GUEST EDITORIAL
Endocardial Lead Systems for Implantable Cardioverter Defibrillators: Uncertain Progress Beyond Base Camp SANJEEV SAKSENA From the Divisions of Cardiology, UMDNJ-NJ Medical School, Newark and the Eastern Heart Institute, Passaic, New Jersey
Endocardial electrode systems were envisioned for implantable cardioverter defibrillators (ICD) since the onset of device development. Prototype leads systems using a dual electrode catheter had unstable endocardial defibrillation thresholds even though lov^r energy shocks could selectively cardiovert slow ventricular tachycardia (VT).^'^ Prospective studies confirmed limited efficacy in rapid VT or ventricular fibrillation (VF) and questioned benefits of low energy endocardial cardioversion with respect to existing pacing modes.^•'* Other dual electrode systems using thoracic patch, right ventricular outflow tract, or coronary sinus electrodes did not provide definitive advantages.^~^ Human trials of a triple electrode configuration in 1985 using an atrial and ventricular electrode in conjunction with a thoracic patch lead were more encouraging, initially for endocardial cardioversion and later for defibrillation.^-^ Wider spatial distribution of current flow through the myocardium was deemed to mediate these advantages. These findings were also consistent with experimental and clinical literature in transthoracic and epicardial defibrillation that had long observed increasing defibrillation efficacy, often with lower energy requirements, using lead systems providing wider distribution of current flow over the heart. A variety of methods using larger electrodes, or-
Address for reprints: Sanjeev Saksena, M.D., 201 Lyons Avenue, Newark, NJ 07112. Fax: (201) 926-3313. Received July 29, 1991; accepted July 29, 1991.
PACE, Vol. 15
thogonal or other multielectrode systems, or contoured leads could achieve this end.^"'^* Recently, quantitative assessment of the voltage gradient that should exist in a minimum myocardial mass (usually the majority and often termed "critical") for effective defibrillation has been established.^^ Concomitantly, acute and chronic experience with first- and second-generation endocardial leads systems in ICD recipients is now accumulating.""*^ Despite this aura of progress, 30%-40% of unselected patients, will continue to require epicardial electrode systems especially if defibrillation thresholds < 20 joules (J) for endocardial lead implant are demanded. Higher yields have been achieved by exhaustive evaluation of optimal patch electrode location ("patch mapping"), multiple electrode configurations, and/or polarity testing or endocardial lead relocation.^^'^^ The multitude of testing procedures for this excess of choices at lead implant severely prolongs procedure duration and negates the thesis of increased implant safety with nonthoracotomy lead systems. The complexity of such implant procedures also undermines another cardinal goal, widespread applicability with more limited implant support requirements. Clinical experience has also unearthed novel problems and resurfaced old ones. Mechanical failures of long conducting elements in multiconductor leads unable to withstand stresses along the chest wall resulted in unnerving clinical events.** Unlike pacing lead failures, dire clinical consequences were fre-
February 1992
123
SAKSENA
quent. An unexplained rise in defibrillation threshold, multiple inappropriate shocks, failure to defibrillate, initiation of VTA'F, and sudden death could ensue. Even more threatening was the lead failure that remained asymptomatic detected only by exhaustive surveillance. Lead failures have occurred during short-term and longterm follow-up. Old pacing lead issues around coronary sinus leads such as lead stability assume new overtones in patients with VTA^F with added concerns of shock delivery in such thinwalled cardiac structures/ A fresh look at the basic tenets and direction for endocardial defibrillation lead development may now be indicated. The major objective of such lead development remains reducing ICD implant risk associated primarily, though not exclusively, with the need for a thoracotomy. Perioperative 30-day mortality in many recent multicenter ICD trials using epicardiai leads can equal the total sudden mortality in the survivors over the next several years.^^ This needs to be taken in context of early endocardial lead trial experiences, which show markedly lower perioperative risk despite arduous implant procedures. However, in the same vein, lessons from prior pacing lead experiences should not necessarily have to be reconfirmed. Less obvious benefits of endocardial leads in ICDs include advantages in long-term pacing threshold stability, particularly for devices using antitachycardia and demand pacing therapies. Another underrated but increasingly used benefit is the availability of an alternative for malfunctioning/infected epicardiai leads or use in conjunction with epicardiai leads in patients with high defibrillation energy requirements. Finally, endocardial lead system replacement should clearly be less traumatic for patients. Notwithstanding these laudable aims, realization of the promise requires intelligent blending of new defibrillation and prior pacing experience and definition of new research objectives. Established lead placement sites for endocardial pacing have strong and obvious reasons for continuing to be endorsed for hybrid pacemakerdefibrillator devices. Most importantly, substantial efficacy has been demonstrated for atriai and ventricular defibrillation electrodes for inclusion as part of the endocardial defibrillation lead sys-
