- Email: [email protected]
An outlook on future trends in the treatment of rhythm disorders
An Outlook on Future Trends in the Treatment of Rhythm Disorders Leonard S. Dreifus, MD
R
emarkably, thedevelopment of newer antiarrhythmic drugs, ablative and surgical techniques, cardiac pacemakers and antitachycardia/antifibrillatory devices in the management of serious cardiac arrhythmias and prevention of sudden death have totally changed our approach to the management of the cardiac patient. Since 1958, with the implantation of the first cardiac pacemaker, rapid advances have been made in the development of sophisticated electronic devices capable of interacting with the intrinsic cardiac mechanism. These devices may have more than 3 trillion programmable features, microprocessor-driven and capable of extended battery life, and may incorporate sensor technology to optimize cardiac output. Since the advent of cardiac delibrillators for the treatment of ventricular tachycardia and ventricular fibrillation, implantable antitachycardia/ antifibrillatory devices have been developed. These have more than 82% long-term effectiveness in preventing sudden cardiac death in high-risk patients. Catheter ablative procedures have evolved rapidly. Attempts to identify the least destructive and most efficient ablative techniques using radio frequency, directcurrent shock, laser or cryoablative techniques are in progress. Novel approaches for ablation of the coronary sinus and even the coronary arteries are also under investigation. Newer surgical ablative techniques for the interruption of accessory pathways, destruction of specific foci for ventricular arrhythmias and, more recently, isolating the sinus node and its connection to the atrioventricular node from the remainder of the atria have been effective in patients with atria1 fibrillation. Finally, new antiarrhythmic drugs, particularly those in class III, such as D-sotalol, clofilium, and a host of experimental agents should attract attention in the next few years. We are now challenged to discover new technologies to treat the dreaded diseases, some of which have not as yet been identified. The following overview clearly identifies the current knowledge and defines our future directions. The future holds great promise for further refinements and discoveries in the management of serious and intractable cardiac arrhythmias but we should remember: “In order to better we often mar what is.” (Shakespeare, King Lear).
CARDIAC PACEMAKERS The first pacemaker was implanted in a patient for complete atrioventricular (AV) heart block in 1958. Remarkably, this pacemaker was powered by a cadmium battery and contained fewer than 12 components. In contrast, modem pacemakers are now completely programmable, and offer the patient over a trillion different op tions. Breakthroughs in electronic design now offer multiprogrammability, microcircuitry, telemetry, extended battery life and almost unlimited capabilities that interact with the physiologic control of the heart. These pacemakers will offer the patient great hemodynamic advantages. Pacemakers can now store pertinent patient information, telemeter programming data, and can also function as Holter monitors. Although lithium battery technology may not be replaced in the near future, improved circuit design will undoubtedly contribute to more efficient use of current and extended pacemaker life. Stable low-threshold electrodes whose activity will not deviate significantly from critical values will enable the physician to measure the threshold at implant, select a safety factor and program the pulse generator accordingly. Future pacemaker designs will be able to self-adapt to intrinsic activity. Antitachycardia algorithms and antifibrillatory options will provide benefit by combination with developments in chemistry for power sources. Research into signal discrimination and interaction with the autonomic nervous system will undoubtedly emerge in the future. Over the past few years considerable research led to the introduction of sensor technology to optimize cardiac physiology. These developments have made a significant impact on pacemaker development. Conceivably, future pacemakers will offer various choices of more than 1 sensor technology. With further developments in artificial intelligence and computer modeling of pacemaker interactions with intrinsic rhythms, almost unlimited op portunities for newer pacemaker designs will emerge.’ Rate-responsive pacing was first introduced with the development of a mechanical sensor for detecting body activity using a piezoelectric crystal-sensing mechanism. Subsequently, automatic, QT interval-driven rate-responsive pacemakers, rate responsivenesslinked to a minute ventilation sensor, oxygen saturation-control pacemakers, and temperature-based modulated rate units have appeared.* Future developments in sensor technology may incorporate several of these disciplines to drive pacemakers in the most efficient physiologic fashion.3
From the Departments of Medicine, Thomas Jefferson University and Lankenau Hospital, Philadelphia, Pennsylvania. Address for reprints: Leonard S. Dreifus, MD, The Lankenau Hospital, Lancaster Avenue West of City Line, Philadelphia, Pennsylvania 19151.
