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(Circulation. 2002;105:258.)
© 2002 American Heart Association, Inc.

Basic Science Reports

Electrical Remodeling of the Atrium in an Anatomic Model of Atrial Flutter

Relationship Between Substrate and Triggers for Conversion to Atrial Fibrillation

Joseph B. Morton, MBBS; Melissa J. Byrne, BSc; John M. Power, BVSc PhD; Jai Raman, MBBS M Med; Jonathan M. Kalman, MBBS PhD

From the Royal Melbourne Hospital (J.B.M., J.M.K.), Department of Cardiology, Melbourne, Australia; Department of Medicine (M.J.B., J.M.P., J.B.M., J.M.K.), The University of Melbourne, Melbourne, Australia; and Department of Cardiac Surgery (J.R.), Austin and Repatriation Medical Centre, Melbourne, Australia.

Correspondence to Assoc Prof Jonathan M. Kalman, MBBS, PhD, Department of Cardiology, The Royal Melbourne Hospital, Grattan St, Parkville 3050, Melbourne, Australia. E-mail jon.kalman{at}mh.org.au

Background— Atrial flutter (AFL) and atrial fibrillation (AF) frequently coexist, yet the specific relationship between these arrhythmias, and particularly whether sustained AFL leads to AF, is unknown.

Methods and Results— We investigated the electrophysiological consequences of chronic AFL using an ovine anatomic right atrial Y-lesion model. AFL was induced in 7 animals, and 4 remained in sinus rhythm (controls). Sheep were monitored for spontaneous conversion of AFL to AF. Six of 7 sheep sustained AFL for 28 days. In 1 of 7 sheep, spontaneous conversion of AFL to AF occurred on day 5. AFL produced a highly significant fall in right and left atrial refractoriness (AERP, P<0.001), with 74±10% of the reduction occurring by day 3. Right atrial conduction velocity also fell significantly (baseline 89±9 cm/s versus day 28 64±14 cm/s, P<0.001) but over a slower time course. AERP and conduction velocity changes coincided with a characteristic biphasic decrease and increase in the AFL cycle length. The excitable gap (percent of AFL cycle length) increased from 13±3% at baseline to 46±8% by day 28 (P<0.001). Sustained AF (>30 seconds) was not inducible at baseline but after 28 days of AFL could be induced in 6 of 6 sheep by critically timed single or multiple extrastimuli delivered either in sinus rhythm or AFL. There was no significant change in any parameter in control sheep.

Conclusions— In this model, AFL produced electrical remodeling and the substrate for sustained AF. However, spontaneous conversion to AF was uncommon, and the development of AF was dependent on specific triggers.

Key Words: atrial flutter • fibrillation • remodeling

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