Electrophysiological correlates of transmural linear ablation.

The purpose of this study is to describe the characteristics of lesions created using radiofrequency (RF) energy delivered through a saline/foam electrode that is designed to simplify ablation of the isthmus between the tricuspid annulus (TA) and the inferior vena cava (IVC). We compared the changes in the electrophysiological parameters produced by the ablation to histological findings. In search of a more practical and effective atrial flutter ablation method, various energy modifications and catheter designs have been tested. It was shown that the efficiency of RF ablation could be improved using an endocardial cooled catheter; resulting in increased lesion size. Thus, we postulate that a similar advantage of the cooled catheter system would allow efficient RF delivery through specially designed long foam electrodes, therefore improving the practicality of TA-IVC isthmus ablation for atrial flutter. The study was performed in two acute and five subacute sheep under general anesthesia and with adequate heparinization. We used a linear ablation catheter system equipped with two 2-cm saline bipole electrode pockets with 1.5-mm separation, each consisting of two 8-mm electrodes with 1-mm spacing, allowing for bipolar pacing and recording. This saline/foam electrode pair were positioned on a support loop. RF energy was applied to the saline electrodes at 50 watts for 90 seconds with a saline flow rate of 0.4 mL/s. Bipolar atrial signal amplitude and pacing thresholds were measured before and after ablation. If necessary, the catheter was pulled back and additional ablation was applied to any viable tissue. Transisthmus ablations were created with a single catheter positioning in five sheep using both saline electrodes in four and one electrode in the other. Pullback and additional ablation to one saline electrode was required in two sheep; in one after RF was delivered to only one electrode. After ablation, atrial signal amplitude was reduced by an average of 76% (range 51%-92%) and its pacing threshold was increased by an average of 617% (range 150%-400%). Transmural lesions were found in all sheep, measuring 8-20 mm in length, 4-10 mm in width, and 1.5-2.0 mm in depth. No charring, coagulum, or remote structural damage was found in any preparation. Continuous transmural TA-IVC isthmus lesions could be produced with stationary RF linear ablation using a saline/foam electrode catheter system. This system allowed for assessment of electrophysiological parameters that correlated with complete necrosis.