A recent study (Morton et al, Circulation 2002; 105: 258-264) assessed the electrophysiologic consequences of chronic atrial flutter in an experimental animal model. The authors were attempting to determine whether similar remodeling phenomena are observed following chronic atrial flutter as had been previously described for atrial fibrillation.

Substantial Abnormalities Demonstrated 

The authors demonstrated a substantial decrease in atrial effective refractory period, with the most precipitous decline occurring within the first 3 days of atrial flutter. Conduction velocity also declined over the 28 days of observation, but the greatest decline occurred late in follow-up, in contradistinction to the changes in refractory periods. Atrial flutter cycle length mirrored the balance between these two opposing effects; atrial flutter cycle length diminished early during the observation period (due to the shortening of refractoriness) and then lengthened toward baseline (as conduction velocity slowed).

Atrial fibrillation was not inducible in any animal at the initiation of the study. However, after 28 days, all animals with atrial flutter had easily inducible atrial fibrillation (by a single extrastimulus), indicating a marked increase in atrial fibrillation vulnerability after chronic atrial flutter.

The authors concluded that in this model of chronic atrial flutter, progression to prolonged atrial fibrillation was achieved due to the interaction between an electrophysiologically remodeled atrium (by atrial flutter) and atrial triggers (atrial extra-stimuli).

Important Interrelationship Between Atrial Flutter and Atrial Fibrillation 

This experimental study provides strong evidence supporting the important interrelationship between atrial flutter and atrial fibrillation, such that prolonged episodes of atrial flutter may lead to a milieu that facilitates the conversion to atrial fibrillation.

An important clinical protocol has recently been developed and is poised to begin‹a study based on similar principles to the abovedescribed research. The protocol, the Hybrid Therapy of Atrial Fibrillation Trial (HYTAFT) was designed at St. Lukešs-Roosevelt, is supported by Medtronic Inc., and was recently approved for an IDE from the FDA. The trial is to be initiated at 10 sites around the country in a pilot IDE phase, in an effort to formalize protocol issues and sample size for a large-scale multicenter trial.

Reduced Likelihood of Recurrent Atrial Fibrillation 

HYTAFT tests the hypothesis that empire atrial flutter ablation (accomplished by a bi-directional line of block in the subeuastacian isthmus of the right atrium) in patients with a clinical history of atrial fibrillation will reduce the likelihood of recurrent atrial fibrillation.

Eligible patients are those who require antiarrhythmic drug therapy to help suppress atrial fibrillation (with the concomitant effect of increasing the likelihood of developing atrial flutter, in approximately 40% of patients treated with antiarrhythmic drugs). Patients will be randomly assigned to receive flutter ablation or not. All patients will also receive the sophisticated GEM III AT device, capable of a variety of antiatrial fibrillation therapies for prevention and/or termination. The device will also greatly facilitate the collection of data describing atrial fibrillation burden, the primary endpoint of the study.

Future Directions 

Enormous advances are being made in the treatment of atrial fibrillation. The phenomenal progress with pulmonary vein ablation to cure atrial fibrillation is a notable example. HYTAFT will test alternative multi-modality approaches for the highest risk and most difficult to treat atrial fibrillation patients. If you have patients who may be eligible for any one of these innovative techniques and clinical trials, please contact our service.

Reproduced with permission. Published by the Arrhythmia Service of St. Luke's-Roosevelt Hospital Center, New York, New York.