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

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.

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) N-NH3 flow positron emission tomography study and a resting 2D echocardiogram before and 12 months after (eight patients) surgery. Myocardial blood flow reserve was defined as dipyridamole/resting mean myocardial blood flow ratio.

Before surgery, the transvalvular maximal pressure gradient was 86+/-19 mmHg, valve area 0.82+/-0.24 cm and left ventricular mass index 185+/-37 g/m. As compared with a positron emission tomography population of normal subjects, patients had a normal resting myocardial blood flow (1.02+/-0.34 vs. 1.04+/-0.22, not significant), a depressed dipyridamole myocardial blood flow (1.58+/-0.69 vs. 3.67+/-0.86, P<0.001) and myocardial blood flow reserve (1.54+/-0.39 vs. 3.63+/-0.97, P<0.001). After surgery, left ventricular mass index decreased (172+/-47 to 118+/-40, 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.

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.