OBJECTIVES: The purpose of this study was to evaluate the efficacy of various antiarrhythmic drugs at prolonging the QT interval into the normal range and preventing ventricular arrhythmias in patients with short QT syndrome. BACKGROUND: Short QT syndrome is a recently described genetic disease characterized by short QT interval, high risk of sudden death, atrial fibrillation, and short refractory periods. METHODS: Six patients with short QT syndrome, five of whom had received an implantable cardioverter-defibrillator (ICD) and one child, were tested with different antiarrhythmic drugs, including flecainide, sotalol, ibutilide, and hydroquinidine, to determine whether they could prolong the QT interval into the normal range and thus prevent symptoms and arrhythmia recurrences. RESULTS: Class IC and III antiarrhythmic drugs did not produce a significant QT interval prolongation. Only hydroquinidine administration caused a QT prolongation, which increased from 263 +/- 12 ms to 362 +/- 25 ms (calculated QT from 290 +/- 13 ms to 405 +/- 26 ms). Ventricular programmed stimulation showed prolongation of ventricular effective refractory period to > or =200 ms, and ventricular fibrillation was no longer induced. CONCLUSIONS: The ability of quinidine to prolong the QT interval has the potential to be an effective therapy for short QT patients. This is particularly important because these patients are at risk of sudden death from birth, and ICD implant is not feasible in very young children.