Cardiac Stress Test.
A cardiac stress test (or Cardiac diagnostic test) is a test used in medicine and cardiology to measure the heart's ability to respond to external stress in a controlled clinical environment.
The stress response is induced by exercise or drug stimulation. Cardiac stress tests compare the coronary circulation while the patient is at rest with the same patient's circulation observed during maximum physical exertion, showing any abnormal blood flow to the heart's muscle tissue (the myocardium). The results can be interpreted as a reflection on the general physical condition of the test patient. This test can be used to diagnose ischemic heart disease, and for patient prognosis after a heart attack (myocardial infarction).
Treadmill Stress test:
Advantage of doing exercise stress test:
This kind of test will help revealing the following:
- Exercise Tolerance: The patient continues to exercise until they achieve a specific target heart rate based on age. This will help to determine exercise tolerance
- Identifying exercise related symptoms: shortness of breath, chest discomfort, dizziness, fatigue and weakness. Any of which could suggest underlying heart disease.
- Blood pressure is monitored during exercise. o High diastolic pressure, could suggest uncontrolled hypertension. An extreme drop in blood pressure could indicate heart disease.
- Identifying arrhythmias or abnormal heart rhythms during exercise
- EKG changes: EKG is monitored constantly during exercise, and any changes in comparison with the baseline EKG, could suggest heart disease.
How does a regular stress test work?
Symptoms and signs of heart disease may become more prominent by exposing the heart to the stress of exercise. Reduced blood flow to a specific area in the heart muscle, caused by a clogged or narrowed artery, may produce symptoms and EKG changes..
How reliable is a regular stress test?
If the patient achieves target heart rate, regular treadmill is capable of diagnosing 67% of patients with coronary artery disease. On the other hand 10% of the patients may have a false-positive test (abnormal test in patients without any narrowed arteries).
Chemical / Pharmalogical Stress Test:
How does it work?
A chemical stress test combines an intravenous medication with an imaging technique:
• Isotope imaging
In these cases the medication will increase the heart load instead of exercise. When the patient has a blocked artery, the blood flow to a specific area of the heart muscle will be reduced, causing decreased movement in the affected heart muscle segment (as seen in the stress echo), or reduced isotope uptake (as seen in the nuclear scan).
When is a chemical stress test performed?
The test of choice is treadmill stress test, because of the physiological effect on the blood pressure and heart rate. However, exercise may not be possible for physical limitation, shortness of breath, etc. in such cases, chemical stress testing may be done.
Types of chemical stress testing:
• Dipyridamole (Persantine) stress test
• Adenosine stress test
• Dobutamine stress test
Since caffeine products can alter the efficacy of any stress test, it is essential that no caffeine or decaffeinated products including coffee, tea, pop, and chocolate, be consumed for 24 hours prior to the test.
Nuclear stress test
Typically, a radiotracer (Tc-99 sestamibi, Myoview or Thallous Chloride 201) may be injected during the test. After a suitable waiting period to ensure proper distribution of the radiotracer, photos are taken with a gamma camera to capture images of the blood flow.
Photos taken before and after exercise are examined to assess the state of the coronary arteries of the patient. Showing the relative amounts of radioisotope within the heart muscle, the nuclear stress tests more accurately identify regional areas of reduced blood flow.
Stress and potential cardiac damage from exercise during the test is a problem in patients with ECG abnormalities at rest or in patients with severe motor disability.
Pharmacological stimulation from vasodilators such as dipyridamole or adenosine, or positive chronotropic agents such as dobutamine can be used. Testing personnel can include a cardiac radiologist, a nuclear medicine physician, a cardiologist, and/or a nurse.
How long does the entire test take?
Approximately 3 to 4 hours should be considered for the entire test, including the preparation.
How safe is an isotope stress test?
The patient is exposed to a very small amount of radiation and the risk is very minimal, if any.
What is the reliability of an isotope stress test?
With good exercise and good images, this test is capable to diagnose heart disease in 85% of patient with narrowing arteries.
- Approximately 10% of patient's may have a false positive test.
- Women could have abnormal images in the front part of the heart because of overlying breast tissue.
- Men could have abnormal findings in the lower portion of the heart because of a prominent diaphragm.
- Patient who have a left bundle branch block on their EKG (abnormal electrical conduction in the heart) could also have a false abnormal test.
A stress echocardiogram, also known as a stress echo or SE, utilizes ultrasound imaging of the heart to assess the wall motion in response to physical stress.
First, images of the heart are taken "at rest" to acquire a baseline of the patient's wall motion at a resting heart rate. The patient then walks on a treadmill or utilizes another exercise modality to increase the heart rate to 80% of the target heart rate (target heart rate = 220 - your age). Finally, images of the heart are taken "at stress" to assess wall motion at the peak heart rate. A stress echo assesses wall motion of the heart; it does not, however, image the coronary arteries directly.
Ischemia of one or more coronary arteries could cause a wall motion abnormality which could indicate coronary artery disease (CAD). The gold standard test to directly image the coronary arteries and directly assess for stenosis or occlusion is a cardiac catheterization.
A stress echo is a non-invasive test and is performed in the presence of a licensed medical professional, such as a cardiologist, and an ultrasound technician.