COMPARISON OF EFFECTS OF ATRIAL AND VENTRICULAR STIMULATION ON SINUS NODE FUNCTION IN MAN

Although sinus node function was evaluated during premature atrial stimulation, no study of retrograde ventriculoatrial sinus node activation following premature ventricular stimuli was reported. This study was to investigate the production of compensatory and noncompensatory pauses by premature ventricular contractions through a comparison of the effects of atrial and ventricular stimulation on sinus node function. Eleven patients in sinus rhythm were studied with programmed introduction of premature atrial and ventricular stimuli outside the ventricular vulnerable period. The onset of sinus node reset, duration of the return sinus cycle (A2-A3) during reset and estimated sinoatrial conduction times were recorded. Sinus node function during premature ventricular stimulation was approximated by utilizing the interval between the last sinus beat and onset of retrograde atrial depolarization (A1-A2 interval). The return cycle length (A2-A3) during sinus reset compared at equal A1-A2 intervals was significantly less with ventriculoatrial conduction (1,145 .+-. 52 ms. atrial vs. 1076 .+-. 52 ms. ventriculoatrial; P < 0.01 by paired t test) and the estimated sinoatrial conduction time was significantly less with ventriculoatrial conduction (71 .+-. 7 ms. atrial vs. 25 .+-. 7 ms. ventriculoatrial; P < 0.01 by paired t test). Ventriculoatrial sinus reset occurred later in the sinus cycle than atrial reset in 3 of 7 patients with sinus reset produced by both atrial and ventricular prematures. The effects of ventriculoatrial conduction on sinus node function are significantly different from those of atrial stimulation alone. The return sinus cycle length during reset and estimated sinoatrial conduction time are significantly reduced with ventriculoatrial conduction. Although the zones of sinus reset with atrial and ventricular stimulation are approximately equal, ventriculoatrial depolarization may produce sinus reset later in the sinus cycle in some cases.