Richard H. Helfant

Catheter Technique for Recording His Bundle Activity in Man

A technique for the routine recording of His bundle (H) activity in man using a bipolar or multipolar catheter is described. The recording catheter is inserted percutaneously, via the Seldinger method, into the right femoral vein and advanced fluoroscopically into the right atrium. Placement of the pre-formed curve at the catheter tip across the tricuspid valve in nine patients resulted in stable recordings of His bundle activity in successive cardiac cycles. Right atrial pacing resulted in progressive lengthening of the P-H interval with increasing frequency but the H to S-wave interval remained constant at all rates. Similar lengthening of the P-H interval was produced during atrial pacing when pressure was applied to the carotid sinus. The use of this recording technique in man will facilitate diagnostic interpretation of the electrocardiogram and can be used in various investigations of atrioventricular and intraventricular conduction in man.

A Study of Heart Block in Man Using His Bundle Recordings

The technique of recording His bundle electrograms in man by a tripolar electrode catheter was applied in a study of patients with first, second, and third-degree heart block. In all patients with first-degree heart block (congenital, acquired, or induced by atrial pacing), the delay in A-V conduction occurred proximal to the His bundle as evidenced by a prolonged P-H interval. The enhancement of A-V conduction (shortening the P-H interval) due to isoproterenol was qualitatively similar in the three forms of first-degree block. In cases of Wenckebach phenomenon the P-H interval progressively increased until a dropped beat occurred. The nonconducted P wave was not followed by a His deflection, indicating block proximal to the His bundle. Cases of 2:1 and 3:1 block occurring proximal to the His bundle were also studied. The usefulness of His-bundle recordings in the diagnosis of cases of complete and incomplete bilateral bundle-branch block is also demonstrated.

Study of atrioventricular conduction in man using electrode catheter recordings of His bundle activity.

The technique of recording electrograms of the His bundle, using a tripolar electrode catheter positioned across the tricuspid valve, was applied in a physiological study of atrioventricular conduction in man. Increasing the heart rate to 160 beats/min by right atrial pacing produced progressive prolongation of the P-H interval while the H-Q interval remained constant. At any given paced heart rate, digitalis caused a prolongation of the P-H interval. Isoproterenol and atropine markedly shortened the P-H interval at any given heart rate. Neither drug had any significant effect on the H-Q interval. Coupled premature atrial stimulation produced prolongation of the P-H interval alone when the resultant ventricular depolarization was normal, and prolongation of both the P-H and H-Q intervals when the resultant ventricular depolarization was aberrant.

The Electrophysiological Properties of Diphenylhydantoin Sodium as Compared to Procaine Amide in the Normal and Digitalis-Intoxicated Heart

The effects of diphenylhydantoin sodium (Dilantin) on ventricular automaticity, intraventricular conduction, atrioventricular (A-V) conduction, and sinus rate have been determined in the digitalis-intoxicated and normal heart. These effects have been compared with procaine amide. Diphenylhydantoin sodium depresses ventricular automaticity and enhances A-V conduction while having little or no effect on intraventricular conduction or sinus rate. Procaine amide differed from diphenylhydantoin sodium in that it caused depression of both A-V and the intraventricular conduction, as well as slowing of the sinus rate.The results indicate that the electrophysiological properties of diphenylhydantoin sodium make it superior to procaine amide in the treatment of digitalis toxicity. Both diphenylhydantoin sodium and procaine amide can suppress digitalis arrhythmias due to enhanced automaticity, but procaine amide may promote “re-entry” arrhythmias by potentiating the intraventricular conduction defect caused by the glycoside. In addition, diphenylhydantoin sodium appears to antagonize the action of digitalis on the A-V node, while procaine amide increases the digitalis-induced A-V block. It is concluded that the electrophysiological properties of diphenylhydantoin sodium make it an excellent agent in treating digitalis-induced arrhythmias.

Protection from Digitalis Toxicity with the Prophylactic Use of Diphenylhydantoin Sodium An Arrhythmic-Inotropic Dissociation

Diphenylhydantoin sodium (Dilantin) given prophylactically increased the dose of digitalis necessary to produce toxicity by 72 to 224%. At constant heart rates, pretreatment with diphenylhydantoin sodium did not alter the elevation of rate of rise of left ventricular pressure produced by the glycoside.Two implications have been drawn from these findings. First, the inotropic and arrhythmic actions of digitalis can be dissociated, since diphenylhydantoin sodium seems specifically to counteract the electrophysiological actions of the glycoside. Second, pretreatment with diphenylhydantoin sodium significantly widened the “toxic-therapeutic” ratio of digitalis. This, therefore, may have important clinical applications.

Controlled Heart Rate by Atrial Pacing in Angina Pectoris A Determinant of Electrocardiographic S-T Depression

This study was undertaken with a consideration of the physiological relationship between myocardial oxygen consumption and heart rate. Atrial pacing was performed in 63 resting subjects, 36 of whom had been referred for evaluation of angina pectoris. Pacing at critical controlled heart rates evoked angina pectoris in six patients of this group with chest pain and, consistently and more frequently, produced significant S-T segmental depression in 28 patients as a manifestation of myocardial ischemia. The functional test employing controlled heart rates has several advantages over other stress tests. The use of the sole stress of controlled atrial tachycardia is a new technique which has provided relatively safe, reproducible results in the objective evaluation and investigation of myocardial ischemia.

