Size matters in atrial fibrillation: the underestimated importance of reduction of contiguous electrical mass underlying the effectiveness of catheter ablation

Abstract

Evidence has accumulated over the last century of the importance of a critical electrical mass in sustaining atrial fibrillation (AF). AF ablation certainly reduces electrically contiguous atrial mass, but this is not widely accepted to be an important part of its mechanism of action. In this article, we review data showing that atrial size is correlated in many settings with AF propensity. Larger mammals are more likely to exhibit AF. This is seen both in the natural world and in animal models, where it is much easier to create a goat model than a mouse model of AF, for example. This also extends to humans-athletes, taller people, and obese individuals all have large atria and are more likely to exhibit AF. Within an individual, risk factors such as hypertension, valvular disease and ischaemia can enlarge the atrium and increase the risk of AF. With respect to AF ablation, we explore how variations in ablation strategy and the relative effectiveness of these strategies may suggest that a reduction in electrical atrial mass is an important mechanism of action. We counter this with examples in which there is no doubt that mass reduction is less important than competing theories such as ganglionated plexus ablation. We conclude that, when considering future strategies for the ablative therapy of AF, it is important not to discount the possibility that contiguous electrical mass reduction is the most important mechanism despite the disappointing consequence being that enhancing success rates in AF ablation may involve greater tissue destruction.

Keywords: Atrial fibrillation; Atrial size; Catheter ablation; Critical mass.

Figure 1

Larger atria are more likely to exhibit atrial fibrillation. If wavelength of atrial tissue is represented by the arrow length, it is logical that if atrial size increases out of proportion to wavelength, more simultaneous wavelets can be simultaneously present in the atrium, vastly reducing the chance of spontaneous termination. AF, atrial fibrillation; LA, left atrium; LV, left ventricle.

Figure 2

Increase in atrial size is more important than electrophysiologic remodelling in progression from paroxysmal to persistent AF. Reproduced with permission from Kojodjojo et al. (A) Right atrial volume (RAV) and left atrial volume (LAV) progressively increase from control patients to those with paroxysmal AF (PAF) with a further increase in those with persistent AF (PsAF). (B) Wave propagation velocity is reduced in both PAF and PsAF to a similar extent. (C) Effective refractory period (ERP) is reduced in both PAF and PsAF to a similar extent. Various locations showed similar findings including high right atrium (HRA), septum and distal coronary sinus (DCS).

Figure 3

The effect of procedural predictors on freedom from atrial fibrillation. Reproduced with permission from Sau et al. AF, atrial fibrillation; CFAE, complex fractionated atrial electrogram; CI, confidence interval; GP, ganglionated plexi; LAA, left atrial appendage.