Invited commentary

Abstract

The device evaluated in this epicardial beating heart study was the specific Boston Scientific multielectrode “Cobra catheter” that delivers nonirrigated unipolar radiofrequency circumferentially around each activated electrode. The authors' observations of heat damage to adjacent organs (pulmonary artery, ascending aorta, trachea, and esophagus) are as a result of the design of this catheter device itself, which delivers radiofrequency energy circumferentially to all tissue touching any activated electrode. This adjacent tissue damage should not therefore be equated with clinically reported esophageal perforations, secondary to excessive unipolar radiofrequency heat transferred from the endocardial side through the atrial wall to adjacent organs. Histological confirmation of cellular death unless gross, as reported in this study, requires animal survival for at least 4 hours. This experimental study's short-term design does not exclude lesser degrees of immediate adjacent tissue damage having occurred (with lower set point temperatures) but that would have resulted in significant injury developing over time. Radiofrequency energy induced perforations are also not necessarily immediate, and may occur a few days later after necrolysis has had time to occur. The nonobservance of perforations may therefore also be merely due to this experimental study's short-term design. The authors' observations of possible heat damage along the coronary arteries, remote from epicardial application of unipolar radiofrequency energy, may imply that the radiofrequency current was preferentially conducted along the epicardial coronary arteries from the active electrode to the neutral electrode plate, thereby potentially causing endothelial damage. The anatomical positioning of the neutral surface electrode plate, in relation to the heart, may therefore be important. The limited number of animals studied (2 pigs per temperature set point) and short-term experimental design does not allow any conclusions to be made regarding the safety or optimal temperature setting for epicardial unipolar radiofrequency isolation of the pulmonary veins with this specific device. The alternative more accurate conclusions of this study are that the device used, Boston Scientific multielectrode “Cobra catheter”, will not produce transmural lesions when applied to the 37°C beating atrial epicardium for 120 seconds at a set point of 60°C. Furthermore, this specific unipolar radiofrequency catheter device design will result in adjacent organ damage proportional to the set point temperature, if used for epicardial left atrial/pulmonary vein ablation.