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 68 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 andor 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