Coronary Artery Disease (CAD) occurs when the coronary arteries become narrowed due to atherosclerotic plaque buildup. This restriction of blood flow to the heart muscle can cause chest pain or a heart attack. Traditionally, diagnosing the location and severity of these narrowings requires invasive coronary angiography, which uses a catheter and injected dye. Because angiography carries risks, discomfort, and high costs, there is a strong demand for effective non-invasive methods to assess blockages.
Initial Screening and Risk Assessment
The initial process for checking for heart blockages starts with evaluating an individual’s medical history and known risk factors. Conditions such as high blood pressure, diabetes, high cholesterol, and a history of smoking strongly suggest underlying CAD. This information helps determine the pre-test probability of disease, which guides the selection of subsequent diagnostic tests.
An Electrocardiogram (ECG or EKG) is an accessible and inexpensive initial test that records the heart’s electrical activity. A resting ECG can show signs of a prior heart attack or suggest increased strain on the heart muscle. However, a normal resting ECG does not rule out significant blockages, as the heart’s electrical activity may appear normal even with narrowed arteries.
Blood tests provide insight into biological markers associated with cardiovascular risk and inflammation. A standard lipid panel measures cholesterol levels, while high-sensitivity C-reactive protein (hs-CRP) provides prognostic data. Hs-CRP is a marker of systemic inflammation; elevated levels suggest an unstable atherosclerotic process.
High-sensitivity Troponin (hs-cTn) is another biomarker used to assess the likelihood of structural heart damage, even in stable patients. Although traditionally used to diagnose a heart attack, slightly elevated hs-cTn levels are associated with adverse outcomes. Using both hs-CRP and hs-cTn offers a comprehensive picture of a patient’s risk profile, helping identify those who require further investigation.
Structural Visualization of Arteries
Non-invasive imaging techniques provide an anatomical picture of the coronary arteries and the plaque within their walls. These methods directly visualize the extent of the disease, rather than inferring its presence from risk factors or electrical signals.
Coronary Artery Calcium (CAC) Scoring is a low-dose, non-contrast Computed Tomography (CT) scan. It measures the amount of calcified plaque in the coronary arteries, resulting in an Agatston score. A score of zero indicates a very low risk of a cardiac event. Conversely, a score greater than 300 suggests a high burden of atherosclerosis and increased risk.
The CAC score quantifies the total disease present but does not show if a blockage restricts blood flow. For this assessment, Coronary CT Angiography (CTA) is used, requiring the injection of an iodinated contrast dye. The contrast allows the CT scanner to create detailed, three-dimensional images of the arterial lumen and the vessel wall.
CTA accurately detects and measures the degree of narrowing (stenosis) caused by both calcified and non-calcified plaque. While useful for planning management, the test is limited by heavy calcification. Excessive calcium creates a “blooming artifact,” which can visually overestimate the degree of plaque and resulting stenosis.
Functional Testing of Blood Flow
The goal of functional testing is to determine if an anatomical narrowing is severe enough to impede oxygenated blood delivery, a condition called ischemia. This assessment subjects the heart to controlled stress, induced either physiologically through exercise or pharmacologically using medications.
Stress Echocardiography uses ultrasound to visualize heart muscle movement at rest and immediately after stress. The test monitors for new or worsening regional wall motion abnormalities (RWMA), which manifest as ischemia. When a muscle segment lacks oxygen, its contraction is impaired, appearing as reduced or absent movement on the ultrasound images. A positive test, indicated by a new RWMA, suggests the corresponding coronary artery restricts blood supply when oxygen demand increases. This non-ionizing technique provides immediate visualization of dynamic heart function.
Myocardial Perfusion Scintigraphy (MPS), or nuclear stress test, provides a physiological map of blood flow to the heart muscle. A small amount of radioactive tracer, such as Technetium-99m, is injected and taken up by healthy heart cells proportional to the blood flow they receive. A specialized camera, typically a SPECT scanner, captures images of the tracer distribution.
The test compares images taken at rest with those taken under peak stress. If a blockage limits flow, the affected muscle area shows a “cold spot” (reduced tracer uptake) during stress. If this spot normalizes in the rest image, it indicates reversible ischemia. If the defect is present in both images, it signifies a fixed defect, typically scar tissue from a previous heart attack.
Specialized and Advanced Techniques
When initial structural and functional tests are inconclusive, specialized non-invasive techniques provide detailed information about heart muscle health. These tools offer a unique combination of anatomical and physiological data.
Cardiac Magnetic Resonance Imaging (CMR) is valued for its exceptional soft-tissue contrast without ionizing radiation. A primary application is assessing myocardial viability, determining if dysfunctional heart muscle is still alive and capable of recovering function if blood flow is restored. This is performed using Late Gadolinium Enhancement (LGE).
LGE involves injecting a gadolinium-based contrast agent. This agent is excluded from healthy cells but accumulates in areas of scar tissue or fibrosis caused by damage. Imaging the heart after injection shows infarcted or scarred areas as bright white, allowing clinicians to quantify irreversible damage. Knowing the amount of viable muscle helps predict which patients will benefit most from revascularization procedures.
A significant advancement is the CT-derived Fractional Flow Reserve (CT-FFR), which adds functional assessment to a standard CTA scan. This technique uses the anatomical CTA data and applies complex mathematical modeling, known as computational fluid dynamics. Specialized software simulates blood flow and pressure within the coronary arteries based on these calculations.
The result is a calculated fractional flow reserve value for each artery segment. This value is the ratio of blood flow pressure distal to a narrowing compared to the pressure in the aorta. A CT-FFR value of 0.80 or less is considered functionally significant, meaning the blockage restricts blood flow to the heart muscle. This approach provides a comprehensive anatomical and functional diagnosis from a single CT scan, reducing the need for additional testing.