What percentage of angiographic stenosis in a main coronary artery, in a patient with suspected or known coronary artery disease (CAD), would prompt consideration for intervention?

Significant Angiographic Stenosis Thresholds for Main Coronary Arteries

For left main coronary artery disease, ≥50% stenosis is considered significant and warrants intervention consideration, while for non-left main coronary arteries, ≥70% stenosis (or ≥50% with FFR ≤0.80) is the threshold for significant obstructive disease. 1

Left Main Coronary Artery

The threshold is ≥50% diameter stenosis:

• CABG is a Class I recommendation (highest level) to improve survival in patients with ≥50% left main stenosis 1
• PCI is reasonable (Class IIa) as an alternative to CABG in selected stable patients with ≥50% left main stenosis who have favorable anatomy (low SYNTAX score <22) and increased surgical risk 1
• This 50% threshold for left main disease is consistently applied across both the 2011 ACC/AHA/SCAI guidelines and the CAD-RADS reporting systems 1

Non-Left Main Coronary Arteries

The threshold is ≥70% diameter stenosis for anatomic significance:

• CABG improves survival in patients with ≥70% stenosis in three major coronary arteries or in the proximal LAD plus one other major vessel 1
• For symptomatic patients, revascularization (CABG or PCI) is Class I indicated for ≥70% stenosis with unacceptable angina despite guideline-directed medical therapy 1
• The CAD-RADS classification system defines severe stenosis as 70-99% diameter narrowing, which triggers consideration for invasive angiography or functional testing 1

The Critical 50-70% "Gray Zone"

Stenoses of 50-69% require functional assessment rather than anatomic criteria alone:

• The 2021 AHA/ACC chest pain guidelines classify 50-69% stenosis as "moderate" and recommend functional testing (FFR-CT, stress imaging) or invasive FFR to determine hemodynamic significance 1
• Research demonstrates that only 35% of angiographic stenoses in the 50-70% range are functionally significant (FFR ≤0.80), while 65% are not 2
• Even in the 71-90% category, 20% of lesions are not functionally significant, highlighting the limitations of visual angiographic assessment alone 2

Physiologic Definition of Significance

FFR ≤0.80 defines hemodynamically significant stenosis regardless of angiographic appearance:

• The ACC/AHA guidelines explicitly state that significant stenosis is defined as either >50% left main or >70% non-left main OR FFR <0.80 1
• This physiologic threshold takes precedence over visual estimation, particularly for intermediate lesions 1, 2

Clinical Context Matters

The 2021 guidelines distinguish between obstructive (≥50%) and nonobstructive (<50%) CAD for risk stratification:

• Patients with ≥50% stenosis on CCTA are directed toward invasive angiography or functional testing pathways 1
• Those with <50% stenosis are considered to have nonobstructive CAD and may be managed with intensified medical therapy alone 1
• For acute chest pain presentations, stenosis of 40-90% in proximal or mid-segments warrants FFR-CT evaluation to guide revascularization decisions 1

Common Pitfalls to Avoid

• Do not rely solely on visual angiographic estimation: Even experienced operators show significant variability, and 20% of 71-90% stenoses are not functionally significant 2
• Do not treat all 50-69% stenoses the same: These require individualized functional assessment rather than automatic intervention 1, 2
• Do not forget the left main exception: The 50% threshold for left main is lower than other vessels due to the large territory at risk 1
• Do not ignore three-vessel disease: Even if individual vessels are 50-69%, the presence of three-vessel obstructive disease (≥70% in all three) changes management to favor CABG 1