QT-Interval Prolongation, Paroxysmal Ventricular Arrhythmias, and Convulsive Syncope

A patient with prolonged QTc interval, paroxysmal ventricular tachycardia, and syncope was studied. Her syncopal episodes were often precipitated by stress or unexpected stimuli. Neurological evaluation showed no abnormalities. Right and left stellate ganglion blockade and intravenous atropine, calcium gluconate, and digoxin did not shorten QTc-interval duration. Ventricular pacing and intravenous phenobarbital suppressed ventricular tachyarrhythmias. Sodium diphenylhydantoin (Dilantin Sodium®) produced QTc shortening and controlled ectopic rhythms. Neural influence on synchrony of ventricular repolarization may predispose to the paroxysmal arrhythmias associated with this syndrome. Central nervous and asymmetrical cardiac sympathetic nervous stimulation may produce an increase in temporal dispersion of repolarization and a prolonged refractory period, thus facilitating reentrant rhythms and tachyarrhythmias. Sodium diphenylhydantoin shortens repolarization and effective refractory period and increases the conduction velocity of ectopic ventricular impulses, reducing temporal dispersion and suppressing reentrant rhythms. QT-prolongation syndromes are potentially lethal and may account for a number of cases of "atypical epilepsy."