J. Vohra

Prediction of sudden death by electrophysiologic studies in high risk patients surviving acute myocardial infarction.

Seventy patients surviving a myocardial infarction complicated by heart failure or arrhythmias, or both, were studied 7 to 20 days after the infarction. Twenty-four hour electrocardiographic ambulatory monitoring and intracardiac electrophysiologic studies were performed in each patient. Electrophysiologic studies included introduction of single right ventricular premature stimuli during sinus rhythm (70 patients), atrial pacing (35 patients) and ventricular pacing (70 patients) at a stimulating voltage of 2 V, with the use of higher stimulating voltages (up to 10 V), and double right ventricular premature stimuli in 33 patients and pacing at a second right ventricular site in 50 patients. A repetitive response was defined as two or more spontaneous ventricular depolarizations in response to the premature stimuli, with His bundle reentry and aberrant conduction of supraventricular impulses excluded by a His bundle recording. Repetitive responses were initiated in 20 patients, and 12 patients had responses that were either sustained ventricular tachycardia or self-terminating ventricular tachycardia of more than five complexes in duration. The finding of a repetitive response was not related to the occurrence of complex ventricular arrhythmias during ambulatory monitoring or in the coronary care unit. Five of the 12 patients with sustained or self-terminating responses of more than five complexes died during the 12 month follow-up period, 4 suddenly, and these responses were significantly associated with late sudden death (p less than 0.05), because only 1 of 25 patients with responses of fewer than five complexes or no response to maximal provocation died suddenly. It is concluded that induced responses of more than five complexes in duration may be an important indicator of a potentially reversible risk of sudden death after myocardial infarction.

Ventricular tachycardia and sudden death in myotonic dystrophy: clinical, electrophysiologic and pathologic features.

A 37 year old man who presented with a cardiomyopathy, conduction defects and atrial and ventricular arrhythmias was found to have the neuromuscular manifestations of myotonic dystrophy. Despite implantation of a permanent cardiac pacemaker, antiarrhythmic drug therapy and antiarrhythmic surgery, sudden death occurred. The results of electrophysiologic studies, coronary arteriography and pathologic findings are described. This case confirms previous observations that ventricular arrhythmias, in addition to atrial arrhythmias and conduction disturbances, are cardiac manifestations of myotonic dystrophy and can lead to sudden death.

Malignant Ventricular Arrhythmias in Patients with Mitral Valve Prolapse and Mild Mitral Regurgitation

Mitral valve prolapse (MVP) is a common disorder that, in general, has a good prognosis. Rare occasions of sudden death have been reported in patients with MVP and it is presumed that the basis of sudden death is arrhythmic. We report seven patients with moderate to severe MVP and malignant ventricular arrhythmias. All patients had trivial to mild mitral regurgitation and normal left ventricular function. Three patients presented with syncope, two with out‐of‐hospital cardiac arrest, and three with recurrent palpitations and presyncope. In a mean follow‐up period of 2.5 years (range 6 months to 5 years), two patients died suddenly despite successful control of their nonsustained ventricular tachycardia (VT) with sotalol as shown by ambulatory monitoring. Two patients, who had sustained VT despite antiarrhythmic drug therapy, had mitral valve surgery, however, monomorphic VT could be induced in both even after surgery. The arrhythmias in the remaining three patients are controlled on antiarrhythmic drugs. We conclude that a selected subset of patients with MVP, malignant ventricular arrhythmias, and miid mitral regurgitation are at risk of sudden death. Syncope, inferolateral repolarization changes, complex ventricular ectopy, and a markedly myxomatous valve may be pointers to higher risk of sudden death and mitral valve surgery may not provide control of ventricular arrhythmias.

