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.

Effect of diphenylhydantoin on left ventricular function in patients with heart disease

The effect of 250 mg of diphenylhydantoin, administered intravenously, on left ventricular function was determined during cardiac catheterization in nine patients with heart disease.

Five minutes after drug administration, left ventricular end-diastolic pressure rose in each patient from an average of 6.0 mm Hg to 10.0 mm Hg. Concurrently, stroke work and stroke power indices decreased in each patient by an average of 22.0% and 22.2%, respectively. Stroke volume index decreased in seven patients and maximum left ventricular dp/dt fell in eight patients. Over the next 25 minutes, all parameters returned to control values. Cardiac index was unchanged, whereas generally small and insignificant changes were observed in heart rate and systemic arterial pressure throughout the study.

Although this study has demonstrated that diphenylhydantoin depresses myocardial function, the effect may have limited clinical significance since it was relatively short-lived and did not reduce cardiac output or greatly elevate ventricular end-diastolic pressure. Furthermore, the absence of a significant systemic hypotensive effect is of distinct clinical importance.

Continuous muscle fibre activity in an Indian male with additional evidence of terminal motor fibre abnormality

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