AUTOMATIC IMPLANTABLE DEFIBRILLATORS In 1967, Mirowski conceived an approach to the prevention of sudden coronary death using a standby auto-
2J
THE AMERICAN
JOURNAL
OF CARDIOLOGY
VOLUME
64
matic defibrillator. The need for such a device emerged from some pertinent observations: first, the magnitude of sudden cardiac death-more than a half million people were dying suddenly in the United States each year; and second, identification of the mechanism of sudden coronary death by numerous observations in acute coronary care units using electrocardiographic monitoring. Cardiopulmonary resuscitation evolved in an agonizingly slow manner when one considers that electrical defibrillation of the heart was routinely used only to salvage animals to be reused in subsequent research experiments in the 1940s and 1950s. Notably, Paul Zoll demonstrated the effect of precordial electrical shock to defibrillate the heart and terminate supraventricular and ventricular tachycardia. Although development of an automatic implantable delibrillating device appeared beyond the capabilities of our technology, numerous obstacles were overcome, and with persistence, imagination and parallel developments in electronics the first implant in humans was performed in 1980.4 In 1985, the Food and Drug Administration approved these devices and thus ushered in the rapid acceptance of this technique in the prevention of sudden death due to ventricular tachycardia and ventricular fibrillation. At the onset of the third decade of this technology we are seeing sophisticated antitachycardia devices appear, which are capable of terminating both atria1 and ventricular tachyarrhythmias as well as affording adequate pacemaker function. In some instances, implantable devices with cardioverter/defibrillator capabilities are replacing the time-honored management of serious cardiac arrhythmias, long dominated by pharmacologic therapies. There are more than 7,600 automatic implantable cardioverter defibrillator (AICD) implants performed in many centers throughout the world. Remarkably, there has been more than 84% survival up to 2 years in these patients5 Furthermore, the potential exists for further reduction in sudden cardiac death due to ventricular tachycardia and fibrillation as the AICD technology and clinical management evolve. On the horizon are implantable cardioverter/defibrillators using nonepicardial electrode systems with electrodes in the right ventricle and left pectoral submuscular epicostal region.6 These sophisticated AICD devices are now interacting with other cardiac pacemaker devices. Many issuesare still unresolved. The selection of patients has become more liberal but not firmly established. The problem of patients with poor cardiac function receiving these units is still under intense investigation.’ Notably, the most efficient electrode configurations, pulse widths and wave forms are being studied. The search for lower-energy shocks that will efficiently control serious ventricular arrhythmias is in progress. The use of gradient maps to create an electrode configuration with more efficient defibrillation fields will ultimately improve our technology. The comparison of single vs double capacitor biphasic wave forms is still a matter for research. Predictably, the AICDs will take on various special functions, e.g., fully transvenous electrodes, totally programmable software, and “limitedneed” devices for apparently healthy patients to senseand defibrillate ventricular fibrillation prophylactically. These units would be capable of only a few shocks, would
have limited life and allow the patient to receive other types of units in the future.* CATHETER ABLATIVE TECHNIQUES The use of physical agents to modify conduction in a restricted area of the myocardium by ablative procedures, in order to treat cardiac arrhythmias, has been extensively explorecL9 The surgical interruption of normal and anomalous pathways, and more recently the foci or pathways of re-entry tachycardias, has offered new hope to patients with incessant and malignant cardiac arrhythmias. Other investigatorslO have demonstrated that altering the shape and polarity of discharge and the geometry of the electrode can greatly increase the amount of voltage and current delivered before arcing occurs. The numerous and meticulous studies of cardiac mapping have clearly made this technique a useful clinical discipline. Furthermore, transvenous catheter ablation procedures have saved many patients from the more traumatic open-chest operations. l i Recent investigations have focused on identifying the most effective means of catheter ablation using directcurrent shock fulguration, radio frequency fulguration, cryomodification procedures and, more recently, various laser radiation techniques. I2 Research as to the most effective medium of lasing is continuing. Investigators