Detection of noncritical coronary stenosis at rest without recourse to exercise or pharmacological stress

Background - Currently, the detection of noncritical coronary stenoses requires some form of stress. We hypothesized that these stenoses can be detected at rest without recourse to stress by assessing adaptive changes that occur distally in the microcirculation. Methods and Results - Phasic changes in myocardial video intensity (VI) were measured at rest with continuous high-mechanical-index (MI) contrast echocardiography in 15 open-chest dogs. Data were acquired at baseline and in the presence of different degrees of noncritical coronary stenosis. In 6 of these dogs, capillary blood volume was also measured at baseline using high-MI intermittent imaging with triggering performed separately at both end diastole and end systole. During continuous high-MI imaging, a significant increase in systolic VI was noted with coronary stenoses that resulted in progressive increases in the systolic/diastolic VI ratio with greater degrees of stenosis (P=0.003), with a mildly quadratic relation noted between the two: y=1.3 · 10⁶·×²+0.01×+0.32, P<0.001, r=0.76, SEE=0.14. There was no difference in capillary blood volume between end diastole and end systole at baseline. Conclusions - Capillary blood volume does not change between diastole and systole in vivo. Phasic changes in VI are noted at baseline during high-MI continuous imaging. The systolic component is negligible at baseline but increases with increasing levels of noncritical coronary stenosis because of adaptive changes in the microcirculation distal to the stenosis. Thus, the measurement of phasic changes in myocardial VI has the potential to detect coronary stenosis at rest without recourse to any form of stress.