Fig. 1.

Chronic total occlusion (CTO) anatomy versus physiology. Because invasive FFR cannot be measured in a CTO before intervention, a default value of 0.50 has been historically assumed. However, cardiac PET distinguishes among four distinct physiologic scenarios, as shown by the examples in which green arrows mark each CTO. Left: the CTO of the mid left anterior descending artery shows normal resting perfusion, indicating viable myocardium, but a large, severe defect during vasodilator stress that would be suitable for revascularization to improve angina. Center left: the CTO of the mid right coronary artery (RCA) has severely reduced resting perfusion but intact glucose metabolism, indicating hibernating myocardium appropriate for revascularization to restore ventricular function. Center right: the CTO of the mid left circumflex artery displays severe and matched reductions in resting perfusion and glucose uptake, indicating a transmural scar without benefit from revascularization. Right: the CTO of the mid RCA has normal resting perfusion, indicating viable myocardium, and only a small, mild defect during vasodilator stress due to robust collaterals from the left coronary artery that prevent ischemia