Parasystole simulating ventricular bigeminy with Wenckebach-type coupling prolongation.

A 65-year old male originally presented with repetitive ventricular bigeminal sequences demonstrating progressive prolongation of successive coupling intervals suggesting Wenckeback-type exit block. An even number distribution of conducted beats always intervened between bigeminal sequences. Subsequent analysis proved this to be a fortuitous "pseudo-Wenckebach" phenomenon, with the actual mechanism being continuous parasystole. Additional recording verified a parasystolic rhythm.