Correlation of human histopathology to electroanatomic mapping and cooled-tip radiofrequency ablation of ischemic ventricular tachycardia

Abstract

Catheter ablation of ischemic ventricular tachycardia (VT) often requires excessive mapping. Documentation of the electrical substrate via electrogram amplitude maps helps to identify regions of altered myocardium as aim of ablation. A patient died due to heart failure 7 days after successful linear cooled-tip ablation for substrate modification to treat multiple VTs. Ablation procedure was performed after electroanatomic substrate mapping (Biosense CARTO™) and defining regions of dense scar (bipolar elctrograms < 0.5mV, normal myocardium (electrograms > 1.5mV) and “altered myocardium” (electrograms in between 0.5 to 1.5 mV). Ablation was directed to regions with “altered myocardium” and pace-map correlation to the clinical VT. Autopsy revealed ablation regions to be within diffusely scarred myocardium (fibrosis in between 25 to 80% of cross sectional mass) bordering dense scar (viable myocardium of only 20% or less in wall cross section). Pathohistology documented transmural coagulation necrosis of myocardium up to a depth of 8.5mm without endocardial damage or thrombotic deposits. Subendocardial intramural hematoma and bleeding were universal findings without tissue removal reaction 7 days after ablation. There is a good correlation in between electroanatomic substrate mapping and human histopathological findings in ischemic myocardium. Bipolar electrograms indicating “altered” myocardium correspond to diffusely fibrotic underlying substrate with myocardial fiber strand interspersed (25 to 80%). Electrograms < 0.5mV identify regions with massiv fibrosis even though myocardial tissue may still be present in the epicardial regions of the ventricular wall. Cooled-tip radiofrequency ablation leads to transmural necrosis up to 8.5mm depth. No charring or endocardial tissue damage occurs.