Effects of Diphenylhydantoin on Atrioventricular Conduction in Man

The effects of intravenous diphenylhydantoin (5 mg/kg) on atrioventricular conduction in man at controlled heart rates in the digitalized and undigitalized state were studied. In undigitalized subjects, diphenylhydantoin administration consistently decreased A-V conduction time in each individual subject when identical heart rates were compared. Ouabain infusion produced an increase in A-V conduction time and this prolongation was always reversed by diphenylhydantoin. In two patients with atrial flutter and in two with atrial fibrillation, diphenylhydantoin caused a decrease in ventricular rate without affecting the atrial arrhythmias.These findings are of clinical importance, especially in the therapy of digitalis toxicity. When digitalis excess is manifested by both ectopic beats and incomplete A-V block, diphenylhydantoin would have special utility since, in contrast with the commonly used antiarrhythmic agents, it decreases A-V conduction time in addition to suppressing ectopic beats. Diphenylhydantoin-induced depression of the ventricular rate in atrial flutter or fibrillation may also be useful clinically. However, since diphenylhydantoin markedly decreases ventricular automaticity, its use in patients with complete heart block is contraindicated.

The clinical use of diphenylhydantoin (Dilantin) in the treatment and prevention of cardiac arrhythmias

Abstract The use of intravenous diphenylhydantoin (5 mg. per kilogram) in the treatment and prevention of cardiac arrhythmias was studied. In the treatment of arrhythmias caused by digitalis, diphenylhydantoin restored 6 of 11 atrial arrhythmias to sinus rhythm and 21 of 24 ventricular arrhythmias responded. In patients whose arrhythmias were not digitalis-induced, only one of 20 patients with atrial and 5 of 16 with ventricular arrhythmias responded. Diphenylhydantoin significantly improved the cardiac rhythm in 10 of 12 patients with ventricular arrhythmias which were unresponsive to procaine amide. In 12 patients, atrial or ventricular arrhythmias developed either during digitalization or maintenance digitalis. In these patients, diphenylhydantoin was given immediately prior to DC cardioversion. In all cases, DC countershock produced sinus rhythm with no immediate postshock arrhythmias. Diphenylhydantoin was given to 11 patients prior to cyclopropane anesthesia. Ten of the 11 patients had no arrhythmias during the anesthetic, whereas only one of 9 patients in the control group was free of arrhythmias. Diphenylhydantoin restored sinus rhythm in 8 patients who developed ventricular arrhythmias during the administration of various anesthetics, but had no effect in 2 patients with atrial arrhythmias. Side effects due to diphenylhydantoin were minor and transient and no deaths occurred. It is concluded that with slow administration and careful electrocardiographic and blood pressure monitoring, diphenylhydantoin is a safe and valuable agent in both the treatment and prevention of cardiac arrhythmias.

Diphenylhydantoin Prevention of Arrhythmias in the Digitalis-Sensitized Dog after Direct-Current Cardioversion

The ability of diphenylhydantoin to prevent arrhythmias induced by synchronized direct current shocks after digitalis sensitization was evaluated. In the control state, an average of 155 watt-seconds was required to produce ventricular tachycardia. Immediately after recovery from digitalis toxicity, an average of 23 watt-seconds produced ventricular tachycardia. The administration of diphenylhydantoin at this time immediately increased the threshold required for ventricular tachycardia to an average of 363 watt-seconds. In eight studies, diphenylhydantoin was given during cardioversion-induced ventricular tachycardia and converted all cases to regular sinus rhythm. These findings indicate that diphenylhydantoin may be of prophylactic value prior to direct current cardioversion in a digitalized patient. Conversely, diphenylhydantoin would also be useful in the management of ectopic beats that may occur in digitalized patients after cardioversion.

Electrophysiological Effects of Direct Current Countershock before and after Ouabain Sensitization and after Diphenylhydantoin Desensitization in the Dog

The effects of synchronized direct current countershock on ventricular automaticity, intraventricular conduction, and atrioventricular conduction were studied before and after ouabain administration and after diphenylhydantoin. At the level of electrical energy that induced ventricular arrhythmias, averaging 159 watt-seconds, countershock transiently increased ventricular automaticity and prolonged both intraventricular and atrioventricular conduction time. Immediately after ouabain-induced ventricular tachycardia returned to regular sinus rhythm, underlying ventricular automaticity and intraventricular and atrioventricular conduction times were increased. An average of 23 watt-seconds produced overt and persistent ventricular tachycardias due to enhanced automaticity or re-entry. Atrioventricular and intraventricular conduction times were also prolonged, and transient complete heart block occurred in two experiments. Diphenylhydantoin administration at this time depressed ventricular automaticity, caused a speeding of atrioventricular and intraventricular conduction times and increased the electrical energy necessary to produce ventricular tachycardia to 355 watt-seconds.