What is Nuclear Cardiology?
Nuclear cardiology is a division of medical imaging that utilises small quantities of radioactive substances to diagnose cardiac-related disorders such as coronary artery disease (CAD). Small and safe amounts of radioactive material called radiotracers are injected into the patient. The radiotracers travel to the heart and emit energy in the form of gamma rays that are discovered by a special camera and a computer to generate images of the inside of your heart. Nuclear cardiology provides unique information that typically cannot be obtained utilising other imaging procedures.
Coronary artery disease occurs due to the narrowing of the blood vessels that supply oxygen-rich blood to the heart. The blood vessels become narrow when fatty deposits accumulate inside the arterial wall. This process is called atherosclerosis. When the arteries become clogged, the blood flow to the heart muscle (myocardium) is hindered and a heart attack can occur.
Types of Nuclear Cardiology Imaging
Nuclear cardiology studies use non-invasive techniques to evaluate myocardial blood flow, assess the pumping function of the heart, as well as visualise the location and size of a heart attack. Some of these non-invasive techniques include:
Cardiac SPECT (single-photon emission computed tomography) scan: This is also referred to as myocardial perfusion imaging (MPI). It is employed to evaluate the function and structure of the heart. SPECT scans utilise small quantities of radioactive material that are introduced into a vein and special cameras to create images of the heart. These images enable your cardiologists to evaluate blood flow within the heart and detect sections of abnormal heart muscle.
The MPI involves two sets of images by the SPECT camera; one with the patient at rest and other under stress that induces the heart to work harder. There are two ways to induce stress on the heart, which include:
- Nuclear exercise stress test: This type of stress test assists your physician to see if your heart is receiving sufficient blood while you exercise. Technicians first generate images of blood flow to your heart while you rest, then again as you exercise on a stationary bike or treadmill.
- Pharmacological nuclear stress test: This is similar to a nuclear exercise stress test, except your physician gives you medication to increase your heart rate if you are unable to exercise.
In cases of significant blockage of the coronary artery, the heart muscle may not receive enough blood supply during exercise or drug-induced stress. A decrease in the blood flow is detected by the images of MPI.
Positron emission tomography (PET) scan: This is a diagnostic study during which a radioactive tracer is administered into the body. This test is used to provide information about both the metabolic activity of the heart and the blood supply to the heart muscle. A PET scan study can outline the heart muscle that is not getting sufficient blood flow because of the blockage in the arteries of the heart. It can also highlight:
- Heart muscle that has been scarred from previous heart attacks
- Section of your heart that could recover if you have cardiac catheterisation or coronary artery bypass graft (CABG) surgery
MUGA (Multiple Gated Acquisition) Scan or Equilibrium Radionuclide Angiocardiography (ERNA): This is a test that is employed to assess heart function by measuring how much blood is pumped out of the heart ventricles with each heartbeat (ejection fraction). A small quantity of a safe radioactive tracer solution is injected into a vein. This substance attaches to red blood cells, which are visualised by a special camera and computer as they travel through the heart, and the heartbeat is calculated based on the computer-produced images.
Indications for Nuclear Cardiology
Your physician may recommend nuclear cardiology imaging tests for the following:
- To identify if you are at high risk of heart attack
- To determine if someone has had a heart attack
- Monitor blood flow to the heart and help detect blockages or CAD
- Assess a patient’s condition after angioplasty or bypass surgery
- Assess how well your heart is pumping blood, which could indicate heart injury, infection, or cardiomyopathy
- Establish the location and size of a heart attack
- Monitor the effects of medications or chemotherapy on your heart
- Determine if your heart-related symptoms such as chest pain and shortness of breath are due to CAD
Preparation for Nuclear Cardiology
Preparation for nuclear cardiology may involve the following:
- Do not eat solids or drink caffeinated products for a specified period before the test.
- Your doctor should be alerted in case you are pregnant or breastfeeding or have any conditions such as heart or lung disorders.
- Your doctor and the technologist should be aware of your medical history, any allergies, and the details of your medications and vitamin supplements.
- You may need to avoid some medicines such as beta-blockers and calcium channel blockers for at least a couple of days before the test.
- Your doctor or technologist should be informed beforehand if you are claustrophobic.
- You should wear a comfortable 2-piece outfit and walking shoes.
Procedure for Nuclear Cardiology
Among all the techniques of nuclear cardiology, myocardial perfusion imaging is the most widely utilised. In general, the MPI procedure may involve the following:
The basic steps involved in myocardial perfusion imaging are as follows:
- The patient is placed on a bed and the radioactive material is injected into the arm vein and will travel to the heart muscle.
- After 45 minutes the patient is again placed on the bed with both arms placed overhead and the patient is asked to remain motionless. A series of images are taken with the specially designed SPECT camera.
- The leads of an electrocardiogram are then placed on the chest of the patient to monitor the rhythm of the heart.
- The patient is then exposed to a stress test either through exercise or drug induced, depending on the patient’s condition.
- The patient’s maximum level of exercise is assessed and a second injection of radioactive tracer is administered.
- The possibility of adverse symptoms such as breathing problems, chest pain, arm pain, palpitations, headache, difficulty in walking, or any other discomfort, after the test, are discussed with the patient.
- After 45 minutes, a second set of images are taken in the same pattern and with the same instrument.
- Finally, the doctor interprets the images and prepares the report.
Post-Procedure Care and Recovery
Other than intravenous injections, most nuclear cardiology procedures are painless. Reports of side effects or significant discomfort are rare. You may feel a slight pinprick sensation during injection of the radiotracer into the vein. You may feel fatigued or short of breath during exercise; however, you will recover naturally after a period of resting. If you are given medication because you are unable to exercise, you may experience dizziness, nausea, anxiety, mild chest discomfort, or shortness of breath for a brief period. These symptoms usually resolve on their own after the infusion is complete. You may resume your normal activities post exam unless your physician instructs otherwise. The small amount of radioactive tracer used in the exam will lose its radioactivity over time through the natural process of radioactive decay or will pass out of your body through your urine or stool. You need to make sure to drink plenty of water following the procedure to help flush the material out of your body.
Summary
Nuclear cardiology tests continue to play an increasingly significant role in the 21st century in the non-invasive diagnosis of coronary artery disease, the evaluation of the pumping function of the heart, prevention of heart attacks, treatment planning for cardiovascular conditions, and in the prediction of outcomes in patients with heart disorders.
