**2. Anatomy and pathology**

Left ventricular noncompaction (LVNC) is defined by essential markers: an inner noncompacted layer with prominent left ventricular (LV) trabeculae and deep intertrabecular recesses, and a thin compacted layer. There is a spectrum of morphologic variability, ranging from hearts with different degrees of noncompaction extension and amount, and right ventricular involvement.

From hearts obtained from autopsies or transplantation, LVNC diagnosis is based on the presence of a two‐layered ventricular wall, comprising a thinner compact epicardial layer and an inner noncompacted layer, with prominent trabeculations associated with deep, intertrabecular recesses that communicate with the ventricular cavity but not with the coronary circulation [2, 3].

Noncompacted areas are commonly located at the LV apex and mid‐apical wall segments, but typically spares the interventricular septum. When associated with hypertrophic cardiomyopathy phenotype (HCM), the hypertrophied septum coexists with the LVNC phenotype. Other described associations include dilated cardiomyopathy (DCM) and, more rarely, restrictive cardiomyopathy (RCM) or arrhythmogenic right ventricular cardiomyopathy (ARVC). Besides the relationship of LVNC with other cardiomyopathies, which may share the same genetic basis, there has been considerable controversy regarding the differentiation from normal LV trabeculation, which seems to occur in some normal asymptomatic individuals as found in analysis from the MESA study [4].

Histopathology has shown continuity between the endothelium of inter‐trabecular recesses and that of the endocardium, distinguishing LVNC from persistent sinusoids. Other findings have included loosely organised myocytes and endocardial and subendocardial replacement fibrosis suggestive of ischaemic necrosis, which has been demonstrated by imaging techniques *in vivo* [5].

LV dilatation and ischemia are frequently present, and thrombus formation in the recesses may occur, which may be associated with possible thromboembolic events.
