Implantation of transvenous nonthoracotomy cardioverter-defibrillator systems in patients with permanent endocardial pacemakers

Implantation of transvenous nonthoracotomy cardioverter-defibrillator systems in patients with permanent endocardial pacemakers

Among 177 patients in whom a nonthoracotomy approach was initially used to implant a cardioverter-defibrillator system, 11 (6%) patients also received a separately implanted permanent pacemaker. The main problem encountered in these patients were previously implanted unipolar pacemakers (n = 3) and ventricular pacing leads positioned at the right ventricular apex, the latter interfering with optimal placement of the tripolar implantable cardioverter-defibrillator (ICD) lead (n = 9). The approaches used to solve these problems were individualized and included placement of the ICD sensing lead at the right ventricular outflow tract (n = 3), initial placement (n = 1) or subsequent repositioning (n = 2) of the right ventricular pacing lead at the outflow tract, upgrade from unipolar to bipolar systems (n = 2), reprogramming from the DDD to AAI mode (n = 2), inactivation of the pacemaker (n = 1), and simultaneous placement of a single-chamber atrial pacemaker with the ICD lead (n = 2). These revisions fulfilled the pacing needs in each patient and prevented unfavorable sensing interaction between the two systems. {AM HEART J 1995;129:45-53.)

Ross Brooks, MD, Hasan Garan, MD, Brian A. McGovern, MD,

and Jeremy N. Ruskin, MD Boston, Mass.

An estimated 15 % to 20 % of patients with implantable cardioverter-defibrillator (ICD) systems require concomitant single- or dual-chamber pacing. 1-3 Be- cause these systems are separately implanted, potential interaction of sensing function may result. Most important, the rate-sensing lead of the ICD system may detect pacemaker stimuli leading to multiple counting and spurious discharges or detection inhibition may occur, potentially resulting in suppression of life-saving ICD therapy during ventricular fibrillation. 4 Newer ICD systems with inte- grated sensing and VVI pacing functions have elim- inated interaction between separately implanted systems. However, these systems do not permit rate responsive pacing, which may be desirable in some patients and may drain the battery prematurely in others who are pacemaker dependent. Moreover, most patients with ICD systems requiring pacemakers need atrial or dual chamber pacing and are not well served by VVI pacing alone. 1-~

With conventional thoracotomy-implanted ICD

From the Cardiac Arrhythmia Service, Massachusetts General Hospital, and Harvard Medical School.

Received for publication Feb. 3, 1994; accepted March 21, 1994.

Reprmt requests: Ross Brooks, MD, Cardiac Unit, Massachusetts General Hospital, Boston, MA 02114.

Copyright ® 1995 by Mosby-Year Book, Inc. 0002-8703/95/$3.00 + 0 4 / 1 / 5 9 1 1 9

systems, interaction between ICD and pacemaker functions can be avoided by implanting epicardial ICD rate-sensing leads remote from endocardial- placed pacemaker leads. Patients with preexisting unipolar pacemaker leads require revision to bipolar pacing systems to prevent sensing of the large unipolar pacer stimuli. 4 With newer nonthoracotomy ICD systems, wide separation of the leads can no longer be achieved because the transvenous ICD and pacemaker leads are both placed in an endocardial position in the right ventricle. In addition to potential sensing interaction, other technical considerations related to lead insertions and placement may also limit transvenous ICD implantation in patients with preexisting permanent pacemakers. No published data have been reported on patients with combined transvenous ICD and permanent endocardial pacemaker systems. Data on the management of patients with combined systems is relevant because >80 % of all ICD systems currently implanted are nonthoracotomy and require placement of one or more transvenous lead. 5 We describe our clinical experience managing 11 patients with combined transvenous ICD and endocardial-placed pacemaker systems.

