A cardiac stress test is a non-invasive diagnostic procedure used to evaluate how the heart functions under increased demand. The test helps determine if the heart muscle receives enough blood flow during high activity, which is key to diagnosing coronary artery disease. By monitoring the heart during controlled physical or chemical stress, these tests assess a patient’s exercise capacity and predict potential cardiac events. The three main types of cardiac stress tests achieve this using different methods of inducing stress and monitoring tools.
Standard Exercise Stress Test
The standard exercise stress test is the most common type of cardiac evaluation, relying solely on physical exertion and electrical monitoring. Patients walk on a treadmill or pedal a stationary bicycle according to a standardized protocol, such as the Bruce protocol. The speed and incline are incrementally increased every few minutes to progressively increase the heart’s workload.
The primary diagnostic tool during this procedure is continuous electrocardiogram (ECG) monitoring. Electrodes placed on the patient’s chest track the heart’s electrical activity, looking for changes in the ST segment, which can indicate reduced blood flow to the heart muscle. The test continues until the patient reaches a target heart rate, usually 85% of their maximum predicted heart rate, or if limiting symptoms like chest pain or significant ECG changes develop. Blood pressure is also monitored frequently to track the heart’s hemodynamic response to the increasing stress.
Exercise Stress Test with Imaging
This category uses the same physical exertion as the standard test but incorporates an imaging modality to provide a visual assessment of the heart’s function and blood supply. Imaging is added to increase diagnostic accuracy, particularly when the patient’s resting ECG has abnormalities that might interfere with interpreting electrical changes alone. The two primary imaging methods are stress echocardiography and nuclear myocardial perfusion imaging.
Stress echocardiography uses ultrasound waves to capture live images of the heart muscle at rest and immediately after peak exercise. This allows the provider to visualize the motion of the heart wall, looking for new areas that move poorly or fail to contract, which is a sign of insufficient blood flow. Nuclear imaging, also called Myocardial Perfusion Imaging (MPI), involves injecting a small amount of a radioactive tracer at peak exercise. A specialized camera then scans the heart to create images showing how the tracer is distributed throughout the heart muscle, revealing any areas of restricted flow.
Pharmacological Stress Test
The pharmacological stress test is utilized for patients who cannot achieve the necessary level of physical exertion due to conditions like severe arthritis, mobility issues, or peripheral artery disease. Instead of exercise, stress is induced chemically through the intravenous injection of medications that mimic the effects of physical activity. These agents can include vasodilators like Regadenoson or Dipyridamole, which widen the coronary arteries, or inotropic agents like Dobutamine, which increases the heart rate and contractility.
Because the chemical stimulation does not produce the same reliable ECG changes as physical exercise, this method is always combined with an imaging technique, typically nuclear imaging or echocardiography. The vasodilating agents create a difference in blood flow between healthy and diseased arteries, which is then visualized by the imaging scan. This approach ensures that even non-ambulatory patients can be accurately assessed for coronary artery disease and other cardiac issues.