The presence of excessive and prominent trabeculae of the ventricular myocardium, together with deep intertrabecular recesses characterises the disease [1].

Three distinctive criteria define left ventricular noncompaction cardiomyopathy (LVNC): prominent left ventricular trabeculae, deep intertrabecular recesses and a thin compact layer of the myocardium [2,3]. Prevalence of the disease is uncertain. In a study with adult patients and using transthoracic echocardiography, 17/37,555 carried LVNC, 0.045 % [4], whereas in children transthoracic ultrasound showed 12/20,341 cases, 0.06 % [5]. Mortality ranges from 5 % to 47 % [6].
The disease was first recognised in the 90's of the last century as a congenital disease, due to a failure in ventricluar myocardium compaction during the 5 to 8 weeks of the embryonic development [7]. The disease was classified as an independent entity, with no age of preferential appearance, and in some cases related with other genetic disorders.
However, evidence is growing that LVNC is not a failure in the pre-existing embryonic trabecular myocardium compaction that forms the compact components of the ventricular walls [8]. When observed in adult patients, the presence of excessive trabeculae does not mean worse outcomes if the ejection fraction (EF) is normal, the risk of the development of complications, e.g. arrhythmias and stroke, being low. In fact, noncompaction images observed in children or autopsies are different from those in adult patients with excessive trabeculation, with or without clinical symptoms. Thus, it has been suggested that left-ventricle wall hypertrabeculation would not be a clinical entity by itself [8,9]. This morphological aspect could be a finding appearing together with additional lesions (as dilated cardiomyopathy) that are responsible for the low EF the patients show. The term itself can be misleading because there is neither compaction failure nor cardiomyopathy in most individuals fulfilling the diagnostic criteria.
Clinical manifestations are quite variable, ranging from asymptomatic to congestive heart failure, arrhythmias, systemic thromboembolism, and sudden death [9]. The AHA has classified the disease as a primary genetic cardiomyopathy [10], but this is controversial [11–14]. The WHO and the European Society of Cardiology classify the disease as unclassified [2], because it can be considered an independent cardiomyopathy or a phenotypical variant of other primary cardiomyopathies fulfilling the echocardiographic criteria of LVNC, i.e. dilated, hypertrophic or restrictive cardiomyopathy (with the current criteria both overlap and are not be mutually exclusive) [14]. LVNC could describe morphologic features, but not a functional profile of the cardiomyopathy [14,15]. There has been a shift in LVNC from underdiagnosis to overdiagnose [16].
Like other hereditary cardiomyopathies, LVNC is genetically heterogeneous [9]. LVNC1 is caused by a heterozygous mutation (autosomal dominant [17]) in the alpha-dystrobrevin gene (DTNA; 601239) in the 18q12 chromosome. However, at least 11 additional forms have been described (see Annex).
It should be taken into account that there might be a possible association between some variants and Barth syndrome or other neuromuscular disorders: dystrophinopathies, dystrobrevinopathy, laminopathy, zaspopathy, myotonic dystrophy, children glycogenosis type II (Pompe's disease), myoadenylate-deaminase deficiency, Friedreich ataxia, Duchenne's disease, Charcot-Marie-Tooth's disease and mitochondrial diseases [3,18–22].
Comprehensive reviews on LVNC are listed in references [6,15,23,24], their respective outcomes (NYHA class III or major cardiovascular complications being the worst ones, but not left ventricle dilation or systolic dysfunction) are dealt with in references [25] and [26]. Moreover, a review of paediatric cases is presented in reference [27].