(P065) BI-ATRIAL MAPPING AND ELEVATED HEART RATES IDENTIFY ABNORMAL ATRIAL SUBSTRATE IN ATRIAL FIBRILLATION PATIENTS WITHOUT LOW-VOLTAGE AREAS IN THE LEFT ATRIUM

Background: Low-voltage areas (LVA) provide the substrate for AF. In AF patients without left atrial (LA) LVA, the presence of abnormal atrial substrate has not been well defined. Our aim was to identify abnormal atrial substrate in AF patients without LA LVA using bi-atrial mapping and elevated heart rates.

METHODS AND RESULTS: Patients with AF undergoing first-time pulmonary vein isolation were prospectively enrolled. High-resolution bi-atrial electroanatomic mapping was performed during right atrial (RA) pacing at 750 and 400ms. LVA (bipolar voltage < 0.5mV) and the slowest conduction velocity (CV) were defined globally and regionally in the RA and LA. Only patients without LA LVA (-LVA), defined as < 5% LA LVA of total LA surface area, were included (n=52). This cohort was compared to prospectively enrolled controls without AF, who underwent bi-atrial electroanatomic mapping during RA pacing (n=10). -LVA had AF for 2(1-5)yr (79% paroxysmal AF). -LVA were older (56±11 vs. 37±10yr, p< 0.001) and predominantly male (94 vs. 40%, p< 0.001) compared to controls. -LVA had larger LA (36±10 vs. 28±4ml/m2, p=0.013) and RA (19±4 vs. 15±3cm2, p=0.022) compared to controls. At 750ms pacing, -LVA had more global LA LVA than controls (1.4(0.5-3.6)% vs. 0.4(0.2-0.4)%, p=0.01), which was most evident in the septum (3.1(0.7-7.4)% vs. 0%, p< 0.01) and PV antra (0.7(0-5.7)% vs. 0%, p=0.02). -LVA also had greater global RA LVA than global LA LVA (3.7(2.2-6.0)% vs. 1.4(0.5-3.6)%, p< 0.001). Regional LA CV was similar between -LVA and controls. Regional RA LVA and CV were also similar between -LVA and controls. At 400ms pacing, -LVA had greater global LA LVA (3.5(1.0-5.8)% vs. 1.4(0.5-3.6)%, p=0.001) and slower global CV (0.74±0.11 vs. 0.83±0.17m/s, p< 0.001) compared to 750ms pacing. These changes were most evident in the septum and PV antra. In contrast, controls had similar LA LVA and CV at 400ms compared to 750ms pacing.

Conclusion: AF patients without LVA in the LA still have bi-atrial structural remodelling as evidenced by (i) greater bi-atrial size, (ii) greater RA LVA, and (iii) greater rate-dependent LA LVA and CV slowing compared to controls without AF. The septum and PV antra are most affected in -LVA. Although these regional abnormalities are mild, they may still provide the substrate for AF and therapeutic targets for ablation.