What is an exercise stress test used for?
Exercise stress test is also known as graded exercise stress test (GXT) or exercise treadmill test (ETT). This test allows doctors to observe the ability of their patients to perform cardiovascular exercise (functional capacity), detect any evidence for lack of blood supply to the heart muscles during exercise due to blockages in the coronary arteries, and to evaluate patients with abnormal heart rhythm. If you already have been diagnosed with coronary heart disease, a stress test may enable the your doctor to estimate the risk and the severity of the blockages. In addition, the doctor can use the information to prescribe appropriate exercise and heart rate target for cardiac rehabilitation purposes. A stress test may also help to monitor the success of cardiac revascularization procedures such as coronary angioplasty or coronary artery bypass graft.
How should I prepare for the test?
In North America, a motorized treadmill is often used while in Europe a stationary bicycle is commonly employed. On the day of the exam you should bring a list of all the medications that you are taking. Depending on the objective of the stress test, you have to check with your doctor whether you have to stop certain cardiac medications before the study. You should wear light clothing with sneakers or comfortable shoes.
How is the test performed?
You will be hooked up with EKG electrodes, and a blood pressure monitor. You will be asked to walk on a treadmill where the speed and slope of the treadmill is increased at predefined intervals that is usually every three minutes. EKG, heart rate, and blood pressure are recorded at rest, during exercise and at recovery. You should exercise as much as you can tolerate and report any symptom, such as chest pain, palpitation, or shortness of breath to the supervising doctor, nurse or technician. When you decide you have exercised as much as you can, you should let the doctor know and they will end the test. Most patients can exercise between three to 15 minutes depending on the age and physical state. The ability to exercise, heart rate, blood pressure response, the EKG, rhythm during exercise and recovery will be compared. In general, for the purposes of diagnosis of lack of blood supply to the heart, we try to exceed the target heart rate which is 85% of the maximal predicted heart rate given by (220-age).
Target heart rate (bpm) = (220-age) * 85%
Are there any conditions where exercise EKG test may be difficult to interpret?
Occasionally some patients may have conditions that can cause erroneous (false positive) changes in the EKG during exercise, such as pre-menopausal females, patients on certain medication such as Digoxin, or patients who have an abnormal EKG to start with.