Various physio- logic measurements can be made in the catheterization laboratory, including coronary flow reserve and FFR. The correlation of ischemia on stress testing with FFR values of 0.75 has been established in numerous comparative studies with high sensitivity (88%), specificity (100%), positive predictive value (100%), and overall accuracy (93%).487 The 5-year outcomes for patients with medical therapy based on an FFR 0.75 were superior compared with PCI in the DEFER (Deferral Versus Performance of Balloon Angio- plasty in Patients Without Documented Ischemia) study.485 The FAME (Fractional Flow Reserve Versus Angiography for Multivessel Evaluation) study identified the benefit for deferring PCI in patients with multivessel disease and lesion FFR 0.80, with reduced rates of cardiac events at both 1 and 2 years.97,486 Whereas both FFR and IVUS have been used for assessment of intermediate angiographic stenosis with favor- able outcomes, FFR may reduce the need for revasculariza- tion when compared with IVUS.488 Although IVUS is often considered in the assessment of equivocal left main stenosis, FFR may be similarly effective.484 5.4.2. IVUS: Recommendations Class IIa 1. IVUS is reasonable for the assessment of angio- graphically indeterminant left main CAD.489 491 (Level of Evidence: B) 2. IVUS and coronary angiography are reasonable 4 to 6 weeks and 1 year after cardiac transplantation to exclude donor CAD, detect rapidly progressive car- diac allograft vasculopathy, and provide prognostic information.492 494 (Level of Evidence: B) 3. IVUS is reasonable to determine the mechanism of stent restenosis.495 (Level of Evidence: C) Class IIb 1. IVUS may be reasonable for the assessment of non left main coronary arteries with angiographi- cally intermediate coronary stenoses (50% to 70% diameter stenosis).489,496,497 (Level of Evidence: B) 2. 