How is sinus node recovery time (SNRT) determined?

Updated: Nov 30, 2018
  • Author: Bharat K Kantharia, MD, FRCP, FAHA, FACC, FESC, FHRS; Chief Editor: Mikhael F El-Chami, MD  more...
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Answer

EP studies can document SND when studying SN automaticity by directly recording electrical activity.

Measurement of SNRT is achieved by pacing the atrium. Pacing should be performed from a catheter placed in the high right atrium (HRA) near the SN at the junction of the superior vena cava (SVC) and the RA for 4-6 trials of 30 seconds each. Each trial should use successively shorter pacing cycle lengths (eg, 600 ms, 550 ms, 500 ms), beginning with a cycle length just shorter than the resting sinus cycle length. SNRT is the time interval between the last paced captured beat to the first spontaneous sinus beat.

Gradual return of the SN to its baseline rate occurs over 5-6 beats. Prolonged pauses (ie, secondary pauses) can occur after the initial recovery interval in SND.

If the longest interval for the recovery interval or secondary pause exceeds 1500 ms, the SNRT is prolonged.

To adjust for heart rate and before each pacing increase, the resting sinus cycle length (SCL) is measured. When the resting SCL is subtracted from the SNRT, the CSNRT is obtained. Its upper reference range limit is 525 ms; if the SNRT exceeds the SCL by more than 525 ms, the SNRT is abnormal. The same occurs if the ratio of SNRT to SCL (ie, SNRT/SCL × 100) is more than 160%.


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