A possible autonomic modulation of sinus node recovery time in overdrive suppression test

The effect of blood pressure fall on sinus node recovery time (SNRT) was studied in 17 patients during the overdrive suppression test. Their maximal SNRT was less than 150% of the mean P-P interval of the control state (=SCL) and CSNRT (=SNRT-SCL) was less than 550msec. Blood pressure was found to fall in about a half of the patients at a high pacing rate. Concomitantly, SNRT was found to shorten in those who showed such a fall in blood pressure. The subjects were then divided into two groups; one with a shorter SNRT at 150bpm than at 90bpm of pacing rate and the other without such shortening. The changes in SNRT and CSNRT were both significant in the first group (p less than 0.02 and p less than 0.001, respectively). The fall in blood pressure at 150 bpm was significant in the group with shortened SNRT and CSNRT and it was larger than in the other group: 23 +/- 14mmHg vs. 1 +/- 5mmHg (p less than 0.001). This result suggests a possible modulation of SNRT by a fall of blood pressure via baroreflex.