Alternate ventriculoatrial Wenckebach conduction.

Three cases are presented showing retrograde alternate Wenckebach periods. Retrograde alternate Wenckebach periods were defined as 2:1 ventriculoatrial (VA) block in which the conducted beats showed progressive prolongation of conduction (VA) time. The sequence terminates with two or three successively blocked ventricular beats. In one of the three cases the level of block was identified as being in the atrioventricular (AV) node. In the other two the level of block could not be clearly identified. This report provides further evidence for the concept of multilevel block within the AV node. Retrograde alternate Wenckebach periods may explain some instances of variation of atrial depolarization intervals during episodes of ventricular tachycardia and may be clinically significant.