-271PCT . ;,' .. '.
by the inventor to be applicable to many types of AICD systems, it is but one such method.
Other methods for measuring and calculating system impedance will be known to those of skill in the art and will work equally well.
The invention may measure impedance at a capacitor prior to shock and following shock.
it a preferred mode, the measurement of impedance will be accomplished at the high voltage (HV) capacitor of the AICD. Again, while this position is one for measuring and calculating the system impedance found by the inventor to be applicable to many types of AICD systems, other positions for measuring and calculating system impedance will be known to those of skill in t.he art and will work equally well.
The impedance thresholds, both high and low are a function of both the particular AICD
system and the particular tissue environment. Thus, each patient's impedance thresholds will be unique to at least some degree. This is especially true where immediately post-implantation, acute phase tissue responses alter the system impedance for at least some time. However, it is possible to approximate certain high impedance thresholds to generally lie approximately between 50 and 100 Ohms. In other embodiments, the high impedance threshold will be approximate:ly between 60 and 80 Ohms. In a preferred mode of practicing the invention, the high impedance threshold will be approximately 70 Ohms. Thus, for example using the preferred mode, should the measured impedance exceed 70 Ohms, at least one electrode, for instance a hot can elect:rode will be switched on in order to lower the impedance to a level at or below 70 Oh ns.
Similarly, it is possible to approximate certain low impedance thresholds to generally lie approximately between 20 and 60 Ohms. In other embodiments, the low impedance thresho].d will be approximately between 30 and 40 Ohms. In a preferred mode of practicing the invention, the low impedance threshold will be approximately 40 Ohrns. Again for example using the preferred mode, should the measured impedance fall below 40 Ohms, the additional electrode added to bring the impedance to a level under the high impedance threshold, for instance the hot can electrode, will be switched off in order to raise the impedance to a level at or above 40 Ohms. Other electrodes can be switched off in lieu of the newly connected electrode, as well.
The invention is utilized with an AICD system which may take a number of configurations. In one of the most common, the system will comprise a hot can electrode, a superior vena cava (SVC) implanted electrode, and a right ventricle (RV) implanted electrode.
As initially implanted, the system may have all three electrodes activated (switched on). In t.his instance, the methods of the invention will monitor for too low impedance and, as necessary, switch one or more electrodes out of the system (typically, either the hot can or the SVC).
Alternatively, the physician may activate only the SVC and RV electrodes, leaving the can electrode as an optional electrode to switch on or off as needed using the methods of the invention. p~E~lo~9 S~
;; CA 02219103 1997-10-23 ITM-271PCT ~ : ;
Other configurations of the system are also possible. The system may comprise a hot can electrode, a superior vena cava implanted electrode, a right ventricle implanted electrode, and a subcutaneously implanted electrode. Or, the system may comprise only a hot can electrode, a right ventricle implanted electrode, and a subcutaneously implanted electrode.
The position of implantation of the electrodes of the invention is at the studied discrc tion of the surgeon. Thus, the invention will work equally well where the can electrode is implanted pectorally or where it is implanted abdominally. Similarly, the superiorly placed electrode rnay be implanted in the superior vena cava or equally as well in the coronary sinus. The implantation of the subcutaneous electrode or patch can be in any number of positions so long as the proper circuits can be established.
The invention also provides for circuits useful in maximizing the likelihood of successful defibrillation or cardioversion from an automatic implantable cardioverter/defibrillator system.
The circuits may be circuits for simply switching on a preselected electrode, or for simply switching off a preselected electrode.
Alternatively, the circuits of the invention may combine the capacity to both switch on and to switch off preselected electrodes. In each such circuit, means for measuring the impedance of the system as a result of a first shock em~n:lting from the AICD are required. As described generally above, these means may take the form of a measurement of the pre-shoc:k and post-shock impedance at the high voltage capacitor of the AICD. Where it is desired to monitor and adjust for too high impedance, means for comparing the measured impedance to a high impedance threshold are required.
