Isolated noncompaction of the left ventricular myocardium -- a review of the literature two decades after the initial case description.

Isolated noncompaction of the left ventricular myocardium (INVM), first described in 1984, is an unclassified cardiomyopathy and is assumed to occur as an arrest of the compaction process during the normal development of the heart. Between weeks 5 to 8 of human fetal development, the ventricular myocardium undergoes gradual compaction with transformation of the relatively large intertrabecular spaces into capillaries while the residual spaces within the trabecular meshwork gradually flatten or disappear. In the case of INVM, the spaces within the intertrabecular meshwork persist while no other cardiac abnormalities exist. Although there is substantial evidence supporting the developmental hypothesis, other pathogenetic processes responsible for INVM have been discussed. It can be assumed that INVM will be better understood in the future as the molecular genetic basis of cardiomyopathies will be further unravelled. Echocardiography has been shown to be the method of choice in diagnosis of INVM. The diagnostic criteria can be summarized as: 1) appearance of at least four prominent trabeculations and deep intertrabecular recesses; 2) appearance of blood flow from the ventricular cavity into the intertrabecular recesses as visualized by color Doppler imaging; 3) the segments of noncompacted myocardium mainly involve the apex and the inferior mid and lateral mid of the left ventricular wall and typically show a two-layered structure with an endsystolic ratio greater than two between the noncompacted subendocardial layer and the compacted subepicardial layer; 4) absence of coexisting cardiac abnormalities. Magnetic resonance imaging using modern gradient echo sequences has also been shown to diagnose INVM accurately. The clinical presentation of INVM is characterized by a high prevalence of heart failure, thromboembolic events and arrhythmias including ventricular tachycardia and atrial fibrillation. The establishment of a registry, which was initiated by the "Arbeitsgemeinschaft Leitende Kardiologische Krankenhausärzte (ALKK)" recently, may provide further clues for diagnosis, risk stratification, and management of this disease.