Corrected sinus node recovery time. Experimental physiologic and pathologic determinants.

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Abstract
To determine the factors affecting reproducibility of sinus node recovery time, the effects of basic pacing rate, pacing duration, milliamperage, vagal and beta-adrenergic stimulation, and sinud node injury, as well as its instantaneous and daily reproducibility, were studied in 36 anesthetized dogs. Corrected sinus node recovery time (CSNRT) showed a mean variation of 9.8 plus or minus 0.4 msec at an atrial pacing rate of 200 beats/min and 29.8 plus or minus 8 msec at an atrial pacing rate of 140 beats/min (P smaller than 0.05). CSNRT increased progressively from 55.4 plus or minus 10 msec to 103.7 plus or minus 13 msec with increase in pacing rate from 140 beats/min to 200 beats/min. It was reproducible when atrial pacing was carried out for 1-5 min, although a wide variation (10-30 msec) was seen from 7-60 minutes (P smaller than 0.05). This measurement was reproducible on two consecutive days and was unaffected by changes in milliamperage. Vagal stimulation consistently prolonged the CSNRT while beta-adrenergic stimulation decreased it from 132.9 plus or minus 34.5 msec to 50.0 plus or minus 6.5 msec. Sinus node injury consistently prolonged CSNRT at all paced rates. In summary, CSNRT is reproducible only if the same pacing rate and duration are utilized. Since vagal stimulation and sinus node injury prolong this measurement while beta-adrenergic stimulation shortens it, an "abnormal" CSNRT should be assessed in terms of the possible influence of the autonomic nervous system as well as sinus node dysfunction per se.