METHODS Patients. Among 177 consecutive patients undergoing

transvenous ICD placement at our institution by means of

45

January 1995 46 Brooks et al. American Heart Journal

Table I. Clinical features of implantable cardioverter-defibri l lator and pacemaker systems

Patient

1 2 3 4 5

Age/Gender 74/M 59/M 58/M 78/F 75/M Heart disease CAD CAD CAD DCM CAD LVEF 0.55 0.30 0.48 0.43 0.30 Arrhythmia

Clinical VT VT VF VT VF Induced VT VT VF VT NI

Indication for SSS CHB SSS SSS SSS pacemaker

Pacemaker CPI Vista 940 CPI Vista 940 CPI Triumph CPI Vista T PS II Mode DDD DDD AAIR DDD -~ AAI DDDR Venous access LSCV LSCV LSCV RSCV LSCV Lead B B B U -~ B U Lead position Apex RVOT Atrium Apex Apex Pacemaker Yes Yes Yes Yes Yes

dependent Transvenous lead Transvene Endotak Endotak Endotak Endotak Venous access RSCV RSCV LSCV LSCV RSCV Lead position RVOT Apex Apex Apex Apex ICD model Medtronic PCD CPI 1600 CPI 1600 CPI PRX CPI P2 Order of implant P --* ICD P --~ ICD P -~ ICD P -~ ICD P --* ICD Pacemaker revision None P implanted before P implanted with New atrial lead P reprogrammed

ICD ICD and P DDD --~ AAI implanted; old P inactivated

CAD, Coronary artery disease; DCM, dilated cardiomyopathy; LVEF, left ventricular ejection fraction; VT, ventricular tachycardia; VF, ventricular fibrillation; NI, noninducible: SSS, sick sinus syndrome; CHB, complete heart block; CPI, Cardiac Pacemakers, Inc.; PS, Pacesetter Synchrony; PP, Pacesetter Paragon; LSCV, left subclavian vein; RSCV, right subclavian vein; RCV, right cephalic vein; B, bipolar; U, unipolar; RVOT, right ventricular outflow tract; RVIT, right ventricu]ar inflow tract; P, pacemaker.

an initial nonthoracotomy approach, the 11 pat ients (10 men, 1 woman) who required concomitant permanent pacemakers are the subject of this report. The clinical features of these pat ients are shown in Table I. Ten pat ients had endocardial pacemaker systems implanted a mean of 3.2 years (0.05 to 12 years) before ICD insertion. Seven pa- t ients received dual-chamber pacemakers (5 bipolar and 2 unipolar systems), one pat ient received a VVI pacemaker, aud 1 pa t ien t each received a unipolar and bipolar VVI pacemaker. In 8 pat ients with previously implanted pacemakers, the ventricular pacing lead was posit ioned at or near the right ventricular apex, interfering with the ideal posit ion of the ICD transvenous lead.

ICD lead insertion. Two investigational nonthoracotomy ICD systems were used. Three pat ients received a Transvene system (Medtronic, Inc., Minneapolis, Minn.) and 8 pat ients received a CPI Endotak system (Cardiac Pacemakers, Inc., St. Paul, Minn.). The 110 cm, 10.5F tripolar Transvene lead (model 6966 [n = 3] and model 6936 [n = 1]) consists of a screw-in tip, an adjacent sensing ring, and an adjacent 50 mm-long coil electrode. A separate 8F unipolar coil electrode is also inserted in conjunction with the t r ipolar lead to serve as the second electrode. The 100 cm, 12F tr ipolar Endotak lead (model 0062 [n = 1], model 0064 In = 3], and model 0074 [n = 3]) consists of a t ined tip,

an adjacent distal coil electrode, and a proximal coil electrode. In 3 pat ients with chronically implanted ventricular pacing leads at the apex of the right ventricle, the active fixation t r ipolar Medtronic lead was posit ioned in the region of the right ventricular outflow tract (Fig. 1). In all 7 pat ients receiving an Endotak system, the t ined t r ipolar Endotak lead was placed at the apex of the right ventricle (Figs. 2 to 4). The transvenous ICD leads were implanted in the pacemaker laboratory before intraoperat ive ICD implanta t ion in 6 pat ients and at the t ime of ICD implanta t ion in the other 5 patients .

