AV Node Modification
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Recently, some authors have suggested that a technique of AV node modification might be applied in patients with established atrial fibrillation, slowing ventricular rates by increasing the overall refractoriness of the AV node and thereby improving ventricular function. This technique may have significant advantages over complete AVJ ablation since conduction would be modified rather than abolished, and no pacemaker would be required. However, more data are needed to evaluate acute and chronic success rates, to establish end-points for the technique, to establish that benefits are maintained, and to compare results with patients undergoing complete ablation, since regularization of heart rhythm would not be achieved by the former method, but would be achieved by the latter, and might provide an unknown proportion of the benefit to left ventricular function.
Curative Procedures for Atrial Fibrillation
The main limitation of both AV node ablation with pacing and AV modification is that sinus rhythm and atrial transport (and therefore the risk of embolization) are not restored. Recently, surgical techniques, involving multiple atriotomies, have been proposed to meet this goals. Current thinking is that atrial fibrillation is due to multiple reentrant wavelets throughout the atria. The “Maze” procedure was devised to create multiple line of conduction block thereby preventing the initiation and maintenance of these reentrant circuits. Preliminary results have been encouraging in selected patients, although the long term stability of sinus rhythm and risk of embolization is not known. In addition there is a significant morbidity and mortality associated with this (and any) type of cardiac surgery. Therefore, a catheter based technique to cure atrial fibrillation would be ideal, and is actively being pursued.
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Currently there are a variety of catheter technologies being developed to facilitate the production of continuous linear lesions in the right and left atrium. These include: catheters with multiple, long ablation coils; multi-electrode catheters with flexible spines to improve tissue contact; and a variety of long molded vascular sheaths to assist in the positioning of standard ablation catheters. Schwartz reports the results of a series of 15 patients undergoing a catheter based curative approach to chronic atrial fibrillation. The procedure involves the production of 8 linear lesions (3 right atrial, 4 left atrial, 1 interatrial septum). These patients had chronic atrial fibrillation (4-192 months, mean 48 months) and had failed multiple antiarrhythmic medications (3-9, 5.5 mean). Atrial fibrillation was terminated acutely in 13/15 patients. The procedure time ranged from 7 16 hours. Nine patients required repeat ablation for intra-atrial reentrant tachycardia. Complications included one CVA and one pericardial effusion. At a mean F/U of 14 months one patient died of heart failure (present prior to ablation), 2 patients remained in atrial fibrillation and 2 patients had atrial flutter. These results are encouraging but clearly this is a procedure early in its evolution. Since there have been multiple reports from multiple centers demonstrating variable results. Clearly there are differences in atrial fibrillation from patient to patient, and we must better identify those amenable to curative ablation. One such group appears to patients with a rapid atrial tachycardia originating most often from the region of the ostia of the pulmonary veins. This atrial tachycardia degenerates into atrial fibrillation or is conducted in a fibrillatory manner across the atria. Ablation of these focal tachycardias appears to cure atrial fibrillation.
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In some patients with atrial fibrillation pharmacologic therapy prevents recurrent fibrillation, but patient have recurrent atrial flutter. In these patients we have recently shown that ablation of the atrial flutter and continued antiarrhythmic therapy is a potential treatment option. This “hybrid” approach has led to good clinical success in a small cohort of patients.