Ventricular parasystole and ventricular couplets: a re-entry within the parasystolic focus?

We report a 62-year-old man with a persistent ventricular rhythm originating in a parasystolic focus associated with frequent ventricular couplets with fixed coupling. Both intravenous (IV) procainamide (1 g) and propafenone (70 mg IV) promptly suppressed only the second component of ventricular couplets, suggesting that re-entry rather than enhanced automaticity was the mechanism of ventricular couplets. On the contrary, the nonresponse of ventricular rhythm and ventricular couplets to verapamil (10 mg IV) suggested that triggered activity should not play a role in the genesis of this ventricular rhythm. The mechanisms of the ventricular couplets (rapidly discharging parasystolic focus vs. re-entry) are discussed.