Magnetic resonance imaging of endocardial exits from epicardial ventricular tachycardia substrates in left ventricular nonischemic cardiomyopathy

Introduction: In patients with left ventricular (LV) nonischemic cardiomyopathy and monomorphic ventricular tachycardia (VT), midmyocardial and epicardial substrates are often involved but endocardial structures may also be affected. Delayed enhancement – magnetic resonance imaging (DE–MRI) was used to characterize the substrates of predominantly epicardial VT to improve identification of target sites for ablation. Methods and Results: 12 patients with LV nonischemic cardiomyopathy and monomorphic VT (prior myocarditis in 9) had a predominantly epicardial (n = 8) or epicardial-only DE-MRI substrate (n = 4). Modest-sized endocardial involvement in predominantly epicardial substrates was identified by DE-MRI in 8 patients. Mapping of 22 VTs was performed in 12 patients using an endo-epicardial approach in 6 patients and an endocardial-only approach in 6 patients. Endocardial VT reentry circuit exit sites as defined by entrainment and pace mapping criteria corresponded to endocardial breakthroughs from predominantly epicardial DE-MRI substrates in 7 patients. The endocardial VT exits were located at the ventricular base near the mitral annulus in 6 patients. Successful endocardial ablation of at least one VT was accomplished in 5 patients. Epicardial ablation as a part of an endo-epicardial approach or as epicardial-only ablation was performed in 6 patients and was successful in 4 patients. Conclusion: Endocardial breakthroughs from predominantly epicardial DE-MRI substrates are often located near the ventricular base in the perivalvular region and correlate with endocardial VT reentry circuit exit sites amenable to ablation.