The accumulation of fatty plaque within the heart’s arteries, known as atherosclerosis, can narrow the vessels and restrict blood flow to the cardiac muscle. This narrowing is medically termed stenosis. When this occurs, a coronary stent—a small mesh tube—is often deployed to mechanically prop the artery open and restore proper circulation. Because this procedure is invasive, doctors rely on specific measurements to determine if a blockage is severe enough to warrant intervention.
The Standard Percentage Criteria for Intervention
The decision to place a stent depends heavily on the anatomical percentage of the vessel that is blocked. This determination is separated into two major clinical scenarios: stable disease and acute emergency. For patients with stable angina (predictable chest pain during physical exertion), guidelines typically recommend stenting for blockages that reduce the artery’s diameter by 70% or more. This 70% threshold is the conventional standard for non-left main coronary arteries.
Blockages in the left main coronary artery are treated with a lower threshold because this vessel supplies blood to a large portion of the heart muscle. A stenosis of 50% or more generally meets the anatomical criteria for revascularization in this case. These percentage guidelines apply when patients have symptoms that persist despite medication. If a patient is experiencing an acute coronary syndrome, such as a heart attack, the unstable blockage requires immediate intervention, often regardless of the measured percentage.
Why Percentage Alone Is Insufficient
While the visual percentage of blockage is a strong initial indicator, it is not the sole determinant for stenting. A lesion that appears severe may not be restricting blood flow enough to cause damage. Symptoms like chest pain or shortness of breath are important factors that can override the strict percentage rule, especially for blockages between 50% and 70%. The location of the blockage also matters, as a 50% narrowing in a large artery can be more significant than a 70% blockage in a smaller vessel.
To determine the functional significance of a blockage, cardiologists utilize Fractional Flow Reserve (FFR). FFR is a pressure-based technique that measures the change in blood pressure across the narrowed segment of the artery. This test determines if the heart muscle downstream from the blockage is starving for oxygen. An FFR value of 0.80 or less is considered functionally significant, meaning the blockage is impeding blood flow enough to cause ischemia. If the FFR value is above 0.80, the lesion is treated with medication alone, even if the visual percentage is high, because blood flow is adequate. The Instantaneous Wave-Free Ratio (iFR) is an alternative measurement that achieves the same goal without requiring a specific drug to maximize blood flow, with a corresponding cutoff of 0.89.
How Blockage Severity Is Assessed
The initial visualization and measurement of a coronary blockage are performed using Coronary Angiography. This procedure involves injecting a contrast dye into the coronary arteries and using X-ray imaging to capture the vessel structure. Angiography provides a two-dimensional view, allowing the physician to estimate the degree of stenosis by comparing the narrowed section to a healthier segment of the vessel.
For a more precise anatomical measurement or to guide the stenting procedure, advanced imaging tools are employed. These internal imaging methods provide a detailed view that helps confirm the percentage found via angiography and ensures the stent is correctly sized and placed.
Intravascular Ultrasound (IVUS)
IVUS uses a catheter-based probe that emits high-frequency sound waves to create a cross-sectional image of the artery wall and lumen.
Optical Coherence Tomography (OCT)
OCT uses near-infrared light to produce high-resolution images, offering superior detail for measuring the exact dimensions of the blockage and optimizing stent deployment.