A cardiac stress test evaluates how the heart and circulatory system function under increased demand. The test simulates physical exertion, often using a treadmill or specialized medication, to reveal problems not apparent when the heart is at rest. Its primary purpose is to help physicians detect coronary artery disease, which involves blockages in the heart’s arteries, or to assess the severity of an existing heart condition.
How Stress Tests Measure Heart Function
A cardiac stress test assesses performance by monitoring physiological metrics that indicate how efficiently the heart responds to an escalating workload. The two primary methods are the exercise stress test (treadmill or stationary bike) and the pharmacological stress test, which uses drugs like dobutamine to mimic exercise for patients unable to be physically active. The goal is to safely increase the heart’s work rate to its near-maximum capacity.
Primary metrics tracked include the patient’s heart rate response compared to their age-predicted maximum (calculated as 220 minus age). The medical team aims for the patient to achieve at least 85% of this maximal rate to ensure the test is diagnostic. The test also measures Exercise Capacity, quantified in Metabolic Equivalents (METs). One MET represents the amount of oxygen consumed at rest, providing an objective score of functional ability.
Blood pressure (BP) monitoring is another component; a normal response is a steady increase in systolic BP as the workload intensifies. The test is stopped when the patient reaches their target heart rate, develops concerning symptoms, or shows specific electrical or hemodynamic changes. This entire collection of data—heart rate, BP, symptoms, and electrical activity—forms the “score” interpreted for signs of heart health or disease.
Defining an Abnormal Stress Test Result
A result is considered abnormal when the heart’s response to stress indicates insufficient blood flow (ischemia) or a high risk for a future cardiac event. The most definitive sign of ischemia is the appearance of specific changes on the electrocardiogram (EKG). A significant finding is an ST-segment depression of one millimeter or more, particularly if horizontal or down-sloping, indicating the heart muscle is not receiving enough oxygen during exertion.
Another major indicator of a poor outcome is a failure of the heart’s pumping mechanism, showing up as dangerous hemodynamic failure. This is recognized by a significant drop in systolic blood pressure—a decrease of 10 to 20 mmHg or more below the resting value—as exercise intensity increases. This finding suggests serious blockages or a weakened heart muscle and is an urgent reason to stop the test.
Exercise capacity, measured in METs, provides a powerful prognostic score. Achieving less than five METs places a patient in a high-risk category. Conversely, a patient who achieves 10 METs or more generally has an excellent prognosis, even with minor EKG changes. The Duke Treadmill Score, a risk-stratification calculation, combines exercise duration, EKG changes, and the presence of chest pain (angina) into a single number. A score of -11 or lower is considered high-risk and strongly suggests severe coronary artery disease.
Severe symptoms occurring early in the test also constitute an abnormal result. The onset of severe chest pain or sustained ventricular arrhythmias (dangerous irregular heartbeats) at a low workload is highly concerning. These clinical symptoms, combined with objective EKG and BP changes, provide a comprehensive view of the heart’s inability to handle stress.
Follow-Up Care After Concerning Findings
An abnormal stress test result signals the need for further diagnostic testing to confirm findings and determine the location and severity of any underlying disease. The next step often involves advanced imaging, such as a stress echocardiogram or a nuclear stress test, to visualize blood flow and heart wall motion. High-risk patients, such as those with a highly negative Duke Treadmill Score or severe symptoms, may be referred directly for a coronary angiography.
Coronary angiography, a more invasive procedure, uses a catheter and dye to take X-ray images of the coronary arteries to locate and measure blockages. The results of these subsequent tests guide the final treatment plan, tailored to the patient’s risk level. For those with moderate findings, initial treatment focuses on aggressive medication management and lifestyle changes.
Medication often includes statins to control cholesterol, beta-blockers to reduce the heart’s workload, and aspirin to prevent blood clots. Patients are advised to adopt a heart-healthy diet, increase physical activity, and cease smoking immediately. This risk stratification ensures that patients with the most severe “bad scores” receive timely interventions, such as angioplasty or bypass surgery, while others are managed through less invasive methods.