State of the art: Evaluation and prognostication of myocarditis using cardiac MRI.

Myocarditis encompasses both primary and secondary processes causing inflammation of the myocardium. Viral infections are a common secondary cause of myocarditis with important clinical relevance. Viral myocarditis has a varied clinical presentation, potentially resulting in significant morbidity and mortality. Acutely, systolic dysfunction and sudden cardiac death may ensue; chronically, myocarditis may result in a dilated cardiomyopathy requiring heart transplantation. Myocarditis is thought to be one of the most common causes of myocardial infarction with nonobstructive coronary arteries (MINOCA), with important consequences for cardiovascular outcomes. Patients with myocarditis are currently underdiagnosed. Cardiac MRI has evolved as the noninvasive test of choice, with cardiac MRI-specific diagnostic requirements defined in the Lake Louise Criteria (LLC). Detecting the presence of tissue edema, hyperemia, and necrosis in both acute and chronic stages form the foundation of the LLC. Cardiac MR for chronic myocarditis (greater than 8 weeks from symptom onset) has decreased sensitivity for diagnosis. Emerging sequences such as T1 and T2 parametric maps provide tissue characterization regarding inflammation without reliance on reference tissue, overcoming limitations of the LLC. Beyond diagnostic criteria, these imaging techniques have proven useful in further characterizing the diseased tissue, prognostication, and clinical decision-making. This review describes the utility and evolving use of cardiac MRI in clinical practice. Level of Evidence: 1 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2018;47:1061-1071.

Cardiovascular magnetic resonance of cardiac morphology and function: impact of different strategies of contour drawing and indexing.

BACKGROUND: Cardiovascular magnetic resonance (CMR) is the gold standard for the quantitative assessment of cardiac volumes, mass and function. There are, however, various strategies for establishing endocardial borders, the cardiac phase used for measurements and the body dimensions used for indexing these results. The aim of the study was to assess the impact of different strategies on reference values. METHODS AND RESULTS: 362 healthy volunteers (190 men, mean age 51 ± 13 years) underwent a standard CMR protocol. Left ventricular end-diastolic (LV-EDV) and end-systolic (LV-ESV) volumes and LV mass (LV-M) were measured at end systole and end diastole in SSFP sequences using two methods, one of which included papillary muscles and trabecular tissue in the LV-M ("include" approach), while the other excluded this tissue ("exclude" approach). There was a strong correlation between the results for LV volumes and LV ejection fraction (LV-EF) between the "include" and the "exclude" approach, while the mean values were different: LV-EDV: 149.7 ± 32.5 ml vs 160.5 ± 35.0 ml, p < 0.0001; LV-ESV: 48.7 ± 14.5 ml vs 56.4 ± 16.7 ml, p < 0.0001; LV-EF: 67.7 ± 5.4% vs 65.1 ± 5.6%, p < 0.0001. When comparing end-systolic with end-diastolic data, values for LV-M were significantly higher in end systole irrespective of whether papillary muscles and trabecular tissues were included or not. Furthermore, LV-M missed overweight-induced LV hypertrophy when indexed to body surface area (BSA) instead of height. CONCLUSION: Quantitative assessment of LV volumes and mass with inclusion of papillary muscles and trabeculae to myocardial mass resulted in significantly different values, while indexing to BSA and not height may miss LV hypertrophy in terms of overweight.