Does a demand-supply mismatch due to coronary artery disease require at least 70% luminal narrowing?

Coronary Artery Stenosis and Demand-Supply Mismatch

Yes, a demand-supply mismatch due to coronary artery disease typically requires at least 70% luminal narrowing in epicardial coronary arteries (non-left main), while left main coronary artery stenosis requires only ≥50% narrowing to cause significant ischemia. 1

Anatomical Thresholds for Hemodynamically Significant Stenosis

According to established guidelines, significant coronary stenosis is defined as:

• ≥70% luminal diameter narrowing for epicardial coronary arteries (non-left main vessels) 1
• ≥50% luminal diameter narrowing for the left main coronary artery 1, 2

These thresholds are based on the relationship between anatomical stenosis severity and physiological impact on coronary blood flow, which determines whether a demand-supply mismatch will occur.

Physiological Basis for These Thresholds

The 70% threshold for epicardial vessels is based on several key physiological principles:

• Coronary flow reserve begins to decrease significantly when luminal narrowing exceeds 70% 1
• Below 70% stenosis, compensatory mechanisms can often maintain adequate coronary flow during increased demand 1
• At 70% stenosis and above, the vessel's ability to increase flow during exercise or stress becomes significantly impaired 1

Prognostic Significance

The prognostic impact of stenosis varies by location and severity:

• Proximal LAD stenosis ≥70% carries particularly high prognostic significance with reduced 3-year survival (82% vs 94% for <70% stenosis) 3
• The CAD Prognostic Index demonstrates increasing mortality risk with increasing stenosis severity and number of affected vessels 1

Special Considerations

Left Main Disease

• Left main stenosis is considered significant at a lower threshold (≥50%) due to the large myocardial territory at risk 1, 4
• Even 50-69% left main stenosis can cause significant ischemia and carries important prognostic implications 4

Intermediate Stenosis (50-69%)

For non-left main stenosis in the 50-69% range:

• May not cause demand-supply mismatch at rest
• May cause ischemia during increased demand (exercise)
• Functional assessment with FFR is recommended to determine hemodynamic significance 1, 2

Clinical Correlation

The relationship between anatomical stenosis and functional ischemia is important:

• Stenosis ≥90% almost always causes ischemia (PPV 74%) 5
• Stenosis <50% rarely causes ischemia (NPV 97%) 5
• For stenosis between 50-89%, additional factors such as lesion length, serial stenoses, and vessel size influence whether demand-supply mismatch occurs 5

Pitfalls and Caveats

1. Visual assessment limitations: Angiographic assessment of stenosis severity is subject to inter-observer variability and may not accurately reflect the functional significance of a lesion 1

2. Multiple factors beyond percent stenosis: Lesion length, vessel size, presence of collaterals, and myocardial territory at risk all influence whether a given stenosis causes ischemia 1, 5

3. Serial stenoses: Multiple moderate stenoses in sequence can cause more significant flow limitation than a single stenosis of the same severity 5

4. Left main vs. other vessels: Different thresholds apply to left main (≥50%) versus other epicardial vessels (≥70%) 1, 2

In conclusion, while the 70% threshold for epicardial vessels (and 50% for left main) is well-established in guidelines, functional assessment with FFR may be necessary for intermediate stenoses to determine their true hemodynamic significance and guide appropriate treatment decisions.