Coronary flow reserve in severe aortic valve stenosis: a positron emission tomography study

Objectives The purpose was to test whether, in patients with severe aortic stenosis, impaired myocardial blood flow reserve is dependent on myocardial hypertrophy and may improve after valve replacement. Methods Fifteen patients with severe aortic stenosis, normal coronary arteries and normal left ventricular systolic function (ejection fraction >50%) underwent a resting/ dipyridamole (0.56 mg/kg over 4 min) 13N-NH3 flow positron emission tomography study and a resting 2D-Echo before and 12 months after (eight patients) surgery. Myocardial blood flow reserve was defined as dipyridamole/resting mean myocardial blood flow ratio. Results Before surgery, the transvalvular maximal pressure gradient was 86W19mmHg, valve area 0.82W0.24cm2 and left ventricular mass index 185W37 g/m2. As compared with a positron emission tomography population of normal subjects, patients had a normal resting myocardial blood flow (1.02W0.34 vs. 1.04W0.22, not significant), a depressed dipyridamole myocardial blood flow (1.58W0.69 vs. 3.67W0.86, P<0.001) and myocardial blood flow reserve (1.54W0.39 vs. 3.63W0.97, P<0.001). After surgery, left ventricular mass index decreased (172W47 to 118W40, P<0.01) but no change was found in resting myocardial blood flow, dipyridamole myocardial blood flow and myocardial blood flow reserve. There was no correlation between flow values and pressure gradient or left ventricular mass index, before or after valve replacement and in pooled data from the two studies. Conclusion In severe aortic stenosis, myocardial blood flow reserve is depressed independent of myocardial hypertrophy and transvalvular pressure gradient. Removal of pressure overload by valve replacement is not able to improve myocardial perfusion.