Histopathology of Heart Block Complicating Acute Myocardial Infarction Correlation with the His Bundle Electrogram

Histopathological studies of the conduction system were related to His bundle electrogram recordings in seven patients with acute myocardial infarction and atrioventricular (A-V) conduction disturbances. The three patients with inferior infarctions had normal width QRS complexes and delay or block of the impulses above the His bundle. Recent ischemic changes were present in the A-V node in two cases and in the distal conduction system in all three cases. In the four patients with antero-septal infarction and right bundle branch block (RBBB), either the H-V interval was prolonged or block was present below the H spike. The A-H interval was normal in each of these cases, and the A-V node was not affected by the recent infarction. The right bundle branch was involved in all four of these cases and two patients also had involvement of the left bundle branch. In general there was a good correlation between the sites of heart block as defined by the His bundle electrogram and the histopathological analysis of the cardiac conduction system.

Cycle length alternation in supraventricular tachycardia after administration of verapamil.

Four patients are reported in whom alternation ofRR cycle length before reversion to sinus rhythm occurred during the administration of intravenous verapamil. In 2 of these 4 patients, alternation of cycle lengths was associated with a changing QRS morphology. It is suggested that one patient had a reciprocating tachycardia using dual AV nodal pathways. The alternating cycle lengths in response to verapamil are explained on the basis of a 2:i block in the antegrade pathway unmasking a third pathway, thus providing two pathways with differing antegrade conduction. In the second patient the mechanism of the supraventricular tachycardia appears to be atrial or AV nodal extrasystolic tachycardia. We attribute the alternating cycle length to a 3:2 Wenckebach block before reversion to sinus rhythm. However, a reciprocating mechanism in this and the other two patients cannot be excluded. The possible mechanismsfor verapamil-induced alternation are discussed.

The effect of tricyclic antidepressant drugs on the heart

SummaryThe effects on the heart rate and ECG of anaesthetised guinea-pigs of amitriptyline, doxepin, imipramine and nortriptyline infused at 1.0 mg/kg/min until death were observed. In addition an in vitro study on guinea-pig atria was performed on the chronotropic and inotropic effects of these drugs and of desmethylimipramine and protriptyline at a concentration of 10−5 M. The effect of sodium bicarbonate (3 mEq/kg i.v.) and propranolol (0.01–0.2 mg/kg i.v.) on amitriptyline and doxepin induced ECG changes was also assessed.A difference in the cardiac effects of the in vivo and in vitro model was observed. Guinea-pigs infused with doxepin survived significantly longer than those infused with amitriptyline, imipramine or nortriptyline. No statistically significant difference was found between the tricyclic drugs with respect to onset of widening of the QRS complex, increased PR and QT intervals. In the spontaneously beating atrial preparation doxepin was the most potent cardio-depressant. Sodium bicarbonate had no effect on arrhythmias induced by tricyclics, while propranolol, apart from the bradycardia induced, was without beneficial effect on the ECG.The guinea-pig provides a good model for studying the arrhythmogenic actions of tricyclic antidepressants.ZusammenfassungUntersucht wurden die Wirkungen intravenöser Infusionen (1.0 mg/kg/min bis zum Erreichen der tödlichen Dosis) von Amitriptylin, Doxepin, Imipramin und Nortriptylin auf die Herzfrequenz und das EKG betäubter Meerschweinchen. Außerdem wurden an isolierten Meerschweinchen-Vorhöfen in vitro die chronotropen und inotropen Effekte dieser Substanzen sowie von Desmethylimipramin und Protriptylin bei einer Konzentration von 10−5 M geprüft. Schließlich interessierte auch der Einfluß von Natriumbicarbonat (3 mÄq/kg i.v.) und Propranolol (0,01–0,2 mg/kg i.v.) auf die durch Amitriptylin und Doxepin ausgelösten EKG-Veränderungen.Die cardialen Effekte der Antidepressiva zeigen am in vivo und in vitro- Modell Unterschiede. Die mit Doxepin infundierten Meerschweinchen wiesen eine signifikant längere Überlebenszeit auf als die mit Amitriptylin, Imipramin und Nortriptylin behandelten. Hinsichtlich des Eintritts der Verbreiterung des QRS-Komplexes, sowie der Verlängerung der PR- und QT-Intervalle zeigten die einzelnen tricyclischen Antidepressiva keine Unterschiede. Am spontanschlagenden Vorhofpräparat hatte Doxepin die stärkste cardiodepressive Wirkung. Natriumbicarbonat hatte keine Wirkung auf die durch die Antidepressiva ausgelösten Arrythmien, während Propranolol — abgesehen von der Bradycardie-Auslösung — keine günstige Wirkung auf das EKG besaß.Das Meerschweinchen stellt ein gutes Modell zum Studium der Arrythmie erzeugenden Wirkungen von tricyclischen Antidepressiva dar.

