How can coronary flow reserve be altered by severe aortic stenosis?

The coronary flow reserve, a well-known characteristic of the distensibility of the coronary arteries, can be measured by means of dipyridamole stress transesophageal echocardiography. This study compared the coronary flow reserve in patients with normal coronary arteries with aortic stenosis (Group 1), in patients with normal coronary arteries without aortic stenosis (Group 2), and in patients with significant left anterior descending coronary artery disease (Group 3).

Groups 1 and 2 were comprised of 21 patients each, while Group 3 was comprised of 37 patients. Transesophageal stress echocardiography was carried out according to a standard protocol, with a vasodilator stimulus of dipyridamole in a dose of 0.56 mg/kg over 4 minutes. The coronary flow reserve was calculated as the ratio of posthyperemic to basal peak (CFR) and mean (mean CFR) diastolic flow velocities.

The left ventricular mass and left ventricular mass index were significantly higher in Group 1 than in Groups 2 and 3. The coronary flow reserve and the posthyperemic mean diastolic flow velocities were significantly lower, while the resting mean diastolic flow velocities were significantly higher in Groups 1 and 3 than in Group 2.

In patients with aortic stenosis and a normal coronary angiogram, the coronary flow reserve is significantly lower, similarly as in the case of significant left anterior descending coronary artery disease. In severe aortic stenosis with left ventricular hypertrophy, stress transesophageal echocardiography is unable to distinguish between the drop in coronary flow reserve caused by a vascular or a myocardial component, and therefore, not suitable for the selection of patients with significant coronary artery disease, even in cases of left anterior descending coronary artery disease.