Electrophysiological correlates of transmural linear ablation

The purpose of this study is to describe the characteristics of lesions cre ated using radiofrequency (RF) energy delivered through a saline/foam elect rode that is designed to simplify ablation of the isthmus between the tricu spid annulus (TA) and the inferior vena cava (IVC). We compared the changes in the electrophysiological parameters produced by the ablation to histolo gical findings. In search of a more practical and effective atrial flutter ablation method, various energy modifications and catheter designs have bee n 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 w ould allow efficient RF delivery through specially designed long foam elect rodes, therefore improving the practicality of TA-IVC isthmus ablation for atrial flutter. The study was performed in two acute and five subacute shee p under general anesthesia and with adequate heparinization. Mle used a lin ear ablation catheter system equipped with two 2-cm saline bipole electrode pockets with 1.5-mm separation, each consisting of two 8-mm electrodes wit h 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 o f 0.4 mL/s. Bipolar atrial signal amplitude and pacing thresholds were meas ured before and after ablation. If necessary, the catheter tvas pulled back and additional ablation was applied to any viable tissue. Transisthmus abl ations 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 si gnal amplitude was reduced by an average of 76% (range 51%-92%) and its pac ing threshold tt was increased by an average of 617% (range 150%-400%). Tra nsmural lesions were found in all sheep, measuring 8-20 mm in length, 4-20 mm in width, and 1.5-2.0 mm in depth. No charring, coagulum, or remote stru ctural damage tvas found in any preparation. Continuous transmural TA-IVC i sthmus 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.