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Myocardial Disarray in HCM and Ventricular Arrhythmias
Study Questions:
What is the relationship between low fractional anisotropy (FA) and ventricular arrhythmia in patients with hypertrophic cardiomyopathy (HCM)?
Methods:
The investigators recruited 50 patients with HCM and 30 age- and sex-matched healthy control subjects prospectively to undergo diffusion tensor cardiac magnetic resonance (DT-CMR) imaging at 3-T using stimulated echo acquisition mode single-shot echo planar imaging sequence with late gadolinium enhancement (LGE), and extracellular volume (ECV) imaging. A logistic regression was used to predict the odds of patients having ventricular arrhythmia from their FA value.
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, 1.2-5.3; p = 0.015) in HCM and remained significant even after correcting for LGE, ECV, and wall thickness (p = 0.036).
Conclusions:
The authors concluded that low diastolic FA in HCM was associated with ventricular arrhythmia and is likely to represent disarray after accounting for fibrosis.
Perspective:
This study reports that DT-CMR provided in vivo visualization of normal and HCM myocardial architecture and that FA, adjusted for fibrosis, remained reduced in HCM. Furthermore, focal reduction of FA in the maximally hypertrophied segment of HCM patients was associated with ventricular arrhythmia and the association of low FA with ventricular arrhythmia persisted even after adjusting for fibrosis and hypertrophy, suggesting that adjusted FA could be measuring disarray and may be a novel, independent risk factor for sudden cardiac death. Additional studies are indicated to assess the clinical utility of detecting FA by DT-CMR to identify patients at risk of ventricular arrhythmia and potentially target those who may benefit from an implantable cardioverter-defibrillator.
Clinical Topics: Arrhythmias and Clinical EP, Cardiovascular Care Team, Heart Failure and Cardiomyopathies, Noninvasive Imaging, Prevention, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure, Magnetic Resonance Imaging
Keywords: Anisotropy, Arrhythmias, Cardiac, Cardiomyopathy, Hypertrophic, Death, Sudden, Cardiac, Defibrillators, Implantable, Diagnostic Imaging, Diastole, Echo-Planar Imaging, Gadolinium, Heart Failure, Hypertrophy, Magnetic Resonance Imaging, Myocardium, Risk Factors, Secondary Prevention
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