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It has been reported that hypertension can cause coronary microvascular dysfunction which was related with increased risk of death and cardiovascular event. Coronary flow reserve (CFR) was calculated as the ratio of hyperemic to rest absolute myocardial blood flow. In the absence of obstructive stenosis of the epicardial arteries, reduced CFR (CFR<3) is a marker of coronary microvascular dysfunction. The aim of this study is to investigate the effects of blood pressure on CFR in patients with hypertension.
We had retrospectively enrolled 236 patients without significant coronary stenosis (defined as <50% luminal narrowing which was confirmed by coronary angiography or coronary artery CT scan) between January 2011 to July 2015. CFR was measured in the left anterior descending coronary artery (LAD) during adenosine triphosphate-induced hyperemia by non-invasive transthoracic Doppler echocardiography. They were divided into hypertension group (n=173) and non-hypertension group (n=63). The hypertension patients were further divided into ideally controlled (n=31, defined as SBP <120 mmHg (1 mmHg=0.133 kPa) and DBP <80 mmHg), controlled (n=82, defined as SBP 120 to 139 mmHg and DBP <90 mmHg) and uncontrolled groups (n=60, defined as SBP≥140 mmHg and/or diastolic DBP≥90 mmHg) based on their blood pressure after systematic antihypertensive therapy. CFR was compared between different groups and univariate and multivariate eregression analyses were performed to identify the independent determinants of reduced CFR in hypertensive patients.
Coronary microvascular dysfunction (CFR<3) was found in 57.8% (100/173) hypertensive patients. Patients with coronary microvascular dysfunction were elder [(63.7±9.6) years vs.(57.7±8.3) years, P<0.001], present significant higher LVMI[(81.7±19.6) g/m2 vs. (74.7±14.8) g/m2, P=0.02] and lower DBP [(74.0±9.1) mmHg vs. (77.6±10.5) mmHg, P=0.02) than that of patients without coronary microvascular dysfunction. We found that higher systolic blood pressure (β= -0.12, P=0.02), age (β= -0.02, P=0.04) and diabetic mellitus as the underlying disease(β= -0.30, P=0.02) was independent predictor of impaired CFR in patients with hypertension. Compared with non-hypertension group, the CFR was significantly lower in controlled (3.27±0.71 vs. 2.87±0.56, p<0.001) and uncontrolled groups (3.27±0.71 vs. 2.61±0.71, P<0.001), but was similar in ideally controlled group (3.27±0.71vs. 3.21±0.85, P=0.68). Furthermore, the CFR was significantly lower in uncontrolled group than that of the other two hypertension groups and was significantly lower in controlled group than that of ideally controlled group.
Age, higher systolic blood pressure and diabetic mellitus as the underlying disease are independent predictors of decreased CFR in patients with hypertension without overt coronary artery stenosis. For hypertensive patients without significant coronary artery stenosis, therapeutically lowering blood pressure less than 120/80mmHg may be more benefical for improvement of CFR.