124
tem. Clarity in dual chamber electrogram sensing and the capability of dual chamber pacing along established lines in this patient population adds strength to the argument. The concept of a generic endocardial pacing and defibrillation lead derived from such considerations and merits serious discussion.*^ Investigational focus on optimizing electrical and mechanical performance of such leads follows. Increasing efficacy and decreasing defibrillation thresholds can be approached by modifications in the energy waveform and lead system rather than excessive manipulation of available devices. Biphasic shock waveforms have been of some value in transthoracic and epicardiai defibrillation but their full promise may not have been realized perhaps due to fewer limitations in electrode design at these locations. Early data suggest greater benefit in reducing endocardial defibrillation thresholds and increasing yields up to 85%-90% of unselected patients using right atriai, ventricular, and left thoracic patch leads.^° Sufficiently low thresholds can raise the possibility of pectoral cardioverter defibrillator pulse generator implant. Continued investigation of the electrical and electrophysiological behavior of endocardial shocks also seems essential to lead design efforts. Quantitative evaluation of current flow and impedance with different shock patterns between different electrode locations established parameters for further development and has also shown inequities in current distribution.^* Refining leads and energy delivery patterns based on such information is an essential intermediate step. The mechanisms of defibrillation with endocardial shocks have begun to be systematically explored but much remains to be done.^^ Optimizing lead dimensions and mechanical performance in light of available experience will inspire greater confidence in such lead systems. Newer leads attempt to increase actual defibrillation electrode area by design changes without modifying external dimensions.*^'^° Yet such innovations cannot compromise other needs such as mechanical performance and ease of implant. In fact, lead tunneling may remain one of the strongest stimuli for efforts towards pectoral or axillary pulse generator implants. Base camp for this Himalayan expedition may only just have been struck.
February 1992
PACE, Vol. 15
ENDOCARDIAL LEAD SYSTEMS FOR ICDS
References Mirowski MM, Mower MM, Gott VL, et al. Feasibility and effectiveness of low energy catheter defibrillation in man. Circulation 1973; 47:79. Zipes DP, Jackman WM, Heger ]J, et al. Clinical transvenous cardioversion of recurrent life-threatening tachyarrhythmias: Low energy synchronised cardioversion of ventricular tachycardia and termination of ventricular fibrillation in patients using a catheter electrode. Am Heart J 1982; 103:789. Ciccone J, Saksena S, Shah Y, et al. A prospective randomised study of the clinical efficacy and safety of transvenous cardioversion for ventricular tachycardia termination. Circulation 1985; 71:571. Saksena S, Chandran P, Shah Y, et al. Comparative efficacy of transvenous cardioversion and pacing in patients with sustained ventricular tachycardia: A prospective, randomized crossover study. Circulation 1985; 72:153. Saksena S, An HL. Clinical efficacy of dual electrode systems for endocardial cardioversion of ventricular tachycardia: A prospective randomised crossover trial. Am Heart J 1990; 119:15. An HL, Saksena S, Mehra R. Effect of right ventricular cathode configuration on endocardial cardioversion and defibrillation with dual electrode systems and monophasic shocks. PACE 1990; 13(4):511. Bardy GH, Allen MD, Mehra R, et al. Transvenous defibrillation in man via the coronary sinus. Circulation 1990; 81:1252. Saksena S, Parsonnet V. Implantation of a cardioverter/defibrillator with thoracotomy using a triple electrode system. J Am Med Assoc 1988; 259:69. Lindsay BD, Saksena S, Rothbart ST, et al. Prospective evaluation of a sequential pacing and highenergy bidirectional shock algorithm for transvenous cardioversion in patients with ventricular tachycardia. Circulation 1987; 76:601. 10. Jones DL, Klein GJ, Kallok MJ. Improved internal defibrillation with twin pulse sequential energy delivery to different lead orientations in pigs. Am J Cardiol 1985; 55:821. 11. Dixon EG, Tang AS, Wolf PD, et al. Improved defibrillation thresholds with large contoured epicar-
PAGE, Vol. 15
12. 13.
14.
15. 16.
