Heritable Q-T prolongation without deafness.

The family, reported on, have a syndrome of prolonged Q-T interval, potentially fatal episodes of ventricular arrhythmias, and normal hearing. The direct familial transmission demonstrated in this pedigree is consistent with an autosomal dominant mode of inheritance. To protect other members of the family from the consequences of ventricular arrhythmia experienced by the irreversibly brain-damaged index patient, a series of physiologic investigations was undertaken on this patient in a search for a suitable prophylactic medical regimen. The attacks of ventricular arrhythmia were found to be precipitated by increase in systemic pressure, sinus tachyeardia, and extrasystoles occurring in the supernornal phase of repolarization (R in T syndrome). Propranolol was demonstrated to be an effective agent in preventing the ventricular arrhythmia in the index case and in other family members. Since administration of the beta-adrenergic stimulator isoproterenol did not produce ventricular fibrillation, it is assumed that the action of propranolol in preventing ventricular arrhythmia is not mediated through beta-adrenergic blockade, but through its direct antiarrhythmic properties. The subject experienced no ill effect from the series of investigations.