Comparative study of two methods of estimating sinoatrial conduction time in patients with abnormal sinus node function.

This study compared a new method to estimate sinoatrial conduction time (SACT) using continuous atrial pacing proposed by Narula et al with the widely used method using premature atrial stimulation originally proposed by Strauss et al. The estimated SACTs by the two methods were obtained in 19 patients with normal sinus node (SN) function (Group A) and 8 patients with abnormal SN function (Group B). Estimate of the SACT by the Narula method was taken as the difference between the first atrial return cycle after pacing and the basic sinus cycle length (BSCL). The Narula method was performed for a train of 8 consecutive beats at three different pacing cycle length (PCL); PCL (1) greater than or equal to BSCL--50, PCL (2) greater than or equal to BSCL--100 and PCL (3) greater than or equal to BSCL--150 msec. In group A, the estimated SACTs by the Strauss method was 185 +/- 49.3 msec, meanwhile the SACTs by the Narula method were 148 +/- 80.7 at PCL (1), 181 +/- 58.7 at PCL (2) and 212 +/- 84.5 msec at PCL (3) (mean +/- SD); the coefficient of correlation between the Strauss method and the Narula method were 0.58, 0.84, and 0.67, respectively. On the other hand, in group B, atrial return cycles by the Narula method were abnormally prolonged (over 215 msec) in 5 of 8 cases (63%) even at PCL (2) and in all of the cases (100%) at PCL (3). By the Strauss method, SACTs in 6 of 8 cases could not be defined; however it was possible to assess the type of SN dysfunction by the pattern of the atrial return cycles. In conclusion, the estimated SACT by the Narula method at PCL (2) corresponded well with the SACT by the Strauss method in patients with normal SN function. However, it was difficult to determine SACT in patients with Sick Sinus Syndrome by both methods.