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What is the value of calcium antagonists for ventricular tachycardia?
543
IJC 0127C
What is the value of calcium antagonists for ventricular tachycardia? * I The Role of Slow Inward Current in the Genesis of Arrhythmias
Fundamentally, there are two kinds of action potentials in cardiac fibers. The action potential of Purkinje fibers, atria, and ventricles has a highly negative resting diastolic potential, a rapid upstroke of depolarization, a rapid early repolarization, a plateau, and a rapid late repolarization. On the other hand, the action potential of the sinus node and the atrioventricular node has a less negative maximum diastolic potential, a slow upstroke, and usually lacks a plateau. The fast inward current mediated by the sodium ions is responsible for the rapid upstroke of action potential seen in Purkinje fibers, atria, and ventricles, while the slow inward current mediated by calcium and sodium ions is responsible for the action potential of the sinus node and the atrioventricular node. Calcium antagonists have profound effects on the slow inward current but little effect on the fast inward current. Two kinds of normal spontaneous automaticity have been identified in cardiac fibers. Sinus automaticity arises from a less negative transmembrane potential, while Purkinje pacemaker automaticity arises from a highly negative transmembrane potential. Overdrive pacing suppresses normal automaticity. Abnormal automaticity may be generated in Purkinje fibers, atria1 fibers, and ventricular fibers under various circumstances when the maximum diastolic transmembrane potential is reduced to a level of -60 or -50 mV [l]. Since the abnormal automaticity arises from a reduced level of transmembrane potential, the difference between the abnormal automaticity and the normal sinus automaticity is not quite clear. Raising the extracellular calcium concentration, lowering the extracellular potassium concentration, or application of isoproterenol all enhance the rate of the abnormal automaticity. Oscillatory afterdepolarizations triggered by a previous action potential can occur in a wide variety of conditions [l]. Triggered afterdepolarizations have been demonstrated in Purkinje fibers, atria1 fibers, ventricular fibers, fibers of the mitral valve, and fibers of the coronary sinus after these fibers were exposed to a toxic concentration of digitalis or sodium free solution. When the amplitude of afterdepolarization reaches the threshold, it can initiate an action potential. Sustained rhythmic activity may result from oscillatory afterdepolarizations. Catecholamine enhances the amplitude of afterdepolarization as does shortening of the driven cycle length or the coupling interval. Verapamil and the manganese ion suppress the depolarization. Automaticity due to afterdepolarization is dependent on triggering of the previous action potential; therefore, it is called “triggered automaticity”. The distinction
* From the Section Angeles, CA.
of Cardiology,
Department
International Journal of Cardiology, 5 (1984) 543-547 0 Elsevier Science Publishers B.V.
of Medicine,
University
of Southern
California,
Los
544
between triggered automaticity and abnormal automaticity is not quite clear. As triggered automaticity depends on triggering of a previous impulse, these cells should be quiescent without a triggering impulse. Automaticity and reentry are the two basic mechanisms of tachyarrhythmias. Ventricular tachyarrhythmias could result from enhanced normal pacemaker automaticity, from abnormal automaticity in diseased Purkinje or ventricular muscle fibers, or from triggered automaticity in diseased Purkinje or ventricular muscle fibers. Just as slow conduction and unidirectional block are crucial for reentry, slow inward current in diseased Purkinje fibers or ventricular muscle fibers could provide a substrate for reentry. Thus a calcium dependent or modulated current may play an important role in the genesis of ventricular tachyarrhythmias. Calcium antagonist could be potentially useful in management of ventricular tachyarrhythmias. Verapamil in the Treatment of Ventricular Tachycardia Verapamil is very effective in terminating acute episodes of paroxysmal supraventricular tachycardia and slowing the ventricular rate in atria1 fibrillation or atria1 flutter. Verapamil is less effective in ventricular tachycardia. Gotsman et al. administered verapamil intravenously to a patient with ventricular tachycardia and Ebstein’s anomaly [2]. The tachycardia failed to convert although the rate slowed dramatically. Heng et al. gave verapamil to 5 patients with ventricular tachycardia; conversion to sinus rhythm was noted in only one patient [3]. Schamroth treated ten patients with ventricular tachycardia, and none responded [4]. Wellens et al. administered verapamil intravenously to 4 patients with chronic recurrent ventricular tachycardia, that was inducible by electrical