Inflammation of conduction tissue is a major determinant of electrical instability in patients with arrhythmic phenotype of myocarditis

Abstract

Abstract Background Arrhythmic presentation of myocarditis can be life-threatening although often associated with a preserved cardiac dimension and function. The involvement of conduction tissue (CT) has been suggested as pro-arrhythmic factor, but its role has not conclusively supported. Purpose CT inflammation in myocarditis with arrhythmic presentation. Methods We retrospectively enrolled consecutive patients from January 2010 to June 2021 with acute myocarditis (< 1 month from the onset of symptoms). Patients were categorized according to clinical presentation in arrhythmic [frequent premature ventricular beats, non-sustained or sustained ventricular tachycardia (VT) and survivors of ventricular fibrillation, associated to preserved cardiac contractility –LVEF ≥ 50%] (Group A) and cardiomyopathy phenotype (signs and symptoms of heart failure with LVEF≤ 45%) (Group B). All patients had a normal coronary network at angiography and an unremarkable valvular pattern at 2D-Echo.They all underwent a LV endomyocardial biopsy; sections of CT (Purkinje fibres) were identified by morphologic (Ashoff and Monkeberg criteria) findings and positive immunohistochemistry for HCN4. CT infiltration was demonstrated by the presence of CD45Ro+ T lymphocytes and the necrosis of adjacent small and loosely arranged myocytes. The extent of myocardial fibrosis, the rate of vasculitis and CT inflammation was compared between the two groups. Results Among 217 consecutive pts with biopsy-proven diagnosis of myocarditis, 107 (49.3%) had an arrhythmic presentation (Group A). CT was observed in 33 (30.8%) patients in the Group A and 31 (28.2%) of Group B. In patients with biopsy-evidence of CT, no significant difference was reported in the mean age (51.2±16.8 vs 53.7±14.7; p-value: 0.53) . Inflamed CT was documented in 2 (6.5%) cases in Group B and in 33 (100%) in Group A (p-value< 0.001). No statistically difference was observed between Group A and B regarding the presence of vasculitis (4 vs 1; p-value: 0.36) and myocardial fibrosis (8.8±4.2% vs 9.5±4.3%; p-value: 0.50). Conclusion CT inflammation is a major determinant of electrical instability in human myocarditis with arrhythmic presentation. Figure Legend Sustained ventricular tachycardia (A) associated to severe infiltration by CD45Ro T lymphocytes of CT in an acute myocarditis with arrhythmic presentation.