The Human Sinus Node Electrogram on the Overdrive Suppression Test and Estimated Sinoatrial Conduction Time Measurements

Sinus node electrograms (SNEs) on atrial overdrive suppression test (AOD) and estimated sinoatrial conduction time (SACT) measurements were recorded. Typical SNE (TSNE), characterized by low-frequency, anatomically localized pre-P wave potentials (Reiffel et al.) were obtained in 12 of 18 patients (pts) with normal sinus node function (group I) and 15 of 26 pts with sick sinus syndrome (SSS) (group II). In 9 of 15 SSS pts but only 2 or 12 in group I “atypical” SNEs (ASNE) with inverted waves at the beginning of P wave were recorded on SNE recordings of the first sinus recovery beat by overdrive atrial pacing (OAP) for either AOD or SACT measurements, or both. On the basis of ASNE following OAP, the 26 SSS pts fell into 3 subgroups: TSNE with the same configuration as recorded before OAP was observed without ASNE throughout the study in 6 pts (IIA). ASNE was observed without TSNE throughout the study in 11 pts (IIB). TSNE before OAP and ASNE following OAP were recorded in 9 pts (IIC). Corrected sinus node recovery time in IIB was significantly longer than in either IIA or IIC (P < 0.0005). Estimated SACT (Narula’s method) for either A, B or C was significantly (P < 0.0005) longer than in group I. There was no significant difference in either estimated SACT or directly measured SACT between IIA and IIC. A significant correlation existed between estimated SACT and directly measured SACT in group I (r = 0.88) and IIA (r = 0.75) (P < 0.01) but not in IIC (r = 0.48). ASNE may result from a pacemaker shift.