Native T1 in Discrimination of Acute and Convalescent Stages in Patients With Clinical Diagnosis of Myocarditis: A Proposed Diagnostic Algorithm Using CMR

Objectives: We investigated whether T1 mapping by cardiac magnetic resonance (CMR) reflects the clinical evolution of disease in myocarditis and supports its diagnosis independently of the disease stages. Background: Acute viral myocarditis is characterized by a range of intracellular changes due to viral replicationand extracellular spill of debris within days of viral infection. Convalescence may be characterized byachroniclow-grade inflammation leading to ventricular remodelling, but also a complete resolution of myocardialchanges. Methods: Patients with clinical diagnosis of viral myocarditis (N= 165) underwent routine clinical CMR protocol (1.5-and 3.0-T) for assessment of cardiac function and structure, and tissue characterization with T2-weighted imaging and late gadolinium enhancement. T1 mapping was obtained in a mid-ventricular short-axis slice before and >20 min after administration of 0.2 mmol/kg of gadobutrol. Results: Compared with control subjects (n= 40), T1 indexes were increased in patients with myocarditis. Patients with acute symptoms (n= 61) had higher values of T1 indexes compared with patients in clinical convalescence (n= 67). Native T1 is an independent discriminator between health and disease, as well as a discriminator between acute and convalescent stage of the disease. Native T1- was superior to T2-weighted imaging and late gadolinium enhancement with high diagnostic accuracy and positive and negative predictive values. Using pre-defined cutoff values for normal ranges, we demonstrated that acute myocarditis can be independently identified by native T1 of >5 SD above the mean of normal range, whereas convalescence is best defined by either abnormal native T1 (>2 SD) or presence of late gadolinium enhancement. We prospectively tested a new diagnostic algorithm in an independent dataset of patients with clinical diagnosis of myocarditis and achieved similar diagnostic performance. Conclusions: The new diagnostic algorithm using native T1 can reliably discriminate between health and disease anddetermine the clinical disease stage inpatients with a clinical diagnosis of myocarditis.