Objective Hypertension is frequently complicated by atrial fibrillation (AF). However, the atrial substrate for AF is not known. This study investigated the electrophysiological properties of atrial repolarisation by monophasic action potential (MAP) in order to explore the mechanism of paroxysmal AF initiation and maintenance.

Methods MAP were recorded from left and right atrium in 14 canine. action potential duration (APD) at 90% repolarisation (APD₉₀), Repetitive atrial firing (RAF, the occurrence of two or more successive premature atrial activations with return cycle of 250 msec or less following atrial stimulation) and APD alternans (the difference in APD between two consecutive beats, were induced by overdrive pacing at LA and RA) were induced by use of programmed stimulation at LA and RA. In the study, episodes of PAF were recorded and analysed.

Results APD₉₀ were significantly shorter in the left atrium compared to the right atrium ((157.4±43.5) vs (170.9±37.9), p<0.05)). The mean S₁S₂ interval induced RAF was (130±32) ms. 15 RAF were induced in 14 dogs. RAF induced in LA were more than in RA (11 vs 4, p<0.05). Alternans of APD were induced at CL of (162±25) ms. 13 APD alternans were induced at LA (8) and RA (5) of 14 dogs. In total, 61 episodes of PAF were induced in 14 canines. 38 episodes of PAF were induced in the left atrium, more than in the right atrium (23, p<0.05).

Conclusions The incidence of RAF and alternans was significantly higher in LA than in RA. Heterogeneity between LA and RA repolarisation creates subatrate for re-entrant arrhythmias and vulnerability to atrial fibrillation.