Cardiac trabecular anatomy is characterized by extreme individual and population variability that corresponds to a sort of individual cardioprinting. In normal hearts, trabeculae undergo continuous and quantifiable geometric changes during the cardiac cycle; they actively provide mechanical leverage during early systolic ejection through contraction, and relaxation occurs during late diastole at larger ventricular volumes.1 In the left ventricle, trabeculae can be minimally represented or may be so numerous and prominent that they confer a “spongy” appearance to the endocardial surface of the ventricles. The latter corresponds to the term left ventricular noncompaction (LVNC).
LVNC describes a ventricular wall anatomy characterized by the presence of disproportionate, 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 and wall thickness and preserved systolic and diastolic function or in combination with hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), restrictive cardiomyopathy (RCM) or arrhythmogenic right ventricular cardiomyopathy (ARVC).7 This latter descriptive approach is the expression of the clinical uncertainties regarding the unique interpretation of LVNC as a cardiomyopathy.8
In the official guidelines of scientific societies, the requirements for the definition of a cardiomyopathy include “diseases of the myocardium associated with mechanical and/or electrical dysfunction” (AHA)5 and “myocardial diseases characterized by structurally and functionally abnormal heart muscle and absence of other diseases sufficient to cause the observed myocardial abnormality” (ESC).6 When isolated and benign, LVNC is not associated with mechanical and/or electrical dysfunction (AHA) and is characterized by some structural abnormality (trabeculation) with potentially normal function.8 By itself, the diagnosis of LVNC is based on one of the attributes that define cardiomyopathies, namely the abnormal LV morphology, but this does not obligatorily imply LV dysfunction. The increasing number of reports that describe LVNC in the normal population questions the definition of LVNC as cardiomyopathy. This chapter illustrates the current criteria for diagnosing LVNC, available data in normal populations, the association of LVNC with cardiomyopathies and disease genes, congenital heart diseases, rare syndromes affecting or not affecting cardiac function, acquired and possibly reversible LVNC, and diagnostic workup.
CURRENT DIAGNOSTIC CRITERIA FOR LEFT VENTRICULAR NONCOMPACTION
Diagnostic criteria have been established for echocardiography, cardiac magnetic resonance (CMR), and multidetector computed tomography ...