Cardiovascular magnetic resonance in myocarditis: A JACC White Paper

Abstract

Cardiovascular magnetic resonance (CMR) has become the primary tool for noninvasive assessment of myocardial inflammation in patients with suspected myocarditis. The International Consensus Group on CMR Diagnosis of Myocarditis was founded in 2006 to achieve consensus among CMR experts and develop recommendations on the current state-of-the-art use of CMR for myocarditis. The recommendations include indications for CMR in patients with suspected myocarditis, CMR protocol standards, terminology for reporting CMR findings, and diagnostic CMR criteria for myocarditis (i.e., "Lake Louise Criteria").

Figure 1. Short axis CMR views in a patient with clinically acute myocarditis

A: Still frames from a cine series at end-diastole (left) and end-systole (right), showing only very mild septal hypokinesis (arrow) with preserved ejection fraction. Small pericardial effusion is present along the lateral segments (arrowhead). These findings represent two supportive criteria for myocarditis. B: T1-weighted spin echo images before (left) and shortly after (right) gadolinium administration with early gadolinium accumulation in the septum (arrows). Quantitative evaluation of the signal enhancement (skeletal-muscle normalized myocardial enhancement ratio of equal to or greater than 4.0 or an absolute enhancement of equal to or greater than 45%) is required to use information from this pulse sequence as a positive criterion. C: Left: T2-weighted spin echo image with high signal intensity of the septum and lateral wall (arrows). Evidence for regional edema, or a signal intensity ratio of equal to or greater than 2.0 (signal intensity normalized to skeletal muscle in the same slice) renders T2 findings positive. Right: Late enhancement image without evidence for significant delay of gadolinium washout. The thin subepicardial layer of high signal intensity in the inferolateral region represents fat.

Figure 2. Late enhancement patterns in myocarditis

A: Normal myocardium with no evidence of irreversible myocyte injury B: Regional sub-epicardial enhancement of the lateral wall (arrow) C: Subepicardial enhancement of lateral and midwall enhancement of the septal wall (arrows) D: Diffuse sub-epicardial enhancement

Figure 3. Signal intensity analysis contours for tissue characterization

T2-weighted image in a short axis orientation with example contours for skeletal muscle (yellow), subepicardial border (green) and subendocardial border (red). The contour for the skeletal muscle was copied from a mid-diastolic SSFP still frame in the same slice position.