Noncompacted Myocardium

Definitions

Noncompacted myocardium (NCM) is a cardiac abnormality involving the myocardial wall, characterized by numerous, excessively prominent trabeculations and deep intertrabecular recesses penetrating into the midmyocardium ( Fig. 64.1 ). Noncompaction of the left ventricle can occur as an isolated cardiac feature (left ventricular noncompaction [LVNC]) or in association with other primary cardiomyopathies as idiopathic dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), or even restrictive cardiomyopathy (RCM). In addition, NCM can occur in metabolic and genetic syndromes, in which it can be associated with HCM or DCM (eg, Barth syndrome) or with congenital heart defects (nonisolated LVNC), and in neuromuscular disorders. It was first described in 1926 by Grant as spongy myocardium, but later the definition of isolated LVNC was first used by Chin et al. in 1990 to describe eight pediatric cases with the cardiac phenotype in the absence of congenital heart defects. Although much attention has been given to this entity in recent years, there is currently no consensus on cause, pathogenesis, diagnosis, or management of LVNC. In the 1995 World Health Organization (WHO)/International Society and Federation of Cardiology (ISFC) classification of cardiomyopathies, LVNC was not included ; it was included in the North American revision and listed among the genetically determined cardiomyopathies, but not all experts agree that it represents a cardiomyopathy or a separate disease.

The diagnosis of noncompaction is challenging and its nosology is still debated. However, when a definite diagnosis of noncompaction is made, the diagnostic process should orient toward a genetic disease with a relatively high probability of sarcomeric mutations. The clinical presentation is with a sporadic or familial heart muscle disorder with presumed persistence of the embryonic pattern of trabeculation of the left ventricle (spongy myocardium). The disruption of the normal trabeculation and compaction processes that occurs between days 30 and 70 of embryogenesis is thought to predispose to systolic and diastolic dysfunction, cavity dilatation, hypertrophy, and arrhythmia.

Many terms were introduced in the literature over the years to identify this heterogeneous entity, showing the need for an internationally recognized definition ( Table 64.1 ).

Epidemiology

Although this condition is thought to be rare, its incidence and prevalence are not yet well defined. However, because of increasing awareness and improvements in the imaging techniques, it is considered the third most common among the cardiomyopathies. In an epidemiological study in Australian children, it has been reported that 9.2% of the population was affected by isolated ventricular noncompaction, ranking third after dilated and hypertrophic cardiomyopathies, similar to what has been reported by Pignatelli et al. According to different echocardiographic studies, the reported prevalence of isolated noncompaction in adults varied from 0.014% to 0.05%, 0.14%, and 0.26%, whereas its prevalence increased to 3.7% among adults with decreased (<45%) ejection fraction (EF) and to 3%, and 4% in heart failure patients. It is important to underline that half of the LVNC patients are children. In most cases the disease occurs congenitally; however, in some it can manifest later in life. In affected families, at least 25% of asymptomatic relatives present with echocardiographic features.