Franchi F, Padeletti L
Eur J Cardiol. 1980;12(2):95-101.
Shortened return cycles after premature atrial stimulation (PAS) are commonly referred to as sinoatrial entrance block and exit delay at the sinoatrial junction or sinus-node reentries. In the 2 reported cases PAS at critical coupling intervals was followed by shortened return cycles characterized by a changed high right electrogram (and surface P waves in 1 case) and a normal sequence of atrial activation with unaltered intraatrial conduction. These changes lasted for some beats and a concomitant shorter or longer atrial cycle length was observed. Electrophysiological events furnish indirect evidence of sinoatrial pacemaker shift as a cause of incomplete interpolation in man.
房性早搏刺激（PAS）后折返周期缩短通常被称为窦房结入口阻滞、窦房结交界处的出口延迟或窦房结折返。在2例报告病例中，临界耦合间期的房性早搏刺激后，折返周期缩短，其特征为高位右心电图改变（1例伴有体表P波改变），心房激动顺序正常，心房内传导未改变。这些改变持续数搏，并观察到伴有较短或较长的心房周期长度。电生理事件为窦房结起搏点移位作为人类不完全插入的原因提供了间接证据。
