CMR Evaluation of Myocardial Inflammation Persistence After Acute Myocarditis: Prognostic Relevance

Background and Significance:

In patients with acute myocarditis (AM), spontaneous improvement can be observed in the majority of cases, but progression towards dilated cardiomyopathy (DCM) is a not rare outcome (around 20% of patients) (Feldmann N Engl J Med 2000;343:1388-98). Differences in the course of the disease may reflect the course of the underlying viral infection. In a large series of patients with AM submitted to two endo-myocardial biopsies (EMBs) in few months, Kuhl demonstrated that viral clearance was associated with spontaneous ejection fraction (EF) improvement, while EF did not improve or even deteriorated in patients with viral and myocardial inflammation persistence (Kühl Circulation 2005;111:887-93. Kühl Circulation 2005;112:1965-70). However, repeated EMBs cannot be proposed in the clinical routine and, hence, non-invasive detection of the subgroup of patients with inflammation persistence should have important implications. Today, cardiac magnetic resonance (CMR) is recognized as an accurate non-invasive imaging tool to diagnose acute myocarditis, because of its ability to detect myocardial inflammation and necrosis (Friedrich J Am Coll Cardiol 2009;53:1475-87).

The introduction of mapping techniques has significantly improved CMR sensitivity, allowing to detect both focal and diffuse involvement, with a substantial benefit in the convalescent phase where conventional Lake Louise criteria often fail.

However, no technical development has been performed for the evaluation of Early Gadolinium Enhancement (EGE), which continues to be assessed on T1-w images, being the less robust Lake Louise criteria and eliminated from the updated Lake Louise criteria [Ferreira J Am Coll Cardiol 2018;72(24):3158-76.].

Therefore, there are two major clinical needs: (a) the first being the improvement in diagnosis fulfilling the lack in technical advancement in the setting of EGE evaluation, (b) the second being risk-stratification and prediction of prognosis. The study hypothesis is that the development of a quantitative method based on T1 mapping for the assessment of EGE may be highly sensitive and specific for the diagnosis of myocarditis. Then, the assessment of early changes in CMR parameters at a short-term CMR study (2 months after symptoms onset) may have great value in outcome prediction.

Preliminary data: A previous study performed on patients with chronic inflammatory cardiomyopathy demonstrated that the positivity of CMR parameters of necrosis (LGE) and inflammation (oedema) is significantly higher in patients with an active inflammation at EMB, compared to patients with borderline histological criteria (De Cobelli 2006 JACC;47:1649-54). These data suggest the possibility to detect with CMR the persistence of subtle myocardial inflammation after the acute phase in patients with myocarditis.

Moreover, Wagner and Colleagues demonstrated, in a small group of patients, a correlation between CMR evidence of myocardial hyperaemia persistence 4 weeks after the onset of acute myocarditis and negative left ventricular (LV) remodelling 30 months later (Wagner A 2003 MAGMA;16:17-20).

Materials and Methods:

This is a prospective multicentre cohort study. 80 patients with diagnosis of acute myocarditis (AM) will be enrolled.

All patients admitted to Hospital with suspect of AM will be submitted to:

collection of detailed anamnesis and physical examination, 12-lead ECG, laboratory exams, transthoracic echocardiography, coronary catheterization or coronary computed tomography (CT) angiography when an ischemic cause of symptoms need to be excluded and CMR imaging within 3-5 days.

CMR protocol will include Lake-Louise criteria, parametric mappings (native T1, T2 mapping and ECV), with an additional early-enhanced T1 mapping acquired 2 minutes after gadolinium injection.

All patients with clinically or EMB confirmed diagnosis of AM will be enrolled and will undergo a second CMR study 2 month later.

All patients will undergo a clinical/instrumental follow-up including: CMR assessment of LV ejection fraction and end-diastolic volume after at least 1 year from diagnosis; registration of all-cause mortality, cardiac death and aborted cardiac sudden death in patients with implantable cardioverter-defibrillator (ICD).

Impact and Translational Implications:

Myocarditis is characterized by significant heterogeneity of long-term evolution. CMR could play a key role in the non-invasive and early identification of patients with persistent myocardial inflammation, at high risk to evolve towards an irreversible post-myocarditis heart failure. Thus, CMR may help to design tailored management of patients. In this perspective, invasive characterization of damage mechanism and aetiology might be reserved to patients with CMR evidence of inflammation persistence.