Novel insights in pathophysiology of postoperative atrial fibrillation

Abstract

Objectives: Atrial extrasystoles are usually benign; however, they can also trigger atrial fibrillation. It is most likely that if atrial extrasystoles provoke a larger amount of conduction disorders and a greater degree of endo-epicardial asynchrony, the risk of postoperative atrial fibrillation increases. To test this hypothesis, we investigated the effect of programmed atrial extrasystoles on endo-epicardial conduction and postoperative atrial fibrillation.

Methods: Twelve patients (58% male, age 68 ± 7 years) underwent simultaneous endo-epicardial mapping (256 electrodes) of the right atrium during sinus rhythm and programmed atrial extrasystoles provoked from the right atrial free wall. Areas of conduction block were defined as conduction delays of ≥12 milliseconds and endo-epicardial asynchrony as activation time differences of exact opposite electrodes of ≥15 milliseconds.

Results: Endo-epicardial mapping data of all programmed atrial extrasystoles were analyzed and compared with sinus rhythm (median preceding cycle length = 531 milliseconds [345-787] and median sinus rhythm cycle length = 843 milliseconds [701-992]). All programmed atrial extrasystoles were aberrant (severe, moderate, and mildly aberrant, respectively, n = 6, 3, and 3) and had a mean prematurity index of 50.1 ± 11.9%. The amount of endo-epicardial asynchrony (1% [1-2] vs 6.7 [2.7-16.9], P = .006) and conduction block (1.4% [0.6-2.6] vs 8.5% [4.2-10.4], P = .005) both increased during programmed atrial extrasystoles. Interestingly, conduction block during programmed atrial extrasystoles was more severe in patients (n = 4, 33.3%) who developed postoperative atrial fibrillation (5.1% [2.9-8.8] vs 11.3% [10.1-12.1], P = .004).

Conclusions: Atrial conduction disorders and endo-epicardial asynchrony, which play an important role in arrhythmogenesis, are enhanced during programmed atrial extrasystoles compared with sinus rhythm. The findings of this pilot study provide a possible explanation for enhanced vulnerability for postoperative atrial extrasystoles to induce postoperative atrial fibrillation in patients after cardiac surgery.

Keywords: AES, atrial extrasystoles; AF, atrial fibrillation; CB, conduction block; CD, conduction delay; EEA, endo-epicardial asynchrony; RA, right atrial/atrium; atrial fibrillation; cardiac mapping; electropathology; electrophysiology.

Graphical abstract

Programmed atrial extrasystoles enhance endo- epicardial conduction disorders.

Figure 1

Simultaneous endo-epicardial mapping of the RA was performed using two 128-electrode arrays secured exactly opposite of each other on 2 spatulas (left panel). Color-coded activation maps of the endo- and epicardium are shown in the middle panel. Black arrows display the main trajectories of the electrical wavefronts. To calculate EEA, for each electrode, the median time delay within the exact opposite electrode and its eight surrounding electrodes was selected. The longest time delay for every endo-epicardial electrode pair is then selected to express local degree of EEA, defined as transmural difference in electrical activation of ≥15 milliseconds between every endo-epicardial electrode pair. Ao, Aorta; SCV, superior caval vein; RA, right atrium; RV, right ventricle; ICV, inferior caval vein; Epi, epicardium; Endo, endocardium; EEA, endo-epicardial asynchrony.

Figure 2

Upper panel: Typical endo-epicardial activation maps of a SR beat (left) and P-AES (right) obtained from the same patient. Black arrows display the main trajectories of the electrical wavefronts and local activation times are depicted at its head and tail. Thick black lines indicate lines of conduction block. The lower panel shows the effect of programmed right atrial stimulation on the amount of conduction block (y-axis) for each patient (x-axis) separately. Increase in total activation time and amount of conduction block is observed during P-AES compared with SR. SR, Sinus rhythm; LAT, local activation times; Epi, epicardium, Endo, endocardium; P-AES, programmed atrial extrasystoles.

Figure 3

Upper panel: Endo-epicardial activation maps and corresponding EEA maps of one single SR beat (left) and P-AES (right) obtained from the same patient. Black arrows display the main trajectories of the electrical wavefronts and local activation times are depicted at its head and tail. Thick black lines indicate lines of conduction block. The lower panel shows the effect of programmed right atrial stimulation on the amount of EEA for each patient separately. An increase in conduction block and EEA is observed during P-AES compared with SR. SR, Sinus rhythm; LAT, local activation times; Epi, epicardium; Endo, endocardium; EEA, endo-epicardial asynchrony; P-AES, programmed atrial extrasystoles.

Figure 4

Left panel: This pilot study revealed that P-AES originating from the free wall of the RA (1) provoked a substantial increase in endo- and epicardial conduction disorders, (2) enhanced electrical asynchrony between both layers up to 44 milliseconds, and (3) provoked more conduction disorders and EEA in patients who developed POAF compared with patients who remained postoperatively in SR. Right panel: Typical endo-epicardial activation maps of a sinus rhythm beat (left) and programmed AES (right) obtained from the same patient are shown. Black arrows display the main trajectories of the electrical wavefronts and local activation times are depicted at the head and tail. Thick black lines indicate lines of conduction block. Enhanced electrical disturbances can be observed during programmed AES compared with sinus rhythm. These findings may explain why postoperative AES may induce POAF.