ICD testing. Defibril lation threshold testing and ICD implanta t ion were performed intraoperat ively under general anesthesia. Defibril lation threshold test ing was performed according to the manufacturer ' s protocol as out- l ined previously. 5 During defibril lation threshold testing all pacemakers were reprogrammed to the asynchronous (DOO or VOO) pacing mode at 80 beats /min the maximal programmable output and pulse width. Ventricular fibril- lat ion was induced by brief delivery of 60 Hz al ternat ing current through the t r ipolar lead. In pat ients receiving an Endotak system (n = 7), the external cardioverting device (model 2806) was set in the automatic mode during defibril lation threshold testing to simulate the actual detect ion algori thm of the ICD. In one pat ient receiving a

Volume 129, Number 1

American Heart Journal ~roo~,3 et al. 47

6 7 8 9 10 I1

66/M 55/M 82/M 43/M 81/M 77/M DCM CAD CAD DCM CAD CAD 0.27 0.29 0.26 0.41 0.29 0.22

VF VT VT VT VT VT VT VT VT VT VT VF CHB CHB SSS SSS SSS SSS

PS PS II PS II Medtronic 8420 PP II PS VVI -~ DDD DDD -~ ODO DDD --~ AAI VVI DDD DDD -- AAI LSCV LSCV RSCV RSCV RSCV RSCV U - ~ B U B B B B Apex Apex Apex RVIT RVIT Apex Yes No Yes No Yes No

Transvene Transvene Endotak Transvene Endotak Endotak RSCV RCV LSCV LSCV LSCV LSCV RVOT RVOT Apex Apex Apex Apex Medtronic PCD Ventritex Cadence CPI PRX Medtronic Jewel CPI PRX CPI P2 P -~ ICD P -* ICD P ~ ICD P - - ICD P ~ ICD P ~ ICD

P revised after P inactivated, Ventricular lead P rate set at <ICD P lead repositioned P reprogrammed ICD: back-up VVI repositioned to rate to RVOT to AAI mode VVI --~ DDD pacing from ICD RVOT

Medtronic jewel ICD, the external cardioverting device (model 9760) also allowed ar rhythmia detect ion during defibril lation testing in an automatic mode. Two pat ients receiving Medtronic PCD systems underwent test ing with an external cardioverting device (model 9715B) in the manual mode. One final pat ient underwent testing in the manual mode with a Ventr i tex (Sunnyvale, Calif.) external cardioverting device (model HVS-02). In these three instances, defibril lat ion was a t t empted after 10 seconds of elapsed arrhythmia. The rate-sensing channel of the ICD and two surface electrocardiograms were recorded on paper (25 mm/sec) before, during, and after all a r rhythmia inductions. The implanted ICD device was tested with the pacemaker programmed in the asyncbronous mode at the aforementioned settings.

Pacemaker system revisions. Revision of the pacemaker system was performed before ICD implanta t ion in 2 patients , in t raoperat ively in 7 patients, and after ICD implanta t ion in 1 pa t ien t (Table I). Pa t ien t 1 did not require revision of his pacemaker system. In pat ient 2 it was determined tha t both a pacemaker and ICD were necessary, and the pacemaker was implanted 10 days before the ICD. In this pat ient the ventr icular pacing lead was posi- t ioned at the right ventr icular outflow tract to allow subsequent placement of an Endotak lead at the right ventricular apex (Fig. 2). In pa t ien t 3, a bipolar atr ial lead and single-chamber pacemaker were placed at the t ime of insertion of the Endotak lead (Fig. 3). In pat ient 4, who had a preexist ing unipolar dual-chamber pacing system, the

