High Prevalence of Myocarditis Mimicking Arrhythmogenic Right Ventricular Cardiomyopathy. Differential Diagnosis by Electroanatomic Mapping-Guided Endomyocardial Biopsy

Objectives: We evaluated the diagnostic contribution and the therapeutic and prognostic implications of 3-dimensional electroanatomic mapping (EAM)-guided endomyocardial biopsy (EMB) in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC). Background: ARVC is a frequent cause of life-threatening ventricular arrhythmias and sudden death in young people. The value of current diagnostic criteria and the role of imaging techniques and EMB are still debated. Methods: We studied 30 consecutive patients (17 male, mean age 43 ± 17 years) with a noninvasive diagnosis of ARVC according to current criteria. All patients underwent 3-dimensional EAM-guided EMB. Results: Twenty-nine (97%) of 30 patients presented an abnormal voltage map. Histology and immunohistochemistry confirmed the diagnosis of ARVC in 15 patients, and showed active myocarditis according to Dallas criteria in the remaining 15 patients. Patients with ARVC were not distinguishable on the basis of clinical features, presence, and severity of structural and functional right ventricular abnormalities and 3-dimensional EAM findings. On the basis of clinical and histological features, a cardioverter-defibrillator was implanted in 13 patients with biopsy-proven ARVC and in 1 patient only with myocarditis. At a mean follow-up of 21 ± 8 months, 7 (47%) patients with ARVC experienced a recurrence of symptomatic sustained ventricular arrhythmias with appropriate defibrillator intervention in all cases. All patients with myocarditis remained asymptomatic and free from arrhythmic events. Conclusions: Right ventricular myocarditis frequently mimics ARVC. Three-dimensional EAM-guided EMB is a safe and effective tool in differential diagnosis and in the selection of the most appropriate therapeutic strategy. © 2009 American College of Cardiology Foundation.