ELECTROPHYSIOLOGICAL EFFECTS OF LONG, LINEAR ATRIAL LESIONS PLACED UNDER INTRACARDIAC ULTRASOUND GUIDANCE

Background A curative atrial fibrillation procedure will most likely r ely on creating transmural linear ablative lesions. However, it is cur rently unknown whether endocardial radiofrequency lesions can create l ines of conduction block. Methods and Results In six pigs, intracardia c echocardiography was used to guide the positioning of multiple coil array catheters to bridge endocardial structures in three right atrial locations: (1) from the crista terminalis to the tricuspid annulus; ( 2) from the fossa ovalis to the crista terminalis; and (3) from the in ferior vena cava to the tricuspid annulus. Once the catheter was posit ioned, linear lesions were made by radiofrequency energy applied seque ntially to each of the four coils. After 15 days, the chest was opened and a 112-electrode epicardial plaque was positioned over the atrial free wall lesion to determine activation patterns. Three lesions were placed in each animal, with a mean procedure time of 47+/-11 minutes. Once adequate contact was determined by intracardiac echocardiography, a single series of radiofrequency application was required to achieve tissue heating (65+/-4 degrees C) with a power of 21+/-10 W. Epicardi al mapping demonstrated complete conduction block across the lesions i n all animals, with split potentials and disparate activation times (6 4+/-16 ms) across the lesion. At autopsy, all lesions were discrete, c ontinuous, and without evidence of charring. The lesions were within 0 .3+/-0.5 mm of their targeted anatomic locations and measured 21+/-4 m m long and 2.8+/-0.6 mm wide. Histology revealed transmural fibrosis t hroughout the length of each lesion. Conclusions Linear lesions that a re electrophysiologically transmural and continuous can be placed in t he right atrium of normal pigs. With intracardiac echocardiography, ad equate tissue contact over several coil electrodes can be ensured, res ulting in short procedure times, efficient energy application, and acc urate anatomically linked lesion placement.