The human sinus nodal electrogram: techniques and clinical results of intra-atrial recordings in patients with and without sick sinus syndrome.

An intra-atrial recording technique previously employed in animal experiments was successfully used to record SNP from the anatomic sinus nodal region of the high right atrium in 29 out of 41 patients (71%) thus examined. Due to the low amplitudes (microvolt range, 40 to 120 microV, mean 79 +/- 20 microV), these potentials were discernible only on high amplification (A = 10(4) to 10(6)), but with a conventional electrode catheter. Against the background of a gradual diastolic depolarization (0.6 to 3.5 microV/msec, mean 1.9 +/- 0.71 msec), SNP stood out distinctly from the subsequent abrupt atrial depolarization. In four patients with SSS, first- and second-degree sinoatrial blocks, respectively, were recorded. SACT were measured both directly and indirectly, and the results were compared in all 18 patients without SSS and in 11 patients with SSS. Although the recordings were not made simultaneously, the paired values for the patients without SSS correlated well (r = 0.890, p less than 0.001), whereas no correlation was found in the patients with SSS (r = 0.163, p = 0.316). In spite of unresolved questions, direct recording of SNP appears to be of potential value in evaluating patients with SSS.