An echocardiogram is a non-invasive procedure that uses ultrasound technology to create moving pictures of the heart. This test primarily focuses on the heart’s structure, the function of its valves, and the overall efficiency of its pumping action. A standard resting echo does not directly visualize the small coronary arteries that wrap around the heart’s surface to look for plaque or blockages. Instead, the test provides crucial, indirect evidence of how a blockage in those arteries is affecting the heart muscle.
What a Standard Echocardiogram Reveals
A standard transthoracic echocardiogram assesses the consequences of reduced blood flow rather than the blockage itself. The most significant indirect sign of coronary artery disease is a Regional Wall Motion Abnormality (RWMA). The left ventricle, the heart’s main pumping chamber, is divided into segments, each supplied by a specific coronary artery.
If a coronary artery is significantly narrowed, the heart muscle it supplies may not contract normally. This lack of proper movement is classified as an RWMA, which can be described as hypokinesia (reduced movement), akinesia (no movement), or dyskinesia (paradoxical outward movement). The presence and location of an RWMA strongly suggest a corresponding problem in the supplying coronary artery. The echo also measures the ejection fraction, which is the percentage of blood pumped out of the ventricle with each beat, providing a measure of the heart’s overall pumping strength.
How Arterial Blockages Impact Heart Function
A blockage in a coronary artery restricts the flow of oxygen-rich blood to the heart muscle, causing ischemia. Heart muscle cells (myocytes) require a constant supply of oxygen and nutrients to contract, so this deprivation immediately impairs their function. The resulting lack of energy causes the affected area of the heart wall to move poorly or not at all, which is the RWMA observed on the echo.
If blood flow is restored quickly, the muscle may recover fully (myocardial stunning). Chronic blockages can lead to myocardial hibernation, where the muscle reduces its activity to match the limited blood supply, remaining viable but dysfunctional. Severe, sustained blockage causes irreversible damage and cell death, resulting in scarring known as an infarct. An infarct leads to permanent RWMA and tissue thinning that the echo can readily detect.
Specialized Echocardiography for Artery Assessment
To overcome the limitation of the resting echo, physicians use Stress Echocardiography to uncover blockages that do not cause symptoms at rest. This procedure involves physically or chemically stressing the heart to increase its oxygen demand. Physical stress is achieved by having the patient exercise on a treadmill or stationary bicycle while images are captured immediately afterward.
For patients unable to exercise, a pharmacological agent like dobutamine is infused to chemically simulate exercise by increasing the heart rate and contractility. In a healthy heart, all segments show increased wall motion during stress. If a coronary artery has a significant blockage, the increased oxygen demand exceeds the limited supply, causing a new or worsening RWMA to appear. The appearance of this abnormality during stress confirms the functional significance of the underlying arterial disease.
Contrast agents, consisting of microscopic gas-filled bubbles, are administered intravenously during an echo to enhance image quality. These microbubbles improve the definition of the inner lining of the heart muscle (endocardium), which is useful when standard ultrasound image quality is poor. Contrast can also be used in advanced techniques to visualize blood flow within the heart muscle, helping to assess perfusion and viability.
Primary Tools for Visualizing Arterial Blockages
While specialized echocardiography provides strong evidence of a functionally significant blockage, other imaging tools are needed for a direct view of the coronary arteries. Coronary Computed Tomography Angiography (CTA) is a non-invasive test that uses X-rays and an injected contrast dye to create detailed three-dimensional images. The CTA can directly visualize the artery walls, measure the amount of plaque, and determine the degree of narrowing (stenosis) within the vessel.
The definitive method for directly visualizing and measuring arterial blockages is Invasive Coronary Angiography, often called cardiac catheterization. This procedure involves inserting a catheter into an artery in the wrist or groin and guiding it to the heart. A dye is injected directly into the coronary arteries while X-ray images are taken, providing a precise, dynamic map of the blockages. This technique is used as both a diagnostic tool and a treatment, allowing physicians to immediately perform an intervention, such as placing a stent, if a severe blockage is found.