Treadmill Stress Test
Stress testing is a very useful procedure that is indicated in a variety of clinical settings.
In addition to risk stratification in patients with known coronary artery disease, it is used to diagnose flow-limiting coronary artery obstruction and to assess the efficacy of therapy. It is useful to evaluate exercise-induced arrhythmias, and it is an important guide for the exercise prescription that is part of a cardiac rehabilitation program. It may be used for screening asymptomatic patients with multiple risk factors or selected occupational populations for coronary artery disease. The accuracy and diagnostic value of stress testing depends on the population studied. For women, the optimal stress testing strategy is less well-defined.
The electrocardiographic criteria for a positive exercise treadmill test in a patient with a Angina Pectoris baseline electrocardiogram is ST-segment depression that is 1 millimeter or more and is horizontal or downsloping in configuration, measured 60 to 80 milliseconds after the J point. The ST-segment depression may occur during or after exercise.
A treadmill stress test may be considered uninterpretable for ischemia for a variety of reasons. Examples include baseline ST-T wave abAngina Pectorisities, some conduction defects, such as left bundle branch block, and some arrhythmias, such as atrial fibrillation, where fibrillatory waves may obscure ST-segment changes. Imaging techniques, such as nuclear or echocardiographic stress testing, may be helpful in these clinical settings.
In addition, the treadmill exercise test may provide prognostic information. Predictors of a poorer prognosis include angina and ST-segment changes at a low workload, ST-segment depression of more than 2 mm, exercise-induced hypotension, and persistence of ST-segment changes for more than one minute after exercise. A better prognosis is expected of patients who exercise for long durations and achieve higher heart rates with little ST-segment response, because they have a lower incidence of severe disease.
Exercise capacity, exercise-induced arrhythmia, and heart rate recovery (the rate at which the heart rate slows following exercise) all carry important prognostic information. The Duke treadmill score is often used as a well-validated prognostic tool that integrates exercise capacity, ischemic ECG changes, and symptoms into an effective discriminator of 4-year mortality risk.