Central Illustration.

Diffusion Tensor-Cardiac Magnetic Resonance in Hypertrophic Cardiomyopathy Disarray and Ventricular Arrhythmia

Multimodal imaging of left ventricular myoarchitecture and disarray using diffusion tensor-cardiac magnetic resonance (DT-CMR), late gadolinium enhancement (LGE), and extracellular volume (ECV) mapping. DT-CMR can provide in vivo assessment of left ventricular myoarchitecture. The helix angle (HA) is the average myocyte orientation, and fractional anisotropy (FA) is a surrogate measure of underlying cell organization. The mid-ventricular slice at diastole in healthy control subjects (A) and patients with hypertrophic cardiomyopathy (HCM) (B–D) demonstrated similar HA distributions, but marked differences in FA. There was an almost complete mid-wall ring of high FA (yellow/orange) in control subjects (A), consistent with the classical description of circumferentially aligned mid-wall myocytes (E), which was also present in the HA map. By contrast, this ring was disrupted by reduced FA (B and C) or was absent (D) in HCM. These patterns were consistent with previously published HCM histology that shows disarray and fibrosis invading the mid-wall at the insertion point and hypertrophied segments (E)(14). Low FA in the anteroseptum matched areas of focal LGE and elevated ECV (C) in keeping with fibrosis contributing to low FA. But low FA could not be explained by fibrosis in all cases. In some instances, low FA in the anteroseptum was present with no detectable LGE or elevated ECV (B). Low FA also extended beyond areas of patchy LGE and elevated ECV, with no remnants of a mid-wall ring (D). Thus, low diastolic FA is likely to represent disarray after accounting for fibrosis, which can, for the first time, be measured in vivo and noninvasively, providing a potentially independent marker for HCM risk stratification. NSVT = nonsustained ventricular tachycardia.