Myocarditis

Basic principles of MRI visualization

Magnetic resonance imaging is the primary diagnostic tool for non-ischemic heart diseases. Verification of the inflammatory process is based on the so-called Lake Louise criteria (Lake Louise criteria).

MRI allows for a detailed assessment of:

• Biventricular global and regional (local) systolic function.
• The presence of concomitant pericardial effusion (with or without contrast enhancement of the pericardial leaves) in the development of myopericarditis.
• Tissue oedema (Tissue oedema): traditionally determined visually on T2-weighted STIR images or using semi-quantitative methods.
• Fibrosis: detected using the late gadolinium enhancement technique (late enhancement, LGE). Unlike ischemic injury, inflammatory fibrosis is most commonly localized intramurally, within the midmyocardium.

Acute myocarditis

Clinically, the acute stage often mimics acute coronary syndrome: the patient complains of chest pain, and a slight elevation of cardiospecific enzymes is recorded in the blood. However, emergency coronary angiography reveals "clean" arteries. Severe manifestations—such as an acute fulminant form or the development of cardiogenic shock—are less common.

Characteristic MRI signs of the acute phase:

1. On T2-STIR (short-axis view), a hyperintense area of subepicardial localization is visualized, indicating pronounced myocardial edema.
2. In late gadolinium enhancement, gadolinium accumulates in a typical non-ischemic pattern—subepicardially, within the area of edema.

Chronic form and tachyarrhythmias

Chronic myocarditis often presents with subtle clinical symptoms. As a rule, it manifests as new-onset heart failure (new-onset cardiac failure) or severe tachyarrhythmias. Echocardiography (EchoCG) in such situations is used primarily to exclude other causes of heart failure.

Tomographic picture of the chronic process:

• On T2-STIR images, signs of active myocardial edema are absent.
• With late gadolinium enhancement, contrast accumulation is less intense than in the acute form. The pattern of accumulation becomes diffuse rather than focal (patchy).
• Changes are most frequently localized in the lateral wall or the interventricular septum (IVS). Furthermore, intramural enhancement in the septum is closely associated with the development of tachyarrhythmias.

To confirm the diagnosis, an endomyocardial biopsy of the IVS may be performed, demonstrating the presence of lymphocytic infiltration and interstitial fibrosis.

Parametric mapping techniques

Previously, T2 ratio—the ratio of myocardial signal intensity to skeletal muscle signal in the same slice—was used for semi-quantitative assessment of edema. This approach is prone to significant errors. First, inflammation is distributed variably (from small infiltrates to total involvement). Second, concomitant skeletal muscle inflammation (myositis) leads to false-negative results.

Today, modern mapping (mapping) techniques are of decisive importance:

• T2 mapping: provides a quantitative assessment of edema without contrast administration. The method is free from the disadvantages of T2-weighted images because it does not require reference tissue for signal normalization.
• Native T1 values: are significantly elevated in patients with myocarditis due to excess water and disrupted electrolyte distribution within the tissue. T1 mapping has been proven to outperform T2 sequences and LGE in diagnostic accuracy.
• Extracellular volume (ECV): the ECV fraction increases in acute processes, reflecting the extent of edema, myocyte necrosis, and subsequent fibrosis formation.

The combined use of mapping and the Lake Louise criteria fundamentally improves diagnostic quality.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Lake Louise criteria: complete classification
• Acute fulminant myocarditis and cardiogenic shock
• The role of endomyocardial biopsy in non-ischemic lesions
• Assessment of extracellular volume (ECV) and interpretation of color maps

Other topics in the «Chest Radiology» section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.