This chapter reviews left ventricular noncompaction (LVNC). LVNC is an anatomical descriptor that does not inform on left ventricular function and size. The three morphologic features of LVNC are prominent trabeculae, deep intertrabecular recesses, and thin compact myocardial layer (see Fuster and Hurst’s Central Illustration). The right ventricle can be involved as isolated right ventricular noncompaction (RVNC) or biventricular noncompaction. LVNC can occur in patients with cardiomyopathies, congenital heart disease, or syndromes with cardiac and multiorgan malformations. Isolated LVNC can also be observed in healthy individuals, including athletes, and in patients with renal failure, and hematological or neuromuscular diseases. LVNC seen in primigravida in the third trimester is reversible and regresses after delivery. Diagnostic criteria are variable for both echocardiography and cardiac magnetic resonance (CMR), and based on the measurement of the ratio of noncompact to compact myocardial layers being ≥2. The presence of LVNC does not influence prognosis nor modify management strategy: both are driven by the underlying cardiac disease. Genetic testing identifies defects associated with the cardiac disease and should be prescribed when a genetic disorder is really suspected. LNVC such as that observed in young athletes with normal left ventricular size and function, unremarkable CMR, and family history for cardiomyopathy should be evaluated with great caution before assigning pathological significance.
In normal hearts, trabeculae undergo continuous and quantifiable geometric changes during the cardiac cycle; their contraction occurs during early systolic ejection while relaxation occurs in late diastole, at larger ventricular volumes. Trabeculae work as small, mechanically active levers during systole and increase perfusion of the subendocardium by expanding the interface between the endocardium and ventricular blood during diastole.1 Their number and size are highly variable, from few and flat to numerous and prominent, to confer a “spongy” appearance to the endocardial surface of the ventricles. This aspect corresponds to the term left ventricular noncompaction (LVNC).
LVNC describes a ventricular wall anatomy characterized by the presence of prominent left ventricular (LV) trabeculae, a thin compacted layer, and deep intertrabecular recesses that are in continuity with the LV cavity and separated from the epicardial coronary arteries.2 By definition, noncompaction pertains to the LV but may also involve the right ventricle, as either a biventricular3 or an isolated right ventricular variant.4 The American Heart Association (AHA) classification defines LVNC as a genetic/congenital cardiomyopathy,5 whereas the European Society of Cardiology (ESC) classification defines LVNC as a nonclassified entity.6 The recent MOGE(S) nosology (Morphofunctional phenotype, Organ(s) involvement, Genetic inheritance pattern, Etiologic annotation including genetic defect or underlying disease/substrate, and functional Status of the disease) proposes a simple description of the trait in individuals with either normal LV size, wall thickness, preserved systolic and diastolic function, or in combination with hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), restrictive cardiomyopathy (RCM), ...