Evidence for microvascular dysfunction in hypertrophic cardiomyopathy - New insights from multiparametric magnetic resonance imaging

Background - Microvascular dysfunction in hypertrophic cardiomyopathy (HCM) may create an ischemic substrate conducive to sudden death, but it remains unknown whether the extent of hypertrophy is associated with proportionally poorer perfusion reserve. Comparisons between magnitude of hypertrophy, impairment of perfusion reserve, and extent of fibrosis may offer new insights for future clinical risk stratification in HCM but require multiparametric imaging with high spatial and temporal resolution. Methods and Results - Degree of hypertrophy, myocardial blood flow at rest and during hyperemia (hMBF), and myocardial fibrosis were assessed with magnetic resonance imaging in 35 HCM patients (9 [26%] male/26 female) and 14 healthy controls (4 [29%] male/10 female), aged 18 to 78 years (mean +/- SD, 42 +/- 14 years) with the use of the American Heart Association left ventricular 16-segment model. Resting MBF was similar in HCM patients and controls. hMBF was lower in HCM patients (1.84 +/- 0.89 mL/min per gram) than in healthy controls (3.42 +/- 1.76 mL/min per gram, with a difference of -0.95 +/- 0.30 [SE] mL/min per gram; P < 0.001) after adjustment for multiple variables, including end-diastolic segmental wall thickness (P < 0.001). In HCM patients, hMBF decreased with increasing end-diastolic wall thickness (P < 0.005) and preferentially in the endocardial layer. The frequency of endocardial hMBF falling below epicardial hMBF rose with wall thickness (P=0.045), as did the incidence of fibrosis (P < 0.001). Conclusions - In HCM the vasodilator response is reduced, particularly in the endocardium, and in proportion to the magnitude of hypertrophy. Microvascular dysfunction and subsequent ischemia may be important components of the risk attributable to HCM.