Dual effects of concealed A-V nodal conduction in man.

An interpolated premature ventricular contraction (PVC) may produce either complete block of the next sinus impulse or depression of A-V nodal conduction with a prolonged A-H interval. When a PVC results in partial depression of a A-V nodal conduction, the effect on subsequent premature atrial stimuli is unknown. The authors have recently observed three patients in which the effect of a premature ventricular stimulus with interpolation on the functional refractory period of the A-V node could be measured. In case one an interpolated PVC sufficient to prolong the A-H interval from 80 to 120 msec was followed by programmed premature atrial stimuli which resulted in no additional A-V nodal delay, and the apparent functional refractory period of the A-V node was reduced from 420 to 330 msec when compared with the atrial extrastimulus technique. In case two a programmed ventricular extrastimulus prolonged the A-H interval in the following sinus beat from 120 to 240 msec; atrial extrastimuli then resulted in only minimal increments in A-V nodal delay and the apparent functional refractory period of the A-V node was reduced from 590 msec. A ventricular extrastimulus in case three increased the resting A-H interval from 60 to 115 msec; conduction of atrial extrastimuli then resulted in a reduction in the functional refractory period of the A-V node from 465 to 400 msec. In each case an interpolated premature ventricular stimulus produced (1) depression of A-V nodal conduction in the ensuing sinus beat A1 and (2) relative facilitation of A-V nodal conduction of a subsequent premature atrial stimulus (A2). The functional refractory period of the A-V node was reduced when compared with the atrial extrastimulus technique alone.