Objectives: We sought to assess the intra- and extra-vascular mechanisms of myocardial perfusion impairment in patients with hypertrophic cardiomyopathy (HCM) by real-time myocardial contrast echocardiography (MCE) and positron emission tomography (PET).
Methods: Fourteen patients with obstructive HCM (mean age 53 ± 10 years, 11 men) underwent intravenous adenosine MCE, PET and cardiac catheterization. Fourteen healthy volunteers (mean age 31 ± 4 years, 11 men) served as a control group. The relative myocardial blood volume (rBV), its exchange flow velocity (β), myocardial blood flow (MBF), its reserve (MFR) and the endocardial-to-subepicardial (endo-to-epi) MBF ratio were measured from the steady state and replenishment time-intensity curves of the ultrasound contrast agents.
Results: HCM patients had lower values of rest MBF (for LVRPP-corrected) with MCE (0.92 ± 0.12 vs. 1.13 ± 0.25 ml.min-1.g-1, P <0.01) compared to healthy controls. Hyperaemic MBF were also lower (2.56 ± 0.49 vs. 4.34 ± 0.78 ml.min-1.g-1, P <0.01) resulting in lower MFR (2.80 ± 0.62 vs. 3.95 ± 0.77, P <0.01) compared to healthy controls. At rest, mean rBV was lower in HCM patients (0.094 ± 0.016 vs. 0.138 ± 0.014 ml.ml-1), and during hyperaemia (0.104 ± 0.018 ml.ml-1 vs. 0.185 ± 0.024 ml.ml-1) (all P <0.001) as compared to healthy controls. β tended to be higher in HCM at rest (9.4 ± 4.6 vs. 7.7 ± 4.2 ml.min-1) and hyperaemia (25.8 ± 6.4 vs. 23.1 ± 6.2 ml.min-1) as compared to healthy controls. Endo-to-epi MBF decreased during hyperaemia (0.86 ± 0.15 to 0.64 ± 0.18, P <0.01) in the septum and (0.92 ± 0.19 to 0.77 ± 0.23, P <0.01) in the lateral wall. The rBV was inversely correlated to left ventricular (LV) mass index (P <0.05). Hyperaemic and endo-to-epi MBF were inversely correlated with LV end-diastolic pressure, LV mass index, and LV outflow tract pressure gradient (all P <0.05). MCE-derived MBF correlated well with PET at rest (r =0.84) and hyperaemia (r =0.87), (all P <0.001).
Conclusions: In HCM patients, the blunted hyperaemic perfusion and MFR are due to exhausted autoregulation of myocardial microcirculation as well extravascular compression forces. LV end-diastolic pressure, LV outflow tract pressure gradient, and LV mass index are independent predictors of rBV and hyperaemic MBF. These findings may have important practical implications for the understanding and follow-up of patients with HCM and can be measured accurately with MCE.
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