pacemaker was init ially reprogrammed to the AAI mode during intraoperat ive testing. However, despite reprogramming to this mode, large pacemaker st imulus art ifacts were present on the ICD rate channel, resulting in multiple counting, part icular ly in the immediate postshock period. At intraoperat ive ICD implantat ion, a new bipolar lead and a single-chamber atr ial pacemaker were implanted with an ICD containing VVI pacing functions (Fig. 4). In pat ients 5 and 11, who had bipolar dual-chamber pacemakers, the Endotak lead was placed in close proximity to the pacemaker lead, which was also posit ioned at the right ventricular apex. These patients , who received ICDs capable of VVt pacing, bad their DDD pacemakers reprogrammed to the AAI mode. Pa t ien t 6 underwent revision of his pacemaker system after ICD implantat ion. The original system consisted of a unipotar VVI pacemaker tha t was upgraded to a dual-chamber system by placing new bipolar atrial and ventricular leads. Pa t ien t 7, who had a unipolar dual-chamber pacemaker placed for t ransient peri infarction heart block, had his pacemaker inactivated in lieu of replacing the pacemaker leads. Pa t ien t 7 also received an ICD with VVI pacing functions. Pa t ien t 8, who had a bipolar dual chamber pacemaker placed 1 month earlier, underwent repositioning of the ventricular pacing lead at the t ime of ICD implantat ion to facilitate placement of an Endotak lead at the right ventricular apex. In pat ient 9 with a bipolar ventricular pacemaker lead implanted at the mid right ventricle, a Medtronic t r ipolar lead was posit ioned at the right ventricular apex (Fig. 5). The

January 1995

48 Brooks et al. American Heart Journal

Fig. 1. Posterior-anterior chest x-ray film shows previously implanted unipolar pacemaker in patient 8, who had transient postinfarction heart block. Pacemaker leads were positioned in atrium and at right ventricular apex. Tripo- lar Medtronic lead was inserted with tip placed at right ventricular outflow tract. Second coil electrode is positioned in right atrium.

rate of the VVI pacemaker was set below ICD VVI pacing rate. Patient 10, who also had a ventricular pacemaker lead positioned at the right ventricular inflow tract, had an En- dotak lead placed at the apex of the right ventricle. How- ever, because of detection of pacemaker stimuli on the ICD rate-sensing lead, this patient's pacemaker lead was repositioned to the right ventricular outflow tract.

RESULTS ICD implantation. Satisfactory R-wave amplitudes

(12 + 3 mV), pacing thresholds (0.64 _+ 0.3V), and lead resistances (445 _+ 41 ohms) were obtained in all patients. In all cases, local pacemaker electrograms were absent or only minimally detectable on the ICD rate-sensing lead, and in no case did the pacemaker stimulus exceed the peak-to-peak R-wave amplitude of the ICD by >20 %. With the final pacemaker revision, no clinically significant sensing interaction was observed during defibrillation threshold or ICD testing in any patient. All patients received an ICD system during the same intraoperative session. Eight (73 % ) of 11 patients received a nonthoracotomy system with a mean defibrillation threshold established

at 15 + 5 J. Three patients required thoracotomy because of inability to achieve satisfactory defibrillation thresholds <18 J by means of a nonthoracotomy approach despite testing multiple configurations. In these patients a hybrid configuration incor- porating a single left ventricular extrapericardial patch and two transvenous coil electrodes were used. The ICD pulse generators implanted are shown in Table I. None of the pacemakers used (Table I) were reset to start-up modes by ICD shock delivery. In two patients there was transient loss of pacemaker capture after ICD shock therapy, which reaolved after one or two noncaptured beats.