17.
18.
19.
20. 21.
22.
February 1992
dial electrodes and biphasic waveforms. Girculation 1987; 76:1176. Chen P-S, Wolf PD, Glaydon FJ, et al. The potential gradient field created by epicardial defibrillation electrodes in dogs. Circulation 1986; 74:626. Saksena S, Tullo NG, Krol RB, et al. Initial clinical experience with endocardial defibrillation using an impiantable cardioverter/defibrillator with a triple electrode system. Arch Int Med 1989; 149:2333. Tullo NG, Saksena S, Krol RB, et al. Management of complications associated with a first-generation endocardial defibrillation lead system for implantable cardioverter-defibrillators. Am J Gardiol 1990; 66:411. Saksena S, Mehta D, Krol RB, et al. Experience with a third generation impiantable cardioverterdefibrillator. Am J Gardiol 1991; 67:1375. Leitch JW, Gillis AM, Wyse DG, et al. Reduction in defibrillator shocks with an impiantable device combining antitachycardia pacing and shock therapy. J Am Goll Gardiol 1991; 18:145. McGowan R, Maloney JD, Wilkoff B, et al. Automatic impiantable cardioverter-defibrillator implantation without thoracotomy using an endocardial and submuscular patch system. J Am Goll Gardiol 1991; 17:415. Saksena S, Poczobutt-Johanas M, Gastle L, et al. Long-term experience with a second generation impiantable pacemaker-defibrillator. J Am Goll Gardiol 1991 (In press). Saksena S, Scott SE, Accorti P, et al. Efficacy and safety of monophasic and biphasic waveform shocks using a braided endocardial defibrillation lead system. Am Heart J 1990; 120:1342. Saksena S, Ward DE, Krol RB, et al. Efficacy of braided endocardial defibrillation leads: Acute testing and chronic implant. PAGE 1991; 14:719. An HL, Saksena S, Tullo NG, et al. Gomparison of epicardial and endocardial lead systems for an impiantable third-generation hybrid cardioverterdefibrillator. J Am Goll Gardiol 1991; 17:55A. Jones JL, Jones RE, Balasky G. Improved cardiac cell excitation with symmetrical biphasic waveforms. Am J Physiol 1987; 253:H1418.
125
Endocardial Lead Systems for Implantable Cardioverter Defibrillators: Uncertain Progress Beyond Base Camp SANJEEV SAKSENA From the Divisions of Cardiology, UMDNJ-NJ Medical School, Newark and the Eastern Heart Institute, Passaic, New Jersey
Endocardial electrode systems were envisioned for implantable cardioverter defibrillators (ICD) since the onset of device development. Prototype leads systems using a dual electrode catheter had unstable endocardial defibrillation thresholds even though lov^r energy shocks could selectively cardiovert slow ventricular tachycardia (VT).^'^ Prospective studies confirmed limited efficacy in rapid VT or ventricular fibrillation (VF) and questioned benefits of low energy endocardial cardioversion with respect to existing pacing modes.^•'* Other dual electrode systems using thoracic patch, right ventricular outflow tract, or coronary sinus electrodes did not provide definitive advantages.^~^ Human trials of a triple electrode configuration in 1985 using an atrial and ventricular electrode in conjunction with a thoracic patch lead were more encouraging, initially for endocardial cardioversion and later for defibrillation.^-^ Wider spatial distribution of current flow through the myocardium was deemed to mediate these advantages. These findings were also consistent with experimental and clinical literature in transthoracic and epicardial defibrillation that had long observed increasing defibrillation efficacy, often with lower energy requirements, using lead systems providing wider distribution of current flow over the heart. A variety of methods using larger electrodes, or-
Address for reprints: Sanjeev Saksena, M.D., 201 Lyons Avenue, Newark, NJ 07112. Fax: (201) 926-3313. Received July 29, 1991; accepted July 29, 1991.
