Burst pacing and SNRT

• how to burst atrium
• why should I do it
• what to expect and what does the respond tell us about Sinus Node

BURST PACING

• Burst pacing involves pacing at a constant cycle length, shorter than the CL of the spontaneous rhythm.
• Burst pacing is carried out in steps (couple of seconds each) while allowing a couple of seconds between each step to monitor the rhythm and check for induced arrhythmias.
• This maneuver is used to study conduction – e.g. Wenckebach cycle length or study the electrophysiological properties of an accessory pathway in the antegrade or retrograde direction. It is also used to induce arrhythmias (those due to triggered activity are more prone to induction by burst in contrast to reentrant ones).
• Stable catheter position is key to ensure constant and reliable capture. It can be verified by fluoroscopy or by the EGM morphology as well.
• To ensure sufficient safety margin of pacing the pacing output should be adjusted to twice the diastolic threshold for each pacing site.
• WARNING: When performing these maneuvres in the EP lab always be prepared that arrhythmias might be induced. Some of them might be life threatening – e.g. ventricular fibrillation or preexcited atrial fibrillation and therefore the EP lab and the whole staff has to be prepared how to react.

SNRT (sinus node recovery time)

• The concept of sinus node recovery time is constant resetting of the sinus node during pacing and measuring the time until next sinus discharge upon cessation of pacing.
• Sinus node recovery time is measured as the time interval between the last paced atrial electrogram from the pacing bipole to the first sinus beat electrogram at the same bipole
• Sinus node recovery time overestimates the genuine sinus node escape interval as it also includes the conduction time from the pacing site to the sinus node and back.
• Normally SNRT is measured at different CLs and the longest value obtained is reported.
• SNRT varies with sinus rate, so the corrected SNRT is a more useful measurement which is calculated as SNRT – sinus CL. Normal values for SNRT and cSNRT are <1500 msec and <500 msec, respectively.
• These two measures do not play a role as an indication for pacemaker implantation according to the current guidelines