Normal left ventricular function does not protect against propafenone-induced incessant ventricular tachycardia

Propafenone is a class Ic anti-arrhythmic agent with mild beta-blocking properties which has recently become available in South Africa. We have used the drug in 3 patients with sustained monomorphic ventricular tachycardia not due to ischaemic heart disease. All had normal left ventricular function; 1 had Wegener's granulomatosis and 2 had arrhythmogenic right ventricular dysplasia. In the latter 2, propafenone provoked incessant monomorphic ventricular tachycardia which persisted for more than 24 hours despite repeated efforts at termination. The morphology was similar to the patients' spontaneous ventricular tachycardia, but the rate was slower and the QRS complexes broader, consistent with propafenone's marked ability to slow intraventricular conduction. It is postulated that incessant tachycardia results from perpetuation of re-entry due to marked conduction slowing produced by the drug. Previous reports have suggested that this is most likely to occur in patients with poor left ventricular function, but our experience indicates that those with normal left ventricular function are also at risk, particularly if the substrate for re-entry is present. Propafenone, like all other powerful anti-arrhythmic agents, may provoke life-threatening arrhythmias and should be used with great caution after due consideration of the indications, even in patients with normal left ventricular function.