# Left Ventricular Non-Compaction Cardiomyopathy-Still More Questions than Answers
## 1 Introduction  
Left ventricular non-compaction describes the phenotypical phenomena characterized by the presence of excessive trabeculation of the left ventricle, which forms a deep recess filled with blood. The first autopsy report describing an \"embryonic spongy pattern of the left ventricle\" in newborns was published in 1926 [1]. The later autopsy reports described single cases of newborns and infants with complex congenital heart disease and specific patterns of the left ventricular muscle. The first case of an isolated sinusoid anomaly of the left ventricle diagnosed with echocardiography by 33 years old woman was published in 1984 [2]. The term \"sinusoid anomaly of the left ventricle\" was used till the publication of [PERSON] et al. in 1990, who used for the first time the term, \"isolated noncompaction of the left ventricular myocardium (INVM)\" [3]. At the same time, the authors suggested disturbance of the embryonic compaction process as the cause of the disease and proposed the first echocardiographic diagnostic criteria. With the dynamic development of imaging techniques such as echocardiography, magnetic resonance, and computer tomography, many different phenotypes of \"noncompaction\" of the left ventricle have been recognized and many definitions have been proposed since the first description [4]. Currently, the term left ventricular noncompaction (LVNC) is used for specific phenotypes of left ventricular anatomy including the presence of prominent trabeculations with deep intertrabecular recesses (non-compacted myocardium) and thin compact layer of the myocardium (compacted myocardium); however, LVNC does not necessarily mean pathology [5]. In some cases, the right ventricle can also be involved. The term LVNC is used by some authors for describing morphological anomalies without impairing LVfunction and LVNC cardiomyopathy or NCCM (non-compaction cardiomyopathy) for cases with impaired left ventricular function [6]. Not only the general definition of LVNC is disputed, but also its classification as cardiomyopathy differs between the European Society of Cardiology and American Heart Association classification. The first defines LVNC as \"non-classified cardiomyopathy\", and the latter as \"genetic cardiomyopathy\" [7; 8]. The MOGE(S) classification proposes a description of left ventricular morphology (M\({}_{\text{LVNC}}\)) for the left ventricle without dilatation and preserved systolic function, (M\({}_{\text{LVNC}\text{ D}}\)) for dilated LV, (M\({}_{\text{LVNC}\text{ H}}\)) for hypertrophied LV, and (M\({}_{\text{LVNC}\text{ A}}\)) for arrhythmogenic right ventricular cardiomyopathy [9]. Different subtypes classifications were suggested because the LVNC is a very heterogeneous morphological anomaly. [PERSON] and colleagues proposed the latter in 2016 [10]. They divided LVNC into seven subtypes (Table 1). Other authors proposed four subtypes of LVNC: Isolated NCCM, NCCM/HCM, NCCM/DCM, and NCCM/HCM/DCM [11]. Most of the cohorts reported in the literature are treated as a whole, without analyzing subgroups, making it difficult to compare individual publications. Considering the lack of a uniform definition of LVNC, as well as the \"golden standard\", it is difficult to estimate the actual incidence of the disease. There are significant differences between the pediatric and adult populations. The incidence of LVNC in children varied according to registers between 4.8 and 9.2% making LVNC the third most common cardiomyopathy [4]. The prevalence in adults is lower, reaching 4.1-5%, and men are almost three times more affected [4]. The familial incidence reaches 40%. A higher degree of trabeculation together with mildly reduced EF was observed in athletes of African ethnicity [12]. Similar results showed the analysis of 1123 participants of the Multi-Ethnic Study of Atherosclerosis (MESA) using CMR fractal analysis [13]. The fractal dimension of 1.3 or more was found more frequently in probands with Afro-American and Hispanic ethnicity.