Innovations: Technology & Techniques in Cardiothoracic & Vascular Surgery:
Abstract: ISMICS 2006 Annual Meeting Abstracts
Department of Surgery, Division of Cardiothoracic Surgery, Washington University School of Medicine, St. Louis, MO, USA
Bipolar radiofrequency (BPRF) ablation has been used to replace many of the surgical incisions of the Cox-Maze procedure for the treatment of atrial fibrillation. Real-time impedance controlled BPRF reliably produces transmural lesions in both experimental and clinical studies. Other available technologies rely on predetermined time and/or temperature criteria to determine ablation duration. The purpose of this study was to determine the energy required in different atrial structures to create transmural lesions, and to evaluate the ability of a novel impedance algorithm to tailor energy delivery to the particular tissue geometry.
Initial impedance, total energy, temperature, and ablation time were measured in 38 patients undergoing the Cox-Maze procedure using an impedance controlled BPRF device (AtriCure Isolator®; Cincinnati, OH). Lesions were categorized into the following groups: right atrial free wall, left atrial free wall, mitral valve annulus, tricuspid valve annulus, and right or left pulmonary veins. Time, energy delivered, impedance, and maximum temperature were recorded for each ablation.
The table summarizes the data from 654 ablations done in 38 patients. There was a wide range of initial impedance (32.3–760.7 Ohms), and this correlated with total energy delivered (r=−0.31, p<0.001). There was also a significant variation in the total energy delivered (15.4–457.3 joules). Ablation times varied widely (2.0–29.9 sec) and were longer on left atrial structures than right (p<0.005) and shortest near the tricuspid annulus (p<0.005). Mean tissue temperature one mm from the electrode was only 45.7 ± 7.8 °C (range 23.7–69.3 oC).
Bipolar radiofrequency ablation of different atrial structures required widely different amounts of energy and ablation times, likely due to the inhomogeneity of atrial geometry and tissue impedance. Impedance controlled ablation optimizes the delivery of BPRF energy. This reduces ablation time, and Results in minimal lateral spread. This customization of ablation decreases the chance for collateral tissue injury.