Abstract 203: Arteriolar but not Capillary Resistance is Increased in Hypertrophic Cardiomyopathy as Compared to Hypertensive Heart Disease
Background: Reduced myocardial blood flow reserve (MBFR) in patients with hypertrophic cardiomyopathy (HCM) and hypertensive heart disease (HHD) correlates with reduced arteriolar and capillary density compared to sedentary individuals (S) in myocardial biopsies. We sought to quantify the parameters involved in the regulation of myocardial blood flow (MBF) in vivo.
Methods and Results: We examined 15 individuals, matched for age (average 33yrs) and gender, in each of the three groups: HCM, HHD and S. rBV (ml/ml), its exchange frequency β (1/min) and MBF (ml/min/g) at rest and during adenosine-induced hyperemia were derived by myocardial contrast echocardiography in mid septal regions. Reserve indices were calculated as the ratio of the respective values during hyperemia and at rest. Left ventricular mass index was not different between HCM (148±47g/m2) and HHD (140±30g/m2), but higher than in S (94±13 g/m2, p<0.01). rBV was not different between HCM (0.084±0.023ml/ml) and HHD (0.097±0.016ml/ml), however lower than in S (0.129±0.026ml/ml, p<0.01). Conversely, MBFR was lower in HCM (1.67±0.93) compared to HHD (2.80±0.65, p<0.01) and S (3.36±1.03, p<0.01). The exchange frequency reserve, inversely reflecting arteriolar resistance, was reduced in HCM (1.54 ±0.85) compared with HHD (2.40±0.85, p<0.01) and S (2.63±1.02, p<0.01), whereas the perfusion pressure reserve was not different (0.99±0.09, 0.95±0.08, and 0.99±0.11, respectively). At rest, an rBV of 0.111ml/ml distinguished between HHD or HCM and S with a sensitivity of 80% and a specificity of 90%. An exchange frequency reserve of 1.79 differentiated between HCM and HHD with a sensitivity of 80% and a specificity of 78%.
Conclusions: Capillary density is reduced in HCM and HHD compared to S. The blunted MBFR in HCM is due to increased arteriolar resistance.