In those instances where too high an impedance is found (when compared to the high impedance threshold), the circuits of the invention will provide means for connecting at least one electrode to the system prior to the next shock to emanate from the AICD. Where low impedance is of particular concern, the circuits of the invention will provide means for comparing the measured impedance to a low impedance threshold, and means for disconnecting at least one electrode from the system prior to the next shock, when that impedance is approximately below the low irnpedance threshold. Combined systems will have all means recited above in order to both connect or disconnect the preselected electrode or electrodes as nl~CP~s~ry when levels fall above or below the impedance thresholds.
The particular device found by the inventor to provide the advantages of the invention will be described in more detail by reference to the following figures and detailed descriptions of the preferred embodiments.
Brief l~)escription of ~rawin~s Figure 1. Shows an operational flow chart illustrating a method of measuring impedance and selecting electrodes.
AMENDF~
I~U-271PCT . ;-Figure ~. A. Heart assisted by a pectoral AICD with electrodes activated in the right ventricle and the superior vena cava. B. Heart assisted by a pectoral AICD with electrodes activated in the right ventricle, the superior vena cava, and subcutaneously. C. Heart assisted by a pectoral AICD with electrodes activated in the right ventricle and subcutaneously D.
Heart assisted by a pectoral AICD with electrodes activated in the right ventricle, the superior vena cava, and at the can. E. Heart assisted by a pectoral AICD with electrodes activated in the right ventricle, the superior vena cava, subcutaneously, and at the can. F. Heart assisted by a pectoral AICD with electrodes activated in the right ventricle, subcutaneously, and at the can. G.
Heart assisted by a pectoral AICD with electrodes activated in the right ventricle and at the c:an.
H. Heart assisted by an abdominal AICD with electrodes activated in the right ventricle and the superior vena cava. I. Heart assisted by an abdominal AICD with electrodes activated at the can and the superior vena cava.
Figure 3. Heart assisted by an AICD with electrodes which may be activated in the right ventricle, the superior vena cava, and at the can, including a block diagram of the AICD capable of switching leads.
Best Mode for Carrying Out the Invention Referring now to FIG. 1, the invention is generally demonstrated in a flow diagram of the decision process. The procedure depicted is that for a combined process of comparing both high and low impedance thresholds. However, each decision junction along with resulting actions may easily be segregated into single decision loops.
In each such method, the impedance of the shock electrode system is measured as previously described. Once that value has been determined, it is compared to an upper limit or high impedance threshold valve. If the measured impedance is above the upper limit, a preselected electrode is electrically connected to the system and is used to establish the shock field for the next shock. In association with that next shock, the system impedance is again measured. If the measured impedance is not greater than the upper limit, the method calls for a second decision. This decision is accomplished by comparing the measured impedance to a lower limit or low impedance threshold valve. If the measured impedance is below the lower limit, the electrode that was previously added to the system in order to compensate for too high of an impedance (or some other pre-selected electrode), is electrically removed or disconnected from the system. Where the electrode is removed prior to the next shock, the method calls for another measurement of system impedance. Where it is not necessary to add or remove an electrode by virtue of system impedance falling within the acceptable range both high and low, the apparatus of the invention awaits the next shock and repeats the decision-making matrix in contimnlm h~,',~''.~'9 S'r~
-8- .. ;
Referring generally to FIG. 2 A-I, it can be seen that a variety of configurations may be used with the system of the invention. While these configurations are those most typically encountered in implantable automatic cardioverter/defibrillators, other configurations, other types of electrodes, and other electrode implantation sites may be used similarly in conjunction with the circuits of the invention.
In FIG. 2A, heart 1 is assisted by an AICD system S by application of shocks capable of cardioverting or defibrillating heart inside tissue. AICD can 2 contains the circuitry and po~;ver supply for system S in a metal housing which may be used as an electrode itself, i.e. a "hot" can.
Issuing from and electrically connected or connectable to can 2 are leads 8 and 10 which are, in turn, electrically connected to electrodes 4 and 6, respectively. Electrode 4 is depicted as being implanted in a superior position relative to heart 1 such as in the superior vena cava (SVC).