Follow-up. All patients underwent repeat ICD testing before discharge. All ICD devices showed normal sensing, antitachycardia pacing, and cardioversion/ defibrillation functions. All patients were discharged alive from hospital and have been monitored for a mean of 8.8 _+ 9 (range 3 to 26) months. The pacemaker and ICD systems have been observed to function normally during follow-up visits, including rou- tine 8-week ventricular fibrillation inductions, as part of the investigational protocols. Four (36 %) patients received appropriate ICD shock or antitachycardia pacing therapy during the follow-up period. No pacemaker resets were noted at the time of therapy delivery in these patients. No additional modification was necessary to any patient's system after discharge.

DISCUSSION

The 11 patients who required combined pacemaker and ICD systems were successfully managed. The main problems were previously implanted unipolar pacemakers (n = 3) and ventricular pacing leads positioned at the right ventricular apex (n = 8), the latter problem interfering with optimal placement of the tripolar ICD lead. The approaches used to solve these problems were individualized to each patient's set of circumstances and included placement of the ICD transvenous lead at the right ventricular outflow tract (n = 3), initial placement (n = 1) or subsequent repositioning (n = 2)' of the right ventricular pacing lead at the outflow ~ract, upgrade from unipolar to bipolar pacemaker systems (n = 2), reprogramming from DDD to AAI pacing modes (n = 2), inactivation of the pacemaker (n = 1), reduction of the VVI pacemaker rate to below the ICD pacing rate (n = 1); and simultaneous placement of a single-chamber atrial pacemaker with the ICD lead (n = 2). These modifications fulfilled the pacing requirements in all patients and prevented adverse sensing interaction between the two systems. Con- siderations in managing patients who required com-

Volume 129, Number 1 American Heart Journal Brooks et al. 49

- ~ ' ' : ' ~ ' I , , .-,',~," " ~ = ,~ ~ .

Fig. 2. Patient 2 had complete heart block and underwent implantation of bipolar dual-chamber pacing system 14 days before ICD implantation. In anticipation of ICD implantation, ventricular pacemaker lead was placed at right ventricular outflow tract to allow position- ing of tripolar Endotak lead at apex of right ventricle. Re- lation between ventricular pacing and ICD leads in this patient is considered optimal when combined systems are required.

bined pacemakers and nonthoracotomy transvenous ICD systems are summarized in Table II.

Determinants of cross-talk between pacemaker and ICD s y s t e m s . The potential incompatability of separately implanted pacemaker and transvenous ICD systems results from the detection of pacemaker stimuli on the ICD rate-sensing channel. Sensing of pacemaker stimuli on the ICD rate lead depends to a large extent on the far-field effect of the pacemaker stimuli, that is, the size of the pacemaker spike relative to the local electrogram on the ICD sensing channel. 6 In general, pacemaker leads that are in close proximity to the ICD lead have a large pace- sense dipole, and are in parallel to them will result in a greater far-field effect and larger signals on the ICD lead. Unipolar pacemaker artifacts may lead to substantial far-field effect and in most cases to very large signals, even if the two leads are placed far apart. The far-field effect of pacemaker stimuli may be more of an issue with the Endotak relative to the Transvene system because of inherent sensing differences be-

' .~ ; :;. =.=, J

• - ~ " i ' ' , , , ' " ~ i " ,

: ~,~-~; : ~ : :;" -.. . ' . . ' .

Fig. 3. Patient 3 had symptomatic sinus bradycardia and underwent implantation of single-chamber atrial pacemaker at time of insertion of tripolar Endotak lead.

tween these two systems. Bipolar sensing in the Medtronic system occurs between the tip of the electrode and an adjacent sensing ring whereas, with the Endotak lead, bipolar sensing occurs between the tip and the distal coil electrode. With the Medtronic system, true bipolar sensing takes place between two closely spaced electrodes, resulting in a smaller pace-sense dipole. In contrast, with the CPI system a relatively greater interelectrode distance is present and results in a larger pace-sense dipole. Conse- quently, the potential for detecting far-field signals may be somewhat greater with the Endotak lead and relatively less with the Transvene lead. Owing to these differences, a pacemaker lead positioned at the right ventricular inflow tract may be compat- ible with a Transvene lead placed at the right ventricular apex despite their parallel positions, as dem- onstrated in one of our patients (Figs. 5 and 6). In contrast, Endotak and pacemaker leads should be placed farther apart, ideally at right angles to one another, to minimize far-field effect. Because the tined Endotak lead must be positioned at the right ventricular apex, the pacemaker lead in effect should optimally be placed at the right ventricular outflow tract (Fig. 2).

