Electrophysiological Correlates of Transmural Linear Ablation

Abstract

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.

Use of a Novel Irrigated Balloon Catheter to Generate Continuous Right Atrial Lesions by Radiofrequency Ablation

“…Electrogram amplitude reduction and pacing threshold increase have been described as means to evaluate effective lesion creation. 15,16) The present results also demonstrated that a lower atrial pacing threshold before ablation (0.5-2.0 V) correlates with higher atrial electrogram amplitudes and greater reduction of atrial electrogram amplitude by ablation, and a larger atrial pacing threshold ratio (> 4, postablation/preablation) correlates with greater reduction of atrial electrogram amplitudes and greater reduction of the atrial electrogram ratio (postablation/preablation) after ablation. However, their predictive accuracy was low regarding continuous and transmural lesion formation in our study.…”

“…Liem, et al produced transmural lesions across the cavo-tricuspid isthmus in all 7 of their sheep by this technique. 15) Their results may be explained by the shorter distance, smooth surface, and easy positioning of the catheter at the cavo-tricuspid isthmus. We achieved a higher success rate (75%) for cavo-tricuspid isthmus ablation than for other lesions.…”

Virtual electrode theory explains pacing threshold increase caused by cardiac tissue damage

“…Although such an outcome might be expected, it may not be true in a broader sense. For example, lesions created by radio-frequency ablation can decrease pacing thresholds (26). The standard deviation for the data (Table 1) does not allow us to conclude whether one of the thresholds is affected more than the other.…”

Effects of Linear Ablation at the Isthmus Between the Tricuspid Annulus and Inferior Vena Cava for Atrial Flutter on Autonomic Nervous Activity

“…35 It is suggested that cavotricuspid isthmus ablation may create a transmural lesion as described by Bing Liem. 36 From these findings, it is suggested that linear ablation of the cavotricuspid isthmus may influence the vagal fibers innervating the sinus node, and may change heart rate and heart rate variability if the vagal nerve fibers to the sinus node are distributed near the isthmus. From the findings of the present study, it is concluded that vagal nerve fibers destined for the sinus node are distributed sparsely in the isthmus.…”

“…Although linear ablation from the endocardium of the cavotricuspid isthmus can create a transmural lesion in canine heart, [34][35][36] it is not possible for this lesion to extend into the fat pad, which is localized on the epicardial surface. 6 However, anatomical and histological investigations were not performed in the present study.…”