Atrioventricular and ventriculo-atrial conduction in patients with symptomatic sinus node dysfunction.

In 14 patients with symptomatic sinus node dysfunction--sinus bradycardia, sino-atrial exit block, or sinus arrest--electrophysiological studies were performed before implantation of a pacemaker. In 8 patients incremental high right atrial pacing showed AV-nodal Wenckebach at pacing rates equal to or above 130/min (group I); in 6 patients AV-nodal Wenckebach was reached at pacing rates less than 130/min (group II). During ventricular pacing at a rate 10-15% faster than the existing sinus rate, ventriculo-atrial (VA) conduction was present in all patients of group I, while VA conduction was present in only 2 patients of group II (p less than 0.05). Patients with symptomatic sinus node dysfunction but with intact AV conduction frequently show VA conduction during ventricular pacing and thus are particularly at risk for developing a pacemaker syndrome when a ventricular demand (VVI) pacemaker is implanted. This complication can be avoided by atrial demand (AAI) pacing or AV sequential (DVI) pacing. When adequate experience has been gathered with AV universal (DDD) pacemakers, the indications for selection of a pacemaker in patients with symptomatic sinus node dysfunction will probably change.