Hypertrophic cardiomyopathy and left ventricular non-compaction:Distinct diseases or variant phenotypes of a single condition?

Hypertrophic cardiomyopathy(HCM)is a genetically determined myocardial disease characterized by an increased thickness of the left ventricle(LV)wall that cannot be solely attributed to abnormal loading conditions.HCM may present with an intraventricular or LV outflow tract obstruction,diastolic dysfunction,myocardial fibrosis and/or ventricular arrhythmias.Differentiating HCM from other diseases associated with LV hypertrophy,such as hypertension,aortic stenosis,or LV non-compaction(LVNC),can at times be challenging.LVNC is defined by excessive LV trabeculation and deep recesses between trabeculae,often accompanied by increased LV myocardial mass.Previous studies indicate that the LVNC phenotype may be observed in up to 5%of the general population;however,in most cases,it is a benign finding with no impact on clinical outcomes.Nevertheless,LVNC can occasionally lead to LV systolic dysfunction,manifesting as a phenotype of dilated or non-dilated left ventricular cardiomyopathy,with an increased risk of thrombus formation and arterial embolism.In extreme cases,where LVNC is associated with a very thickened LV wall,it can even mimic HCM.There is growing evidence of an overlap between HCM and LVNC,including similar genetic mutations and clinical presentations.This raises the question of whether HCM and LVNC represent different phenotypes of the same disease or are,in fact,two distinct entities.