have now turned their attention toward developing the most effective means for ablation of specific electrophysiologic problems. Attempts have been made to modulate AV conduction rather than interrupt conduction completely. Direct transseptal approaches to destroying free wall anomalous pathways in difficult locations, appears as an attractive alternative to surgical ablation. Other unique procedures to ablate posterior septal pathways and other left-sided pathways are being intensively studied. Temperature-guided radio frequency coagulative techniques and unique approaches using the coronary arteries and foramen ovale are now being studied. With the establishment of precise precordial catheter and epicardial/endocardial mapping procedures, attempts to ablate ventricular tachycardia appear to be achieving clinical success. Questions still remain as to where to ablate in the case of ventricular tachycardia. Other issues remain, such as whether to ablate the earliest endocardial activation or areas of slow conduction. Attempts to identify the critical area for treatment of tachycardia will enhance the effectiveness of ventricular ablation.13 More precise selection of patients for these procedures is required Anodal unipolar shocks, altemative energy sources and balloon or suction electrode catheter ablation may lead to correct localization of the ablative shocksi At present, the advantage of transvenous catheter ablation is quite apparent, especially in poor-risk patients. ABLATIVE TECHNIQUES From the first attempts to ablate the AV node and producing AV heart block in canine models to the initial clinical experience, surgical ablative techniques have been extremely successful and life-saving in many inSURGICAL
THE AMERICAN
JOURNAL
OF CARDIOLOGY
DECEMBER5.1989
3J
A SYMPUSIUM:
NEW TRENDS IN THE TREATMENT
OF RHYTHM DISORDERS
~tances.*~ Interruption of specific accessory pathway@ introduced mapping-directed techniques to correct serious cardiac arrhythmias. Subsequently, these surgical procedures have become accepted therapy for patients with Wolff-Parkinson-White syndrome with either a history of atria1 fibrillation engendering ventricular fibrillation or incessant arrhythmias due to the operation of anomalous bypass tracts. I7 The treatment of Wolff-Parkinson-white arrhythmias using both endo- and epicardial approaches can be effective for mid- and left free wall pathways, although endocardial techniques appear preferable for anterior and left free wall anomalous pathwaysi The epicardial approach will remain for posterior septal pathways. Extension of these mapping techniques to patients with ventricular aneurysms and refractory ventricular tachycardias has led to the development of endocardial resection as well as endo- and epicardial encircling procedures. l9 Imaginative methods to interrupt AV nodal re-entry tachycardias by interruption of the perinodal fibers have been extremely effective. Surgical isolation of the sinus node and its conduction pathway to the AV node from the rest of the atria has been uniquely useful in patients with recurrent paroxysmal atria1 fibrillation.20
intractable cardiac arrhythmias. Imaginative engineering should be able to resolve the annoying and dreaded consequences of abnormal impulse formation and conduction in the human heart. Many of these goals have already been met, and with the rapid advances in our knowledge of electrophysiology it is hoped that there will be little left to do in the ensuing years. REFERENCES I. Ward DE and Camm AJ, eds. Clinical Electrophysiology of the Heart. Introductory Remarks. London, Edward Arnold: 1987. 2. Bloomfield P, Macareavey D, Kerr F, Fananapaxir L. Long-term follow-up of patients with the QT rate adaptive pacemaker. PACE 1989;12:111-114. 3. Stangl K, Wertxfeld A, Lochschmidt 0, Basler B, Mittnacht A. Physical movement sensitive pacing: comparison of two “activity’‘-triggered pacing systems. PACE 1989;12:102-110. 4. Mirowski M, Reid PR, Mower MM, Watkins L, Gott VL, Schauble JF, Langer A, Heihnan MS, Kolenik SA, Fischell RE, Weisfeldt ML. Termination of malignant ventricular arrhythmias with an implanted automatic defibrillator in human beings. N Engl J Med 1980;303:322-324. 5. Mercando AD, Furman S, Johnston D, Frame R, Brodman R, Kim Xi, Fisher JD. Survival of patients with the automatic implantable cardioverter defibrillator. PACE 1988;11:2059-2063.
6. Saksena S, Tulle N, Parsonnet V. Gielchinsky I, Karanam R. Initial experience with an implantable cardioverter/deIibriUator using a nonepicardial electrode system (abstr). Circulation 1988;78:suppl Il:ll-220. 7. Tchou PJ, Kadri N, Anderson J, Caceses JH, Jaxayeri M, Akhtar M. Automatic implantable cardioverter detibrillators and survival of patients with left ventricular dysfunction and malignant ventricular arrhythmias. Ann Intern Med 1988;109:529-534.
