A stress test is used to identify the hemodynamic response of the heart to a large load of physical stress and compare it to the resting response. The heart rate must increase to provide oxygenated blood flow to exercising muscles. The blood pressure should increase related to the increased work as well. The heart rhythm is monitored through and ECG. The healthcare providers are looking to see if there are changes in the ECG with activity.
There are multiple leads used for the ECG, as the healthcare provider is observing the heart at each different angle, not as a flat surface. If the ECG shows changes in what is called the ST segment, the contraction portion of the ventricle or bottom chamber of the heart this can be a clue that there may be poor blood flow in this region. There are very characteristic patterns in the ECG regions which can clue the healthcare provider in as to what region of the heart is showing poor blood flow. They would diagnose this as ischemia.
There are many different ways of imaging the heart in addition to the ECG. Often the stress test is combined with an echo cardiogram, in which ultrasound is used to visualize the movement of the heart walls. When the blood supply is limited to the wall of the heart there will be evidence of poor contraction of the heart muscle or sometimes it become aneurysmal instead of squeezing itself inwards it bulges out. The other common imaging is a nuclear scan in which radioactive isotopes are injected into the the body. The heart is then scanned at rest and post intensive exercise. The isotopes tag on to the heart muscle. If there is a reduction noted in the scan it is usually a result of ischemia. If there are locations where there is no uptake both at rest and with physical stress than this is an are that is most likely scarred permanently due to a previous heart attack.
The walking on the treadmill is very physical. Some patients cannot tolerate this level of exertion due to other issues, knee, hip or foot issues, neuropathy, poor gait, fear, uncontrolled blood pressure etc. In this case the healthcare provider can chemically stimulate the heart to speed up and put enough strain on the heart to simulate the response it would give with physical exertion.
If you have had a heart condition in the past such as a heart attack, coronary artery bypass surgery, stents or progressive angina you can expect your healthcare provider to stress test your heart every one to two years. It is felt it is better to be proactive and catch ischemic issues before they cause a heart attack. As a heart attack scars the heart muscle. Scar tissue in the heart is not flexible and thus reduces the pumping ability of heart. As the pumping ability decreased the heart cannot keep up with the demand for blood flow to sustain necessary work loads. This is not only a physical problem causing shortness of breath, weakness and fatigue, but it also means not getting enough blood flow to major organs. Particularly of note are the kidneys. Approximately 25% of the blood pumped out with each beat goes directly to the kidneys. For many patients a severe heart problem can also lead to kidney damage. Again it is better to be proactive and address poor blood flow before damage can be done.
If you are concerned or fearful of having a stress test let your healthcare provider know. There are different stress test protocols that can be used. One thing I was always concerned about in cardiac rehabilitation was patients practicing for their stress test. There is a reason the stress test is done under physician supervision. By bringing the heart to such strenuous workloads vulnerable plaques or unstable plaques can cause problems. Therefore I always advise do not give yourself your own stress test! Plan your daily exercise as just that daily exercise not a stress test.
As any test it is not a perfect test. There are some people who can pass a stress test with no problem yet may have heart problems that just can’t be detected by this test. The important thing to remember is being persistent in working with your healthcare provider to discuss your symptoms and what provokes them as well as what relieves them. Keep a diary of symptoms and share that on each office visit.