Local conduction heterogeneities promoted by premature atrial contractions in patients with and without atrial fibrillation

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): NWO-Vidi Medical Delta Background The atrial conduction velocity (CV) provides important information about the underlying myocardium and is therefore widely used to identify potential mechanisms for arrhythmogenesis. Loss of cell-to-cell communication, which results in enhanced non-uniform anisotropy, contributes to local conduction disorders and conduction heterogeneity (CH). However, it remains challenging to clinically measure CV. Using discrete velocity vectors, areas of local CHs can be most accurately identified without smoothing of wavefront propagation. Purpose To quantify local CH using CV vectors and to examine differences between sinus rhythm (SR) and spontaneous premature atrial contractions (PAC) in patients with and without history of atrial fibrillation (AF). Methods Intra-operative epicardial mapping (128 or 192 electrodes, interelectrode distance 2mm) of the right and left atrium (RA, LA), Bachmann’s Bundle (BB) and pulmonary vein area (PVA) was performed in 228 patients (158 male, 68±10 years, 54 history of AF). PACs were defined as abnormal atrial contractions with at least 25% shortening of cycle length as compared to the previous SR cycle length. CV vectors were computed at each electrode using a discrete velocity vectors method. Direction and speed of these vectors were compared to the surrounding electrodes to identify local CH. Results In total, 503 PACs were included with a prematurity index of 45±12%. Compared to SR beats, PACs had decreased CV (89.9 [80.7–99.3] cm/s vs 80.1 [70.7–89.6] cm/s, P<0.001) and, in 96% of the PACs, more CH (3.3 [1.6–5.9] % vs 12.1 [8.5–16.3] %, P<0.001). During SR, most CH were found at BB and LA (5.6 [3.4 – 8.6] % and 5.0 [2.7–6.4] %). Compared to SR, the largest increase in CH during PAC was found at BB and PVA (+8.7 [5.4–13.6] % and +8.9 [4.8–12.6] %, all P<0.001). During PAC, CV decreased particularly at BB, PVA and LA (-8.4 [-20.3–-0.6] cm/s, -10.4 [-19.3–0.3] cm/s and -10.1 [-19.1–0.3] cm/s, all P<0.001). Compared to patients without AF, more CH were found during SR in AF patients at BB (P<0.001), while there was no difference in CH increase during PAC between both patient groups. Conclusions Intra-operative high-resolution mapping showed that PACs are characterized by decreased CV and an increased amount of local CH, particularly at BB and PVA. Patients with history of AF are characterized by considerable CH already present during SR at BB. These differences indicate local enhanced non-uniform anisotropy and hence possibly arrhythmogenic substrates underlying AF.