Treadmill stress test
The treadmill stress test is an ischemic heart disease test that provides a physiologic assessment of cardiac capacity and coronary reserve. Various protocols exist but the standard Bruce protocol is the most commonly utilized and consists of incremental increases in treadmill speed and grade every 3 minutes. The degree of exertion is measured in metabolic equivalents or METS (one MET = sitting) such as 3 minutes of exercise (Stage 1 = 5 METS), 6 minutes (Stage 2 = 7 METS), and 9 minutes (Stage 3 = 10 METS) on the Bruce protocol. As a general rule, completion of Stage 2 (7 METS) signifies reasonable cardiac reserve. In addition to exercise duration, heart rate achieved, blood pressure response, the occurrence of symptoms, electrocardiographic ST segment changes, and the development of ventricular arrhythmias also have diagnostic and prognostic significance. The inability of the heart rate to decrease more than 10 beats per minute in the first 60 seconds following termination of the exercise confers increased risk of cardiac events.