A stress echocardiogram (stress echo) is a diagnostic test that combines a standard heart ultrasound with physical or chemical stress to evaluate cardiac function. The procedure uses high-frequency sound waves to create moving images of the heart’s muscle and valves. By comparing images taken while the heart is resting to those taken immediately after the heart is stressed, physicians can detect abnormalities not visible otherwise. This comparison allows for a precise assessment of how well the heart muscle is supplied with blood when it is forced to work harder and faster.
Why the Test is Performed
The foundation for ordering a stress echo lies in the principle that heart problems caused by narrowed arteries may only become evident when the heart is stressed. At rest, a partially blocked coronary artery may still deliver enough blood to the heart muscle, resulting in normal function. When the heart rate increases, however, the muscle needs significantly more oxygen-rich blood, and a blockage prevents this increased supply, leading to temporary dysfunction.
The most frequent reason for this test is to diagnose or rule out coronary artery disease, which involves blockages in the vessels supplying the heart muscle. By intentionally increasing the heart’s workload, the test reveals areas of the heart that suffer from ischemia, indicated by a failure of the muscle wall to contract properly. This technique is also used to investigate the cause of chest pain, or angina.
Beyond detecting blockages, the stress echo helps assess the functional capacity of the heart after a cardiac event, such as a heart attack or bypass surgery. It can also be used to evaluate the function of heart valves under stress or to determine a safe level of physical activity for a patient beginning a rehabilitation program.
Preparing for the Stress Echo
Patients are generally instructed to avoid eating or drinking anything for a specific period before the test, typically three to four hours, to help prevent potential nausea during the physical exertion phase.
Medication adjustments are often required, particularly if a pharmacological stress test is planned. Patients may be asked to temporarily stop certain heart medications, such as beta-blockers, which can lower the heart rate and interfere with reaching a target heart rate.
For patients undergoing a pharmacological stress test, avoiding caffeine for 24 hours prior is often required, as caffeine can interact with the stress-inducing medication and skew the test results. Patients should wear comfortable, loose-fitting clothing and athletic shoes suitable for walking or running on a treadmill.
The Step-by-Step Procedure
The stress echo procedure begins with the patient being prepared for monitoring. Small electrode patches are attached to the chest, connecting to an electrocardiogram (EKG) machine that continuously monitors the heart’s electrical activity, rate, and rhythm. Blood pressure is also monitored using a cuff on the arm, and a sonographer applies gel to the chest for initial ultrasound imaging.
The first phase is baseline imaging, where the patient lies on their left side while the sonographer captures resting images of the heart. These images establish the heart’s size, structure, and wall motion at rest. After the baseline images are secured, the stress phase begins, induced by either exercise or medication.
For those able to exercise, stress is typically achieved by walking on a treadmill or pedaling a stationary bicycle, with intensity gradually increasing every few minutes. The goal is to safely raise the heart rate to a predetermined target. If the patient is unable to exercise due to physical limitations, a pharmacological agent like Dobutamine is administered through an intravenous line to make the heart beat faster and harder.
The final and most time-sensitive phase involves post-stress imaging, which must occur immediately after the patient reaches peak heart rate. This immediate capture is necessary because the heart rate begins to drop quickly once the stress is removed, requiring the images to be taken while the heart is still working at its maximum capacity.
Interpreting the Test Results
The cardiologist interprets the stress echo by comparing the resting images with the post-stress images, focusing specifically on the motion of the heart’s muscle walls. In a normal, negative result, all segments of the left ventricle should contract vigorously and uniformly under stress. This indicates that the blood flow to the heart muscle is adequate.
An abnormal, positive result is signified by the presence of new or worsening wall motion abnormalities in one or more segments of the heart muscle. These abnormalities, such as hypokinesis (reduced movement) or akinesis (no movement), suggest that the corresponding area of the heart is not receiving enough blood supply due to a narrowed coronary artery.
In addition to imaging, the cardiologist reviews the EKG for any stress-induced changes, such as ST segment depression, and checks for significant drops in blood pressure or the onset of chest pain during the test. The combination of wall motion abnormalities and EKG changes confirms the diagnosis of ischemia and helps localize the potential blockage. A completely normal stress echo is associated with a low risk of future cardiac events, while a positive result often leads to further diagnostic testing, such as a coronary angiogram.