Left atrial effective conducting size predicts atrial fibrillation vulnerability in persistent but not paroxysmal...

The multiple wavelets and functional re-entry hypotheses are mechanistic theories to explain atrial fibrillation (AF). If valid, a chamber's ability to support AF should depend upon the left atrial size, conduction velocity (CV), and refractoriness. Measurement of these parameters could provide a new therapeutic target for AF. We investigated the relationship between left atrial effective conducting size (LA_ECS ), a function of area, CV and refractoriness, and AF vulnerability in patients undergoing AF ablation.

Activation mapping was performed in patients with paroxysmal (n = 21) and persistent AF (n = 18) undergoing pulmonary vein isolation. Parameters used for calculating LA_ECS were: (a) left atrial body area (A); (b) effective refractory period (ERP); and (c) total activation time (T). Global CV was estimated as $\surd A/T$ . Effective atrial conducting size was calculated as ${\mathrm{LA}}_{\text{ECS}}=A/\left(\mathrm{CV}\times \mathrm{ERP}\right)$ . Post ablation, AF inducibility testing was performed. The critical LA_ECS required for multiple wavelet termination was determined from computational modeling. LA_ECS was greater in patients with persistent vs paroxysmal AF (4.4 ± 2.0 cm vs 3.2 ± 1.4 cm; P = .049). AF was inducible in 14/39 patients. LA_ECS was greater in AF-inducible patients (4.4 ± 1.8 cm vs 3.3 ± 1.7 cm; P = .035, respectively). The difference in LA_ECS between inducible and noninducible patients was significant in patients with persistent (P = .0046) but not paroxysmal AF (P = .6359). Computational modeling confirmed that LA_ECS  > 4 cm was required for continuation of AF.

LA_ECS measured post ablation was associated with AF inducibility in patients with persistent, but not paroxysmal AF. These data support a role for this method in electrical substrate assessment in AF patients.