Microwave catheter ablation of myocardium in vitro. Assessment of the characteristics of tissue heating and injury.

Whayne, James G.; Nath, Sunil; Haines, David E.

doi:10.1161/01.cir.89.5.2390

Cited by 112 publications

(58 citation statements)

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“…[1][2][3] A precise measurement of the lethal isotherm for radiofrequency ablation is important to clinical practice and the development of new ablation technology. However, the value of the lethal isotherm has not been measured directly.…”

Section: Clinical Perspective On P 378mentioning

confidence: 99%

“…[1][2][3] For myocardial tissue, the minimal tissue temperature necessary to produce permanent tissue destruction around the radiofrequency electrode, the lethal isotherm, has only been estimated indirectly. [1][2][3] Using spaced thermocouples and the mathematical relationship of tissue temperature to distance from the radiofrequency electrode, the lethal isotherm for intact myocardium has been estimated to be 47.9°to 53.6°C. 1,3 On the basis of these studies, a tissue temperature of 50°C has been widely…”

mentioning

confidence: 99%

“…[1][2][3] Using spaced thermocouples and the mathematical relationship of tissue temperature to distance from the radiofrequency electrode, the lethal isotherm for intact myocardium has been estimated to be 47.9°to 53.6°C. 1,3 On the basis of these studies, a tissue temperature of 50°C has been widely…”

mentioning

confidence: 99%

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

Wood

Goldberg

Lau

et al. 2011

Circ: Arrhythmia and Electrophysiology

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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.)

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Section: Clinical Perspective On P 378mentioning

confidence: 99%

mentioning

confidence: 99%

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

Wood

Goldberg

Lau

et al. 2011

Circ: Arrhythmia and Electrophysiology

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“…To improve the success rate in attempts to coagulate the critical parts of the reentrant circuits, 2 approaches can be taken: improving the accuracy of the mapping technique and increasing the size of the lesion created by catheter ablation. Several methods for increasing lesion size have been investigated, ranging from surgery to ablation with direct current, 7,8 laser, 9 microwaves, 10 and alcohol injection 11 to radiofrequency ablation with large-tip [12][13][14][15] or saline-irrigated 16 -19 electrodes. The chosen ablation site may have significant influence on lesion size because of various degrees of cooling of the electrode tip from the intracavitary blood flow, although this has not yet been evaluated systematically.…”

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confidence: 99%

Lesion Dimensions During Temperature-Controlled Radiofrequency Catheter Ablation of Left Ventricular Porcine Myocardium

et al. 1999

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Background-It is important to increase lesion size to improve the success rate for radiofrequency ablation of ischemic ventricular tachycardia. This study of radiofrequency ablation, with adjustment of power to approach a preset target temperature, ie, temperature-controlled ablation, explores the effect of catheter-tip length, ablation site, and convective cooling on lesion dimensions. Methods and Results-In vitro strips of porcine left ventricular myocardium during different levels of convective cooling and in vivo pig hearts at 2 or 3 left ventricular sites were ablated with 2-to 12-mm-tip catheters. We found increased lesion volume for increased catheter-tip length Յ8 mm in vitro (PϽ0.05) and 6 mm in vivo (PϽ0.0001), but no further increase was found for longer tips. For the 4-to 10-mm catheter tips, we found smaller lesion volume in low-flow areas (apex) than in high-flow areas (free wall and septum) (PϽ0.05). Increasing convective cooling of the catheter tip in vitro increased lesion volume (PϽ0.0005) for the 4-and 8-mm tips but not for the 12-mm tip as the generator reached maximum output. In contrast to power-controlled ablation, we found a negative correlation between tip temperature reached and lesion volume for applications in which maximum generator output was not achieved (PϽ0.0001), whereas delivered power and lesion volume correlated positively (PϽ0.0001). Conclusions-Lesion size differs in different left ventricular target sites, which is probably related to convective cooling, as illustrated in vitro. Longer electrode tips increase lesion size for tip lengths Յ6 to 8 mm. For temperature-controlled ablation, the tip temperature achieved is a poor predictor of lesion size. (Circulation. 1999;99:319-325.)

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“…Third, the studies that provide the lethal isotherm estimates of 50°C to 56°C also used the tetrazolium staining method to define acute lesion size. 3,4 These studies found the lethal isotherm to be less than the thermal inactivation temperature of dehydrogenase enzymes (62°C for porcine isoforms), suggesting that thermal enzymatic inactivation is not the limiting factor in determining lesion boundaries. 3,4 The discrepancy between these estimates and our work is likely due to the direct measurement of the temperature at the edge of the lesion in our study and estimation of that temperature by extrapolation in the prior studies.…”

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confidence: 99%

Response to Letter Regarding Article, “Direct Measurement of the Lethal Isotherm for Radiofrequency Ablation of Myocardial Tissue”

Wood¹,

Goldberg²,

Wang³

et al. 2011

Circ: Arrhythmia and Electrophysiology

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We thank Dr Haines for his interest in our article. As my mentor and a pioneer in radiofrequency catheter ablation, his insights carry much weight. At issue is the use of tetrazolium staining to define the acute radiofrequency lesion boundary. Specifically, the consideration is raised that for acute radiofrequency lesions, the tetrazolium staining method represents the isotherm for heat denaturation of cellular dehydrogenase enzymes rather than the boundary of cell death. If true, tetrazolium staining performed late after lesion formation would define a larger lesion size because of timedependent dissipation of enzymatic activity in a perimeter of devitalized tissue. The definition of the lethal isotherm for radiofrequency ablation is an important issue for evolving temperature monitoring technologies, and all possible sources of error should be examined. We believe, however, that latent enzymatic activity in otherwise devitalized tissue does not significantly distort the determination of the lethal isotherm for the following reasons. First, the issue of latent tetrazolium staining in thermally devitalized tissue has been addressed by direct experimentation. 1 The dimensions of tissue necrosis as determined by tetrazolium staining are the same when samples are studied 10 minutes, 24 hours, or 48 hours after laser-induced thermal injury. 1 Second, using glass microelectrode recordings, our laboratory has shown that electric activity is recorded 0.1 mm from the visible edge of an acute radiofrequency lesion. 2 This finding is consistent with the absence of a significant zone of stain-reactive but devitalized tissue about the lesion. Third, the studies that provide the lethal isotherm estimates of 50°C to 56°C also used the tetrazolium staining method to define acute lesion size. 3,4 These studies found the lethal isotherm to be less than the thermal inactivation temperature of dehydrogenase enzymes (62°C for porcine isoforms), suggesting that thermal enzymatic inactivation is not the limiting factor in determining lesion boundaries. 3,4 The discrepancy between these estimates and our work is likely due to the direct measurement of the temperature at the edge of the lesion in our study and estimation of that temperature by extrapolation in the prior studies. DisclosuresNone. (Circ Arrhythm Electrophysiol. 2011;4:e68.) Mark

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Microwave catheter ablation of myocardium in vitro. Assessment of the characteristics of tissue heating and injury.

Abstract: Microwave ablation has the potential to directly heat a greater volume of tissue than RF ablation but only with efficient MW antennas. The primary mechanism of tissue injury for both MW and RF ablation appears to be thermal.

Cited by 112 publications

References 11 publications

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

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

Lesion Dimensions During Temperature-Controlled Radiofrequency Catheter Ablation of Left Ventricular Porcine Myocardium

Response to Letter Regarding Article, “Direct Measurement of the Lethal Isotherm for Radiofrequency Ablation of Myocardial Tissue”

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