Defining phenotypes and disease progression in sarcomeric cardiomyopathies: Contemporary role of clinical investigations

Mutations in cardiac sarcomere protein genes are associated with a variety of clinical phenotypes, including hypertrophic (HCM), dilated (DCM), and restrictive (RCM) cardiomyopathy as well as left ventricular non-compaction, with the overlap of morpho-functional manifestations in individual patients and families. Over time, initial phenotypes may undergo profound changes which determine clinical course and disease progression. Although genetic defects causing HCM and DCM have opposite effects at the myofilament level, a number of downstream maladaptive mechanisms, ranging from microvascular dysfunction and ischaemia to myocardial fibrosis and from diastolic dysfunction to abnormal sympathetic activation and arrhythmogenesis, seem to recur in sarcomeric cardiomyopathies, independent of the presenting phenotype. The extent and rate at which each of these features occur and evolve may be radically different in each form of cardiomyopathy, determining a clinical heterogeneity that is not only cross-sectional, but also longitudinal, i.e. time-related. Timely and sensitive detection of these long-term modifications in the clinical setting is a key to preventing advanced disease and identifying novel therapeutic targets. The present review evaluates the contribution of contemporary technology to pre-clinical diagnosis, characterization of phenotypes, and assessment of disease progression in sarcomere cardiomyopathies, including echocardiography, positron emission tomography, magnetic resonance, pathology, and circulating biomarkers.