The iFRCT study is a prospective, multicenter study to evaluate the diagnostic performance of iFRCT with the use of ≥64-detector row CT scanners for the detection and exclusion of significant obstructive coronary artery disease, defined by invasive fractiona flow reserve (FFR) as the reference standard.

Noninvasive fractional flow reserve (FFR) computed from CT (FFRCT) is a novel method for determining the physiologic significance of coronary artery disease (CAD), and several clinical trials have revealed that the FFRCT has a good correlation with invasive FFR, also use of noninvasive FFRCT plus Computed Tomography (CT ) among stable patients with suspected or known CAD was associated with improved diagnostic accuracy and discrimination vs CT alone for the diagnosis of hemodynamically significant CAD.

The cornerstone of FFR is the linear relationship between pressure and flow under conditions of constant (and minimized) intracoronary resistance, so is FFRCT. Under such conditions, pressure and flow are assumed to be directly proportional, and a decrease in pressure across a stenosis reflects a decrease in blood flow to the dependent myocardium. However, even after administration of potent pharmacologic agents such as adenosine, intracoronary resistance is not static, but instead fluctuates in a phasic pattern throughout the cardiac cycle. In addition, for patients who are allergic to pharmacologic agents or with sever lesions which response little to pharmacologic agents, the measurement of FFR is challenging and the lesion are always underestimated. The ADVISE trial revealed that intracoronary resistance is naturally constant and minimized during the wave-free period. The instantaneous wave-free ratio calculated over this period produces a drug-free index of stenosis severity comparable to FFR. But whether iFR calculated from Computed Tomography(iFRCT) is comparable to FFRCT or FFR, and its diagnostic performance remains unknown. Thus the investigators conduct this trial to assess the diagnostic performance of Instantaneous Wave-Free Ratio for diagnosis of hemodynamically significant coronary stenosis.

Instantaneous Wave-Free Ratio calculated from reconstructed heart model.Wave-intensity analysis identified a wave-free period in which intracoronary resistance at rest is similar in variability and magnitude.The investigators define the resting distal-to-proximal pressure ratio during this period as the instantaneous wave-free ratio (iFR).

Inclusion Criteria:

• Coronary computed tomographic angiography(CCTA) with over 50 percent stenosis in a major coronary artery over 2mm diameter
• Undergoing clinically indicated invasive coronary angiography with FFR

Exclusion Criteria:

• A history of CABG surgery
• Prior percutaneous coronary intervention with suspected instent restenosis
• Suspicion of or recent acute coronary syndrome
• Complex congenital heart disease
• Prior pacemaker or defibrillator
• Prosthetic heart valve
• Significant arrhythmia
• heart rate >100 beats/min
• systolic blood pressure≤90 mmHg
• contraindication to beta blockers, nitroglycerin or adenosine
• Serum creatinine level greater than 1.5 mg per dL
• Allergy to iodinated contrast
• Pregnant state
• Body mass index greater than 35
• Evidence of active clinical instability or lifethreatening disease
• Canadian Cardiovascular Society class IV angina
• nonevaluable CCTA as determined by the CCTA core laboratory
• Inability to adhere to study procedures