stimulation, and failed to terminate the tachycardia in all patients [5]. In these patients verapamil did not affect the rate of tachycardia or the ventricular stimulating intervals that induced tachycardia. Nevertheless, Mason et al. gave verapamil intravenously to 24 patients with chronic recurrent ventricular tachycardia that was inducible at electrophysiology study [6]. Seven of the 24 patients (29%) responded to verapamil, 5 were not inducible and 2 lost the ability to sustain their ventricular tachycardia. They noted that patients who responded to verapamil were younger and had better left ventricular function; 4 patients without demonstrable organic heart disease responded to verapamil, and only one did not. The morphology of ventricular tachycardia on the 1Zlead electrocardiogram in verapamil responders more frequently showed a pattern of right bundle branch block and left axis deviation. The efficacy of verapamil in their study compared well with that of other individual antiarrhythmic agents assessed in their laboratory. They recommended that verapamil should be tried when other antiarrhythmic agents fail to control the arrhythmia. It was unclear from their study whether the salutary effects of verapamil on the responders reflected a different mechanism of tachycardia as compared to the non-responders. Verapamil and Exercise-triggered
Paroxysmal Ventricular Tachycardia
Exercise can provoke ventricular tachyarrhythmias through several mechanisms. For example, in patients with coronary artery disease exercise may provoke ventricu-
545
lar tachyarrhythmias because of increased sympathetic tone, an increase in heart rate, hypoxia, or local acidosis. In patients with ventricular tachycardia in whom the tachycardia is inducible by atria1 pacing at a critical rate, exercise may provoke tachycardia when a critical sinus rate is achieved during exercise. Recently my associates and I noted that in patients without organic heart disease in whom paroxysmal ventricular tachycardia developed with a QRS pattern of left bundle branch block and right axis deviation during exercise, the tachycardia was inducible with isoproterenol infusion, but not by electrical stimulation [7]. In these patients, the rate of the tachycardia varied from 160 to 240 beats/mm. Propranolol effectively terminated and prevented recurrence of the tachycardia. Verapamil effectively terminated the tachycardia but was less effective in preventing exercise provocation of ventricular tachycardia. We suggested that a catecholamine sensitive calcium dependent automatic focus was responsible for the tachycardia. Enhanced normal pacemaker automaticity seemed unlikely to be the mechanism of the tachycardia. The normal pacemaker automaticity of the Purkinje fibers is independent of the slow inward current and is not likely to respond to verapamil. It could not be ascertained whether the tachycardia resulted from an abnormally automatic focus or a triggered automatic focus. The fact that the tachycardia was not inducible with incremental and premature stimulations favored the possibility of abnormal automaticity. However, repetitive subthreshold oscillatory afterdepolarizations that were triggered by the sinus impulses were equally possible. The subthreshold oscillatory afterdepolarizations could become manifest only when the amplitude was enhanced by the catecholamines of exercise or during isoproterenol infusion. Verapamil and Idiopathic Paroxysmal Ventricular Tachycardia A unique type of ventricular tachycardia occurring in young patients without obvious organic heart disease was recently reported from my laboratory as well as others [&lo]. The electrocardiogram during sinus rhythm in these patients frequently showed a repolarization abnormality over the inferior and lateral precordial leads. The QRS complex during the episodes of ventricular tachycardia showed a pattern of right bundle branch block and left axis deviation while the QRS duration during the episodes of ventricular tachycardia was relatively narrow and ranged from 0.10 to 0.12 sec. The ventricular tachycardia could be induced with ventricular as well as atria1 stimulation. Exercise could also provoke tachycardia when a critical sinus rate was achieved. Electrical induction of tachycardia in most patients showed an inverse relation between the ventricular paced cycle length and the interval of the last ventricular paced beat to the initiating beat of ventricular tachycardia or between the ventricular coupling interval and the interval of the ventricular coupled beat to the initiating beat of ventricular tachycardia. Alternation of cycle length was occasionally seen during tachycardia. The ventricular tachycardia was responsive to verapamil, partially responsive to procainamide, and not responsive to either lidocaine or propranolol. Although the findings were consistent with reentry involving the slow inward current, we could not exclude the possibility of triggered automaticity.
