P1769Microvascular resistance increases with left ventricular mass in hypertrophic cardiomyopathy

Introduction Hypertrophic cardiomyopathy is often associated with myocardial ischemia despite lack of focal epicardial coronary stenoses and this is partially attributable to microvascular dysfunction. The index of microvascular resistance (IMR) is a hemodynamic index that is independent of epicardial stenoses and reflects coronary microvascular function. Purpose To investigate the relationship between microvascular dysfunction and the degree of hypertrophy in hypertrophic cardiomyopathy patients. Methods We performed a prospective study to assess epicardial and microvascular coronary hemodynamics in 12 subjects with hypertrophic cardiomyopathy undergoing diagnostic coronary angiography. A pressure-temperature sensor coronary guidewire was used with intracoronary injections of room-temperature saline to measure mean coronary transit time during rest and hyperemia induced with intravenous adenosine. IMR was calculated by multiplying mean coronary transit time during hyperemia by distal coronary pressure in each subject. Left ventricular mass was calculated from baseline echocardiographic studies using established methods. Continuous variables are shown as mean ± standard deviation. Results Six subjects were male; mean age was 59.8±11.6 years. Baseline body mass index was 30.5±6.1 kg/m2 and left ventricular ejection fraction was 76.7% ± 11.0% with mean left ventricular mass 230.1±76.6 grams by echocardiography. Ten subjects had asymmetric septal hypertrophy; one subject had marked apical hypertrophy and one subject had asymmetric septal and inferolateral hypertrophy. Resting left ventricular outflow tract gradient was 59.4±37.8 mmHg and increased to 90.0±54.1 mmHg with Valsalva maneuver. Systolic anterior motion of the mitral valve was present in 10 subjects. Hemodynamic variables included coronary flow reserve (2.1±1.2); hyperemic mean transit time (0.29±0.15 sec.), and IMR (21.7±10.2). Index of microvascular resistance was strongly positively correlated with left ventricular mass (Figure 1; Pearson r=0.68, p=0.021). Figure 1. IMR is correlated with LV mass Conclusion(s) Microvascular dysfunction as assessed by IMR is strongly correlated with left ventricular mass and may contribute to symptoms in patients with hypertrophic cardiomyopathy.