ANTIARRRYTHMIC DRUGS Intense investigation of new antiarrhythmic agents as well as critical studies attempting to identify new and clearer mechanisms of the older standbys is continuing. The classification of antiarrhythmic agents based on single-cell electrophysiologic principles remains complex, as many of the newer agents belong to more than 1 category. Any new clinical classification of antiarrhythmic drugs must consider the characteristics and origin of the arrhythmia.21 In many instances these characteristics are either vague or entirely unknown. Newer additions to the fast channel blocking agents (class I) that prolong refractoriness, and in some instances conduction velocity, can be effective in both supraventricular and ventricular arrhythmias. However, recent attention has been directed to classIII agents such as D-sotalol, clofiiium and experimental E-403 1.22The latter drug may have novel actions in that it may influence the effective refractory period of the normal myocardium quite differently from the myocardium of the ischemic zone. Amiodarone still shares a focal position in the investigation of antiarrhythmic agents. The characteristics of amiodarone are so atypical, and it influences the physiology of so many other organ systems, that it will remain a challenge to pharmacologists. In fact, Griffin and Mande123cited 37 published reports in 1987 in their recent review. Other class I agents, such as indecainide, propafenone, moricizine, pirmenol and ACC-9358, are also likely to attract important attention in the next few years as effective antiarrhythmic agents.
Publishing,
CONCLUSION The future holds great promise for further refinements and discoveries in the management of serious and
22. Katok H, Ogawa S, Furuno I, Sato Y, Yoh S, Saeki K, Nakamura Y. Patient electrophysiological effects of E-4031, a novel class III antiarrhythmic agent on reentrant ventricular tachycardia. Circulation I988:78:suppl II:&I 48. 23. Griffin JC, Mandel WJ. Clinical Concepts in Arrhythmias-An Annual Review--1988. Mount K&o, NYr Futura Publishing, 1988.
4J
THE AMERICAN
JOURNAL
OF CARDIOLOGY
VOLUME
64
8. Mower MM, Nisam S. AICD indications (patient selection): past, present and future. PACE 1988:11:2064-2070. 9. Fontaine G, Scheinman MM. Ablation in Cardiac Arrhythmias. Mount Kisco, NY: Futura
Publishing,
1987.
10. Ahsan AJ, Cunningham D, Rowland E, Richards AF. Catheter ablations fulguration: design and performance of a new system. PACE 1989;12:f 3f135. 11. Yagi Y, Schuessler RB, Boineau JP, COY. JL. Closed cheat cryomodification of atrioventricular conduction-is it feasible? (abstr). Circulation 1988;78:supp/ ll:ll-445. 12. Waldo AL. Chronology of the development of ablation techniques in the
treatment of cardiac arrhythmias. In: Scheinman MM, Fontaine G, eds. Ablation in Cardiac Arrhythmias. New York: Futura Publishing, 1987:1-4. 13. Fontaine G, Frank R, Tinet J, Grosgageat Y. Identification of a mne of slow conduction appropriate for VT ablation: theoretical and practical considerations. PACE
1989:12:262-267.
14. Beard TJ, Lavergne TL, Brunewald PR, Von Euw DJ, LeGrand BH, Guixe LJ, Heuxey JY, Peronneau PA. Efficiency of suction electrode catheter for radio frequency ablation of canine ventricular myocardium (abstr). Circulation 1988; 78:suppl ll:ll-307.
IS. Dreifus LS, Nichols H, Morse D, Watanabe Y, Truex R. Control of recurrent tachycardia of Wolff-Parkinson-White syndrome by surgical ligature of the A-V bundle. Circulation I %8:38:1030-1036. 16. Scaly WC, Gallagher JJ. Surgical treatment of left free wall accessory pathways of atrioventricular conduction of the Kent type. J Thorac Cardiomsc Surg 1981;81.698-706. 17. Dreifus LS, Haiat
R, Watanabe Y, Arriaga J, Reitman N. Ventricular fibrillation: a possible mechanism of sudden death in patients with Wolff-Parkinson-white syndrome. Circulation 1971;43:520-527. 18. Hoissaguerre M, Saoudi N, LeMetayer P, Kirkorian G, Alattah G, Touboul P, Warin JF. Closed cheat transseptal ablation of left free wall accessory pathway (abstr). Circulation 1988:78:suppl ll:ll-401. 19. Josephson ME, Horowitz LN, Spielman SR, Greenspan AM, Vandepol C, Harken AH. Comparison of endwardial catheter mapping with intra-operative mapping of ventricular tachycardia. Circulation 1980,61:395-404. 20. Defauw JJ, Van Hemel NM, Vermeulen FE, Kingma JH, Verrastte JM, Guirauden GM. Short-term results of the “corridor operation” for drug-refractory paroxysmal atria1 fibrillation (abstr). Circulation 1988;78:suppl ll:lI-48. 21. Puech P, Brugada J. A clinical classification of antiarrhythmic drugs. In: Brugada P, Wellens HJJ, eds. Where to Go from Here. New York Futura 1987:485-493.
