Reliable pace termination of postoperative atrial fibrillation in the canine sterile pericarditis model: Implications for atypical atrial flutter

Abstract

Background: We have identified a reentrant circuit in the pulmonary vein region, which drives the atria, producing fibrillatory conduction, as one mechanism of postoperative atrial fibrillation (POAF) in the canine sterile pericarditis model.

Objective: In this model, we tested the hypothesis that overdrive pacing from a site at or near such a reentrant circuit would interrupt it and thereby terminate POAF.

Methods: We studied 11 sterile pericarditis dogs on postoperative days 1-4. Atrial electrograms (AEGs) were recorded during POAF, overdrive pacing, and pace termination from 3 sites simultaneously: Bachmann's bundle, posterior left atrium, and right atrial appendage. When recorded AEGs demonstrated regular activation, pace termination was attempted at that site by delivering a drive train starting with 4 consecutive beats at a cycle length (CL) of 2-5 ms shorter than that of the intrinsic CL.

Results: Sixteen episodes of sustained POAF (>5 minutes) diagnosed by electrocardiogram were induced. During all episodes of POAF, AEGs recorded from the left atrium exhibited regular activation, ie, constant AEG morphology and CL. When capture of the reentrant circuit by overdrive pacing occurred (mean 13 ± 5, range 5-23 beats), all 16 POAF episodes were successfully terminated. In all termination episodes, at the end of pacing but prior to the return of sinus rhythm, there was disorganized atrial activation in the previously organized sites (mean 2 seconds, range 0.1-8 seconds). However, these beats did not sustain POAF in the absence of a reentrant circuit ("driver").

Conclusion: Overdrive pacing from a site demonstrating regular activation during sustained POAF terminated the POAF by interrupting the reentrant circuit.

Keywords: Entrainment; Nonpharmacologic rhythm control therapy; Overdrive atrial pacing; Postoperative atrial fibrillation; Reentry.

Figure 1

Simultaneous recordings from selected atrial sites (right atrial appendage [RAA], Bachmann's bundle [BB], and posterior left atrium [PLA]) during postoperative atrial fibrillation (POAF) in the canine sterile pericarditis model (the first episode in dog #8 in Table 1). Electrocardiogram lead II shows an irregular baseline with an absence of P waves and atrial electrograms (AEGs) from the RAA, demonstrating changing morphology of AEGs consistent with POAF. AEGs from BB and the PLA show regular morphology and cycle length. S = stimulus artifact during ventricular pacing after the creation of the atrioventricular block.

Figure 2

Same recording sites from the same episode as Figure 1, before, during, and after overdrive atrial pacing from the posterior left atrium (PLA) at cycle length of 100 ms that interrupted postoperative atrial fibrillation. BB = Bachmann's bundle; RAA = right atrial appendage; S = stimulus artifact during ventricular pacing after the creation of the atrioventricular block.