Direct Measurement of the Lethal Isotherm for Radiofrequency Ablation of Myocardial Tissue

Abstract

Background-The lethal isotherm for radiofrequency catheter ablation of cardiac myocardium is widely accepted to be 50°C, but this has not been directly measured. The purpose of this study was to directly measure the tissue temperature at the edge of radiofrequency lesions in real time using infrared thermal imaging. Methods and Results-Fifteen radiofrequency lesions of 6 to 240 seconds in duration were applied to the left ventricular surface of isolated perfused pig hearts. At the end of radiofrequency delivery, a thermal image of the tissue surface was acquired with an infrared camera. The lesion was then stained and an optical image of the lesion was obtained. The thermal and optical images were electronically merged to allow determination of the tissue temperature at the edge of the lesion at the end of radiofrequency delivery. By adjusting the temperature overlay display to conform with the edge of the radiofrequency lesion, the lethal isotherm was measured to be 60.6°C (interquartile ranges, 59.7°to 62.4°C; range, 58.1°to 64.2°C). The areas encompassed by the lesion border in the optical image and the lethal isotherm in the thermal image were statistically similar and highly correlated (Spearman ϭ0.99, PϽ0.001). The lethal isotherm temperature was not related to the duration of radiofrequency delivery or to lesion size (both PϾ0.64). The areas circumscribed by 50°C isotherms were significantly larger than the areas of the lesions on optical imaging (Pϭ0.002). Conclusions-By direct measurement, the lethal isotherm for cardiac myocardium is near 61°C for radiofrequency energy deliveries Ͻ240 seconds in duration. A 50°C isotherm overestimates lesion size. Accurate knowledge of the lethal isotherm for radiofrequency ablation is important to clinical practice as well as mathematical modeling of radiofrequency lesions. (Circ Arrhythm Electrophysiol. 2011;4:373-378.)

Radiofrequency cardiac ablation with catheters placed on opposing sides of the ventricular wall: Computer modelling comparing bipolar and unipolar modes

“…This is in agreement with the findings by Wood et al [30], in which the discoloration zone in the cardiac tissue matched the ~60ºC isotherm. Although Wood et al [30] concluded that the lethal isotherm for cardiac myocardium is near 61ºC, the staining procedure they used to measure the area of acute necrosis has been criticized for underestimating the extent of irreversible tissue injury [29].…”

“…Although Wood et al [30] concluded that the lethal isotherm for cardiac myocardium is near 61ºC, the staining procedure they used to measure the area of acute necrosis has been criticized for underestimating the extent of irreversible tissue injury [29]. Although we are aware that our results could be different whether we had considered other Arrhenius parameters or a 50ºC isotherm to assess the thermal lesions, the aim of our study was not to exactly predict lesion size, but to compare the effectiveness of bipolar versus unipolar modes in terms of their capacities to create transmural lesions across both ventricular walls.…”

Comparative Analysis of Different Methods of Modeling the Thermal Effect of Circulating Blood Flow During RF Cardiac Ablation

“…Although Wood et al concluded that the lethal isotherm for cardiac myocardium is near 61ºC [34], their staining procedure to measure the area of acute necrosis has been criticized for underestimating the extent of irreversible tissue injury [35]. Consequently, the range between 50-56ºC is usually considered to faithfully represent the isotherm of irreversible myocardial injury in hyperthermic ablation.…”

Development of a Simultaneous Cryo-Anchoring and Radiofrequency Ablation Catheter for Percutaneous Treatment of Mitral Valve Prolapse

“…Previous studies have used IR imaging to identify the lethal isotherm of RF lesions. 27,44 Leaflets were imaged in a custom built bath, and the camera was placed below the bath for imaging of full thickness changes in temperature distribution (Fig. 8B).…”