Absolute flow or myocardial flow reserve for the detection of significant coronary artery disease?

OBJECTIVES We compared the accuracy of quantified myocardial flow reserve and absolute stress myocardial blood flow (MBF) alone in the detection of coronary artery disease (CAD). BACKGROUND Myocardial flow reserve, i.e. ratio of stress and rest flow, has been commonly used to detect CAD with many imaging modalities. However, it is not known whether absolute stress flow alone is sufficient for detection of significant CAD. METHODS We enrolled 104 patients with moderate (30-70%) pre-test likelihood of CAD without previous myocardial infarction. MBF was measured by positron emission tomography and O-15-water at rest and during the adenosine stress in the regions of the left anterior descending, left circumflex, and right coronary artery. All the patients underwent invasive coronary angiography including the measurement of fractional flow reserve when appropriate. RESULTS Quantified myocardial flow reserve (optimal cut-off value 2.5) detected significant coronary stenosis with sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 81, 87, 66 and 94%, respectively. When compared with flow reserve, absolute MBF at stress (optimal cut-off value of 2.4 mL/min/g) was more accurate in detecting significant coronary stenosis [area under the curve (AUC) 0.94 vs. 0.90, P = 0.02] with sensitivity, specificity, PPV, and NPV of 95% (P = 0.03 vs. flow reserve), 90, 73, and 98%, respectively. An absolute increase of MBF from rest to stress by <1.5 mL/g/min had also similar accuracy in detecting CAD (AUC: 0.95). The results were comparable in patients who did and did not receive i.v. beta-blockers prior imaging. CONCLUSIONS Absolute stress perfusion alone was superior to perfusion reserve in the detection of haemodynamically significant CAD and allows shorter imaging protocols with smaller radiation dose.