Imaging and Physiologic Lesion Assessment
Core concepts
Know IVUS and OCT: IVUS for vessel sizing, plaque burden, and left main assessment; OCT for high-resolution surface detail, stent strut coverage, and thrombus characterization. Understand physiology: FFR (hyperemic, ≤0.80), iFR (resting, ≤0.89), and their limitations (microvascular disease, serial lesions). Know quantitative coronary angiography (QCA) and its limits. Master intravascular imaging-guided PCI benefits (larger stent area, fewer complications). Understand CT coronary angiography for anatomy and its role in stable chest pain. Know when imaging changes management: left main, bifurcations, in-stent restenosis, and ambiguous lesions.
Traps
- Using FFR in acute STEMI culprit lesions (not validated acutely).
- Missing that iFR avoids adenosine but has different thresholds.
- Overlooking that OCT requires contrast clearance and cannot assess ostial lesions well.
- Confusing plaque burden with lumen area in IVUS interpretation.
- Forgetting that CT angiography is anatomic, not physiologic.
Rule of thumb
Use FFR/iFR for intermediate lesions (40–70%) to decide PCI. Use IVUS/OCT for left main, complex bifurcations, and stent optimization. FFR ≤0.80 = ischemic; iFR ≤0.89 = ischemic.
Worked example
A 55% left main lesion is assessed by IVUS showing minimal lumen area 5.5 mm². This supports revascularization even though angiography looked moderate.