Myocardial fibrosis: why image, how to image and clinical implications

### Learning objectives The current era has seen major advances in myocardial imaging. We are now able to assess cardiac anatomy, function, tissue composition and disease activity across a wide range of disease states. Recently, there has been major interest in imaging myocardial fibrosis, predominantly with cardiovascular magnetic resonance (CMR). Fibrosis represents a common response to injury in most cardiomyopathies, but the distribution and pattern of fibrosis differ between pathologies, underscoring its potential role as a diagnostic marker. Furthermore, fibrosis is closely associated with impaired left ventricular function, as well as cardiac arrhythmias; as such, fibrosis imaging also provides powerful prognostic information. In this review, we discuss the pathophysiology of myocardial fibrosis, review the applications of CMR in the non-invasive detection of myocardial fibrosis and provide an overview of common pathologies in which fibrosis imaging may be of clinical utility. Our understanding of myocardial function and disease is largely focused on cardiomyocytes. However, the majority of cardiac cells in the adult mammalian heart are non-myocytes. Cardiac fibroblasts are one such cell type that play a crucial role in myocardial disease and healing. These cells are responsible for the production and deposition of extracellular matrix proteins—type 1 collagen being the prototype—which serve as a scaffold for other cellular components and are integral to the structural integrity and function of the myocardium. Fibroblasts respond to cytokines and neurohormal factors, differentiating into activated fibroblasts and smooth muscle-like myofibroblasts that are critical in the healing response of diseased or injured myocardium. These cells exert their effects on the extracellular matrix via regulation of matrix metalloproteinases and fibronectin. Although the primary response to myocardial injury—wound healing, reparative scar formation and …