Clinical and electrophysiologic characteristics of sinoatrial entrance block evaluated by direct sinus node electrography: prevalence, relation to antegrade sinoatrial conduction time, and relevance to sinus node disease.

When AV conduction is normal, the absence of VA conduction is not abnormal. Analogous information about retrograde sinoatrial conduction is not available. Although the premature atrial stimulas (PAS) technique can demonstrate the presence of sinoatrial entrance block (SAEB), both its prevalence and its relationship to antegrade SA conduction are unknown. Using PAS, we determined the incidence of SAEB in 59 patients with known or suspected dysrrhythmias or conduction defects to be 6.8%. Using catheter recorded sinus node electrograms (SNE), we then directly measured sinoatrial conduction time (SACT) in three patients with SAEB. Antegrade SACT was normal in two and prolonged in one. Only the latter had sinus node dysfunction recognized by ECG and/or conventional sinus node testing. We conclude that SAEB occurs infrequently, may occur when antegrade SACT is normal, is probably analogous to behavior at the AV node, and should not be used as an indicator of sick sinus syndrome.