R
emarkably, thedevelopment of newer antiarrhythmic drugs, ablative and surgical techniques, cardiac pacemakers and antitachycardia/antifibrillatory devices in the management of serious cardiac arrhythmias and prevention of sudden death have totally changed our approach to the management of the cardiac patient. Since 1958, with the implantation of the first cardiac pacemaker, rapid advances have been made in the development of sophisticated electronic devices capable of interacting with the intrinsic cardiac mechanism. These devices may have more than 3 trillion programmable features, microprocessor-driven and capable of extended battery life, and may incorporate sensor technology to optimize cardiac output. Since the advent of cardiac delibrillators for the treatment of ventricular tachycardia and ventricular fibrillation, implantable antitachycardia/ antifibrillatory devices have been developed. These have more than 82% long-term effectiveness in preventing sudden cardiac death in high-risk patients. Catheter ablative procedures have evolved rapidly. Attempts to identify the least destructive and most efficient ablative techniques using radio frequency, directcurrent shock, laser or cryoablative techniques are in progress. Novel approaches for ablation of the coronary sinus and even the coronary arteries are also under investigation. Newer surgical ablative techniques for the interruption of accessory pathways, destruction of specific foci for ventricular arrhythmias and, more recently, isolating the sinus node and its connection to the atrioventricular node from the remainder of the atria have been effective in patients with atria1 fibrillation. Finally, new antiarrhythmic drugs, particularly those in class III, such as D-sotalol, clofilium, and a host of experimental agents should attract attention in the next few years. We are now challenged to discover new technologies to treat the dreaded diseases, some of which have not as yet been identified. The following overview clearly identifies the current knowledge and defines our future directions. The future holds great promise for further refinements and discoveries in the management of serious and intractable cardiac arrhythmias but we should remember: “In order to better we often mar what is.” (Shakespeare, King Lear).
CARDIAC PACEMAKERS The first pacemaker was implanted in a patient for complete atrioventricular (AV) heart block in 1958. Remarkably, this pacemaker was powered by a cadmium battery and contained fewer than 12 components. In contrast, modem pacemakers are now completely programmable, and offer the patient over a trillion different op tions. Breakthroughs in electronic design now offer multiprogrammability, microcircuitry, telemetry, extended battery life and almost unlimited capabilities that interact with the physiologic control of the heart. These pacemakers will offer the patient great hemodynamic advantages. Pacemakers can now store pertinent patient information, telemeter programming data, and can also function as Holter monitors. Although lithium battery technology may not be replaced in the near future, improved circuit design will undoubtedly contribute to more efficient use of current and extended pacemaker life. Stable low-threshold electrodes whose activity will not deviate significantly from critical values will enable the physician to measure the threshold at implant, select a safety factor and program the pulse generator accordingly. Future pacemaker designs will be able to self-adapt to intrinsic activity. Antitachycardia algorithms and antifibrillatory options will provide benefit by combination with developments in chemistry for power sources. Research into signal discrimination and interaction with the autonomic nervous system will undoubtedly emerge in the future. Over the past few years considerable research led to the introduction of sensor technology to optimize cardiac physiology. These developments have made a significant impact on pacemaker development. Conceivably, future pacemakers will offer various choices of more than 1 sensor technology. With further developments in artificial intelligence and computer modeling of pacemaker interactions with intrinsic rhythms, almost unlimited op portunities for newer pacemaker designs will emerge.’ Rate-responsive pacing was first introduced with the development of a mechanical sensor for detecting body activity using a piezoelectric crystal-sensing mechanism. Subsequently, automatic, QT interval-driven rate-responsive pacemakers, rate responsivenesslinked to a minute ventilation sensor, oxygen saturation-control pacemakers, and temperature-based modulated rate units have appeared.* Future developments in sensor technology may incorporate several of these disciplines to drive pacemakers in the most efficient physiologic fashion.3
From the Departments of Medicine, Thomas Jefferson University and Lankenau Hospital, Philadelphia, Pennsylvania. Address for reprints: Leonard S. Dreifus, MD, The Lankenau Hospital, Lancaster Avenue West of City Line, Philadelphia, Pennsylvania 19151.
