Effects of multipolar electrode radiofrequency energy delivery on ventricular endocardium

This study examined the effects of radiofrequency energy applied in a bipolar fashion with single as compared with multiple sequential applications at the canine endocardium. In this closed-chest model, radiofrequency energy (750 kHz) was delivered between two adjacent poles of an electrode catheter. Single applications were performed at distinct sites in the left ( n=30) and right ventricles ( n=29) of 13 normal dogs. A multiple sequential technique, which enlarges the ablated endocardial surface, was applied in the left ( n=13) and right ventricles ( n=4) of seven normal dogs and six dogs with remote myocardial infarction. Single applications (199±200 joules) resulted in lesions with a volume of 0.12±0.06 cm 3 (range 0.03 to 0.31 cm 3) and an endocardial surface area of 0.29±0.15 cm 2 (range 0.06 to 0.63 cm 2). Changes at the catheter/tissue interface led to a rise in impedance, restricting further enlargement of the necrosis. Sequential delivery of radiofrequency energy between poles 1 and 2, 2 and 3, and 3 and 4 of a quadripolar electrode catheter repeated 9 to 11 times in slightly different positions allowed a cumulative energy of 6571±3857 joules to be applied to the endocardium, resulting in a lesion volume of 0.84±0.38 cm 3, with an endocardial lesion surface area of 3.7±1.2 cm 2 (range 2.9 to 5.1 cm 2). Histologically, all radiofrequency lesions were restricted to the endocardium/subendocardium with a small border zone of injury. Aggressive stimulation techniques did not induce ventricular tachycardia in any of the dogs before and 19±11.4 days after multiple sequential ablations. Thus the multiple sequential ablation technique using radiofrequency energy produces large subendocardial scars and may be suitable for ablation of ventricular arrhythmia foci. The lesions produced showed no evidence of chronic arrhythmogenicity.