Intramural Coronary Vasculature Prevents Transmural Radiofrequency Lesion Formation

Abstract

Background-Blood flow near a radiofrequency (RF) lesion can reduce lesion size by convective cooling. It is unknown whether blood flow through small vasculature within an RF lesion can prevent transmural lesion formation. Methods and Results-In 40 rabbit right ventricle preparations, 2 epicardial RF lesions were created straddling a selectively perfused (0 to 12 mL/min) marginal artery (diameter, 0.34Ϯ0.1 mm). RF lesions were created at either 60°C or 80°C and delivered either sequentially or simultaneously. Conduction through the lesion area was measured. The lesions were analyzed histologically. At a perfusion rate of 0 mL/min, all RF lesions were transmural and without conduction. As little as 1 mL of flow through the artery during RF delivery could prevent transmural lesion formation by preserving a cuff of tissue along the length of the vessel. High-energy delivery (45 W) and very high tissue temperatures (93°C) were needed to overcome the protective effect of vascular perfusion at 12 mL/min. The volume of preserved myocardium was related to arterial perfusion rate, artery diameter, and lesion temperature but not to the sequence of RF delivery (sequential versus simultaneous). Conduction persisted through the RF lesion in 20 experiments. Conduction through the lesion was related to the arterial perfusion rate and volume or cross-sectional area of preserved myocardium. Conclusions-Flow through even small intramyocardial vessels can prevent transmural lesion formation and preserve conduction through an RF lesion. These findings may represent an unrecognized obstacle to the creation of linear RF lesions in the clinical setting.

Effects of Gap Geometry on Conduction Through Discontinuous Radiofrequency Lesions

“…Our laboratory has shown that cross-sectional area is a determinant of conduction through gaps in RF lesions in the rabbit RV flap preparation. 12 The gap geometry in all of these studies was linear, comparable to the straight gap in our current study.…”

“…12 New Zealand White rabbits (Robinson Services, Inc, Clemmons, NC) were anesthetized with xylazine (7 mg/kg) and ketamine (100 mg/kg), according to American Veterinary Association Panel on Euthanasia guidelines. The hearts were rapidly removed, and the aortic root was perfused under continuous pressure (80 cm H 2 O) with oxygenated Krebs-Henseleit buffer (37°C).…”

“…This technique has been previously demonstrated to produce electrically conductive gaps in RF lesions. 12 The cannula was perfused with room temperature saline at 12 mL/min and shaped to produce the desired gap geometry. Three morphologies of gaps through the RF lesions were produced: straight, bifurcated, and angled ( Figure 1).…”

“…9,12 Still digital images of the epicardial and endocardial surfaces were taken. The path length of the gaps was measured electronically from the still images (ImageJ software, NIH, Bethesda, Md).…”

Idiopathic Epicardial Left Ventricular Tachycardia Originating Remote From the Sinus of Valsalva

“…In addition, coronary blood flow may shield and cool the subepicardium beneath the vasculature. 27 Alternate energy sources potentially could be more effective. In this study, catheter cryoablation was successful in 1 patient when used as initial therapy but not in a second patient after unsuccessful irrigated-tip radiofrequency ablation.…”