AUTOMATIC IMPLANTABLE DEFIBRILLATORS In 1967, Mirowski conceived an approach to the prevention of sudden coronary death using a standby auto-
2J
THE AMERICAN
JOURNAL
OF CARDIOLOGY
VOLUME
64
matic defibrillator. The need for such a device emerged from some pertinent observations: first, the magnitude of sudden cardiac death-more than a half million people were dying suddenly in the United States each year; and second, identification of the mechanism of sudden coronary death by numerous observations in acute coronary care units using electrocardiographic monitoring. Cardiopulmonary resuscitation evolved in an agonizingly slow manner when one considers that electrical defibrillation of the heart was routinely used only to salvage animals to be reused in subsequent research experiments in the 1940s and 1950s. Notably, Paul Zoll demonstrated the effect of precordial electrical shock to defibrillate the heart and terminate supraventricular and ventricular tachycardia. Although development of an automatic implantable delibrillating device appeared beyond the capabilities of our technology, numerous obstacles were overcome, and with persistence, imagination and parallel developments in electronics the first implant in humans was performed in 1980.4 In 1985, the Food and Drug Administration approved these devices and thus ushered in the rapid acceptance of this technique in the prevention of sudden death due to ventricular tachycardia and ventricular fibrillation. At the onset of the third decade of this technology we are seeing sophisticated antitachycardia devices appear, which are capable of terminating both atria1 and ventricular tachyarrhythmias as well as affording adequate pacemaker function. In some instances, implantable devices with cardioverter/defibrillator capabilities are replacing the time-honored management of serious cardiac arrhythmias, long dominated by pharmacologic therapies. There are more than 7,600 automatic implantable cardioverter defibrillator (AICD) implants performed in many centers throughout the world. Remarkably, there has been more than 84% survival up to 2 years in these patients5 Furthermore, the potential exists for further reduction in sudden cardiac death due to ventricular tachycardia and fibrillation as the AICD technology and clinical management evolve. On the horizon are implantable cardioverter/defibrillators using nonepicardial electrode systems with electrodes in the right ventricle and left pectoral submuscular epicostal region.6 These sophisticated AICD devices are now interacting with other cardiac pacemaker devices. Many issuesare still unresolved. The selection of patients has become more liberal but not firmly established. The problem of patients with poor cardiac function receiving these units is still under intense investigation.’ Notably, the most efficient electrode configurations, pulse widths and wave forms are being studied. The search for lower-energy shocks that will efficiently control serious ventricular arrhythmias is in progress. The use of gradient maps to create an electrode configuration with more efficient defibrillation fields will ultimately improve our technology. The comparison of single vs double capacitor biphasic wave forms is still a matter for research. Predictably, the AICDs will take on various special functions, e.g., fully transvenous electrodes, totally programmable software, and “limitedneed” devices for apparently healthy patients to senseand defibrillate ventricular fibrillation prophylactically. These units would be capable of only a few shocks, would
have limited life and allow the patient to receive other types of units in the future.* CATHETER ABLATIVE TECHNIQUES The use of physical agents to modify conduction in a restricted area of the myocardium by ablative procedures, in order to treat cardiac arrhythmias, has been extensively explorecL9 The surgical interruption of normal and anomalous pathways, and more recently the foci or pathways of re-entry tachycardias, has offered new hope to patients with incessant and malignant cardiac arrhythmias. Other investigatorslO have demonstrated that altering the shape and polarity of discharge and the geometry of the electrode can greatly increase the amount of voltage and current delivered before arcing occurs. The numerous and meticulous studies of cardiac mapping have clearly made this technique a useful clinical discipline. Furthermore, transvenous catheter ablation procedures have saved many patients from the more traumatic open-chest operations. l i Recent investigations have focused on identifying the most effective means of catheter ablation using directcurrent shock fulguration, radio frequency fulguration, cryomodification procedures and, more recently, various laser radiation techniques. I2 Research as to the most effective medium of lasing is continuing. Investigators