Electrode 6 is depicted as being irnplanted in an inferior position in heart 1 such as in the right ventricle (RV). When a sufficient charge is developed a~ the high voltage capacitor of the AICD
(not shown), and at a regulated interval, a shock typically comprising 600 or more volts, is electrically transferred from can 2 through lead 10 to the RV electrode 6. The current passes from RV electrode 6, into the surrounding tissue of heart 1 through the current path 12. The circuit is completed by passage of the current to SVC electrode 4 and back to can 2 via lead 8.
Where the invention is employed, it is possible in one embodiment to add an electrode if the impedance of the system rises above an acceptable impedance range. In FIG. 2D, system S
is shown to have can 2 connected as an electrode. This results in the generation of an additional current path 20 by which the current arising from RV electrode 6 passes through heart 1 along both the original current path 12 and the new current path 20. Alternatively, where it is desired to remove an electrode from the system shown in FIG. 2A, it is possible to redirect the current path altogether along path 20 as shown in FIG. 2G. In this mode of operation, impedance measurement resulted in a value below the lower threshold, which in turn resulted in the disconnection of SVC electrode 4 and lead 8 while m~int~ining the electrical connection to the hot can electrode 2.
In a similar configuration, the AICD system S may have a can implanted in an abdorninal position such as shown in FIGS. 2H and 2I. System S of FIG. 2H generates current path 12 in a manner consistent with that described for FIG. 2A, above. Where comparison of the measured impedance to the high impedance threshold results in a decision to add an electrode, hot can electrode 22 is connected into system S resulting in current path 24. This may result in dual current paths 12 and 24 (not shown). However, as shown in FIG. 2I, RV electrode 6 and lead A~END~ S~Er :
-W 096/372~,8 PCTrUS96/07770 g 10 have been electrically disconnected from system S resulting in the single vector 24 through heart 1, as would be n~cPc~ " y where RV lead dislodgement of lead 10 or electrode failure of ~'V
electrode 6 occurred.
In more complicated configurations, more all~llldliv~s exist for switching electrodes into or out of connection to the AICD system. Thus, in FIGS. 2B, C, E, and F, AICD systems are depicted with subcutaneously implanted electrode 14 in electrical cormection with, or connectable through, lead 18 to can 2. Typieally, such systems will initially be configured with dual current paths c"~n~li"g from RV electrode 6--one vectoring to SVC electrode 4 along current path 12 and the other veetoring through heart 1 along eurrent path 16 to ~,ub~u~ eous electrode 14.
Alternatively, as shown in FIG. 2C, SVC electrode 4 and lead 8 have been electrically diseonneeted from system S resulting in the single vector 16 from RV electrode 6 to subcutaneous electrode 14.
FIG. 2E depicts the resulting vectors (12, 16, and 20) operating .ciml-lt~n~-ously when can 2 is connected into system S which system has bùbcuL~lleous electrode 14 in addition to standarcl electrodes 4 and 6 implanted in or around the tissue of heart 1. When the methods and systems of the ir,~vention are used to switch off selected electrodes, the resulting vectors ~,~llelal~ current paths such as those shown in FIG. 2F (current paths 16 and 20) and that shown in FIG. 2C
(current path 16). In each instance, one or more of the electrodes which were electrically connected to system S are disconnected in order to raise the impedance above the low impedance threshold.
In FIG. 3, a general block diagram of the ~,wiL~ illg circuit block is shown. FIG. 3 is analogous to FIGS. 2A, 2D and 2G (can electrode 2 disconn~ct~d, can electrode 2 connPctetl, and SVC eleetrode 4 diseo}-n~cte~i respectively). Can 2 houses the cil~:uiLly of the AICD
capable of switching among electrodes. Can 2 has a housing 26 which is electrically connPcted through eleetrical connection 36 to lead selection switehes 28. Similarly, leads 8 and 10 connec~
respectively to SVC electrode 4 and RV electrode 10, and also are electrically connected to lead selection switches 28. The lead selection switches 28 comprise a plurality of switches which can be opened or shut, as desired, to electrically connect or disconnect electrodes 4, 6 and housing 2,6 to the energy source 34. Selection of switch position, either conn~cting or disconnPcring each electrode/lead as n~ocPc.c~ry, is regulated by signals tr~ncmirt~d through the data bus 38. The data bus 38 interconnects lead selection switches 28 with memo;y 30 and microprocessor 32.