Verapamil and Accelerated Idioventricular Rhythm It has been suggested that the accelerated idioventricular rhythm occasionally complicating acute myocardial infarction might result from triggered automaticity due to oscillatory afterdepolarizations. However, no study has been directed to examine the responses of accelerated idioventricular rhythm to pacing or premature stimulation. Recently, Sclarovsky et al. administered verapamil intravenously to 6 patients with accelerated idioventricular rhythm complicating acute myocardial infarction Ill]. Verapamil abolished the arrhythmia in four patients, slowed the rate in one patient, and had no effect in the remaining patient. Their findings suggest that slow inward current might have been involved in the genesis of accelerated idioventricular rhythm. Whether abnormal automaticity or triggered automaticity was responsible for the arrhythmia was unclear. Conclusions The significance of the slow inward current in the genesis of clinical ventricular arrhythmias has remained unclear. Three specific types of ventricular tachyarrhythmias appear to be related to the slow inward current: (1) exercise-triggered paroxysmal ventricular tachycardia with a QRS pattern of left bundle branch block and right axis deviation in patients without organic heart disease; (2) idiopathic paroxysmal ventricular tachycardia with a QRS pattern of right bundle branch block and left axis deviation in young patients without obvious heart disease; and (3) accelerated idioventricular rhythm complicating acute myocardial infarction. Verapamil, or possibly another calcium antagonist, is effective and can be used in terminating and preventing the recurrence of ventricular tachycardia of the first two types but is not recommended for the third type of accelerated idioventricular rhythm complicating acute myocardial infarction, because this arrhythmia is clinically benign. Although verapamil or another calcium antagonist may be useful in other types of ventricular tachycardia, indiscriminative trial of these agents is not recommended without careful electrophysiologic evaluation. When ineffective, these agents could potentially cause hemodynamic deterioration due to the vasodilatory and cardiac depressive effects. Section of Cardiology University of Southern California 2025 Zonal Avenue Los Angeles, CA 90033, U.S.A.
Delon Wu References
1 Hoffman BF, Rosen MR. Cellular mechanisms for cardiac arrhythmias. Circ Res 1981;49:1-14. 2 Gotsman MS, Lewis BS, Bakst A, Mitha AS. Verapamil in life-threatening tachyarrhythmias. S Afr Med J 1972;46:2017-2019. 3 Heng MK, Singh BN, Roche AHG, Norris RM, Mercer CJ. Effects of intravenous verapamil on cardiac arrhythmias and on the electrocardiogram. Am Heart J 1975;90:487-497.
547
4 Schamroth L. The clinical use of intravenous verapamil. Am Heart J 1980;100:1070-1075. propranolol and 5 Wellens HJJ, B&r FWHM, Lie KI, D&en DR, Dohmen HJ. Effect of procainamide, verapamil on mechanism of tachycardia in patients with chronic recurrent ventricular tachycardia. Am J Cardiol 1977;40:579-585. in chronic, recurrent ventricular 6 Mason JW, Swerdlow CD, Mitchell LB. Efficacy of verapamil tachycardia. Am J Cardiol 1983;51:1614-1617. 7 Wu D, Kou HC, Hung JS. Exercise-triggered paroxysmal ventricular tachycardia. Ann Int Med 1981;95:410-414. SH, Wu D. Idiopathic paroxysmal ventricular tachycardia with a QRS 8 Lin FC, Finley D, Rahimtoola pattern of right bundle branch block and left axis deviation: a unique clinical entity with specific properties. Am J Cardiol 1983;52:95-100. tachycardia: reentry 9 Zipes DP, Foster PR, Troup PJ, Pedersen DH. Atrial induction of ventricular versus triggered automaticity. Am J Cardiol 1979;44:1-8. tachycardia to verapamil. 10 Belhassen B, Rotmensch HH, Laniado S. Response of recurrent ventncular Br Heart J 1981;46:679-682. 11 Sclarovsky S, Strasberg B, Fuchs J, et al. Multiform accelerated idioventricular rhythm in acute myocardial infarction: electrocardiographic characteristics and response to verapamil. Am J Cardiol 1983;52:43-47.