PACE, Vol. 15
thogonal or other multielectrode systems, or contoured leads could achieve this end.^"'^* Recently, quantitative assessment of the voltage gradient that should exist in a minimum myocardial mass (usually the majority and often termed "critical") for effective defibrillation has been established.^^ Concomitantly, acute and chronic experience with first- and second-generation endocardial leads systems in ICD recipients is now accumulating.""*^ Despite this aura of progress, 30%-40% of unselected patients, will continue to require epicardial electrode systems especially if defibrillation thresholds < 20 joules (J) for endocardial lead implant are demanded. Higher yields have been achieved by exhaustive evaluation of optimal patch electrode location ("patch mapping"), multiple electrode configurations, and/or polarity testing or endocardial lead relocation.^^'^^ The multitude of testing procedures for this excess of choices at lead implant severely prolongs procedure duration and negates the thesis of increased implant safety with nonthoracotomy lead systems. The complexity of such implant procedures also undermines another cardinal goal, widespread applicability with more limited implant support requirements. Clinical experience has also unearthed novel problems and resurfaced old ones. Mechanical failures of long conducting elements in multiconductor leads unable to withstand stresses along the chest wall resulted in unnerving clinical events.** Unlike pacing lead failures, dire clinical consequences were fre-
February 1992
123
SAKSENA
quent. An unexplained rise in defibrillation threshold, multiple inappropriate shocks, failure to defibrillate, initiation of VTA'F, and sudden death could ensue. Even more threatening was the lead failure that remained asymptomatic detected only by exhaustive surveillance. Lead failures have occurred during short-term and longterm follow-up. Old pacing lead issues around coronary sinus leads such as lead stability assume new overtones in patients with VTA^F with added concerns of shock delivery in such thinwalled cardiac structures/ A fresh look at the basic tenets and direction for endocardial defibrillation lead development may now be indicated. The major objective of such lead development remains reducing ICD implant risk associated primarily, though not exclusively, with the need for a thoracotomy. Perioperative 30-day mortality in many recent multicenter ICD trials using epicardiai leads can equal the total sudden mortality in the survivors over the next several years.^^ This needs to be taken in context of early endocardial lead trial experiences, which show markedly lower perioperative risk despite arduous implant procedures. However, in the same vein, lessons from prior pacing lead experiences should not necessarily have to be reconfirmed. Less obvious benefits of endocardial leads in ICDs include advantages in long-term pacing threshold stability, particularly for devices using antitachycardia and demand pacing therapies. Another underrated but increasingly used benefit is the availability of an alternative for malfunctioning/infected epicardiai leads or use in conjunction with epicardiai leads in patients with high defibrillation energy requirements. Finally, endocardial lead system replacement should clearly be less traumatic for patients. Notwithstanding these laudable aims, realization of the promise requires intelligent blending of new defibrillation and prior pacing experience and definition of new research objectives. Established lead placement sites for endocardial pacing have strong and obvious reasons for continuing to be endorsed for hybrid pacemakerdefibrillator devices. Most importantly, substantial efficacy has been demonstrated for atriai and ventricular defibrillation electrodes for inclusion as part of the endocardial defibrillation lead sys-
124
tem. Clarity in dual chamber electrogram sensing and the capability of dual chamber pacing along established lines in this patient population adds strength to the argument. The concept of a generic endocardial pacing and defibrillation lead derived from such considerations and merits serious discussion.*^ Investigational focus on optimizing electrical and mechanical performance of such leads follows. Increasing efficacy and decreasing defibrillation thresholds can be approached by modifications in the energy waveform and lead system rather than excessive manipulation of available devices. Biphasic shock waveforms have been of some value in transthoracic and epicardiai defibrillation but their full promise may not have been realized perhaps due to fewer limitations in electrode design at these locations. Early data suggest greater benefit in reducing endocardial defibrillation thresholds and increasing yields up to 85%-90% of unselected patients using right atriai, ventricular, and left thoracic patch leads.^° Sufficiently low thresholds can raise the possibility of pectoral cardioverter defibrillator pulse generator implant. Continued investigation of the electrical and electrophysiological behavior of endocardial shocks also seems essential to lead design efforts. Quantitative evaluation of current flow and impedance with different shock patterns between different electrode locations established parameters for further development and has also shown inequities in current distribution.^* Refining leads and energy delivery patterns based on such information is an essential intermediate step. The mechanisms of defibrillation with endocardial shocks have begun to be systematically explored but much remains to be done.^^ Optimizing lead dimensions and mechanical performance in light of available experience will inspire greater confidence in such lead systems. Newer leads attempt to increase actual defibrillation electrode area by design changes without modifying external dimensions.*^'^° Yet such innovations cannot compromise other needs such as mechanical performance and ease of implant. In fact, lead tunneling may remain one of the strongest stimuli for efforts towards pectoral or axillary pulse generator implants. Base camp for this Himalayan expedition may only just have been struck.
