Temperature-controlled radiofrequency ablation of cardiac tissue: an in vitro study of the impact of electrode orientation, electrode tissue contact pressure and external convective cooling.

Abstract

A variety of basic factors such as electrode tip pressure, flow around the electrode and electrode orientation influence lesion size during radiofrequency ablation, but importantly is dependent on the chosen mode of ablation. However, only little information is available for the frequently used temperature-controlled mode. The purpose of the present experimental study was to evaluate the impact during temperature-controlled radiofrequency ablation of three basic factors regarding electrode-tissue contact and convective cooling on lesion size. In vitro strips of porcine left ventricular myocardium were ablated in a tissue bath. Temperature-controlled ablation at 80 degrees C for 60 s was performed using a 7F 4 mm tip electrode in either perpendicular or parallel contact with the endocardium at a pressure of 10 or 20 g. Increased flow around the electrode was induced by circulating the saline in the tissue bath at a flow-velocity of 0.1 m/s. Lesion volume was determined by cutting lesions in 1 mm thick slices, staining with nitroblue tetrazolium and planimetering. A total of 107 lesions was created. Lesion size was significantly larger for perpendicular electrode orientation compared to parallel for both pressure-settings and both levels of flow around the electrode (p < 0.05). Increased flow around the electrode enlarged lesion size (p < 0.005). Electrode-tissue contact pressure had no significant impact on lesion size. During temperature-controlled radiofrequency ablation increased external cooling of the electrode tip due to either flow of the surrounding liquid or poor electrode tissue contact, as exemplified by perpendicular versus parallel electrode orientation, increases lesion size significantly. This is in contrast to the impact of these factors during power-controlled ablation due to the lack of increased power-delivery in the latter situation.