Background: Transthoracic epicardial catheter ablation is an emerging catheter ablation strategy being used clinically at increasing frequency. However, the efficacy of standard RF ablation on the epicardial surface of the heart is hindered by (1) the lack of convective cooling of the ablation electrode and (2) the varying presence of epicardial adipose tissue interposed between the ablation electrode and the target site. This experimental animal study examines the biophysical characteristics of radiofrequency (RF) ablation lesions generated by either standard or cooled-tip ablation of the ventricular epicardium.
Methods and results: Nonsurgical subxyphoid pericardial access was achieved in 10 normal goats and 7 pigs with healed myocardial infarctions. A 4-mm cooled-tip RF ablation catheter (continuous 0.9% saline circulation at 0.6 mL/s; goal temperature, 40 degrees C; 60 seconds) was used to deliver epicardial ventricular lesions: 47 in normal tissue and 22 in infarcted tissue. Standard RF ablation lesions (n=33) using a 4-mm top catheter (goal temperature, 70 degrees C; 60 seconds) were also placed on normal epicardial tissue. Lesions created with standard and cooled-tip RF ablation were 3.7+/-1.3 mm (25+/-16.8 W) and 6.7+/-1.7 mm (44.8+/-6.8 W) in depth, respectively. On scar tissue, lesions made with the cooled-tip catheter measured 14.6+/-2.7 mm in length, 11.8+/-2.9 mm in width, and 5.6+/-1.2 mm in depth (35.6+/-7.1 W). In areas covered by epicardial fat (3.1+/-1.2 mm thick), standard RF energy did not generate any appreciable lesions, but cooled-tip RF lesions were 4.1+/-2 mm in depth (45+/-4.4 W).
Conclusions: Cooled-tip RF ablation can generate epicardial lesions more effectively than standard RF ablation and appears to be of particular benefit in ablating areas with overlying epicardial fat.