Diurnal changes and reproducibility of corrected sinus node recovery time

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Abstract
Corrected sinus node recovery time (CSRT) has been found unreliable in identifying all cases of sick sinus syndrome. Since other factors than sinus node dysfunction might add to the pathologic significance of the CSRT, we assessed it in 15 patients (nine group I patients with “prolonged” CSRT max = 3,196 + 2,740 msec and six group II patients with “short” CSRT max = 367 + 79 msec) at 0800, 1100, 1400, 1700, 2000, and 2300 hours with atrial overdrive stimulation rates (AST) of 90, 110, 140, 170, and 200 bpm on three consective days using a loop‐mounted stable atrial electrode. Only with AST ≧ 140 beats per minute (bpm) did all CSRTI values prove prolonged (≧ 560 msec). CSRTI values at corresponding time intervals were reproducible with AST ≧ 140 bpm (day 1 vs 2 vs 3, P > .05), but not at AST 90 bpm and 110 bpm (P < .05); CSRTII results, however, varied from day to day (< .05) due to less scatter of single results. CSRTI results increased progressively with AST 90, 110, and 140 bpm from 301 + 256 msec by 60% for each pacing rate up to 785 + 848 msec. With AST ≧ 140 bpm, the pattern of CSRT changes was inconsistent; this was also reflected by the distribution of the mean maxima of CSRTI: For 0800 hours at AST 140 bpm = 822 + 937 msec; for 1100 hours at AST 200 bpm = 824 + 1446 msec; for 1400 hours at AST 140 bpm = 780 + 814 msec; for 1700 hours at AST 170 bpm = 1,099 + 1,008 msec; for 2000 hours at AST 200 bpm = 1,156 + 1,280 msec; and for 2300 hours at AST 170 bpm = 1,021 + 1,102 msec.We conclude therefore that the optimal diagnostic yield for sick sinus syndrome testing is influenced by the time of the day and the AST used for CSRT testing.