Overdrive pacing-induced action potential alternans at the isthmus occurred in all patients who developed atrial fibrillation compared to 50% of those who did not (P<0.0003).
Observational (n=38)
Does overdrive pacing induce action potential alternans at the isthmus preceding the transition from atrial flutter to atrial fibrillation in patients with typical atrial flutter?
Action potential duration alternans and conduction block at the isthmus precede the transition from typical atrial flutter to atrial fibrillation, providing a mechanistic rationale for the efficacy of isthmus ablation in preventing AF recurrence.
Absolute Event Rate: 100% vs 50%
p-value: p=<0.0003
BACKGROUND: The mechanisms underlying the transition of typical atrial flutter (Afl) to fibrillation (AF) remain unclear. We set out to test the hypothesis that Afl disorganizes to AF via alternans of atrial action potentials. METHODS AND RESULTS: In 38 patients with Afl, monophasic action potentials (MAPs) were recorded at the isthmus and either high or low right atrium (HRA, LRA) during overdrive pacing to 160 ms or to the initiation of AF, whichever came first. MAP duration measured at 90% repolarization was longer at the isthmus in all patients, and failed to shorten with rate, compared with the HRA (n=38) or LRA (n=5). In 20 patients who developed AF, progressive pacing first caused alternans of isthmus MAP duration and amplitude at mean cycle length of 219+/-45 ms, followed by AF at a mean onset cycle length of 184+/-38 ms. Subsets of this group showed spontaneous action potential duration alternans at the isthmus (11 of 20 patients) and 2:1 isthmus conduction block immediately preceding AF (4 of 20 patients). In the 18 patients who did not develop AF, MAP alternans was less common (9 of 18 patients; P<0.0003), and occurred only at faster pacing (cycle length=169+/-25 ms; P<0.05). CONCLUSIONS: In patients with typical Afl, action potential duration rate maladaptation at the isthmus may lead to action potential duration alternans and conduction block preceding the transition to AF. These isthmus characteristics may enable the spontaneous initiation of AF through wavefront fractionation and may explain the benefits of isthmus ablation in preventing AF recurrence.
Narayan et al. (2002) conducted an observational in Typical atrial flutter (n=38). Overdrive pacing vs. Patients who did not develop atrial fibrillation was evaluated on Occurrence of monophasic action potential alternans (p=<0.0003). Overdrive pacing-induced action potential alternans at the isthmus occurred in all patients who developed atrial fibrillation compared to 50% of those who did not (P<0.0003).