Bigeminy in ventricular interpolation.

T he occurrence of a premature beat between two consecutive conducted sinus beats is termed an interpolated premature systole or extrasystole.1 An interpolated premature ventricular systole can effect the conduction of the subsequent sinus beat by concealed retrograde penetration into the His-Purkinje system or AV node or both. This retrograde concealed penetration can result in a prolongation of the PR interval, with normal or aberrant intraventricular conduction of the first postextrasystolic sinus beat. The aberrant intraventricular conduction of the first postectopic sinus beat may mimic the occurrence of ventricular couplets (two premature yen-