Assessment of patients presenting with life-threatening ventricular arrhythmias and suspected myocarditis: the key role of endomyocardial biopsy

Background: Life-threatening ventricular tachyarrhythmias (VAs) represent a significant cause of death in myocarditis. Objective: To identify predictors of sustained VAs in patients with myocarditis and ventricular phenotype diagnosed by workflow including endomyocardial biopsy (EMB) guided by 3D-electroanatomic mapping (3D-EAM). Methods: We prospectively enrolled patients with suspected myocarditis and VAs, undergoing cardiac magnetic resonance (CMR), coronary angiography, 3D-EAM and EMB guided by 3D-EAM. At follow-up, sustained VAs were detected by device interrogation and Holter-ECG monitoring. Results: We enrolled 54 consecutive patients (32 males, mean age 41 years), with normal ventricular function; left ventricular (LV) and right ventricular (RV) late gadolinium enhancement was present in 21 (46%) and 6 (13%) of the 46 patients who underwent CMR, respectively. In 31 patients histological diagnosis was myocarditis, while in 14 patients focal replacement myocardial fibrosis (FRMF); in 9 patients specimens were inadequate (diagnostic yield of EMB= 83%). 3D-EAM showed a larger endocardial scar area for both ventricles in myocarditis than in FRMF (RV bipolar mean scar area 22±16 cm2 vs. 3±2 cm2, p= 0.02; LV bipolar mean scar area 13±5 cm2 vs. 4±2 cm2, p= 0.02, respectively). At a follow-up of 21 months, freedom from sustained VAs was 58% in myocarditis and 92% in FRMF (p-log-rank= 0.008). Histological diagnosis of myocarditis and RV endocardial scar were independent predictors of sustained VAs (p= 0.02 for both). Conclusion: Our data highlight the need for 3D-EAM-guided EMB in apparently healthy young patients with suspected myocarditis and VAs.