Histopathological Characterization of Radiofrequency Ablation in Ventricular Scar Tissue

Objectives: This study sought to characterize the histopathological features of radiofrequency ablation (RFA) in heterogeneous ventricular scar in comparison to those in healthy myocardium. Background: The histopathological features of RFA have been studied largely in normal myocardium. However, its effect on clinically relevant heterogeneous scar is not well understood. Methods: Five swine with chronic infarction underwent RFA using 35-W, 45-s, 10-20 g (Biosense Webster, Irwindale, California) in heterogenous scar tissue (voltage ≤1.5 mV) and healthy myocardium (≥3.0 mV). The location of each application was marked using the electroanatomical mapping system. Histological sections at intervals of 0.5 mm with hematoxylin and eosin and Masson's trichrome stained intervals were created. A pathologist blinded to the myocardium type characterized the extent of RF injury in cellular, extracellular, and vascular structures. Results: In healthy myocardium, 23 of 23 lesions (100%) were well demarcated and could be precisely measured (width: 11.3 ± 3.3 mm; depth: 7.3 ± 2.0 mm). In scar tissue, only 3 of 30 lesions (10%) were identified, and none could be measured due to a lack of defined borders. Lesions in healthy myocardium had a distinctive architecture showing a coagulative necrosis core surrounded by an outer rim of contraction band necrosis. Lesions in scar had ill-defined tissue injury without a distinct architecture. In all ablated regions, viable myocytes remained interspersed between necrotic myocytes exhibiting characteristics of both coagulative and contraction band necrosis. Connective tissue was more resistant to thermal injury in comparison to cardiomyocytes. Conclusions: RFA in scarred myocardium results in irregular tissue injury and unpredictable effect on surviving cardiomyocytes. This may be related to biophysical differences between healthy and scarred myocardium.