January 1995


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, ' e l

irish: ,.r

, i.~,~,

1 . . . .

Fig. 4. Patient 4 had sinus node dysfunction and previously implanted unipolar dual-chamber pacemaker underwent placement of tripolar Endotak lead at right ventricular apex. Despite reprogramming pacemaker to AAI mode, large pacemaker stimuli were present on ICD rate-sensing channel. At time of ICD implantation new bipolar atrial lead placed in conjunction with single-chamber pacemaker resolved sensing interaction. Old pacemaker system was not removed.

Fig. 5. Patient 9 with previously implanted bipolar VVI pacemaker lead in mid right ventricle underwent placement of Medtronic tripolar lead at right ventricular apex. Despite close proximity of two ventricular leads, ventricular pacemaker spikes were not detected on ICD rate-sensing channel (see Fig. 6).

Table II, Considerations in patients receiving combined transvenous ICD and endocardial pacemaker systems

1. In a patient with a previously implanted pacemaker, does the patient still need the pacemaker?

2. Is the current mode of pacing necessary (e.g., DDD) or adequate (e.g., VVI)?

3. Is the lead system unipolar or bipolar? 4. With the present pacemaker generator, is there potential for

reset to unipolar pacing during ICD shock therapy? 5. Could the patient be managed with VVI pacing from the ICD

system alone? 6. In a patient requiring separately implanted DDD or VVI

pacemaker systems, the ventricular pacing lead (rather than the ICD transvenous lead) should be preferentially implanted in the region of the RVOT.

7. In a patient with a DDD pacemaker, could the patient be managed with AAI pacing along with back-up VVI pacing from the ICD?

8. Be sure to test the pacemaker in the asynchronous mode during defibrillation and ICD testing to ensure appropriate ICD sensing.

Reprogramming of pacemakers to eliminate interaction. Consistent with other reported series, a major- ity of our patients (n = 9) required atrial or dual- chamber pacing, most commonly for sinus node dysfunct ion (Table I). Because most pat ients with sinus node dysfunct ion can be satisfactorily managed by single-chamber atrial pacing, 7, s one option tha t can be used to prevent sensing interaction in pat ients

Volume 129, Number 1 American Heart Journal Brooks et al. 51

Oct. 6, 1993 . . . 25mm/sec

,~ SINUS RHYTHM WITH VO0 PACING

ECG 2 --.~ I j - ~ r . ~ , . . - -

M A R K E R CHANNEL

[ I I 0.44 0:48 0 :50

Arrhythmia Induction

VENTRICULAR - - FIBRILLATION

I • ' ' 1 ' " I 0:46 0:52 0:54

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ICD Shock I

- - ~ - VENTRICULAR FIBRILLATION ~ f - - SINUS RHYTHM WITH VO0 PACING

I

I

ECG 1

ECG 2

M A R K E R CHANNEL

0:56 ~ O: 58 t :00 |

Detection Satisfied

v - - 7 I ̧ I

1'02 t : 04 1 0 6

Fig. 6. Two surface ECG leads and ICD marker channel during testing in patient 9, who had VVI pacemaker placed previously in conjunction with Medtronic transvene ICD system. Pacemaker is reprogrammed to VOO mode during testing. Despite presence of bipolar pacemaker spike artifact on ECG leads, no pacemaker spike artifact is detected on ICD marker channel and sensing before, during, and after induced yen- tricular fibrillation is normal.

