Characterization of the Thermal Properties of Healthy vs Infarcted Ventricular Tissue: Implications for Radiofrequency Ablation.

Background: Radiofrequency (RF) ablation is the technique of choice for treating ventricular tachycardias in ischemic cardiomyopathy. However, recent experimental studies have found it to be ineffective. Poor heat transmission in collagen-rich scar tissue was 1 of the explanations given, even though the thermal properties of infarcted tissue have never been studied.

Objectives: The purpose of the present study was to measure the thermal properties of chronically infarcted myocardium.

Methods: A total of 5 freshly explanted human hearts from patients undergoing heart transplantation with previous chronic myocardial infarction were studied in the operating room. A 2-needle thermal sensor model SH-3 Tempos (Meter Group) was introduced into different infarcted and healthy areas in the left ventricle to measure the thermal conductivity, volumetric heat capacity, and thermal diffusivity. All the measured areas were excised for histological analysis. An in silico model of radiofrequency catheter ablation was then built to evaluate the impact of the thermal parameters obtained. Stiffness, electrical properties, and vascularization were also included to simulate realistic healthy and infarcted myocardium according to previously published data.

Results: More than one-half of the area of the infarcted samples was composed of collagen. No significant differences were found between the thermal properties of infarcted and healthy tissue. The RF lesion depths obtained from the computational model did not have any clinically relevant differences (<0.4 mm in depth) between the infarcted and healthy tissue.

Conclusions: Thermal properties of infarcted tissue are not sufficiently different from healthy tissue to justify different RF lesion sizes, according to our computational model.