have now turned their attention toward developing the most effective means for ablation of specific electrophysiologic problems. Attempts have been made to modulate AV conduction rather than interrupt conduction completely. Direct transseptal approaches to destroying free wall anomalous pathways in difficult locations, appears as an attractive alternative to surgical ablation. Other unique procedures to ablate posterior septal pathways and other left-sided pathways are being intensively studied. Temperature-guided radio frequency coagulative techniques and unique approaches using the coronary arteries and foramen ovale are now being studied. With the establishment of precise precordial catheter and epicardial/endocardial mapping procedures, attempts to ablate ventricular tachycardia appear to be achieving clinical success. Questions still remain as to where to ablate in the case of ventricular tachycardia. Other issues remain, such as whether to ablate the earliest endocardial activation or areas of slow conduction. Attempts to identify the critical area for treatment of tachycardia will enhance the effectiveness of ventricular ablation.13 More precise selection of patients for these procedures is required Anodal unipolar shocks, altemative energy sources and balloon or suction electrode catheter ablation may lead to correct localization of the ablative shocksi At present, the advantage of transvenous catheter ablation is quite apparent, especially in poor-risk patients. ABLATIVE TECHNIQUES From the first attempts to ablate the AV node and producing AV heart block in canine models to the initial clinical experience, surgical ablative techniques have been extremely successful and life-saving in many inSURGICAL
THE AMERICAN
JOURNAL
OF CARDIOLOGY
DECEMBER5.1989
3J
A SYMPUSIUM:
NEW TRENDS IN THE TREATMENT
OF RHYTHM DISORDERS
~tances.*~ Interruption of specific accessory pathway@ introduced mapping-directed techniques to correct serious cardiac arrhythmias. Subsequently, these surgical procedures have become accepted therapy for patients with Wolff-Parkinson-White syndrome with either a history of atria1 fibrillation engendering ventricular fibrillation or incessant arrhythmias due to the operation of anomalous bypass tracts. I7 The treatment of Wolff-Parkinson-white arrhythmias using both endo- and epicardial approaches can be effective for mid- and left free wall pathways, although endocardial techniques appear preferable for anterior and left free wall anomalous pathwaysi The epicardial approach will remain for posterior septal pathways. Extension of these mapping techniques to patients with ventricular aneurysms and refractory ventricular tachycardias has led to the development of endocardial resection as well as endo- and epicardial encircling procedures. l9 Imaginative methods to interrupt AV nodal re-entry tachycardias by interruption of the perinodal fibers have been extremely effective. Surgical isolation of the sinus node and its conduction pathway to the AV node from the rest of the atria has been uniquely useful in patients with recurrent paroxysmal atria1 fibrillation.20
intractable cardiac arrhythmias. Imaginative engineering should be able to resolve the annoying and dreaded consequences of abnormal impulse formation and conduction in the human heart. Many of these goals have already been met, and with the rapid advances in our knowledge of electrophysiology it is hoped that there will be little left to do in the ensuing years. REFERENCES I. Ward DE and Camm AJ, eds. Clinical Electrophysiology of the Heart. Introductory Remarks. London, Edward Arnold: 1987. 2. Bloomfield P, Macareavey D, Kerr F, Fananapaxir L. Long-term follow-up of patients with the QT rate adaptive pacemaker. PACE 1989;12:111-114. 3. Stangl K, Wertxfeld A, Lochschmidt 0, Basler B, Mittnacht A. Physical movement sensitive pacing: comparison of two “activity’‘-triggered pacing systems. PACE 1989;12:102-110. 4. Mirowski M, Reid PR, Mower MM, Watkins L, Gott VL, Schauble JF, Langer A, Heihnan MS, Kolenik SA, Fischell RE, Weisfeldt ML. Termination of malignant ventricular arrhythmias with an implanted automatic defibrillator in human beings. N Engl J Med 1980;303:322-324. 5. Mercando AD, Furman S, Johnston D, Frame R, Brodman R, Kim Xi, Fisher JD. Survival of patients with the automatic implantable cardioverter defibrillator. PACE 1988;11:2059-2063.
6. Saksena S, Tulle N, Parsonnet V. Gielchinsky I, Karanam R. Initial experience with an implantable cardioverter/deIibriUator using a nonepicardial electrode system (abstr). Circulation 1988;78:suppl Il:ll-220. 7. Tchou PJ, Kadri N, Anderson J, Caceses JH, Jaxayeri M, Akhtar M. Automatic implantable cardioverter detibrillators and survival of patients with left ventricular dysfunction and malignant ventricular arrhythmias. Ann Intern Med 1988;109:529-534.