with previously implanted bipolar dual-chamber pacemaker systems is to reprogram the pacemaker to the AAI mode. The atrial bipolar stimulus is remote from the ventricular lead and generally so small on the ICD rate-sensing channel that it does not inter- fete with arrhythmia detection. Four patients in the present series were managed by AAI pacing alone. Two patients with preexisting bipolar DDD pacemakers were reprogrammed to the AAI mode. A third patient with a unipolar DDD system had her pacemaker inactivated. In this patient a new bipolar atrial lead was placed in conjunction with a single-chamber atrial pacemaker. In each patient reprogramming from DDD to AAI pacing proved satisfactory and, of practical importance, obviated the need to revise the

chronically implanted ventricular pacing lead, which was left in its original position. Moreover, it permit- ted placement of an Endotak lead at the right ventricular apex in all three patients. A fourth patient with no previously implanted pacemaker received a single-chamber atrial pacemaker at the time of implantation of an Endotak lead. All three patients with previously implanted DDD pacemakers who received AAI pacing also received an ICD with VVI pacing functions (Table I). Although AAI pacing satisfied the needs of these patients, we preferred to have back-up VVI pacing available because of the potential risk of heart block.

Frequency of combined ICD and pacemaker systems. The frequency of combined pacemaker and ICD sys-

January 1995


tems in the present series is 6 %, well below the 15 % to 20 % reported previously in series of patients with thoracotomy-implanted systems. 1-3 The lower number in the present series may in part be accounted for by the use of ICD pulse generators that incorporated VVI pacing functions in 9 of 11 patients. The pacemaker function of ICDs subserves a back-up role and is generally satisfactory in patients with postshock bradyarrhythmias or long pauses during atrial fibrillation or in patients at potential risk for heart block. In the past, patients who required back~up VVI pacing for these indications required separate pacemakers in conjunction with their ICD systems; this practice may account for the higher percentage of patients with pacemakers in earlier series of ICD recipients.

Frequency of ICD-pacemaker interaction. In earlier series the reported frequency of significant pacemaker-ICD interaction was <1% .1 The low rate of interaction is the result of widespread recognition of potential problems and meticulous intraoperative testing to ensure that sensing interaction is absent. The most significant problems encountered were double rate counting and arrhythmia nondetection. These problems were first recognized in patients with unipolar pacing systems because of the large pacemaker stimulus artifact, but have also been described in patients with bipolar systems in which the pacemaker stimulus is also large. 9 Another potential problem in patients with pacemakers is transient loss of capture and "reset" of the pacemaker to the start-up mode (usually unipolar) after ICD shock delivery. The potential for the reset problem exists in patients with older pacemakers, particularly those capable of unipolar and bipolar pacing, but is not a problem in those with a dedicated bipolar system. This problem did not occur in the patients in the present series with the pacemakers used (Table I), and therefore the potential risk of inadvertent unipolar pacing was considered extremely small.

ICDs with pacemaker functions. The latest genera- tion of ICD pulse generators also contain VVI pacing functions. However, in VVI pacemaker-dependent patients continuous pacing will result in substantial battery drain, even if the pacemaker function of the ICD is programmed at nominal settings. With all of the ICDs implanted in the present series, continuous pacing would potentially result in premature battery depletion and, in some cases, shorten the life of the battery by _>50% or more. Because of the high cost of the ICD, it is not cost-effective to use it as the primary pacing modality in pacemaker-dependent patients. In these patients separate pacemaker and ICD systems are necessary. Although 9 patients received

an ICD with VVI pacing functions, 8 of the 11 patients in the present series were pacemaker dependent and required separately implanted pacemakers. Technologic advances in future generations of ICD pulse generators may require less energy to perform pacing functions and may not substantially reduce battery life in pacemaker-dependent patients. More advanced ICD systems may contain dual- chamber pacing capabilities, rendering separately implanted pacemaker-ICD systems unnecessary in most patients. Until these systems become available, separately implanted pacemaker systems will be required in appropriately selected patients with transvenous ICDs. The present study suggests that implantation of separate endocardial pacing and ICD systems is feasible, that potential technical difficul- ties can be overcome, and that potentially adverse interactions can be avoided with careful planning and meticulous testing in these patients. Physicians implanting pacemakers into potential ICD recipients are encouraged to use dedicated bipolar systems and to ideally implant these leads at the right ventricular outflow tract.