IJC 0127D
Endocardial fibroelastosis and left heart hypoplasia revisited * The voluminous literature on endocardial fibroelastosis deals at length with possible etiologic mechanisms [1,2], clinical manifestations [3,4], and pathologic variations [5]. Less attention has been paid to the effects it may produce on the developing heart. Although endocardial thickening or sclerosis can be seen at all ages following myocardial hypoxia [6], the true fibroelastic reaction, with many of the endocardium, seems regular layers of elastic tissue causing “aorticisation” virtually confined to the period of growth and development in utero and in early infancy. The frequent association of neonatal left ventricular outflow obstruction and endocardial fibroelastosis has long been recognised [7]. The fibroelastotic process is described as “secondary” when a cardiac malformation is present and “primary” when the heart is structurally normal. However, Keith [8] states that “eighteen percent of primary endocardial fibroelastosis patients have bicuspid aortic valves” and also comments on hypoplasia of the left ventricle with a small aortic valve ring as an intermediate form of hypoplastic left heart syndrome. Several recent developments renewed our interest in this ostensibly discouraging grey zone between fibroelastosis and left heart hypoplasia. First, the development of
* From the Department of Pediatric Cardiology, Johns Hopkins Hospital, Baltimore, the Department of Pathology, Columbia Universrty, New York, and the Department of Paediatrics, Brompton Hospital, London.
International Journal of Cardio/ogv, 5 (1984) 547-550 0 Elsevier Science Publishers B.V.
IJC 0127C
What is the value of calcium antagonists for ventricular tachycardia? * I The Role of Slow Inward Current in the Genesis of Arrhythmias
Fundamentally, there are two kinds of action potentials in cardiac fibers. The action potential of Purkinje fibers, atria, and ventricles has a highly negative resting diastolic potential, a rapid upstroke of depolarization, a rapid early repolarization, a plateau, and a rapid late repolarization. On the other hand, the action potential of the sinus node and the atrioventricular node has a less negative maximum diastolic potential, a slow upstroke, and usually lacks a plateau. The fast inward current mediated by the sodium ions is responsible for the rapid upstroke of action potential seen in Purkinje fibers, atria, and ventricles, while the slow inward current mediated by calcium and sodium ions is responsible for the action potential of the sinus node and the atrioventricular node. Calcium antagonists have profound effects on the slow inward current but little effect on the fast inward current. Two kinds of normal spontaneous automaticity have been identified in cardiac fibers. Sinus automaticity arises from a less negative transmembrane potential, while Purkinje pacemaker automaticity arises from a highly negative transmembrane potential. Overdrive pacing suppresses normal automaticity. Abnormal automaticity may be generated in Purkinje fibers, atria1 fibers, and ventricular fibers under various circumstances when the maximum diastolic transmembrane potential is reduced to a level of -60 or -50 mV [l]. Since the abnormal automaticity arises from a reduced level of transmembrane potential, the difference between the abnormal automaticity and the normal sinus automaticity is not quite clear. Raising the extracellular calcium concentration, lowering the extracellular potassium concentration, or application of isoproterenol all enhance the rate of the abnormal automaticity. Oscillatory afterdepolarizations triggered by a previous action potential can occur in a wide variety of conditions [l]. Triggered afterdepolarizations have been demonstrated in Purkinje fibers, atria1 fibers, ventricular fibers, fibers of the mitral valve, and fibers of the coronary sinus after these fibers were exposed to a toxic concentration of digitalis or sodium free solution. When the amplitude of afterdepolarization reaches the threshold, it can initiate an action potential. Sustained rhythmic activity may result from oscillatory afterdepolarizations. Catecholamine enhances the amplitude of afterdepolarization as does shortening of the driven cycle length or the coupling interval. Verapamil and the manganese ion suppress the depolarization. Automaticity due to afterdepolarization is dependent on triggering of the previous action potential; therefore, it is called “triggered automaticity”. The distinction
* From the Section Angeles, CA.