ANTIARRRYTHMIC DRUGS Intense investigation of new antiarrhythmic agents as well as critical studies attempting to identify new and clearer mechanisms of the older standbys is continuing. The classification of antiarrhythmic agents based on single-cell electrophysiologic principles remains complex, as many of the newer agents belong to more than 1 category. Any new clinical classification of antiarrhythmic drugs must consider the characteristics and origin of the arrhythmia.21 In many instances these characteristics are either vague or entirely unknown. Newer additions to the fast channel blocking agents (class I) that prolong refractoriness, and in some instances conduction velocity, can be effective in both supraventricular and ventricular arrhythmias. However, recent attention has been directed to classIII agents such as D-sotalol, clofiiium and experimental E-403 1.22The latter drug may have novel actions in that it may influence the effective refractory period of the normal myocardium quite differently from the myocardium of the ischemic zone. Amiodarone still shares a focal position in the investigation of antiarrhythmic agents. The characteristics of amiodarone are so atypical, and it influences the physiology of so many other organ systems, that it will remain a challenge to pharmacologists. In fact, Griffin and Mande123cited 37 published reports in 1987 in their recent review. Other class I agents, such as indecainide, propafenone, moricizine, pirmenol and ACC-9358, are also likely to attract important attention in the next few years as effective antiarrhythmic agents.
Publishing,
CONCLUSION The future holds great promise for further refinements and discoveries in the management of serious and
22. Katok H, Ogawa S, Furuno I, Sato Y, Yoh S, Saeki K, Nakamura Y. Patient electrophysiological effects of E-4031, a novel class III antiarrhythmic agent on reentrant ventricular tachycardia. Circulation I988:78:suppl II:&I 48. 23. Griffin JC, Mandel WJ. Clinical Concepts in Arrhythmias-An Annual Review--1988. Mount K&o, NYr Futura Publishing, 1988.
4J
THE AMERICAN
JOURNAL
OF CARDIOLOGY
VOLUME
64
8. Mower MM, Nisam S. AICD indications (patient selection): past, present and future. PACE 1988:11:2064-2070. 9. Fontaine G, Scheinman MM. Ablation in Cardiac Arrhythmias. Mount Kisco, NY: Futura
Publishing,
1987.
10. Ahsan AJ, Cunningham D, Rowland E, Richards AF. Catheter ablations fulguration: design and performance of a new system. PACE 1989;12:f 3f135. 11. Yagi Y, Schuessler RB, Boineau JP, COY. JL. Closed cheat cryomodification of atrioventricular conduction-is it feasible? (abstr). Circulation 1988;78:supp/ ll:ll-445. 12. Waldo AL. Chronology of the development of ablation techniques in the
treatment of cardiac arrhythmias. In: Scheinman MM, Fontaine G, eds. Ablation in Cardiac Arrhythmias. New York: Futura Publishing, 1987:1-4. 13. Fontaine G, Frank R, Tinet J, Grosgageat Y. Identification of a mne of slow conduction appropriate for VT ablation: theoretical and practical considerations. PACE
1989:12:262-267.
14. Beard TJ, Lavergne TL, Brunewald PR, Von Euw DJ, LeGrand BH, Guixe LJ, Heuxey JY, Peronneau PA. Efficiency of suction electrode catheter for radio frequency ablation of canine ventricular myocardium (abstr). Circulation 1988; 78:suppl ll:ll-307.
IS. Dreifus LS, Nichols H, Morse D, Watanabe Y, Truex R. Control of recurrent tachycardia of Wolff-Parkinson-White syndrome by surgical ligature of the A-V bundle. Circulation I %8:38:1030-1036. 16. Scaly WC, Gallagher JJ. Surgical treatment of left free wall accessory pathways of atrioventricular conduction of the Kent type. J Thorac Cardiomsc Surg 1981;81.698-706. 17. Dreifus LS, Haiat
R, Watanabe Y, Arriaga J, Reitman N. Ventricular fibrillation: a possible mechanism of sudden death in patients with Wolff-Parkinson-white syndrome. Circulation 1971;43:520-527. 18. Hoissaguerre M, Saoudi N, LeMetayer P, Kirkorian G, Alattah G, Touboul P, Warin JF. Closed cheat transseptal ablation of left free wall accessory pathway (abstr). Circulation 1988:78:suppl ll:ll-401. 19. Josephson ME, Horowitz LN, Spielman SR, Greenspan AM, Vandepol C, Harken AH. Comparison of endwardial catheter mapping with intra-operative mapping of ventricular tachycardia. Circulation 1980,61:395-404. 20. Defauw JJ, Van Hemel NM, Vermeulen FE, Kingma JH, Verrastte JM, Guirauden GM. Short-term results of the “corridor operation” for drug-refractory paroxysmal atria1 fibrillation (abstr). Circulation 1988;78:suppl ll:lI-48. 21. Puech P, Brugada J. A clinical classification of antiarrhythmic drugs. In: Brugada P, Wellens HJJ, eds. Where to Go from Here. New York Futura 1987:485-493.