Left Ventricular Noncompaction Cardiomyopathy

Excerpt

Left ventricular non-compaction (LVNC) is a rare cardiomyopathy in which the two-layered myocardium has an abnormally thick sponge-like, noncompacted trabecular layer and a thinner, compacted myocardial layer. It is characterized by prominent trabeculae, showing continuity between the deep trabecular recesses and the ventricular cavity. It has been classified as a primary cardiomyopathy of genetic origin that usually affects the left ventricle; however, right ventricular and biventricular non-compaction have also been described. It can be associated with neuromuscular disorders, cardiac structural abnormalities, and chromosomal defects. However, this classification is somewhat controversial, as the ratio of increased trabecular tissue to compact myocardial tissue used to diagnose LVNC is also found in up to 20% of individuals without cardiomyopathy. In addition, this increased ratio of trabecular tissue has been found in normal physiologic processes such as pregnancy and athletes, likely due to increased preload.

LVNC is most commonly asymptomatic; however, in some instances, it can carry a high risk of thromboembolic phenomena, left ventricular dysfunction, malignant arrhythmia, and sudden cardiac death. It can also be associated with congenital heart defects such as ventricular septal defects, pulmonic stenosis, Ebstein's anomaly, hypoplastic left heart syndrome, and bicuspid aortic valve.

Recent studies have shown that the term "noncompaction" may be a misnomer because evidence shows the enlarged trabecular tissue layers and compacted myocardial layers develop independently of each other. However, given the current classification systems recognizing left ventricular noncompaction cardiomyopathy as a distinct entity, for the purpose of this article, we will use LVNC to mean excessive trabecular cardiac tissue.

It is likely that there are two distinct processes causing the phenotype of increased left ventricular trabecular tissue: 1) Genetic mutations causing the trabeculated layer of the myocardium to overdevelop in comparison to the compacted layer. This condition often presents during childhood and is often associated with known gene mutations, neuromuscular disorders, and cardiac structural abnormalities. 2) Physiologic conditions causing increased preload resulting in increased trabeculation in the left ventricle, such as pregnancy, athletic training, and hemoglobinopathies. These conditions present in adults and are often reversible. This may also be a normal variant in some people.