Abstract 2483: Relative Contribution of Capillary Flow Velocity and Myocardial Blood Volume to the Reduction in Myocardial Flow Reserve Seen in Patients With Coronary Risk Factors.
Background. Clinical studies suggest that myocardial flow reserve (MFR) is abnormal in individuals without coronary disease (CAD) but with coronary risk factors (RF). It remains uncertain, however, which component of myocardial blood flow, i.e. capillary flow velocity (CFV) or myocardial blood volume (MBV), is responsible for the RF-related decrease in MFR and whether the decrease in MFR seen with RFs is independent of age.
Methods. 86 subjects (35 controls and 51 isolated RFs) aged 28 to 77 years, underwent high-dose (0.84 mg/kg) dipyridamole real-time myocardial contrast echocardiography (RT-MCE) to measure MFR, MBV and CFV. Among the 51 RFs subjects, 26 had hypertension, 18 had hypercholesterolemia (LDL-C > 4 mM) and 7 had type 2 diabetes. Prior to MCE, all subjects underwent a 64-slice coronary CT to exclude significant CAD. Rest and hyperhemic MBV and CFV were calculated from microbubble replenishment curves during real-time low mechanical index MCE and corrected for rate-pressure product.
Results. At rest, CFV and MBV were similar among controls and RFs. With dipyridamole, CFV increased in all subjects, albeit significantly more in controls (from 0.48 ± 0.19 s-1 to 1.54 ± 0.63 s-1) than RFs (from 0.5 ± 14 s-1 to 1.29 ± 0.39 s-1, p < 0.01), whereas MBV remained unchanged. In controls, MFR was inversely correlated with age (r=0.5). In RFs, MFR was signicantly less than in controls, and was independent of age.
Conclusions. Myocardial flow reserve, measured during dipyridamole MCE, is impaired in subjects with RFs. This impairment is independent of age and appears to be due to a decrease in maximal capilary flow velocity rather than to either capillary loss or capillary derecruitment.