Derivatives of sinus node recovery time
Sinus node recovery time is measured by overdrive atrial pacing for 30 seconds and noting the time required for recovery of sinus node activity after cessation of pacing. Overdrive pacing is done at different cycle lengths in sequence. The interval from the last paced beat to the next spontaneous sinus beat is taken as the sinus node recovery time (SNRT). SNRT is the longest time measured at any of the different pacing cycle lengths. If there is a subsequent longer pause, it is known as a secondary pause. When the sinus cycle length prior to pacing is subtracted from the sinus node recovery time, we get the corrected sinus node recovery time (CSNRT). CSNRT is usually less than 550 milliseconds. The time taken for the sinus rate to reach the rate prior to pacing is taken as the total recovery time. Total recovery time is usually less than 5 seconds.