SAN DIEGO, CALIFORNIA. Since 1998 when Prof. Haissaguerre and colleagues in Bordeaux discovered that 94% of AF episodes are triggered by impulses originating in the pulmonary veins, the mainstay of catheter ablation for atrial fibrillation (AF) has been pulmonary vein isolation (PVI) in which the pulmonary veins are electrically isolated from the left atrium by rings of lesions created by cauterizing the heart tissue with catheters powered by radiofrequency energy or liquid nitrogen (cryoablation). There are two mapping approaches used to guide the ablation catheter.
- Segmental PVI (Haissaguerre/Natale protocol) in which electrophysiological mapping (using a multipolar Lasso catheter) is used to locate the pathways taken by aberrant impulses from the pulmonary veins. Once found, the pathways are eliminated by ablation around the veins approximately 5 to 10 mm from the ostium of the veins.Circumferential anatomical PVI (Pappone protocol) in which the anatomy, rather than the electrophysiological properties of the junction between the pulmonary veins and the left atrium are mapped, usually using a CARTO or Nav-X system. The anatomical structure shown on a computer screen is used to guide the creation of two lesions rings in the left atrium – one completely encircling the left pulmonary veins and another completely encircling the right pulmonary veins; the two rings are usually joined by a linear lesion
The two protocols are about equally effective when it comes to paroxysmal AF; however, in the case of persistent and permanent AF, the Haissaguerre/Natale protocol is superior because the "trouble spots" or focal points involved in persistent/permanent AF, as well as in paroxysmal AF with long episodes (24 hours or greater) are located, not within the lesion rings encircling the pulmonary veins, but rather on the walls of the left and right atria, or in specific structures of the heart such as the left atrial appendage or the crista terminalis or superior vena cava in the right atrium. An electrophysiologist (EP) skilled in interpreting the information received during an electrophysiological study is far more likely to find and successfully ablate these trouble spots than an EP who relies solely on anatomical mapping.
The existence of focal points (reentrant circuits) in the atria liable to initiate AF has probably been known for a hundred years and ablation based on eliminating them was the norm prior to 1998, but with rather limited success. We now appear to have come full circle with the rediscovery of the importance of targeting these focal points or rather areas (local electrical rotors and focal impulse sources) in ablations, especially in the case of persistent AF.
Dr. Sanjiv Narayan and colleagues at the University of California at San Diego now report the results of the CONFIRM trial involving the mapping and elimination of focal impulse and rotor modulation (FIRM) with the aid of a 64-pole basket catheter and a sophisticated computer program known as the Topera system. The clinical trial involved 92 patients who underwent a total of 107 procedures (31 for paroxysmal AF and 76 for persistent AF). Thirty-six (34%) of the procedures were performed using FIRM-guided ablation followed by an anatomically-guided PVI. The FIRM-guided procedures included mapping and appropriate ablation in the right atrium as well.
The remaining 71 procedures were conventional anatomically-guided PVIs with an added left atrial roof line, again based on anatomic guidance. It would appear that no electrophysiological mapping was used during these procedures, nor was the right atrium mapped, or any effort made to locate and eliminate focal sources which can only be found using electrophysiological mapping. This would seem to be an unfortunate omission for the patients with persistent AF (66% of procedures were for persistent AF).
Not surprisingly, the outcome of the FIRM-guided procedures was far superior to the outcome of the conventional procedures. Patients were evaluated at 3, 6, 9, 12, 18 and 24 months and the incidence of AF episodes (recorded on implanted ECG monitors/ICDs, or with 7-day patient activated event recorders) was noted. An average (median) 273 days after their procedure, 82.4% of the participants of the FIRM-guided ablation group were AF-free as compared to only 44.9% in the conventional ablation group. The UCLA researchers conclude that the results of the FIRM-guided approach offer "a novel mechanistic framework and treatment paradigm for AF."Narayan, SM, et al. Treatment of atrial fibrillation by the ablation of localized sources. Journal of the American College of Cardiology, Vol. 60, August 14, 2012, pp. 628-36
Kuck, K-H and Wissner, E. A FIRM grip on atrial fibrillation. Journal of the American College of Cardiology, Vol. 60, August 14, 2012, pp. 637-38
: Despite the clearly biased design of this trial, it certainly is encouraging to see a 2-year success rate of 82% for persistent afibbers. However, it should be kept in mind that the FIRM-guided approach was only used in 36 procedures. Independent confirmation of the efficacy of the approach obviously needs to be obtained before it can be declared "the future of ablation". Nevertheless, if efficacy is indeed confirmed, the approach will be of significant benefit, especially for EPs who are now relying on anatomical rather than electrophysiological mapping to guide their ablation procedures. NOTE: I find it difficult to reconcile the statements "single-procedure success rate" and "repeat ablation was not permitted" with the fact that the trial involved 92 patients who underwent a total of 107 procedures.