Memory 30 preferably encodes predetermined high and low impedance threshold values.
Microprocessor 32 includes logic to conduct the algoliLlllllic comparison of the memorized threshold values stored in memory with the measured impedance values obtained from impe-l~nce measurement circuit 40. Microprocessor 32 also controls the AICD circuits in manners known to W O 96/37258 PCTrUS96/07770 those of skill in the art in order to produce defibrillation/cardioversion shocks from the c-~nt~in~od energy source 34. Polarity output terminals 46 and 48 (minus and plus, respectively) of the defibrillation/cardioversion energy source 34 are electrically connected through the lead selection switches 28 to the ap~ iat~ leads and electrodes.
Thus, for example, the configuration of FIG. 2A would require that the lead selection switches 28 be configured to connect the positive polarity output terminal 48 to RV electrode 6 through lead 10. Current applied to electrode 6 then is tr~ncmitted across vector 12 (FIG. 2A) to SVC electrode 4, and back to terminal 46 via return lead 8 to complete the circuit. Where the metal housing 26 of can 2 is c- nnPcted into system S, lead switches 28 are configured by suitable signals from memory 20 and microprocessor 32 to cause housing 26 to accept current via current path 20 (FIG. 2D). This result is achieved by disconnPcting electrode 4 from negative output terminal 46 of the energy source 34, and connPcting lead 36 to the negative output terminal. As a result, housing 26 of can 2 functions as the ground electrode for energy source 34 by ap~ iat~ configuration of the selection switches 28. Where SVC electrode 4 and lead 8 are sensed by memory 30 and microprocessor 32 to be causing the measured impedance to drop below the low impedance threshold, lead selection switches 28 are configured to electrically disconnect lead 8 and SVC electrode 4 from the negative output terminal 46, and to connect lead 36 thereto, resulting in the current path 20 between electrode 6 and can 2 (FIG. 2G). The impedance is measured by the impedance mea~u~ circuit 40 which monitors the defibrillation/cardioversion energy source 34 via connection 42 and c-""""l"ic~l~s the measurement to the microprocessor 32 via data bus 38.
The present invention has been described in terms of particular embodiments found or proposed to comprise preferred modes for the practice of the invention. It will be appreciated by those of skill in the art that, in light of the present disclosure, llUlllt~l~JUS modifications and changes can be made in the particular embodiments exemplified without departing from the inten~d scope of the invention. For example, while the inventor has described the practice of his invention in a best mode of operation as a fully ~ntom~tic, implantable system, at least certain functions carried out in fully ?l.t.-m~tic mode may be conducted in a semi~ u"",li~ or strictly manual mode. Likewise, certain of the steps may be conducted telemetrically or otherwise external to the AICD itself. Thus, for instance, where a subcutaneous electrode is used, a simple out-patient operation may be conducted to connect or disconnect that electrode from the system.
Similarly, while the invention described is designed to make one or a few connect/disconnect operations, fully dynamic systems capable of constantly ~ccPccing and modifying the electrode configuration necessary for long-term cardioversion/ defibrillation management are possible. All such modifications are in~Pn~led to be inrlncled within the scope of the appended claims.
Claims (4)
1. An automatic implantable cardioverter/defibrillation system (S) for maximizing likelihood of successful defibrillation or cardioversion, the system comprising:
an hermetically sealed can (2) containing therapy controlling circuitry (32, 30), an energy source (34), at least one lead (8, 10), at least one electrode (4,6) attached to said lead, and at least two other electrodes (26, 6) an impedance measurement device (40) for measuring the shock electrode impedance of said system between said at least three electrodes; and a comparator for comparing said impedance to an impedance threshold value stored in memory;
characterized by a plurality of switches (28) for connecting or disconnecting at least one of said electrodes to said system, when said impedance passes said impedance threshold; and means (32) for controlling said switches to select electrodes capable of creating at least one shocking current vector to pass through a mass of cardiac tissue sufficient to cardiovert/defibrillate the heart.
an hermetically sealed can (2) containing therapy controlling circuitry (32, 30), an energy source (34), at least one lead (8, 10), at least one electrode (4,6) attached to said lead, and at least two other electrodes (26, 6) an impedance measurement device (40) for measuring the shock electrode impedance of said system between said at least three electrodes; and a comparator for comparing said impedance to an impedance threshold value stored in memory;
characterized by a plurality of switches (28) for connecting or disconnecting at least one of said electrodes to said system, when said impedance passes said impedance threshold; and means (32) for controlling said switches to select electrodes capable of creating at least one shocking current vector to pass through a mass of cardiac tissue sufficient to cardiovert/defibrillate the heart.