A Fuzzy Logic‐Controlled Classifier for Use in Implantable Cardioverter Defibrillators

Purpose: Implantable cardioverters defibrillators (ICDs) are increasingly used in the management of life‐threatening arrhythmias. Correct recognition of a treatable arrhythmia is crucial to this application. However, the computational power of microprocessors currently used in ICDs limits the range of traditional algorithms available for this application. Methods: Classification based on fuzzy inference systems (FIS) were trained to recognize different cardiac rhythms (AF, VF, SVT, VT) from the Ann Arbor Electrogram Library. The FIS used were designed using adaptive‐network‐based fuzzy inference methods to optimize the classification procedure. Only computational techniques suitable for ICD design were used. Results: After pretraining with the ANFIS correct rhythm classification was observed for the rhythms studied. Conclusion: In this preliminary study, successful rhythm classification was demonstrated using fuzzy logic techniques. In view of the computational efficiency this may have application in ICD design.

His bundle electrogram in patients with acute myocardial infarction complicated by atrioventricular or intraventricular conduction disturbances.

Seventy-two patients with acute myocardial infarction complicated by atrioventricular or bundle-branch block or a combination of both had His bundle electrogram studies performed during their stay in the coronary care unit. In 19 of the 72 patients a repeat His bundle electrogram was performed before discharge from hospital. These studies demonstrated that 30 of the 32 patients with atrioventricular block and narrow QRS complexes had a block above the origin othe His spike (proximal block). Eleven patients in this group had repeat His bundle electrograms performed before discharge and in 3 patients there was evidence of residual atrioventricular nodal dysfunction. Both the hospital and follow-up mortality in this group was low and there was no evidence to suggest that permanent pacing would benefit these patients. Of the 18 patients with bundle-branch block and a normal PR interval, 9 had prolongation of the HV interval, but there was no difference in mortality in patients with normal or prolonged HV intervals. Twenty-two patients with bundle-branch block also developed atrioventricular block. In 5 of these patients the site of the AV block was proximal and in 14 it was distal, while 3 patients had both proximal and distal block. The hospital mortality in those patients who progressed to second- or third-degree atrioventricular block was considerably higher than in those patients who remained in first-degree atrioventricular block.

Tricyclic antidepressant drugs and cardiac conduction

Abstract 1. 1. Distal intracardiac conduction defects were observed inpatients ingesting both toxic and therapeutic doses of tricyclic antidepressants (TCA). 2. 2. In a crossover comparative study of doxepin-nortriptyline (150 mg/day for 3 weeks) six out of seventeen patients on nortriptyline and only one patient on doxepin showed significant prolongation of the QRS interval. 3. 3. Plasma levels of doxepin (52 ± 6 ng/ml) were lower than those of nortriptyline (196 ± 29 ng/ml). 4. 4. An in vitro study of TCA has shown that the isolated perfused guinea pig heart could provide a toxicological model for studying the arrhythmogenic effects of TCA in man.

Multiform ventricular tachycardia.

Electrophysiological studies were performed in three patients with chronic recurrent ventricular tachycardia (VT) associated with coronary artery disease. In each case the ventricular origin of the tachycardia was confirmed and induction of tachycardia by programmed stimulation suggested a re‐entry mechanism. Multiple types of ventricular tachycardia were observed which differed in cycle length, QRS morphology, timing of local epicardial and endocardial ventricular electrograms and the use of the specialized conduction system for propagation. There was evidence of one or more re‐entry circuits arising in or near previously infarcted areas, with features of cycle length alternation, change in exit points and variations in subsequent conduction through the myocardium and specialized conduction tissues. These findings suggest multiform VT can be due to a number of factors. A modified surgical approach is recommended for management of medically refractory VT when there is evidence of multiple types.