Detection of coronary stenoses at rest with myocardial contrast echocardiography

Background - We hypothesized that autoregulatory changes in arteriolar blood volume (aBV) that develop distal to a stenosis can be measured with myocardial contrast echocardiography, allowing coronary stenosis detection at rest without recourse to stress. Methods and Results - Patients with varying degrees of coronary artery stenosis on quantitative angiography underwent high-mechanical-index myocardial contrast echocardiography at 15 Hz to allow measurement of phasic changes in aBV in large intramyocardial vessels using either Definity (group 1; n=22) or Imagent (group 2; n=22). Progressive increases in the background-subtracted systolic/diastolic aBV signal ratio were noted between each level (none, mild [<50%], moderate [50% to 75%], and severe [>75%]) of stenosis severity for both group 1 (0.09±0.13, 0.13±0.08, 0.58±0.22, and 0.77±0.40; P<0.001) and group 2 (0.10±0.05, 0.27±0.18, 0.39±0.28, and 0.74±0.37; P<0.0001) patients. A systolic/diastolic aBV signal ratio of >0.34 provided a sensitivity and specificity of 80% and 71%, respectively, for the detection of >75% coronary stenosis in group 1 patients, whereas a ratio of >0.43 provided a sensitivity and specificity of 89% and 74%, respectively, for the detection of >75% stenosis in group 2 patients. Conclusions - Both the presence and severity of a physiologically significant coronary stenosis can be detected at rest by measuring the increase in aBV on myocardial contrast echocardiography that occurs distally to the stenosis without recourse to any form of stress.