Diagnosis

Exercise Stress Test

The primary value of exercise stress tests is not to detect coronary artery disease but to help determine the severity and predict the outcome of an existing heart condition. It is considered for the following people:

• Patients with possible or probable angina and low or intermediate risk for adverse heart events.
• Selected adults who do not have symptoms of heart disease but are at moderate risk to high risk for developing heart disease (a 10 - 20% chance within 10 years). Moreover, heart blockage without angina (silent ischemia) may suggest a more severe condition, at least in men.

Basic Procedure. A stress test (exercise tolerance test) monitors the patient's heart rhythms, blood pressure, and clinical status. It can tell how well the heart handles work and if parts of the heart have decreased blood supply. A typical stress test involves:

• The patient walks on a treadmill or rides a stationary bicycle. Exercise continues until the heart is beating at least 85% of its maximum rate, until symptoms of heart trouble occur (changes in blood pressure, heart rhythm abnormalities, angina, fatigue), or the patient simply wants to stop.
• For patients who cannot exercise, the doctor may administer dobutamine or arbutamine, which are drugs that simulate the stress of exercise.
• An ECG is used to monitor heart rhythms during a stress test. (An echocardiogram or more advanced imaging technique may also be used to visualize the actions of the heart and blood flow.)

More than 25% of patients stop exercising before they reach their own maximum limits because of fear of a heart event. Patients should be reassured that the activities performed in the test under the guidance of a professional are safe.

Interpreting Results. To accurately assess heart problems, experts look at a number of findings derived from the ECG and other tools during exercise. They include:

• Exercise capacity. This is a measure of a person's capacity to reach certain metabolic rates.
• Heart rate and ST waves. On ECGs, doctors specifically look for abnormalities in part of the wave tracing called an ST segment. A certain type of ST segment depression may suggest the presence of heart disease. However, gender, drugs and other medical conditions can affect the ST segment. Using a measurement that adjusts the ST segment to heart rate improves accuracy.
• Dukes Treadmill Score. This important score uses the number of minutes a patient can exercise and other factors that are present in patients with exercise-limiting angina.
• Heart rate recovery.
• Chronotropic index. This is the percentage of the heart-rate reserve that is used during the exercise. A result of 80% or less suggests a significant risk for serious heart problems in most patients.
• Changes in systolic blood pressure.