Isolated non-compaction of the left ventricle (LVNC) is a rare disorder, classified as a primary genetic cardiomyopathy by the American Heart Association . The European Society of Cardiology Working Group on Myocardial and Pericardial Diseases classified LVNC as an unclassified cardiomyopathy . LVNC was previously also named spongy myocardium or hypertrabeculation syndrome; these terms should not be used as interchangeable terms .
LVNC is characterized by the following features:
- An altered myocardial wall with prominent trabeculae and deep intertrabecular recesses resulting in thickened myocardium with two layers consisting of compacted and non-compacted myocardium (picture 1) [4,5].
- Continuity between the left ventricular cavity and the deep intratrabecular recesses, which are filled with blood from the ventricular cavity without evidence of communication to the epicardial coronary artery system.
LVNC as an isolated disorder will be reviewed here. Non-compacted myocardium may also be seen in association with other abnormalities:
- Non-compacted myocardium with intramyocardial sinusoids and coronary artery fistulae may be associated with congenital right or left ventricular outflow tract abnormalities, such as pulmonary atresia with intact ventricular septum . Coronary artery abnormalities are common, which differentiate right or left ventricular outflow tract abnormalities from LVNC. In LVNC, coronary artery circulation is usually normal.
- Non-compacted myocardium is occasionally seen accompanying other congenital cardiac disorders, such as Ebstein's anomaly, bicuspid aortic valve, ventricular septal defect, coarctation, aorta-to-left ventricular tunnel, congenitally corrected transposition, hypoplastic left heart syndrome , and isomerism of the left atrial appendage [8-10]. Non-compacted myocardium has also been found in patients with ventricular and atrial septal defects and patent ductus arteriosus [10,11].
- Non-compacted myocardium has also been noted in patients with cardiomyopathies due to neuromuscular disorders . (See 'Diagnosis' below.) Non-compaction of the left ventricle can occur in metabolic diseases and genetic syndromes, including Barth syndrome, Charcot-Marie-Tooth disease 1A, and Melnick-Needles syndrome, as well as nail-patella syndrome .
- Features of LVNC can overlap with dilated cardiomyopathy, hypertrophic cardiomyopathy (especially the apical variant), and restrictive cardiomyopathy [14-17]. Within the same family, the phenotypic expression can vary considerably .