What is a ‘stress test’ and why is this called a stress test?
The resting heart muscle’s blood supply needs are usually well met even in the presence of blocked arteries. When the heart is stressed either by exercise or chemicals, the heart’s demand for blood increases. The blood flow through the blocked arteries- while adequate at rest- may not be able to keep up with the demands of a stressed heart. This can show up on the pictures of the heart taken after stress. This is the principle behind all the stress tests. The word stress test is used for any means used to increase heart muscle’s demand for blood. This can be done by exercise or by chemical means.
What is an exercise treadmill test?
For this test, your chest area is cleaned and if need be, shaved. Some stick-ons called electrodes are placed on the chest. After this, you are asked to walk on the treadmill. Most of the treadmill tests are done according to certain set protocols. These protocols have different names like modified Bruce protocol, Bruce protocol, McNaughton, Balke protocol etc. The speed and incline of the treadmill increase by preset degree at preset time intervals governed by each protocol. While you are walking on the treadmill, your heart rhythm is watched, blood pressure is measured and serial EKGs are taken. EKG or ECG stands for electrocardiogram. It appears as lines on a piece of paper. The person doing the test needs to know if you are having chest pain, dizziness or any other unusual symptoms during the test. You will be asked to walk on the treadmill till one or more of the following are achieved:
- You cannot keep walking due to variety of reasons including shortness of breath, dizziness, joint pains, fatigue, leg pain, chest pain etc.
- The person doing the test sees some signs that may mean that continuing the test could be harmful. These include: very high blood pressure, chest pain, plummeting blood pressure, significant rhythm or other EKG changes.
- For a test to be useful, you should achieve at least 85% predicted heart rate. Predicted heart rate is calculated by a formula: 220 minus age. You should achieve at least 85% of this number.
The person doing this test will study the following:
- Any symptoms you may have during the test including chest pain, shortness of breath, etc.
- The EKG changes that could be suggestive of blockages in heart arteries.
- Rhythm changes.
- Blood pressure response and heart rate response to exercise.
- Exercise capacity.
How do I prepare for this test?
You should wear comfortable shoes and clothes. Simply put, wear clothes that you will wear if you were going exercising.
How does this test help?
This test can give indication toward blockage in heart arteries. It also helps measure exercise capacity. In certain cases, it can tell us about propensity toward certain arrhythmias.
Are there any shortcomings of exercise treadmill test?
This test cannot be done in patients who cannot walk. Because this test studies EKG changes that appear on exercise, it will not be useful if your baseline EKG is abnormal. This test is also not helpful if you are on a medicine called digoxin. The sensitivity of this test is around 70%. That means that this test can miss up to 1/3 of the cases with blockages of heart arteries. This test cannot help us localize the area of blockages. Because of some of these factors, simple exercise treadmill test may not be the right test for you.
Can you die during a stress test?
With well-selected cases, incidence of death during any stress test should be extremely rare.