Microwave linear ablation of the isthmus between the inferior vena cava and tricuspid annulus.

The purpose of this study is to assess the potential utility and practicality of microwave (MW) ablation in the creation of linear lesion for the treatment of atrial flutter. In the search for a more versatile form of energy for ablation of complex arrhythmias, MW, with its more direct form of heating, has been considered a potential alternative to radiofrequency. MW ablation is expected to offer an advantage in creating deeper or more uniform linear lesions but data on its usefulness remain lacking. Microwave ablation was applied to the inferior vena cava and tricuspid annulus isthmus in eight canines weighing 67.2 +/- 4.8 lbs. We applied stationary ablations across the isthmus using 60-75 W power of 2,450-MHz MW energy delivered through a deflectable catheter with a 12- or 18-mm antenna, achieving 70.1 degrees +/- 9.0 degrees C antenna's temperature. Ablations were made between the coronary sinus os and the low lateral right atrium. Bidirectional block at the isthmus was accomplished in seven canines with an average of 2.7 +/- 1.3 ablations while in one canine, only unidirectional block was achieved after five ablations. Gross pathological examination identified 16 transmural ovaloid and linear lesions measuring 9.4 +/- 3.4 mm long, 4.9 +/- 2.0 mm wide, and 2.1 +/- 0.6 mm deep. In one canine the lesion extended to the surface of the tricuspid valve leaflet and in two other to the opposing anterior right ventricular wall. There were no coronary vascular or other structural damage. Histopathological examination showed hemolyzed blood on the surface, subendocardial hemorrhage and necrosis, and degeneration and fragmentation of the atrial myocardium. We concluded that single application ablation could achieve complete isthmus block using MW energy delivered through appropriately sized antenna. Such ablation may be useful for producing linear lesions for the treatment of atrial flutter.