February 1992
PACE, Vol. 15
ENDOCARDIAL LEAD SYSTEMS FOR ICDS
References Mirowski MM, Mower MM, Gott VL, et al. Feasibility and effectiveness of low energy catheter defibrillation in man. Circulation 1973; 47:79. Zipes DP, Jackman WM, Heger ]J, et al. Clinical transvenous cardioversion of recurrent life-threatening tachyarrhythmias: Low energy synchronised cardioversion of ventricular tachycardia and termination of ventricular fibrillation in patients using a catheter electrode. Am Heart J 1982; 103:789. Ciccone J, Saksena S, Shah Y, et al. A prospective randomised study of the clinical efficacy and safety of transvenous cardioversion for ventricular tachycardia termination. Circulation 1985; 71:571. Saksena S, Chandran P, Shah Y, et al. Comparative efficacy of transvenous cardioversion and pacing in patients with sustained ventricular tachycardia: A prospective, randomized crossover study. Circulation 1985; 72:153. Saksena S, An HL. Clinical efficacy of dual electrode systems for endocardial cardioversion of ventricular tachycardia: A prospective randomised crossover trial. Am Heart J 1990; 119:15. An HL, Saksena S, Mehra R. Effect of right ventricular cathode configuration on endocardial cardioversion and defibrillation with dual electrode systems and monophasic shocks. PACE 1990; 13(4):511. Bardy GH, Allen MD, Mehra R, et al. Transvenous defibrillation in man via the coronary sinus. Circulation 1990; 81:1252. Saksena S, Parsonnet V. Implantation of a cardioverter/defibrillator with thoracotomy using a triple electrode system. J Am Med Assoc 1988; 259:69. Lindsay BD, Saksena S, Rothbart ST, et al. Prospective evaluation of a sequential pacing and highenergy bidirectional shock algorithm for transvenous cardioversion in patients with ventricular tachycardia. Circulation 1987; 76:601. 10. Jones DL, Klein GJ, Kallok MJ. Improved internal defibrillation with twin pulse sequential energy delivery to different lead orientations in pigs. Am J Cardiol 1985; 55:821. 11. Dixon EG, Tang AS, Wolf PD, et al. Improved defibrillation thresholds with large contoured epicar-
PAGE, Vol. 15
12. 13.
14.
15. 16.
17.
18.
19.
20. 21.
22.
February 1992
dial electrodes and biphasic waveforms. Girculation 1987; 76:1176. Chen P-S, Wolf PD, Glaydon FJ, et al. The potential gradient field created by epicardial defibrillation electrodes in dogs. Circulation 1986; 74:626. Saksena S, Tullo NG, Krol RB, et al. Initial clinical experience with endocardial defibrillation using an impiantable cardioverter/defibrillator with a triple electrode system. Arch Int Med 1989; 149:2333. Tullo NG, Saksena S, Krol RB, et al. Management of complications associated with a first-generation endocardial defibrillation lead system for implantable cardioverter-defibrillators. Am J Gardiol 1990; 66:411. Saksena S, Mehta D, Krol RB, et al. Experience with a third generation impiantable cardioverterdefibrillator. Am J Gardiol 1991; 67:1375. Leitch JW, Gillis AM, Wyse DG, et al. Reduction in defibrillator shocks with an impiantable device combining antitachycardia pacing and shock therapy. J Am Goll Gardiol 1991; 18:145. McGowan R, Maloney JD, Wilkoff B, et al. Automatic impiantable cardioverter-defibrillator implantation without thoracotomy using an endocardial and submuscular patch system. J Am Goll Gardiol 1991; 17:415. Saksena S, Poczobutt-Johanas M, Gastle L, et al. Long-term experience with a second generation impiantable pacemaker-defibrillator. J Am Goll Gardiol 1991 (In press). Saksena S, Scott SE, Accorti P, et al. Efficacy and safety of monophasic and biphasic waveform shocks using a braided endocardial defibrillation lead system. Am Heart J 1990; 120:1342. Saksena S, Ward DE, Krol RB, et al. Efficacy of braided endocardial defibrillation leads: Acute testing and chronic implant. PAGE 1991; 14:719. An HL, Saksena S, Tullo NG, et al. Gomparison of epicardial and endocardial lead systems for an impiantable third-generation hybrid cardioverterdefibrillator. J Am Goll Gardiol 1991; 17:55A. Jones JL, Jones RE, Balasky G. Improved cardiac cell excitation with symmetrical biphasic waveforms. Am J Physiol 1987; 253:H1418.
125