of Cardiology,
Department
International Journal of Cardiology, 5 (1984) 543-547 0 Elsevier Science Publishers B.V.
of Medicine,
University
of Southern
California,
Los
544
between triggered automaticity and abnormal automaticity is not quite clear. As triggered automaticity depends on triggering of a previous impulse, these cells should be quiescent without a triggering impulse. Automaticity and reentry are the two basic mechanisms of tachyarrhythmias. Ventricular tachyarrhythmias could result from enhanced normal pacemaker automaticity, from abnormal automaticity in diseased Purkinje or ventricular muscle fibers, or from triggered automaticity in diseased Purkinje or ventricular muscle fibers. Just as slow conduction and unidirectional block are crucial for reentry, slow inward current in diseased Purkinje fibers or ventricular muscle fibers could provide a substrate for reentry. Thus a calcium dependent or modulated current may play an important role in the genesis of ventricular tachyarrhythmias. Calcium antagonist could be potentially useful in management of ventricular tachyarrhythmias. Verapamil in the Treatment of Ventricular Tachycardia Verapamil is very effective in terminating acute episodes of paroxysmal supraventricular tachycardia and slowing the ventricular rate in atria1 fibrillation or atria1 flutter. Verapamil is less effective in ventricular tachycardia. Gotsman et al. administered verapamil intravenously to a patient with ventricular tachycardia and Ebstein’s anomaly [2]. The tachycardia failed to convert although the rate slowed dramatically. Heng et al. gave verapamil to 5 patients with ventricular tachycardia; conversion to sinus rhythm was noted in only one patient [3]. Schamroth treated ten patients with ventricular tachycardia, and none responded [4]. Wellens et al. administered verapamil intravenously to 4 patients with chronic recurrent ventricular tachycardia, that was inducible by electrical stimulation, and failed to terminate the tachycardia in all patients [5]. In these patients verapamil did not affect the rate of tachycardia or the ventricular stimulating intervals that induced tachycardia. Nevertheless, Mason et al. gave verapamil intravenously to 24 patients with chronic recurrent ventricular tachycardia that was inducible at electrophysiology study [6]. Seven of the 24 patients (29%) responded to verapamil, 5 were not inducible and 2 lost the ability to sustain their ventricular tachycardia. They noted that patients who responded to verapamil were younger and had better left ventricular function; 4 patients without demonstrable organic heart disease responded to verapamil, and only one did not. The morphology of ventricular tachycardia on the 1Zlead electrocardiogram in verapamil responders more frequently showed a pattern of right bundle branch block and left axis deviation. The efficacy of verapamil in their study compared well with that of other individual antiarrhythmic agents assessed in their laboratory. They recommended that verapamil should be tried when other antiarrhythmic agents fail to control the arrhythmia. It was unclear from their study whether the salutary effects of verapamil on the responders reflected a different mechanism of tachycardia as compared to the non-responders. Verapamil and Exercise-triggered
Paroxysmal Ventricular Tachycardia
Exercise can provoke ventricular tachyarrhythmias through several mechanisms. For example, in patients with coronary artery disease exercise may provoke ventricu-
545
lar tachyarrhythmias because of increased sympathetic tone, an increase in heart rate, hypoxia, or local acidosis. In patients with ventricular tachycardia in whom the tachycardia is inducible by atria1 pacing at a critical rate, exercise may provoke tachycardia when a critical sinus rate is achieved during exercise. Recently my associates and I noted that in patients without organic heart disease in whom paroxysmal ventricular tachycardia developed with a QRS pattern of left bundle branch block and right axis deviation during exercise, the tachycardia was inducible with isoproterenol infusion, but not by electrical stimulation [7]. In these patients, the rate of the tachycardia varied from 160 to 240 beats/mm. Propranolol effectively terminated and prevented recurrence of the tachycardia. Verapamil effectively terminated the tachycardia but was less effective in preventing exercise provocation of ventricular tachycardia. We suggested that a catecholamine sensitive calcium dependent automatic focus was responsible for the tachycardia. Enhanced normal pacemaker automaticity seemed unlikely to be the mechanism of the