Controlling cardiac arrhythmias: to delay conduction or to prolong refractoriness.

Recent data with encainide and flecainide (CAST study) question the benefit of reducing premature ventricular contractions in survivors of myocardial infarction. Proarrhythmic mechanisms might include excessive slowing of conduction. In patients with supraventricular tachycardias, proarrhythmic effects of Class 1c agents are very uncommon.