[Sinus node function evaluated by spontaneous atrial premature contractions]

Sinus node function was evaluated according to spontaneous premature atrial contractions (APC). In 33 patients, who showed evidence of more than 10 APCs in 24-hour Holter ECG, sinoatrial conduction times (SACT) were measured by the Strauss' method. Time difference between the interval preceding PP, the APC and return cycle following APC was expressed as RC-SC. Patients were categorized in three groups; CSRT less than 500 and 2SACT less than 180 msec (A), 500 less than or equal to CSRT less than 1000 and/or 180 less than or equal to 2SACT less than 250 msec (B), and CSRT greater than or equal to 1000 and or 2SACT greater than or equal to 250 msec (C). There was significant correlation between the mean RC-SC and 2SACT (r = 0.69). Mean RC-SC was greater than 2SACT in all seven patients whose CSRTs exceeded 2000 msec. The mean RC-SC was 0.15 +/- 0.03 in group A, 0.20 +/- 0.02 in group B and 0.25 +/- 0.06 (sec; mean +/- SD) in group C. The max RC-SC was 0.20 +/- 0.03 in group A, 0.28 +/- 0.03 in group B and 0.36 +/- 0.07 sec in group C. The mean RC-SC and max RC-SC differed significantly among the three groups (p less than 0.05). The standard deviation in distribution of the RC-SC was 0.033 +/- 0.008 in group A, 0.044 +/- 0.007 in group B and 0.052 +/- 0.017 sec in group C. RC-SCs equal to or longer than 0.24 sec were observed in 1% in group A, 26% in group B and 58% in group C, and that equal to or longer than 0.30 sec was found in 0, 3 and 28% in groups A, B and C, respectively. The RC-SC reflects not only SACT but sinus node automaticity, and provides more simple detection of sinus dysfunction. Sinus dysfunction may exist when the RC-SC is greater than 0.30 sec.