Knowledge of Hyperemic Myocardial Blood Flow in Healthy Subjects Helps Identify Myocardial Ischemia in Patients With Coronary Artery Disease

BackgroundsDynamic CT myocardial perfusion imaging (CT-MPI) allows absolute quantification of myocardial blood flow (MBF). Although appealing, CT-MPI has not yet been widely applied in clinical practice, partly due to our relatively limited knowledge of CT-MPI. Knowledge of distribution and variability of MBF in healthy subjects helps in recognition of physiological and pathological states of coronary artery disease (CAD). ObjectivesTo describe the distribution and normal range of hyperemic MBF in healthy subjects obtained by dynamic CT-MPI and validate whether it can accurately identify functional myocardial ischemia when the cut-off value of hyperemia MBF is set to the lower limit of the normal range. Materials and MethodsFifty-one healthy volunteers (age, 38 +/- 12 years; 15 men) were prospectively recruited. Eighty patients (age, 58 +/- 10 years; 55 men) with suspected or known CAD who underwent interventional coronary angiography (ICA) examinations were retrospectively recruited. Comprehensive CCTA + dynamic CT-MPI protocol was performed by the third - generation dual-source CT scanner. Invasive fractional flow reserve (FFR) measurements were performed in vessels with 30-90% diameter reduction. ICA/FFR was used as the reference standard for diagnosing functional ischemia. The normal range for the hyperemic MBF were defined as the mean +/- 1.96 SD. The cut-off value of hyperemic MBF was set to the lower limit of the normal range. ResultsThe global hyperemic MBF were 164 +/- 24 ml/100 ml/min and 123 +/- 26 ml/100 ml/min for healthy participants and patients. The normal range of the hyperemic MBF was 116-211 ml/100 ml/min. Of vessels with an ICA/FFR result (n = 198), 67 (34%) were functionally significant. In the per-vessel analysis, an MBF cutoff value of <116 ml/100 ml/min can identify myocardial ischemia with a diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of 85.9% (170/198), 91.0% (61/67), 83.2 % (109/131), 73.5% (61/83), and 94.8% (109/115). CT-MPI showed good consistency with ICA/FFR in diagnosing functional ischemia, with a Cohen's kappa statistic of 0.7016 (95%CI, 0.6009 - 0.8023). ConclusionRecognizing hyperemic MBF in healthy subjects helps better understand myocardial ischemia in CAD patients.