Background: Hypertensive patients show a blunted coronary flow reserve (CFR) that, in the absence of epicardial disease, is an index of microvascular dysfunction. We aimed at assessing subendocardial and subepicardial myocardial blood flow (MBF) and CFR using high-resolution PET and determine the influence of haemodynamic load and ventricular mass in patients with arterial hypertension and left ventricular hypertrophy.
Methods: We measured MBF (ml/min per g) using PET with oxygen-15 labelled water. Thirty patients (56 ± 8 years, 21 men) with stage 1-2 hypertension in therapy wash-out, except for thiazides, and 10 healthy volunteers were studied at baseline and during dipyridamole-induced hyperaemia (0.56 mg/kg over 4 min). Data are mean ± SD.
Results: In patients, left ventricular mass index was 144 ± 40 g/m² and septal thickness 14.8 ± 1.9 mm. Baseline MBF was similar in patients and healthy volunteers in subendocardial (ENDO) (P = 0.08) and subepicardial (EPI) (P = 0.5), but patients had significantly lower hyperaemic MBF-EPI and MBF-ENDO (P < 0.001) and significantly lower CFR (EPI P < 0.001; ENDO P = 0.003). In patients, the degree of impairment of CFR-EPI (R = 0.52, P = 0.003) and CFR-ENDO (R = 0.51, P = 0.004) was inversely related to SBP, but not to left ventricular mass index.
Conclusion: In patients with stage 1-2 hypertension and left ventricular hypertrophy, CFR is transmurally blunted due to a reduced hyperaemic response to stress, which is inversely related to SBP. In the absence of coronary stenosis, this phenomenon is most likely the expression of severe coronary microvascular dysfunction.