Lower catheter tip temperatures are associated with inhomogeneous lesion formation during radiofrequency catheter ablation in a canine thigh muscle model

Abstract

Purpose: Previous studies on open irrigation radiofrequency (RF) ablation catheters focused on created lesion volumes, and did not evaluate lesion quality. The aim of this study was to evaluate the effect of different irrigation levels on lesion quality and volume. Methods: A canine thigh model was used. A skin incision was made and a cradle was created and filled with blood (37 °C, 250 ml/min). The ablation catheter was positioned parallel or perpendicular to the muscle surface using a constant force of 10 g. RF lesions were created using a gold tip electrode catheter with 12 irrigation holes and a PtIr catheter with 6 irrigation holes (Biotronik, Berlin, Germany). Both catheters were 7F and had a 3.5 mm electrode tip. RF current was delivered for 60 s at either 50 W (n=18) or 30 W (n=39). Temperature probes were inserted immediately below the surface and at 3.5 and 7 mm depth. Histological examination was performed to evaluate lesion size as well as the homogeneity of the RF lesions. Inhomogeneity was defined as a visual observed multi-band lesion pattern indicating different histological characteristics. Electrode temperature and lesion dimensions were measured. Results: Data of 57 lesions, created in a mongrel dog model, were analyzed. A total number of 47 inhomogeneous and 10 homogeneous lesions were detected. Inhomogeneous lesions were deeper (7.5±1.4 vs. 6.3±2.1 mm, p=0.036), however lesion volume was comparable between the two groups (652±487 vs. 834±396, p=0.249). Lesions with inhomogeneous histological characteristics had lower maximum electrode temperatures during ablation (42.9±6.6 vs. 48.2±8.6 °C, p=0.049). The mean temperatures at 3,5 and 7 mm below the muscle surface were lower for inhomogeneous lesions (41.2±8.1 vs. 50.2±21.4 °C, p=0.035; 38.7±4.0 vs. 45.2±19.0 °C, p=0.034). Inhomogeneity of the lesion was not associated with catheter type (p=0.164), orientation (p=0.185), amount of saline infusion (p=0.305) and power output (p=0.213). Conclusions: Our data suggest that lower catheter tip and tissue temperatures are associated with the development of inhomogeneous acute RF lesion formation. The presence of inhomogeneous RF lesions can theoretically be responsible for the differences between acute and chronic ablation success rates.