Clinical significance of junctional pacemaker automaticity in patients with sick sinus syndrome.

This study aimed to examine the characteristics and the clinical significance of atrio-ventricular (AV) junctional automaticity in sick sinus syndrome. Maximum sinus node recovery time (max SRT) or maximum junctional recovery time (max JRT), and AV nodal Wenckebach block rate were evaluated before and after pharmacologic autonomic blockade (AB) in 43 patients with sick sinus syndrome. Max JRT shorter than 3000 msec was obtained after AB in 13 patients (group 1) and apparent enhancement of junctional automaticity after AB was observed in these patients. Thirty patients showed max JRT or max SRT longer than 3000 msec after AB (group 2). The Wenckebach block rate increased significantly after AB in group 1 but did not change significantly in group 2. The Wenckebach block rate after AB in group 1 was significantly higher than that in group 2. Max JRT was obtained only after AB in 8 patients in group 1 (subgroup 1), and in 9 in group 2 (subgroup 2). Max SRT before AB and the intrinsic heart rate were not significantly different between these subgroups. Only one of 8 patients in subgroup 1 had a history of near syncope. On the other hand, syncope was observed in 5 patients, and near syncope in one, in group 2. In conclusion, intrinsic junctional automaticity is preserved in some patients with sick sinus syndrome, and might compensate for sinus node dysfunction to prevent clinical symptoms. Organic impairment should affect conductivity as well as automaticity in the AV junction.