Rapid ventricular parasystole with possible multilevel exit block

A case of ventricular parasystole firing at the extremely rapid rate of 214 beats per minute in a 73 year old woman is described. Manifest cycle lengths of parasystolic complexes varied widely due to variable degrees of exit block, which could be best interpreted by the concept of multilevel block or alternating Wenckebach periodicity in the ventriculo-ectopic junction. Discontinuation of digoxin reduced the degree of exit block and unmasked parasystolic tachycardia.