Microvascular function is selectively impaired in patients with hypertrophic cardiomyopathy and sarcomere myofilament gene mutations

Objectives: The purpose of this study was to assess myocardial blood flow (MBF) using positron emission tomography in patients with hypertrophic cardiomyopathy (HCM) according to genetic status. Background: Coronary microvascular dysfunction is an important feature of HCM, associated with ventricular remodeling and heart failure. We recently demonstrated the increased prevalence of systolic dysfunction in patients with HCM with sarcomere myofilament gene mutations and postulated an association between genetic status and coronary microvascular dysfunction. Methods: Maximum MBF (intravenous dipyridamole, 0.56 mg/kg; Dip-MBF) was measured using ¹³N-labeled ammonia in 61 patients with HCM (age 38 ± 14 years), genotyped by automatic DNA sequencing of 8 myofilament-encoding genes (myosin-binding protein C, beta-myosin heavy chain, regulatory and essential light chains, troponin T, troponin I, troponin C, alpha-tropomyosin, and alpha-actin). In 35 patients, cardiac magnetic resonance imaging was performed. Results: Fifty-three mutations were identified in 42 of the 61 patients (genotype positive; 69%). Despite similar clinical profiles, genotype-positive patients with HCM showed substantially lower Dip-MBF compared with that of genotype-negative patients (1.7 ± 0.6 ml/min/g vs. 2.4 ± 1.2 ml/min/g; p < 0.02). A Dip-MBF <1.5 ml/min/g had 81% positive predictive value for genotype-positive status and implied a 3.5-fold independent increase in likelihood of carrying myofilament gene mutations (hazard ratio: 3.52; 95% confidence interval: 1.05 to 11.7; p = 0.04). At cardiac magnetic resonance imaging, the prevalence of late gadolinium enhancement was greater in genotype-positive patients (22 of 23 [96%] compared with 8 of 12 [67%] genotype-negative patients; p = 0.038). Conclusions: Patients with HCM with sarcomere myofilament mutations are characterized by more severe impairment of microvascular function and increased prevalence of myocardial fibrosis, compared with genotype-negative individuals. These findings suggest a direct link between sarcomere gene mutations and adverse remodeling of the microcirculation in HCM, accounting for the increased long-term prevalence of ventricular dysfunction and heart failure in genotype-positive patients.