2. The system according to claim 1 further comprising:
an comparator for comparing said impedance to a high impedance threshold value stored in memory; and the plurality of switches for connecting at least one electrode to said system, when said impedance rises above said high impedance threshold.
an comparator for comparing said impedance to a high impedance threshold value stored in memory; and the plurality of switches for connecting at least one electrode to said system, when said impedance rises above said high impedance threshold.
3. The system according to claim 1 further comprising a comparator for comparing said impedance to a low impedance threshold value stored in memory; and the plurality of switches for disconnecting at least one electrode from said system, when said impedance is approximately below said low impedance threshold.
4. The system according to claim 1 further comprising:
a comparator for comparing said impedance measurements to a high impedance threshold value stored in memory;
the plurality of switches for electrically connecting at least one additional electrode to said system when said impedance measurements are approximately above said high impedance threshold;
a comparator for comparing said impedance measurements to a low impedance threshold value stored in memory; and the plurality of switches for electrically disconnecting at least one electrode from said system when said impedance measurements are approximately below said low impedance threshold.
a comparator for comparing said impedance measurements to a high impedance threshold value stored in memory;
the plurality of switches for electrically connecting at least one additional electrode to said system when said impedance measurements are approximately above said high impedance threshold;
a comparator for comparing said impedance measurements to a low impedance threshold value stored in memory; and the plurality of switches for electrically disconnecting at least one electrode from said system when said impedance measurements are approximately below said low impedance threshold.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/450,105 | 1995-05-25 | ||
| US08/450,105 US5607455A (en) | 1995-05-25 | 1995-05-25 | Method and apparatus for automatic shock electrode enabling |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2219103A1 true CA2219103A1 (en) | 1996-11-28 |
Family
ID=23786781
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002219103A Abandoned CA2219103A1 (en) | 1995-05-25 | 1996-05-24 | Method and apparatus for automatic shock electrode enabling |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5607455A (en) |
| EP (1) | EP0830177A1 (en) |
| JP (1) | JP2001501486A (en) |
| CA (1) | CA2219103A1 (en) |
| WO (1) | WO1996037258A1 (en) |
Families Citing this family (75)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6016445A (en) * | 1996-04-16 | 2000-01-18 | Cardiotronics | Method and apparatus for electrode and transthoracic impedance estimation |
| US6253103B1 (en) * | 1996-04-16 | 2001-06-26 | Kimberly-Clark Worldwide, Inc. | Method and apparatus for high current electrode, transthoracic and transmyocardial impedance estimation |
| US5722997A (en) * | 1996-09-17 | 1998-03-03 | Sulzer Intermedics Inc. | Method and apparatus for cardiac impedance sensing |
| US6152954A (en) | 1998-07-22 | 2000-11-28 | Cardiac Pacemakers, Inc. | Single pass lead having retractable, actively attached electrode for pacing and sensing |
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-
1995
- 1995-05-25 US US08/450,105 patent/US5607455A/en not_active Expired - Lifetime
-
1996
- 1996-05-24 CA CA002219103A patent/CA2219103A1/en not_active Abandoned
- 1996-05-24 WO PCT/US1996/007770 patent/WO1996037258A1/en not_active Application Discontinuation
- 1996-05-24 JP JP08535940A patent/JP2001501486A/en active Pending
- 1996-05-24 EP EP96917834A patent/EP0830177A1/en not_active Withdrawn
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| US5607455A (en) | 1997-03-04 |
| JP2001501486A (en) | 2001-02-06 |
| EP0830177A1 (en) | 1998-03-25 |
| WO1996037258A1 (en) | 1996-11-28 |
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