HEART TESTS YOU NEED TO KNOW
Rafat Padaria, MD
What is an exercise stress test?
An exercise stress test helps to determine if blockages exist in the arteries of the heart. A narrowing in those arteries can cause lack of blood supply to the heart, particularly when the heart is under stress. A stress test simulates physical stress and allows the physician to determine whether a narrowing exists in the coronary arteries.
During a stress test, the electrocardiogram (ECG) monitors the electricity of the heart. If blood supply under stress is insufficient, the ECG generally will show characteristic changes that can allow the doctor to conclude whether blockages exist or not.
What types of stress tests are there?
There are many ways of stressing the heart. This test can be performed by a treadmill (treadmill stress test) or by medications (pharmacologic stress test). The 2 most common medications used for pharmacologic stress testing are adenosine and dobutamine.
Irrespective of how the heart is stressed, the reaction of the heart under stress can be monitored by several ways: observing the ECG changes or taking pictures of the heart immediately after the stress test using a nuclear camera or an ultrasound machine (echocardiogram).
What is a treadmill stress test?
A treadmill stress test involves stressing the heart by having the patient exercise on a treadmill. By using different grades of elevation and speeds at regular time intervals, the heart will be subjected to monitored stress. The higher the heart rate and blood pressure during stress, the more stress is applied to the heart. In order for the test to be meaningful, patients should exercise to at least 85% of the maximum predicted heart rate for their age calculated by ([220–age] x 85%).
A regular treadmill stress test involves only monitoring the ECG during stress. Unfortunately, this test can carry a 20–30% risk of false normal or false abnormal readings and might not be always accurate. However, a lot of information can be obtained from this test.
What information can be obtained from a regular treadmill stress test?
The exercise stress test may reproduce the patient's symptoms, such as shortness of breath or chest pain. This can be helpful to determine whether these symptoms are exertional or random. Exertional symptoms (that is, those that occur during exercise) are more likely to be related to the heart.
Also, the ECG may show changes suggestive of blockages in the heart arteries or rhythm problems.
Furthermore, the blood pressure response to exercise will show if a patient is responding appropriately to exercise or has poorly controlled high blood pressure.
Finally, functional capacity or conditioning can be assessed from an exercise treadmill test. Functional conditioning is the most important information generated by a stress test, since it can predict patient prognosis. In other words, if patients meet a good functional capacity during the stress test, their risks are generally low for cardiac events for 2 to 4 years after the stress test.
It is important to know that a stress test does not predict a heart attack. Heart attacks can happen in blockages less than 50% in severity (such blockages typically require no mechanical treatment, such as surgery or angioplasty). These blockages do not show up on a stress test. It is important for patients with normal stress tests to continue to aggressively modify their risk factors, such as by lowering high blood pressure, cholesterol, or blood sugar with diabetes, as well as quitting smoking, exercising, eating a low-fat diet, and reducing stress.
What is a nuclear stress test?
The nuclear stress test is similar to the exercise stress test but in addition evaluates blood flow to the heart and assesses heart pump function. In other words, during a nuclear stress test, pictures of the heart are taken in addition to interpreting the ECG. The nuclear stress test is more expensive than the regular stress test but also provides more accurate information about the heart. The nuclear stress test still, however, carries a 15–20% chance of a false abnormal or false normal test.
How is a nuclear stress test performed?
A nuclear stress test is performed by injecting a radioactive substance in the arm vein immediately after exercise or while stressing the heart with medications.The patient is then placed under a camera and images are obtained. This takes about 30 minutes. Repeat images are obtained by injecting the radioactive agent at rest as well, generally the next day. The 2 sets of images are compared to each other to look for any areas of reduced blood flow to the arteries of the heart during the stress. If blood flow to the heart is seen during the stress part of the stress test and not during the rest part, this usually indicates the presence of a blockage in the coronary arteries.
