Chemical Stress Test
• What Is Stress Testing?
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Heart Disease in Women
|What Is Stress Testing?
Stress tests are a group of diagnostic tests that doctors use to evaluate the heart’s ability to cope with increased demand. Primarily they are used to check for the presence of coronary heart disease (CHD) or it’s variant coronary artery disease (CAD). There are many different types of 'stress' and many different types of 'tests'. Exercise is the most common ‘stress’ which doctors use to induce the heart to work harder. The patient for example is required to walk on a treadmill for a set duration of time, or until they reach a target heart rate. The other common type of 'stress' is chemical and involves injecting the patient with a substance that will artificially cause their heart to dilate, mimicking the effects of exercise. The types of 'tests' used in both instances are likely to be electrocardiogram (ECG/EKG), echocardiogram (echo) and occasionally PET scans.
Also referred to as a pharmacological stress test, the patient is injected with a medication via IV. The purpose of the procedure is to test the heart at 'stress' and it does this by causing the arteries to dilate so that blood flow is allowed to flow at maximum volume. The patient has electrode patches attached to the chest which is hooked up to an ECG machine so that the heart's reaction can be monitored at all times. It is usually performed in place of an exercise stress test because the patient is physically unable to exercise. Instances include those with signs of arthritis, joint or back problems, disability, inability to hold a steady gait, fainting and dizziness or shortness of breath.
The main types of chemical used for chemical stress tests are dobutamine, adenosine and dipyridamole (brand name Persantine). Dobutamine is an intravenous (IV) medication that causes the heart to pump faster and it is often used in conjunction with an ECG or echo. When the heart pumps faster it requires more oxygen and nutrients, and creating this type of metabolic stress can be helpful in diagnosing disease of the heart's arteries or muscle. Dobutamine is used with caution in patients with dangerous cardiac arrhythmia or critical CHD. Adenosine is a natural compound that dilates the blood vessels in the heart and Persantine works by increasing the levels of adenosine in the heart. Both are called vasodilators and both are used in PET or SPECT scans - the main difference between the two being how long the effects last. Caution is used in patients with asthma, low blood pressure (hypotension), and emphysema or conduction disease of the heart.
Most doctors prefer to use the traditional treadmill stress test; however this is not possible if the patient is physically unable. A chemical test is normally carried out to evaluate patients showing symptoms of CHD.
It may be that the patient:
Before starting the test the doctor may:
Carry out a physical examination and review medications you are taking.
Take a resting ECG test, to record the heart's activity at rest before being 'stressed'. This will be used for comparison purposes.
Carry out an echocardiogram. This uses ultrasound technology so that the doctor can visualize the size, shape and motion of the heart at rest.
You will be asked to lie on an examination table. A technician will place sticky patches called electrodes on your chest which are then hooked up to an ECG machine. Your resting blood pressure will be taken and it will be continually monitored throughout the procedure. A hollow needle and thin tube (IV) will be inserted in your arm. A small amount of chemical will be injected through the IV and depending on which chemical is used, the heart will start to beat faster and/or the blood vessels will dilate. An ECG may be performed at this point. If you are getting a stress echocardiogram, ultrasound images will be taken at specific points of time. The doctor will later compare the pictures with pictures of your heart at rest. After the test, the heart rate and blood pressure will be monitored until levels return to normal. The patient can then go home. Typically the test takes 3 to 4 hours to complete.
A full report usually takes 2 to 3 working days, but the doctor may be able to make some initial observations on the day of the test.
1. ECG readings show low oxygen supply to the heart.
2. Chest pain and breathing difficulties were noted and linked with ECG changes.
3. Significant drop in blood pressure and changes in heart rhythm.
4. Echo images show areas of the heart with low blood flow or abnormal movements. An artery is probably blocked.
Based on the results, your doctor may recommend more heart disease testing or treatment.
Complications (dangers) are quite rare but may include:
• Chest pain
• Shortness of breath
• Heart attack (extremely rare). All test centers will carry resuscitation facilities in case they are needed.
After the test, do call your doctor or 911 if you have any of the following symptoms:
• Chest pain
• Difficulties breathing
• Irregular or racing heartbeat
• Weakness or dizziness
2 Ensure you have a good night's sleep beforehand. The procedure is lengthy and you may find it exhausting.
3 Avoid eating or drinking after midnight before the test. The chemical used can cause nausea and undigested food may be vomited back up.
4 Bring a list of medications you are taking with you and tell your doctor if you have chronic obstructive pulmonary disease (COPD) or asthma. If you have diabetes, bring your glucose monitor with you.
5 Try to relax as much as possible while the test is being set up and the IV line is inserted. Practice visualization and imagine yourself on a warm sun-soaked beach.
6 Focus on staying calm as the chemicals are injected through the IV. This will help to reduce some of the immediate side effects. Possible symptoms include headache, the need to throw up and hot flushes - they should subside as the chemical works its way through the bloodstream. If you feel overwhelmed by symptoms, you can demand that the test finish early. However keep in mind that it may still need to be repeated another day.
7 Throughout the procedure raise your legs to your stomach and down again. This seems to help minimize side effects.
8 Immediately report any symptoms your technician did not mention - such as chest pain and breathing difficulties.
Thallium is an isotope or radioactive substance which is used for a nuclear heart scan (the other common isotope is called technetium). Thallium can be used in combination with an exercise stress test or a chemical stress test. When it is used with a chemical stress test, the same procedure as above is followed. However, once the stress chemical has been injected, it is then followed by a thallium injection. Half an hour to an hour later the patient is moved to a SPECT or PET scan which can track the radioactive material of the thallium as it makes its way through the heart. The images produced by the scan will show how much blood is reaching the different areas of the heart. If supply to certain areas is restricted it can indicate a blockage in an artery. If no blood is reaching an area, it can indicate that the tissue is dead (scar tissue) after a previous heart attack. The flow of blood is compared to the at-rest stage before chemical induced stress. This test should not be performed on pregnant women.
Cardiolite is a brand name for another chemical used in nuclear imaging. Its generic name is much longer: Technetium Tc99m Sestamibi. Both Cardiolite and Thallium tests are also known as nuclear perfusion studies. Perfusion is the flow of blood through a specific organ (in this instance, the heart). A Cardiolite test is carried out the same way as a Thallium test. It can be used in conjunction with a chemical stress test or a treadmill test. A Myoview test is a similar study but uses the radionuclide chemical 99m-Tc-tetrofosmin (brand name Myoview).
Other Types of Heart Tests
|Related Articles on Stress Testing
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