Cardiovascular magnetic resonance imaging to assess myocardial fibrosis in valvular heart disease

Abstract

The left ventricular (LV) remodeling process associated with significant valvular heart disease (VHD) is characterized by an increase of myocardial interstitial space with deposition of collagen and loss of myofibers. These changes occur before LV systolic function deteriorates or the patient develops symptoms. Cardiovascular magnetic resonance (CMR) permits assessment of reactive fibrosis, with the use of T1 mapping techniques, and replacement fibrosis, with the use of late gadolinium contrast enhancement. In addition, functional consequences of these structural changes can be evaluated with myocardial tagging and feature tracking CMR, which assess the active deformation (strain) of the LV myocardium. Several studies have demonstrated that CMR techniques may be more sensitive than the conventional measures (LV ejection fraction or LV dimensions) to detect these structural and functional changes in patients with severe left-sided VHD and have shown that myocardial fibrosis may not be reversible after valve surgery. More important, the presence of myocardial fibrosis has been associated with lesser improvement in clinical symptoms and recovery of LV systolic function. Whether assessment of myocardial fibrosis may better select the patients with severe left-sided VHD who may benefit from surgery in terms of LV function and clinical symptoms improvement needs to be demonstrated in prospective studies. The present review article summarizes the current status of CMR techniques to assess myocardial fibrosis and appraises the current evidence on the use of these techniques for risk stratification of patients with severe aortic stenosis or regurgitation and mitral regurgitation.

Imaging the Cardiac Extracellular Matrix

“…Organ-scale imaging methods measure bulk properties across large regions of the heart, e.g., the left ventricle. These methods can be used for noninvasive patient imaging, with applications including detection of myocardial fibrosis and monitoring scar tissue formation after myocardial infarction [52, 58]. Cellular-scale imaging methods visualize the ECM components directly at high-resolutions.…”

“…2.2) [38, 42, 73]. For cardiac collagen imaging, the collagen properties of interest include the absolute abundance of collagen, the relative abundance of collagen types, the structure/location of the fiber network, and the connection to other constituents of the ECM [23, 49, 52, 56, 73]. …”

“…The main clinical method for organ-scale collagen imaging is magnetic resonance imaging (MRI) [52]. MRI, also known as cardiac magnetic resonance (CMR), is a noninvasive imaging method that perturbs atomic protons/neutrons (typically hydrogen protons) with radiofrequency energy and measures the behavior of those perturbed atoms.…”

“…Measured values can be different for normal and diseased tissue, and changes in these values are also associated with other ECM altering diseases (e.g., edema). T1 mapping sequences are not standardized, making measurements difficult to reproduce or interpret across institutions [52]. A final set of techniques, tagging and feature tracking MRI, are reproducible and quantitative, but only indirectly measure collagen or other ECM biology [55].…”

Role of Cardiac Magnetic Resonance Imaging in Valvular Heart Disease: Diagnosis, Assessment, and Management

“…CMR research in valvular heart disease is focused on a number of areas such as free breathing sequences [69], fibrosis evaluation [70, 71], CMR-derived right ventricular strain evaluation [72], and microvascular disease assessment [73]. These advances in CMR technology will provide new information for assessing the heart in patients with valvular heart disease, which may yield new diagnostic and prognostic information.…”