Measurement of aortic blood flow by magnetic resonance below and above the origin of the coronary arteries in postmenopausal hormone replacement therapy.

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Principal blood flow measures might be assessable by velocity-encoded cine magnetic resonance (VENC MR) of aortic blood flow. The feasibility of using VENC MR for clinical research was tested in a contemporary and controversial human model: the effects of 17beta-estradiol (E) and cyclic norethisterone acetate (NETA) in postmenopausal women. Sixteen postmenopausal women were included in a crossover study (two 12-week periods, 3-month washout) and randomized to E and NETA or placebo. Aortic blood flow (ABF) was measured eight times by VENC MR below and above the coronary arteries (CA) and was used for estimation of coronary artery blood flow (CABF) and peak flow velocity (Vmax). The calculated value of CABF was negative and was corrected by averaging systolic flow. Data were analyzed in a repeated measurement model including analysis of repeatability (CR) and group variability (CV). The CR and CV of ABF were low (11% and 7%) and corresponded at the two levels. Vmax showed similar levels of reproducibility at the two levels. The coronary artery blood flow was less reproducible (39% and 31%). During treatment, ABF above CA was reduced after 12 weeks (p=0.03), ABF below CA was unchanged, and CABF was significantly increased without detrimental effects of NETA. Vmax was increased at NETA addition (p<0.01). Aortic flow quantification by VENC MR is reproducible and useful for assessment of principal haemodynamic changes in smaller studies. Derived measurement of CABF lacks precision. Differences in change below and above CA indicate that oral high-dose E and NETA may induce coronary artery dilatation.