A chemical stress test serves as an alternative to cardiac stress test, and is used as a preventive and prognostic measure for coronary heart diseases. Know all about the procedure, side effects, instructions, and cost of the test.
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Stress test is usually done to determine how a particular body organ or system functions when it is subjected to controlled amount of stress. Chemical stress test helps evaluate how the heart responds to stress and determines the risks of Coronary Heart Disease (CHD). In this test, the heart is subjected to stress using a stress-inducing chemical, and the response is imaged using a radioactive substance or nuclear medicine. The heart is also imaged under a normal resting state. The images in the two states are then compared, to determine the presence of any abnormalities in the blood flow and muscle function.
When is Chemical Stress Test Needed?
The amount of stress that the heart can withstand, is generally tested with the cardiac stress test (treadmill test). Here, the patient is asked to exercise in order to induce stress on the heart, and nuclear imaging is performed. However, certain patients are unable to exercise owing to their age or due to various health problems like paralysis, long-term heart problems, arthritis, asthma or other breathing problems, fatigue, physical impairments, etc. Hence, the need for a chemical stress test arises.
Procedure
♦ The patient is asked to lie down on the imaging table and electrocardiogram (ECG) sensors are attached to the chest in order to constantly monitor the heart condition. The blood pressure is checked and an IV line is attached to administer the drugs.
♦ Now the patient is ready for stress induction. The commonly used stress-inducing drugs are dobutamine, dipyridamole, adenosine, and regadenoson. The choice of the drug depends on the patient’s medical history and the mechanism of the drug. The drugs dipyridamole, adenosine, and regadenoson are vasodilators and directly cause the coronary arteries to expand. This increases the blood flow through these arteries. Dobutamine, on the other hand, leads to coronary expansion indirectly. It creates an increased oxygen demand in the heart muscles. As a result, the heart rate and blood pressure increases. Thus, the physiological conditions that occur during a heavy exercise are simulated.
♦ A few minutes after the stress induction, a nuclear medicine (also called radionuclide or radiotracer) is injected, which serves as an imaging agent. The most widely used radiotracers are thallium (Tl-201) and technetium-99m (Tc-99m)-labeled agents like sestamibi and tetrofosmin. The nuclear medicine, is taken up specifically by the heart muscles with a rate proportional to the rate of blood flow. Hence, it can serve as an indicator of blood flow to the heart.
♦ The radionuclide emits gamma rays, and the movements of the cardiac muscles are imaged using an imaging technique called SPECT (Single-photon emission computed tomography) which involves the use of a gamma camera.
♦ During the test, the ECG, heart rate, and blood pressure of the patient are monitored.
For testing under resting condition, the basic procedure remains the same but the stress agent is not administered. Only the radionuclide is administered and images are obtained. The resting state test may either be performed on the same day, or on the next or previous day. If, performed on the same day, it must be scheduled at least two hours before or after the stress test.
Note: The combination, dosage, and frequency of administering the medicines to be injected, as well as the exact protocol are determined taking into consideration the patient’s age, weight, medical condition, medical history, and other relevant factors.
Results and their Indications
- Presence and location of blockages in the coronary arteries.
- Prognosis of patients suffering from CHD or those who had an acute myocardial infarction (heart attack).
- Assessing the risk factors in patients undergoing a major surgery.
- Monitoring the effect of revascularization and other treatment measures employed to rectify coronary blockages, and determine the reappearance of blockages or narrowing of arteries.
- A combination of the drug dobutamine and a radiotracer may help to determine the activity level of heart muscles and their viability.
Possible Risks and Side Effects
Chemical stress test can be extremely uncomfortable for some people due to the side effects caused by the stress-inducing drug and/or the nuclear medicine.
Headache and chest pain are the most commonly experienced side effects. Other side effects include:
- Dizziness
- Nausea
- Vomiting
- Abdominal discomfort
- Excessive sweating
- Tingling sensation throughout the body
- Flushing sensation
- Anxiety or panic
- Injection site reaction
In pregnant women, the developing fetus may suffer an injury due to the nuclear medicine. Lactating women run the risk of their breast milk getting contaminated with the nuclear medicine. Patients with heart problems are at a risk of suffering a heart attack during the test.
Important Test Instructions
- Patients are advised not to eat and drink, two to three hours before the test.
- Caffeine intake and smoking must be avoided for at least a day before and after the test. Caffeine and nicotine are known to interfere with the test results and may enhance certain side effects like nausea and vomiting.
- Patients must inform the doctor about their medical history, allergies, and any medicines that they are taking. Heart patients are generally advised to stop taking medicines for one or two days before the test.
- Any unusual experience, other than what the doctor has informed at the beginning of the test, must be reported to avoid any complications.
- The test can be exhausting, so prepare yourself mentally and get a good sleep. Have a well-balanced dinner. Avoid eating after midnight, as it can lead to vomiting during the test.
Still have Some Questions?
How long does it take to complete the test?
The procedure generally takes about five to six hours, if both the stress and resting state tests are conducted on the same day. In case they are conducted on consecutive days, the time required for one set of test is about one to two hours.
How much does it cost?
Between $2,000 to $4000 depending on the diagnostic center and the state.
How frequently should a chemical stress test be conducted?
It depends on the patient’s heart condition and other existing medical problems. It is best to consult your doctor and plan the tests.
The chemical stress test serves as a good alternative for people with a risk of heart diseases. It determines the irregularities in blood flow to the heart and also the reasons for it. Apart from that, it helps to decide the treatment methods to be followed and monitor the effects of the treatment as well. Thus, many of the diagnostic requirements are catered to, rather than having to undergo an array of tests.
Disclaimer: This HealthHearty article is for informative purposes only, and should not be used as a replacement for expert medical advice.
