Published online before print September 23, 2002,
10.1161/01.CIR.0000037062.35762.B4
© 2002 American Heart Association, Inc.
Clinical Investigation
and Reports
|
Sanjiv M.
Narayan, MB, MD, MRCP; Frank Bode, MD; Pamela L. Karasik, MD; Michael R. Franz,
MD, PhD
From the University of California and Veterans
Affairs Medical Center, San Diego, Calif (S.M.N.), and Georgetown University
and Veterans Affairs Medical Center, Washington, DC (F.B., P.K., M.R.F.).
Correspondence and reprint requests to Michael R. Franz, MD, PhD, Professor of Medicine, Georgetown University and VA Medical Center, Washington DC. E-mail mfranz@washington.va.gov
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.
Key Words: alternans • atrial flutter • fibrillation • action
potentials • waves