tachycardia. The normal pacemaker automaticity of the Purkinje fibers is independent of the slow inward current and is not likely to respond to verapamil. It could not be ascertained whether the tachycardia resulted from an abnormally automatic focus or a triggered automatic focus. The fact that the tachycardia was not inducible with incremental and premature stimulations favored the possibility of abnormal automaticity. However, repetitive subthreshold oscillatory afterdepolarizations that were triggered by the sinus impulses were equally possible. The subthreshold oscillatory afterdepolarizations could become manifest only when the amplitude was enhanced by the catecholamines of exercise or during isoproterenol infusion. Verapamil and Idiopathic Paroxysmal Ventricular Tachycardia A unique type of ventricular tachycardia occurring in young patients without obvious organic heart disease was recently reported from my laboratory as well as others [&lo]. The electrocardiogram during sinus rhythm in these patients frequently showed a repolarization abnormality over the inferior and lateral precordial leads. The QRS complex during the episodes of ventricular tachycardia showed a pattern of right bundle branch block and left axis deviation while the QRS duration during the episodes of ventricular tachycardia was relatively narrow and ranged from 0.10 to 0.12 sec. The ventricular tachycardia could be induced with ventricular as well as atria1 stimulation. Exercise could also provoke tachycardia when a critical sinus rate was achieved. Electrical induction of tachycardia in most patients showed an inverse relation between the ventricular paced cycle length and the interval of the last ventricular paced beat to the initiating beat of ventricular tachycardia or between the ventricular coupling interval and the interval of the ventricular coupled beat to the initiating beat of ventricular tachycardia. Alternation of cycle length was occasionally seen during tachycardia. The ventricular tachycardia was responsive to verapamil, partially responsive to procainamide, and not responsive to either lidocaine or propranolol. Although the findings were consistent with reentry involving the slow inward current, we could not exclude the possibility of triggered automaticity.
Verapamil and Accelerated Idioventricular Rhythm It has been suggested that the accelerated idioventricular rhythm occasionally complicating acute myocardial infarction might result from triggered automaticity due to oscillatory afterdepolarizations. However, no study has been directed to examine the responses of accelerated idioventricular rhythm to pacing or premature stimulation. Recently, Sclarovsky et al. administered verapamil intravenously to 6 patients with accelerated idioventricular rhythm complicating acute myocardial infarction Ill]. Verapamil abolished the arrhythmia in four patients, slowed the rate in one patient, and had no effect in the remaining patient. Their findings suggest that slow inward current might have been involved in the genesis of accelerated idioventricular rhythm. Whether abnormal automaticity or triggered automaticity was responsible for the arrhythmia was unclear. Conclusions The significance of the slow inward current in the genesis of clinical ventricular arrhythmias has remained unclear. Three specific types of ventricular tachyarrhythmias appear to be related to the slow inward current: (1) exercise-triggered paroxysmal ventricular tachycardia with a QRS pattern of left bundle branch block and right axis deviation in patients without organic heart disease; (2) idiopathic paroxysmal ventricular tachycardia with a QRS pattern of right bundle branch block and left axis deviation in young patients without obvious heart disease; and (3) accelerated idioventricular rhythm complicating acute myocardial infarction. Verapamil, or possibly another calcium antagonist, is effective and can be used in terminating and preventing the recurrence of ventricular tachycardia of the first two types but is not recommended for the third type of accelerated idioventricular rhythm complicating acute myocardial infarction, because this arrhythmia is clinically benign. Although verapamil or another calcium antagonist may be useful in other types of ventricular tachycardia, indiscriminative trial of these agents is not recommended without careful electrophysiologic evaluation. When ineffective, these agents could potentially cause hemodynamic deterioration due to the vasodilatory and cardiac depressive effects. Section of Cardiology University of Southern California 2025 Zonal Avenue Los Angeles, CA 90033, U.S.A.
