Abstract 10435: Dynamic Conduction Slowing Predicts the Site of Initiation of Human Atrial Fibrillation
OBJECTIVE: To determine whether conduction slows with rate acceleration at the site of atrial fibrillation (AF) initiation.
BACKGROUND: It is difficult to identify the sites of AF initiation within human atria. Since conduction slowing is a prerequisite for reentry, we hypothesized that AF may initiate at sites that exhibit rate-dependent conduction velocity slowing (CV restitution).
METHODS: In 28 AF patients (n=13 persistent) and 2 controls (no AF) at EP study, we measured atrial conduction time (CT) via 64-electrode baskets placed in both (n=14) or left (n=16) atria while pacing at accelerating cycle lengths (CL) from 500 ms to AF onset. We determined CV restitution and the atrial activation vector at each rate and just prior to AF initiation.
RESULTS: On rate acceleration, left atrial (LA) conduction slowed in 23/28 AF patients (vs. no controls, p<0.01). AF initiated at sites throughout the LA (Figure A) in 19/28 patients with clinical AF and no controls. Conduction slowed dynamically at the site of AF initiation in 3 patterns: (a) Broad (gradual slowing; n=7); (b) Steep (abrupt slowing prior to AF; Figure B-F; n=8); (c) Flat (no slowing) in 4 AF patients and both controls, with concordant results at the last activated site (p=NS). CT prolonged from 79±23 ms to 107±40 ms (p < 0.001) and slowed most in persistent AF and least in controls (p<0.05). AF initiated in most patients with rate related conduction slowing (17/23), and few when conduction slowing was not present (2/7; p=0.03). With rate acceleration, the atrial activation vector shifted further in patients with broad vs. steep restitution (p=0.004).
CONCLUSIONS: Slowing of atrial conduction on rate acceleration (CV restitution) preceded human AF initiation at the site of AF initiation, while absence of conduction slowing was associated with inability to induce AF. Dynamic conduction slowing may thus track the functional milieu enabling AF initiation, and has implications for guiding AF ablation.
- © 2011 by American Heart Association, Inc.