Limitations. One option we did not use to facilitate optimal placement of the transvenous ICD leads was extraction of chronically implanted pacing leads. We did not believe that this procedure was generally worth the risk or effort because in most cases the lead had been implanted for many years. Of potential concern to defibrillation threshold testing with nonthoracotomy configurations is the position of the distal coil electrode at the right ventricular outflow tract rather than its customary location at the apex. In the present series two patients with leads positioned at the right ventricular outflow tract required thoracotomy, although a third patient did not. Al- though the eccentric position of the lead may have contributed to a failure to achieve adequate defibrillation thresholds, it was not believed to be the primary factor responsible for unsuccessful nonthoracotomy implantation in these patients because other variables were identified. 5 Nevertheless, for reasons of optimal defibrillating efficacy with nonthoracotomy configurations and to ensure long-term lead stability, the tripolar lead should ideally be positioned at the apex of the right ventricle. Finally, in some patients a more practical solution was sought, for example, reprogramming from DDD to AAI modes. It may be argued that this avoided rather than solved potential sensing interaction between the two ventricular leads, although in these instances the modification was sufficient and the patient was thereby exposed to a minimal number of interven- tions.

Volume 129, Number 1 American Heart Journal ~roo~8 et aL 53

REFERENCES

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2. Epstein AE, Kay GN, Plumb VJ, Shepard RB, Kirkhn JK. Combined automatic implantable cardioverter-defibrillator and pacemaker systems: implantation techniques and follow-up. J Am Coil Cardiol 1989;13:121-31.

3. Calkins H, Brinker J, Velm E, Guarnieri T, Levine JH. Clinical rater- actions between pacemakers and automatic implantable cardioverter- defibrillators. J Am Cell Cardiol 1990;16:666-73.

4. Kim SG, Gurman S, Waspe LE, Brodman R, Fisher JD. Unipolar pacer artifacts induced failure of automatic implantable cardioverter-defibri]lator to detect ventricular fibrillation. Am J Cardio11986;57:880-1.

5. Brooks R, Garan H, Torchiana D, Vlahakes GJ, Newell J, McGovern

BA, Garan H, Ruskin JN. Determinants of successful nonthoracotomy cardieverter-defibrillator implantation: experience in 101 patients us- ing two different lead systems. J Am Cell Cardiel 1993;22:1835-42.

6. Furman S. Sensing and timmg the cardiac electrogram. In: Furman S, Hayes DL, and Holmes DR, eds. A practice of cardiac pacing. Mount Kisco, N.Y.: Futura, 1989:79-114.

7. Rosenqvist M, Obel I. Atrial pacing and the risk of AV block: is there a time for change in attitude? PACE 1989;12:97-10L

8. Barold SS. The fourth decade of cardiac pacing: optimal modes of stimulation. Primary Cardiol 1993;19:16-32.

9. Kelly PA, Cannom DS, Garan H, Mirabal GS, Harthorne JW, Hurvitz RT. Vlahakes GJ, Jacobs MA, Ilvento JP, BuckIey M J, Ruskin JN. The automatic implantable cardioverter-defibrillator; efficacy, complica- tions, and survival in patients with malignant ventricular arrhythmias. J Am Cell Cardiol. 1988;11: 1278-86.

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Documents

Implantation of transvenous nonthoracotomy cardioverter-defibrillator systems in patients with permanent endocardial pacemakers