Coronary artery disease occurs when the arteries supplying blood to the heart muscle become narrowed or blocked, a condition known as stenosis, typically due to the buildup of fatty deposits called plaque. This narrowing can restrict blood flow and oxygen delivery to the heart, leading to symptoms like chest pain or even a heart attack. To restore proper circulation, physicians may recommend placing a stent, which is a small, mesh-like tube permanently inserted into the artery to hold the passageway open and improve blood flow. The decision to use a stent depends on a careful assessment that goes beyond a simple visual check of the blockage.
Quantifying Coronary Artery Stenosis
Doctors determine the severity of an artery blockage, or stenosis, by measuring the reduction in the vessel’s diameter. This measurement is expressed as a percentage, indicating how much of the original artery opening has been closed off by plaque buildup. Assessment is frequently performed using a coronary angiogram, where a special dye is injected into the arteries, allowing them to be visualized under X-ray imaging.
The angiogram provides a visual estimate of the narrowing. More advanced techniques, such as Intravascular Ultrasound (IVUS) or Optical Coherence Tomography (OCT), can also be used during the procedure to gain a detailed cross-sectional view of the artery and plaque. These precise imaging tools help confirm the percentage of blockage and guide the treatment strategy.
Anatomical Thresholds for Stent Placement
The percentage of physical narrowing serves as the initial anatomical guideline for considering a stent procedure. For patients with stable symptoms, such as predictable chest pain, the standard threshold for intervention in a major non-left main coronary artery is a blockage of 70% or greater. This degree of narrowing is severe enough to significantly impair blood flow and cause symptoms.
A lower threshold applies to blockages in the left main coronary artery, which supplies most of the heart muscle. Because of its importance, a narrowing of 50% or more in this location is considered significant and often prompts revascularization. This is frequently achieved with bypass surgery, though stenting may be an option for selected patients. In the context of an acute coronary syndrome, such as a heart attack, stenting is typically performed urgently on the affected vessel regardless of the initial percentage, as the goal is immediate restoration of blood flow.
Functional Assessment and Symptom Influence
The ultimate decision to place a stent relies heavily on the functional impact of the blockage on blood flow, not just the anatomical percentage. A blockage appearing moderate (50% to 70%) may not require a stent if it is not significantly reducing blood delivery to the heart muscle. However, the presence of unacceptable symptoms, such as chest pain (angina) despite medical therapy, is a primary driver for intervention, even with a borderline blockage.
To measure the physiological significance of a moderate blockage, doctors use tools like Fractional Flow Reserve (FFR) or Instantaneous Wave-free Ratio (iFR). These techniques involve inserting a specialized pressure wire across the stenosis to measure the pressure drop and blood flow. An FFR value of 0.80 or less, or a comparable iFR measurement, indicates that the blockage is functionally significant and causing insufficient blood flow, supporting the need for a stent.
A non-invasive stress test, such as an exercise electrocardiogram or a nuclear scan, can also demonstrate if a blockage limits blood flow. If the heart muscle shows signs of oxygen deprivation during physical exertion, it indicates the artery cannot supply enough blood when demand increases. This suggests a stent may be necessary to improve the patient’s quality of life and reduce symptoms.
Treatment When a Stent Is Not Required
For blockages that do not meet the anatomical or functional criteria for stenting (e.g., narrowing less than 70% without severe functional limitation), the primary strategy is aggressive medical management. This approach focuses on preventing disease progression and stabilizing existing plaque. Medications such as statins are prescribed to lower cholesterol, along with blood pressure medications and antiplatelet drugs like aspirin, to reduce the risk of a heart attack.
Intensive lifestyle modification, including dietary changes and regular exercise, is also a significant component of the treatment plan. For patients with severe or widespread disease involving multiple vessels or complex anatomy, an alternative surgical procedure called Coronary Artery Bypass Grafting (CABG) may be recommended. CABG creates new pathways for blood flow around the blockages using healthy vessels, and it is often preferred over stenting in these complex cases.