Diagnostic Methods Electrophysiology

Sinus node recovery time (SNRT) is frequently used to assess sinus node function in patients with suspected sick sinus syndrome (SSS). Although SNRT is assumed to reflect sinus node automaticity, this assumption remains unproven. The purpose of this study was (1) to test the hypothesis that SNRT in patients with and without SSS reflects sinus node automaticity, and (2) to assess the role of sinoatrial conduction time in the measurement of SNRT. A total of 16 patients (mean + SD age 63 ± 9 years), seven of which had SSS, form the basis of this report. An electrogram of the sinus node was obtained for each of the 16 patients, and overdrive pacing was performed in each at cycle lengths of 1000 to 300 msec. SNRT was measured (1) on the sinus node electrogram (direct method, measuring SNRTd) as the interval from the last pacing stimulus artifact to the onset of the upstroke slope of first postpacing sinus beat and (2) on the high right atrial electrogram (indirect method, measuring SNRTi). Results were as follows: (1) The longest SNRTd was significantly shorter than the longest SNRTi (989 + 304 vs 1309 ± 356 msec, p < .001). (2) For the first postpacing sinus beat there was a significant prolongation of sinoatrial conduction time as compared with that for sinus beats before pacing (319 + 152 vs 99 + 35 msec, p < .001). Sinoatrial conduction time normalized within 3.6 + 0.96 postpacing sinus beats. (3) At the pacing cycle length that resulted in the longest recovery time, sinus node depression was seen in 56% of patients, sinus node acceleration was noted in 26%, and no appreciable change in sinus node automaticity was observed in 19%. (4) Sinoatrial conduction time for the sinus beat before pacing and that for the first postpacing beat was longer in patients with SSS when compared with in patients without SSS. (5) In patients with SSS the abnormal SNRTi, when corrected for the degree of prolongation of sinoatrial conduction time for the first postpacing beat, became normal in five of six patients. We conclude that (1) SNRTi reflects both sinus node automaticity and sinoatrial conduction time, whereas SNRTd reflects sinus node automaticity, (2) overdrive atrial pacing results in marked prolongation of sinoatrial conduction time for the first postpacing beat, which is longer in patients with SSS when compared with in those without SSS, and (3) in patients with SSS the inference of abnormal sinus node automaticity on the basis of a prolonged corrected SNRTi is usually incorrect. Circulation 70, No. 4, 663-671, 1984. THE PHENOMENON of postpacing depression of cardiac pacemakers'-7 has been used to evaluate sinus node function in man.8-7 Clinical studies have focused on the response of the human sinus node to atrial pacing at rates above the sinus rate. The method has been used to determine the time required for a sinus beat to resume activity after abrupt cessation of atrial pacing. This sinus node recovery time (SNRT) has been used in the evaluation of sinus node function in patients with sick sinus syndrome (SSS).5-17 Although SNRT is asFrom the Electrophysiology Laboratory Department of Cardiology, Brooklyn V.A. Medical Center, Brooklyn, and the Department of Cardiology, the Mount Sinai Medical Center, New York. Address for correspondence: Joseph A. Gomes, M.D., Director Clinical Electrophysiology, Electrocardiography Service, ECG Department, Mount Sinai Medical Center, One Gustave L. Levy P1., New York, NY 10029. Received Dec. 5, 1983; revision accepted July 5, 1984. sumed to reflect sinus node automaticity in man, the contribution of sinoatrial conduction in the measurement of SNRT remains undefined. The purpose of this study was (1) to test the hypothesis that SNRT in patients with and without SSS reflects sinus node automaticity and (2) to assess the role of sinoatrial conduction in the measurement of SNRT. Materials and methods A total of 22 male patients were studied after the nature of the procedure was explained to them and after they gave signed informed consent. Sixteen patients who satisfied the following criteria were included in the study: (1) Each had stable, reproducible sinus node electrograms free of baseline drift during sinus rhythm and after overdrive pacing. (2) In each the sinus node electrograms were clearly separable from the T and U wave deflections both during sinus rhythm and after atrial overdrive pacing. The 16 patients ranged in age from 38 to 78 years (mean age, 63 + 9 years). Nine of the 16 patients had no evidence of SSS, whereas seven of 16 had symptomatic SSS. Vol. 70, No. 4, October 1984 663 by gest on A ril 8, 2017 http://ciajournals.org/ D ow nladed from