The decision to use a stent, a small mesh tube deployed to keep a blood vessel open, is a complex medical judgment in cases of Coronary Artery Disease (CAD). CAD involves the narrowing of the heart’s arteries due to plaque buildup, a process known as stenosis. While the percentage of blockage is a starting point, it is not the only factor determining the need for a percutaneous coronary intervention (PCI), the procedure to place a stent. The ultimate choice depends on a detailed assessment considering the physical severity of the narrowing, its functional impact on blood flow, and the patient’s clinical situation.
Methods for Determining Stenosis Severity
The initial method for visually assessing coronary artery narrowing is coronary angiography. During this invasive test, a contrast dye is injected into the arteries, and X-ray images are taken to map the vessels. This technique allows a cardiologist to estimate the percentage of diameter reduction caused by the atherosclerotic plaque.
However, angiography provides only a two-dimensional silhouette, which can lead to inaccuracies, especially with complex lesions. To gain a more precise measurement and characterize the plaque, supplementary tools are often used. Intravascular Ultrasound (IVUS) employs a miniature ultrasound probe to create cross-sectional images of the vessel wall and lumen. Optical Coherence Tomography (OCT) uses light waves to generate higher-resolution images, useful for assessing plaque composition and ensuring optimal stent placement.
Standard Anatomical Blockage Thresholds
Medical guidelines have established anatomical blockage percentages that trigger a recommendation for stenting in stable patients. For non-left main coronary arteries, a narrowing of 70% or greater is considered severe enough to warrant intervention, especially if the patient has symptoms like angina despite medical therapy. This threshold reflects the likelihood that a blockage of this magnitude will significantly restrict blood flow to the heart muscle.
The left main coronary artery is treated more aggressively because it supplies a large portion of the heart muscle. A blockage of 50% or more in this vessel is considered significant and meets the anatomical criteria for revascularization. For intermediate lesions, typically between 50% and 70%, the decision to intervene is rarely based on the visual percentage alone. In these moderate cases, the visual assessment must be supplemented with further testing to confirm if the lesion is flow-limiting.
Functional Assessment Beyond Percentage
Relying solely on a visual percentage can be misleading, as the functional impact varies widely between patients. The modern approach focuses on determining the functional significance of the blockage—whether it limits the supply of oxygenated blood to the heart muscle, a condition called ischemia. This assessment is particularly important for intermediate lesions where the visual assessment is ambiguous.
The standard for this functional assessment is Fractional Flow Reserve (FFR). This involves inserting a specialized pressure wire past the stenosis to measure the pressure difference across the blockage during maximum blood flow. An FFR value of 0.80 or less indicates that the stenosis is hemodynamically significant, meaning intervention is warranted. Instantaneous Wave-free Ratio (iFR) is a similar physiological measurement that assesses the pressure gradient without requiring hyperemic drugs. These tests provide an objective measure of the blockage’s impact, helping doctors defer unnecessary stenting when the anatomical percentage is high but the functional restriction is low.
Immediate Intervention in Acute Coronary Syndrome
In situations involving an Acute Coronary Syndrome (ACS), such as a heart attack (Myocardial Infarction), the standard anatomical thresholds and functional tests are often bypassed. ACS includes conditions like ST-elevation myocardial infarction (STEMI), where an artery is completely blocked by a clot, or high-risk non-ST-elevation myocardial infarction (NSTEMI). In these urgent scenarios, the life-saving procedure is immediate percutaneous coronary intervention (PCI), often referred to as primary PCI.
The goal is to rapidly restore blood flow to the heart muscle, and the procedure is performed immediately, regardless of the precise percentage of the underlying plaque. The intervention is driven by the evidence of an acute, unstable event, such as an occluded artery or a ruptured plaque that triggered a major clot formation. For the vessel responsible for the heart attack, intervention is immediate. If other non-critical arteries also show narrowing, treating those is often deferred until the patient is stable and a functional assessment can be performed.