Catheter ablation therapy for atrial fibrillation (AF) remains in an early developmental stage. As such, the ablation success rates for AF are somewhat lower than those for other forms of supraventricular tachycardia. In addition, the optimal technique utilized to achieve the highest success rates is uncertain. Evidence is accumulating which suggests that the addition of sub Eustachian isthmus ablation, the standard technique for the ablation of atrial flutter (AFL), can prevent recurrence in ablation for AF. This article will review the rationale for this approach.

Ablation for Atrial Fibrillation

For purposes of ablation therapy, AF is typically divided into two distinct entities: "focal" and "multiple reentrant circuit". For AF to sustain, a critical number wavelets in the atrial tissue are necessary. Attempts at ablating multiple reentrant wavelet AF center on the creation of multiple linear lesions within the right and/or left atria. This is the catheter equivalent of the surgical "maze" procedure which attempts to limit the number of wavelets and makes the atria unable to sustain AF. These procedures have produced less than acceptable success rates and have significant reported morbidity including thromboembolic stroke. These disappointing results have tempered enthusiasm for linear ablation; however, research continues in the use of catheter ablation for this type of AF.

In patients with "focal' AF, uniform and often frequent APCs or tachycardia initiate AF which ultimately also has multiple disorganized wavelets in part or all of the atria. The APCs arise from a single focus within the atria, typically in the superior pulmonary veins of the left atrium, or from the tricuspid annulus or crista terminalis of the right atrium. Spontaneous or isoproterenol-induced APCs can be mapped and ablated. While the technique is promising in this highly select group of patients which are typically young with structurally normal hearts, success rates are not equal to those for other types of supraventricular tachycardia. It is in this population that adjacent AFL ablation may play its greatest role by improving long term success rates.

Ablation for Atrial Flutter

In contrast, catheter ablation is well-established therapy for AFL. In these procedures, a linear series of ablation lesions are created from the tricuspid annulus to the inferior vena cava in the isthmus of right atrial tissue bordering the Eustachian ridge. This isthmus of tissue is critical to the large right atrial reentrant circuit responsible for AFL. The ablation lesions damage atrial tissue preventing the conduction of electrical impulses through the critical isthmus; when the line of conduction block is complete, the AFL circuit can no longer persist and the arrhythmia is cured.

Relationship between Atrial Fibrillation and Atrial Flutter

Patients in whom both AF and AFL occur provide an interesting source of information about both arrhythmias and about the role of catheter ablation in their treatment. Interest in this area arose out of the observation that patients with AF treated with type 1-c antiarrhythmic drugs sometimes develop AFL as their only recurrent clinical arrhythmia. Reports from several groups suggest that isthmus ablation procedures for this form of AFL produced improvement in AF symptoms in 80 - 85%. While AF continued to occur in the majority of patients, the frequency of AF episodes were significantly reduced.

Additional data published by Hein Wellens and his group evaluated the role of isthmus ablation in patients with both AF and AFL (Am J Cardiol 1999;83:785-7). Dividing patients by predominant clinical arrhythmia (AF or AFL), Wellens found that 13 of 21 (62%) patients with predominant AFL were free of AF (as well as AFL) in a 20 month follow-up. In addition, 5 patients with recurrent AF were more easily controlled on antiarrhythmic drug post ablation. Of the 15 patients with predominant AF only 2 (14%) were free of AF following isthmus ablation.

The mechanism responsible for the clinical coexistence of both arrhythmias may be that AFL occurs in the right atrium and eventually degenerates to AF or that two distinct precipitating mechanisms are present and result in two distinct arrhythmias. Intuitively, AFL ablation would help prevent AF with the former mechanism, but play a lesser role with the latter. Ablation of the isthmus may also interrupt a significant pathway for conduction between the left and right atria. As such, AF occurring in the left atrium may not be able to involve the right atrium; the "critical mass" necessary to sustain AF may be lost. These potential mechanisms remain hypothetical.

Further clinical investigation is first necessary to definitively demonstrate the efficacy of isthmus ablation in AF ablation. The arrhythmia service at St. Luke's-Roosevelt Hospital Center is leading the development of a multi-center, randomized protocol to evaluate the role of this promising addition to existing AF treatments.

Arrhythmia Service Adds New Electrophysiologist

The Arrhythmia Service is pleased to announce the addition of a new electrophysiologist to its staff. Bengt Herweg, M.D. began on the service February 1, 2000; he will perform the full range of electrophysiologic consultative and procedural services at St. Luke's-Roosevelt Hospital and at St. Vincent's Hospital in Staten Island.

A native of Germany, Dr. Herweg graduated cum laude from the University of Essen School of Medicine and completed his internal medicine training at Beth Israel Medical Center in New York, where he was also Chief Resident. He received his fellowship training in cardiology and electrophysiology at Montefiore Medical Center in the Bronx. Since 1998, he has been studying atrial fibrillation in the laboratory of Dr. Michael Rosen at Columbia University.

Annual Arrhythmia Symposium To Be Held May 6

The annual Diagnosis and Management of Cardiac Arrhythmias Symposium will be held on Saturday, May 6, 2000 at the Conference Center of Roosevelt Hospital, located at 1000 Tenth Avenue (at 59th Street) in Manhattan.

The theme of this year's symposium will be Focus on CHF. Guest faculty will include Andrew Epstein, M.D. from the University of Alabama at Birmingham, whose lecture is entitled "Atrial Fibrillation in Patients with CHF: Therapeutic Strategies", and Brian McGovern, M.D. from the Massachusetts General Hospital and Harvard Medical School who will discuss "Syncope in the Patient with Dilated Cardiomyopathy: Controversies and Unresolved Questions".

Contact the Arrhythmia Service office at 212-523-4017 to make your reservations.

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