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Figure 5 Atrial fibrillation induced by 1 µmol/l acetylcholine. On the atrial unipolar electrogram at the top, A indicates atrial signal and V indicates ventricular signal. The impulses A to A5 are those in the subsequent maps. The impulses A and A1 are shown as isolated beats, and the impulses A2 to A5 are shown as consecutive cycles. Small squares indicate sites of unipolar electrodes; numbers indicate the activation time. Lines show isochrones. Arrows show the spread of excitation over the right atrium. This paroxysm started from a stable sinus rhythm with a cycle length (CL) of 384 ms. Beats A and A1 had a normal activation sequence similar to that in control (not shown). The earliest activation site was in the sinoatrial node region. The right atrium was activated for 45 ms. An atrial premature beat (A2) following beat A1 at a CL of 138 ms arose from the crista terminalis. In the free wall of right atrium, the conduction was blocked, and the impulse turned around an area of block counterclockwise. The area distal to the initial block was then activated retrogradely, and the impulse A3 re-entered the sites proximal to the initial block. Beats A4 and A5 were also re-entrant with a shortening revolution time. PV = pulmonary vein. Other abbreviations as in Figure 1.
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