Abstract 2343: Decreased Myocardial Blood Flow During Hyperemia Is Due to the Reduction of Myocardial Blood Volume in Patients with Hypertrophic Cardiomyopathy
Background: It has been reported that myocardial blood flow (MBF) per unit time is preserved normal at rest but decreased during hyperemia in patients with hypertrophic cardiomyopathy (HCM). However, it remains to be determined whether reduced myocardial blood volume (MBV) or impaired blood velocity within the microcirculation is responsible for this phenomenon.
Methods: In 22 HCM patients (H) with asymmetric septal hypertrophy and 15 normal volunteers (N), myocardial contrast echocardiography (MCE) was performed at rest and during hyperemia induced by ATP under continuous infusion of Levovist. On harmonic power Doppler images acquired at end-diastole of every 6 beat, relative contrast intensity (RelCI, subtraction of contrast intensity [dB] in the adjacent blood pool from that in the myocardium) was measured in the interventricular septum (IVS). MBV [%] was derived as 10RelCI/10×100. In 13 out of H and 9 out of N, 15O-water PET was performed to measure MBF in the IVS. Intramyocardial blood velocity was calculated as β [sec-1] (MBF/MBV).
Results: At rest, MBF in H was preserved normal, whereas MBV was significantly lower and β was significantly greater than those in N (Table⇓). During hyperemia, β did not differ between N and H, whereas MBF and MBV were significantly lower in H than those in N. Among 22 subjects who underwent both MCE and PET, MBF during hyperemia significantly correlated with MBV (r=0.74, p<0.0001), but not with β(r=0.06, p=0.78).
Conclusions: MBV is reduced in the hypertrophied IVS of HCM patients. MBF is preserved normal at rest due to an increase in the intramyocardial blood velocity as a compensatory mechanism for the decreased MBV. During hyperemia, however, this mechanism can no longer fully compensate for the reduction of MBV, resulting in a substantial decrease in MBF.