Stress Myocardial Blood Flow Ratio by Dynamic CT Perfusion Identifies Hemodynamically Significant CAD

Objectives: The aim of this study was to evaluate the diagnostic accuracy of stress myocardial blood flow ratio (SFR), a novel parameter derived from stress dynamic computed tomographic perfusion (CTP), for the detection of hemodynamically significant coronary stenosis.

Background: A comprehensive cardiac computed tomographic protocol combining coronary computed tomographic angiography (CTA) and CTP can provide a simultaneous assessment of both coronary artery anatomy and ischemia.

Methods: Patients with chest pain scheduled for invasive angiography were prospectively enrolled in this study. Stress dynamic CTP was performed followed by coronary CTA using a second-generation dual-source computed tomographic system. At subsequent invasive angiography, fractional flow reserve was performed to identify hemodynamically significant stenosis. For each coronary territory, SFR was defined as the ratio of hyperemic myocardial blood flow (MBF) in an artery with stenosis to hyperemic MBF in a nondiseased artery. The diagnostic accuracy of SFR to identify hemodynamically significant stenosis was determined against the reference standard of invasive fractional flow reserve ≤0.80.

Results: A total of 82 patients (mean age 58.5 ± 10 years) with 101 vessels with either 1- or 2-vessel disease were included. By FFR, 48 (47.5%) vessels were deemed hemodynamically significant. Hyperemic MBF and SFR were lower for vessels with hemodynamically significant lesions (95.1 ± 32.4 ml/100 ml/min vs. 142.5 ± 31.2 ml/100 ml/min and 0.66 ± 0.14 vs. 0.90 ± 0.07, respectively; p < 0.01 for both). When compared with ≥50% stenosis by CTA, the specificity for detecting ischemia by SFR increased from 43% to 91%, while the sensitivity decreased from 95% to 62%. Accordingly, the positive and negative predictive values were 85% and 73%, respectively. The combination of stenosis ≥50% by CTA and SFR resulted in an area under the curve of 0.91, which was significantly higher compared with hyperemic MBF (area under the curve = 0.79; p = 0.013).

Conclusions: Calculation of SFR by dynamic CTP provides a novel and accurate method to identify flow-limiting coronary stenosis.