Key result
Reduced fractional anisotropy on DT-CMR linked to ~150% higher ventricular arrhythmia odds in HCM.
Why the study?
Myocardial disarray is a likely focus for fatal arrhythmia in HCM, but whether fractional anisotropy measured by DT-CMR can serve as an in vivo biomarker of myoarchitecture and relate to ventricular arrhythmia was unknown.
Does fractional anisotropy measured by DT-CMR identify myocardial disarray and associate with ventricular arrhythmias in patients with hypertrophic cardiomyopathy?
Does fractional anisotropy measured by DT-CMR identify myocardial disarray and associate with ventricular arrhythmias in patients with hypertrophic cardiomyopathy?
Diastolic fractional anisotropy measured by DT-CMR is reduced in HCM and independently associated with ventricular arrhythmias, suggesting its potential as an in vivo marker of myocardial disarray.
Lower FA may signal elevated ventricular arrhythmia risk in HCM; leaves open its incremental value for clinical risk stratification.
BACKGROUND: Myocardial disarray is a likely focus for fatal arrhythmia in hypertrophic cardiomyopathy (HCM). This microstructural abnormality can be inferred by mapping the preferential diffusion of water along cardiac muscle fibers using diffusion tensor cardiac magnetic resonance (DT-CMR) imaging. Fractional anisotropy (FA) quantifies directionality of diffusion in 3 dimensions. The authors hypothesized that FA would be reduced in HCM due to disarray and fibrosis that may represent the anatomic substrate for ventricular arrhythmia. OBJECTIVES: This study sought to assess FA as a noninvasive in vivo biomarker of HCM myoarchitecture and its association with ventricular arrhythmia. METHODS: A total of 50 HCM patients (47 ± 15 years of age, 77% male) and 30 healthy control subjects (46 ± 16 years of age, 70% male) underwent DT-CMR in diastole, cine, late gadolinium enhancement (LGE), and extracellular volume (ECV) imaging at 3-T. RESULTS: Diastolic FA was reduced in HCM compared with control subjects (0.49 ± 0.05 vs. 0.52 ± 0.03; p = 0.0005). Control subjects had a mid-wall ring of high FA. In HCM, this ring was disrupted by reduced FA, consistent with published histology demonstrating that disarray and fibrosis invade circumferentially aligned mid-wall myocytes. LGE and ECV were significant predictors of FA, in line with fibrosis contributing to low FA. Yet FA adjusted for LGE and ECV remained reduced in HCM (p = 0.028). FA in the hypertrophied segment was reduced in HCM patients with ventricular arrhythmia compared to patients without (n = 15; 0.41 ± 0.03 vs. 0.46 ± 0.06; p = 0.007). A decrease in FA of 0.05 increased odds of ventricular arrhythmia by 2.5 (95% confidence interval: 1.2 to 5.3; p = 0.015) in HCM and remained significant even after correcting for LGE, ECV, and wall thickness (p = 0.036). CONCLUSIONS: DT-CMR assessment of left ventricular myoarchitecture matched patterns reported previously on histology. Low diastolic FA in HCM was associated with ventricular arrhythmia and is likely to represent disarray after accounting for fibrosis. The authors propose that diastolic FA could be the first in vivo marker of disarray in HCM and a potential independent risk factor.
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Ariga et al. (2019) studied this question. Reduced fractional anisotropy on DT-CMR increased the odds of ventricular arrhythmia by 2.5 per 0.05 decrease (95% CI: 1.2-5.3; p=0.015) in hypertrophic cardiomyopathy patients.
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