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Myocardium

The myocardium is the muscular middle layer of the heart wall, situated between the endocardium (inner lining) and the epicardium (outer layer). It is composed of specialized striated cardiac muscle fibers that are involuntary, branched, and interconnected by intercalated discs, which allow synchronized contraction.

The myocardium varies in thickness according to functional demands: it is thickest in the left ventricle, reflecting its role in systemic circulation, thinner in the right ventricle, and thinnest in the atria. The myocardium receives blood supply from the coronary arteries and drains into the coronary veins. Its contraction is coordinated by the cardiac conduction system, ensuring efficient blood ejection with each heartbeat.

Pathologies involving the myocardium include ischemia, infarction, myocarditis, cardiomyopathies, hypertrophy, fibrosis, and infiltration (e.g., amyloidosis). Imaging of the myocardium is essential for diagnosis, management, and treatment planning in cardiovascular disease.

Synonyms

  • Cardiac muscle

  • Heart muscle

  • Muscular layer of heart wall

Function

  • Provides contractile force for pumping blood through systemic and pulmonary circulation

  • Maintains synchronous contraction via conduction system and intercalated discs

  • Supports adaptation to increased workload (hypertrophy in athletes or pathology)

  • Plays a central role in cardiac physiology and hemodynamics

MRI Appearance

T1-weighted images:

  • Normal myocardium appears as intermediate signal intensity

  • Fat and blood pools provide natural contrast

  • Fibrosis or scar tissue may appear slightly hyperintense

T2-weighted images:

  • Normal myocardium is intermediate signal

  • Myocardial edema (e.g., in myocarditis or infarction) appears hyperintense

  • Useful for detecting acute injury and inflammation

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, highlighting myocardial edema or inflammation as hyperintense

  • Critical for assessing acute myocarditis, infarction, or rejection in transplant patients

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal myocardium enhances uniformly

  • Late gadolinium enhancement (LGE): shows scar tissue or fibrosis as hyperintense regions

  • Distinguishes ischemic infarcts (subendocardial or transmural) from non-ischemic patterns (mid-wall, patchy, subepicardial)

MRI Non-Contrast Cardiac-Gated 3D Imaging:

  • ECG-gated, high-resolution 3D sequences visualize myocardium in relation to chambers and coronary arteries

  • Useful for volumetric analysis, wall motion studies, and anatomical mapping

MRA (Magnetic Resonance Angiography):

  • Depicts coronary arteries and major vessels supplying the myocardium

  • Used to assess perfusion and vascular anomalies in conjunction with myocardial imaging

CT Appearance

CT (non-contrast):

  • Myocardium appears as a homogeneous soft tissue density surrounding cardiac chambers

  • Coronary artery calcification and gross hypertrophy can be detected

CT Coronary Angiography (CCTA):

  • Provides excellent evaluation of myocardial thickness, chamber size, wall motion, and perfusion

  • Detects myocardial hypoenhancement (ischemia), hyperenhancement (scar, infarct), and masses

  • Dynamic CT perfusion can assess ischemia and viability in LAD, LCx, and RCA territories

CT image

Myocardium anatomy CT axial image -img-00000-00000

MRI images

Myocardium (2)

MRI images

Myocardium