Delon Wu References
1 Hoffman BF, Rosen MR. Cellular mechanisms for cardiac arrhythmias. Circ Res 1981;49:1-14. 2 Gotsman MS, Lewis BS, Bakst A, Mitha AS. Verapamil in life-threatening tachyarrhythmias. S Afr Med J 1972;46:2017-2019. 3 Heng MK, Singh BN, Roche AHG, Norris RM, Mercer CJ. Effects of intravenous verapamil on cardiac arrhythmias and on the electrocardiogram. Am Heart J 1975;90:487-497.
547
4 Schamroth L. The clinical use of intravenous verapamil. Am Heart J 1980;100:1070-1075. propranolol and 5 Wellens HJJ, B&r FWHM, Lie KI, D&en DR, Dohmen HJ. Effect of procainamide, verapamil on mechanism of tachycardia in patients with chronic recurrent ventricular tachycardia. Am J Cardiol 1977;40:579-585. in chronic, recurrent ventricular 6 Mason JW, Swerdlow CD, Mitchell LB. Efficacy of verapamil tachycardia. Am J Cardiol 1983;51:1614-1617. 7 Wu D, Kou HC, Hung JS. Exercise-triggered paroxysmal ventricular tachycardia. Ann Int Med 1981;95:410-414. SH, Wu D. Idiopathic paroxysmal ventricular tachycardia with a QRS 8 Lin FC, Finley D, Rahimtoola pattern of right bundle branch block and left axis deviation: a unique clinical entity with specific properties. Am J Cardiol 1983;52:95-100. tachycardia: reentry 9 Zipes DP, Foster PR, Troup PJ, Pedersen DH. Atrial induction of ventricular versus triggered automaticity. Am J Cardiol 1979;44:1-8. tachycardia to verapamil. 10 Belhassen B, Rotmensch HH, Laniado S. Response of recurrent ventncular Br Heart J 1981;46:679-682. 11 Sclarovsky S, Strasberg B, Fuchs J, et al. Multiform accelerated idioventricular rhythm in acute myocardial infarction: electrocardiographic characteristics and response to verapamil. Am J Cardiol 1983;52:43-47.
IJC 0127D
Endocardial fibroelastosis and left heart hypoplasia revisited * The voluminous literature on endocardial fibroelastosis deals at length with possible etiologic mechanisms [1,2], clinical manifestations [3,4], and pathologic variations [5]. Less attention has been paid to the effects it may produce on the developing heart. Although endocardial thickening or sclerosis can be seen at all ages following myocardial hypoxia [6], the true fibroelastic reaction, with many of the endocardium, seems regular layers of elastic tissue causing “aorticisation” virtually confined to the period of growth and development in utero and in early infancy. The frequent association of neonatal left ventricular outflow obstruction and endocardial fibroelastosis has long been recognised [7]. The fibroelastotic process is described as “secondary” when a cardiac malformation is present and “primary” when the heart is structurally normal. However, Keith [8] states that “eighteen percent of primary endocardial fibroelastosis patients have bicuspid aortic valves” and also comments on hypoplasia of the left ventricle with a small aortic valve ring as an intermediate form of hypoplastic left heart syndrome. Several recent developments renewed our interest in this ostensibly discouraging grey zone between fibroelastosis and left heart hypoplasia. First, the development of
* From the Department of Pediatric Cardiology, Johns Hopkins Hospital, Baltimore, the Department of Pathology, Columbia Universrty, New York, and the Department of Paediatrics, Brompton Hospital, London.
International Journal of Cardio/ogv, 5 (1984) 547-550 0 Elsevier Science Publishers B.V.