Cardiovascular Magnetic Resonance Imaging of Myocardial Interstitial Expansion in Hypertrophic Cardiomyopathy

Abstract

Hypertrophic cardiomyopathy (HCM) is a cardiovascular genetic disease with a varied clinical presentation and phenotype. Although mutations are typically found in genes coding for sarcomeric proteins, phenotypic derangements extend beyond the myocyte to include the extracellular compartment. Myocardial fibrosis is commonly detected by histology, and is associated with clinical vulnerability to adverse outcomes. Over the past decade, the noninvasive visualization of myocardial fibrosis by cardiovascular magnetic resonance (CMR) techniques has garnered much interest given the potential applications toward improving our understanding of pathophysiologic mechanisms of disease, as well as diagnosis and prognosis. Late gadolinium enhancement (LGE) imaging techniques are able to detect focal (typically replacement) fibrosis. Newer CMR techniques that measure absolute T1 relaxation time allow the quantification of the entire range of focal to diffuse (interstitial) fibrosis and may overcome potential limitations of LGE. This review will discuss the methodology and current status of these novel techniques, with a focus on extracellular volume fraction (ECV). Recent findings describing ECV measurement in HCM will be summarized.

Keywords: Cardiovascular magnetic resonance; Extracellular volume fraction; Gadolinium contrast; Hypertrophic cardiomyopathy; Myocardial fibrosis; T1 mapping.

Fig. 1

(Adapted from Wong et al [32], with permission from Lippincott Williams & Wilkins - Wolters Kluwer Health). Measurement of pre and postcontrast T1 in an individual with normal ECV. Short axis imaging at varying time points (precontrast images top row, postcontrast images bottom row) along with the corresponding fitting curves used to derive absolute T1 measurement. Calculations are performed at the pixel level to generate pre and postcontrast T1 maps

Fig. 2

CMR images of a patient with hypertrophic cardiomyopathy. a Four-chamber steady state free precession (SSFP) image demonstrating asymmetric septal hypertrophy. b Three-chamber SSFP image. c Midventricular short axis LGE image ~15 minutes postgadolinium contrast showing focal LGE in the vicinity of the right ventricular insertion point. d Precontrast T1 map. e postcontrast T1map ~ 20 minutes postgadolinium contrast. f ECV map calculated using the T1 data and hematocrit. The horizontal dashed white line notes the color range of the upper limit of normal of ECV (~29.5 % at our center). The black arrows point to the anterior septal region where more diffuse fibrosis is identified, which was not as readily apparent on the LGE image (panel (c). Note: panels c, d, e, f are the same short axis slice