Incremental value of extracellular volume assessment by cardiovascular magnetic resonance imaging in risk stratifying patients with suspected myocarditis.

Cardiovascular magnetic resonance imaging (CMR) has become a key investigative tool in patients with suspected myocarditis. However, the prognostic implications of T1 mapping, including extracellular volume (ECV) calculation, is less clear. Patients with suspected myocarditis who underwent CMR evaluation, including T1 mapping at our institution were included. CMR findings including late gadolinium enhancement (LGE), left ventricular ejection fraction (LVEF), native T1 mapping, and ECV calculation were associated with first major adverse cardiac events (MACE). MACE included a composite of all-cause death, heart failure hospitalization, heart transplantation, documented sustained ventricular arrhythmia, and recurrent myocarditis. One hundred seventy-nine patients with a mean age of 49 ± 15 years were identified. Seventy nine individuals (44%) were female. Mean LVEF was 48 ± 16. At a median follow-up of 4.1 [interquartile-range (IQR) 2.2-6.1] years, 22 (12%) patients experienced a MACE. Mean ECV (per 10%) was significantly associated with MACE (HR 2.09, 95% CI 1.07-4.08, p = 0.031). Presence of ECV ≥ 35% demonstrated significant univariable association with MACE (HR 3.3, 95% CI 1.43-7.97, p = 0.005) and such association was maintained when adjusted to LVEF (HR 3.42, 95% CI 1.42-7.94, p = 0.006). ECV ≥ 35% portended a greater than threefold increased hazards to MACE adjusted to LGE presence (HR 3.14, 95% CI 1.29-7.36, p = 0.012). In patients without LGE, ECV ≥ 35% portended a greater than sixfold increased hazards (HR 6.6, p = 0.010). In the multivariable model including age, LVEF and LGE size, only ECV ≥ 35% maintained its significant association with outcome. ECV calculation by CMR is a useful tool in the risk stratification of patients with clinically suspected myocarditis, incremental to LGE and LVEF.