The differential diagnosis of bigeminal rhythms.

Bigeminal rhythms may arise from ectopic firing or from failure of impulse generation or conduction. In atrial bigeminy a premature atrial beat beat follows each sinus beat. If the PAC is not conducted bradycardia may result; if it is symptomatic treatment with digitalis or quinidine is indicated. Junctional bigeminy may be coupled to sinus beats or may accompany atrial fibrillation. Ventricular bigeminy, the most common type of bigeminy involving ectopic firing, usually requires treatment with suppressive drugs. Concealed bigeminy manifested as PVCs separated by an odd number of sinus beats has the same clinical implications as ventricular bigeminy. Re-entrant premature beats may also be triggered by an artificial ventricular pacemaker. Bigeminy associated with delayed impulse conduction is most often caused by a 3:2 Wenckebach block at the A-V junction but the block may also be at the S-A node or around an ectopic pacemaker. Conduction or production delay may produce "escape-capture" bigeminy in which successive beats are produced by the dominant pacemaker and an alternate one. Implantation of an artificial pacemaker may be appropriate. It is important for the observer to be able to identify the mechanism of any bigeminal rhythm since crucial clinical decisions may attend such identification.