Phenotyping hypertrophic cardiomyopathy using cardiac diffusion magnetic resonance imaging: the relationship between...

Area of Science:

• Cardiovascular Imaging
• Cardiac MRI
• Diffusion Tensor Imaging

Background:

• Microvascular dysfunction in hypertrophic cardiomyopathy (HCM) predicts clinical decline, but underlying mechanisms are unclear.
• Cardiac diffusion tensor imaging (cDTI) offers in vivo myocardial microstructure characterization using mean diffusivity (MD), fractional anisotropy (FA), and secondary eigenvector angle (E2A).

Purpose of the Study:

• To investigate the relationship between myocardial perfusion and cDTI parameters in HCM.
• To understand the sequence of pathophysiology and the interplay between vascular function and microstructure in HCM.

Main Methods:

• A cardiac magnetic resonance (CMR) study involving 20 HCM patients and 10 controls.
• Utilized 3.0T CMR for spin-echo cDTI, adenosine stress/rest perfusion mapping, cine-imaging, and late gadolinium enhancement (LGE).
• Calculated Myocardial Perfusion Reserve (MPR), MD, FA, and E2A per segment, divided into subendocardial and subepicardial regions. 'Normal' segments were defined by specific criteria (wall thickness ≤11 mm, MPR ≥2.2, no LGE).

Main Results:

• Normal HCM segments exhibited increased MD and E2A, with decreased FA compared to controls, suggesting cardiomyocyte disarray.
• Subendocardial regions in HCM patients showed significantly higher MD and lower MPR than subepicardial regions.
• Increased subendocardial MD correlates with reduced subendocardial blood flow, indicating regional remodeling.

Conclusions:

• Even in HCM segments without wall thickening, scarring, or perfusion deficits, diffusion is more isotropic, pointing to underlying cardiomyocyte disarray.
• Elevated E2A suggests abnormal myocardial sheetlet angulation during systole in HCM.
• Increased subendocardial MD in HCM is linked to regional remodeling and may explain impaired subendocardial blood flow.