Linear lesions in myocardium created by Nd : YAG laser using diffusing optical fibers: In vitro and in vivo results

Background and Objective: Linear lesions may be necessary for successful ca theter ablation of cardiac arrhythmias such as atrial fibrillation. This st udy uses laser energy delivered through diffusing optical fibers as an alte rnative to radiofrequency energy for the creation of linear lesions in card iac tissue in a single application. Study Design/Materials and Methods: Samples of canine myocardium were place d in a heated, circulating saline bath and irradiated with a 1.06-mum, cont inuous-wave Nd:YAG laser during in vitro studies. Laser ablation was then p erformed in vivo on the epicardial surface of the right ventricle during an open-chest procedure by using similar ablation parameters. Laser energy wa s delivered to the tissue by being diffused radially through flexible optic al fiber tips oriented parallel to the tissue surface. Histology and temper ature measurements verified transmurality, continuity, and linearity of the lesions. Results: Peak tissue temperatures measured in vitro remained low (51 +/- 1 degreesC at the endocardial surface, 61 +/- 6 degreesC in the mid-myocardiu m, and 55 +/- 6 degreesC at the epicardial surface) with no evidence of tis sue charring or vaporization. Lesion dimensions produced in vitro and in vi vo were similar (depth, 6 mm; width, 8-10 mm; length, 16-22 mm), demonstrat ing that tissue perfusion in vivo did not significantly alter the heating. Conclusion: Long linear lesions, necessary for duplication of the surgical maze procedure during catheter ablation of atrial fibrillation, may be crea ted by using laser radiation delivered through flexible diffusing optical f iber tips. Further development of steerable catheters for endocardial atria l ablation and studies correlating thermal damage zones with electrophysiol ogic indicators of irreversible conduction block are warranted. (C) 2000 Wi ley-Liss, Inc.