Cardiac PET Scan

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What is a cardiac PET scan?

A cardiac pet scan is a diagnostic imaging procedure that is done using radioactive substances to visualize the blood flow to the heart and the functioning of the heart muscles. A cardiac pet scan stress test is more accurate at assessing the blood flow (perfusion) defects as well as assessing the functioning of the left ventricle.

Alternate names

  • Myocardial perfusion imaging
  • Cardiac stress test
  • Myocardial perfusion scanning
  • Cardiac positron emission tomography scan

Is this procedure an elective or an emergency procedure?

A cardiac PET scan is an elective procedure.

Indications of cardiac PET scan

Some of the common indications for a cardiac pet scan include:

  • Detection of suspected coronary artery disease
  • Evaluation of individuals with known coronary artery disease to assess the severity of the blood vessel involvement
  • Assessment of damage and heart muscle viability after a myocardial infarction
  • Assessment of damage and heart muscle viability in left ventricular dysfunction
  • Assessment of response to treatment in coronary artery disease and myocardial infarction

Myocardial perfusion imaging is specifically recommended for the following conditions:

  • It is to be used if there are any conditions causing ECG abnormalities that could interfere with stress ECG testing such as left ventricular hypertrophy, bundle branch blocks, or if on digoxin therapy
  • It is also recommended as a support procedure when cardiac stress testing is being done with a pharmacological agent (drug induced) instead of normal exercise or physical activity.
  • It is also recommended in those who are at a higher risk for cardiovascular adverse events such as individuals with diabetes mellitus

Contraindications and risk factors of cardiac PET scan

  • Some of the contraindications for a cardiac PET scan include:

    • Pregnant women or nursing mothers
    • History of an allergic response to dyes is a risk factor
    • Severe claustrophobia
  • Contraindication for cardiac PET stress test include:

    • ECG abnormalities at rest such as left bundle branch block, pre-excitation syndromes, inability to exercise (better suited to pharmacologic testing)
    • Acute myocardial infarction (MI)
    • Sustained ventricular arrhythmias
    • High-grade heart block
    • Aortic stenosis that is severe and causing significant blood flow obstruction
    • Severely raised blood pressure
    • Serious medical conditions such as pneumonia
    • Severe and uncontrolled diabetes with diabetic ketoacidosis
    • Severe congestive heart failure which is symptomatic
    • Deep venous thrombosis
    • Pulmonary embolism
    • Pericarditis
    • Myocarditis
    • Endocarditis

Investigations before the procedure

A cardiac pet scan is usually done after an echocardiogram or a cardiac stress test, especially if the results from these tests are inconclusive or need further evaluation.

Pre-operative advice

Before performing a cardiac PET stress test the following may be done

  • Risks and benefits of the procedure are explained
  • Avoid caffeine or caffeinated drinks 24 hours before the procedure
  • Avoid smoking on the day of the test
  • Nothing by mouth from 4 hours before the procedure
  • Medications with caffeine are to be stopped 24 hours before the test
  • Medications with theophylline to be stopped 48-72 hours before the test
  • Medications that are being taken for indications related to cardiac disease should be stopped only as advised by the attending specialist

Intra-operative details

  • Duration: A cardiac PET stress test can last between 1-4 hours
  • Anesthesia: No anesthesia is required for a cardiac PET scan

Description of the procedure

Before the start of the procedure, an ECG is done and an IV line is put in place and a radiotracer is injected through it. The radiotracer agent that is used could be thallium(TI-201) or technitium (Tc-99), the individual is then shifted to the PET scan machine room after about 20-45 minutes, which is the time it takes for the radiotracer to be absorbed and circulate in the body. The individual is then made to lie on a table that glides into the cardiac PET scan machine. The cardiac PET scan machine has a revolving gamma camera that takes images of the coronary arteries, the heart muscle. A vasodilator may then be injected to study the response of the heart to the drug, and another series of images are taken. ECG recordings are also done during the procedure. Once the images are recorded, and the testing is completed, the table is moved out from the PET scan machine and the connected ECG leads and the IV line is removed.

Cardiac PET scan stress test

As physical activity and exercise place additional stress on the heart muscle, increase the heart rate, blood pressure, and increase the requirement of blood flow to it, a stress test is a procedure that can induce ischemia (absence of blood flow) in the heart muscle if there is a presence of coronary artery disease. A cardiac PET scan stress test may be done by making the individual perform physical activity (such as cycling or walking on a treadmill) to increase the heart activity while monitoring the ECG and the blood pressure, and then injecting the radiotracer to capture images of the blood flow and the heart muscle. The radiotracer is injected at the peak of exercise or shortly after a drug to simulate physical activity is injected. Images are taken immediately after the injection of the radiotracer and again after a gap of 3-4 hours (called delayed imaging). Areas of the heart muscle that are at risk of damage are seen to be filled with the radiotracer in the delayed imaging while dead heart tissue does not take up any radiotracer (called as a fixed defect). This helps to differentiate between the areas of the heart that are damaged beyond repair due to a previous myocardial infarction (heart attack) and the ones that are at risk of damage due to a future myocardial infarction.

Post-operative details

A cardiac PET scan is an outpatient procedure and the individual is free to leave after the test is completed. Soreness at the site of insertion of the IV line and the back muscles may be noticed. The reports of a cardiac PET stress test are usually available in a day or two after the procedure for interpretation by the attending specialists.

Complications of cardiac PET scan

There are no complications after a cardiac PET scan which is a very safe procedure.

Prognosis

Cardiac PET scans are safe procedures and no complications are seen. They are useful in the detection of the severity and extent of known or suspected coronary artery disease, as well as the after-effects of a heart attack.

Indications for hospitalization if required

Hospitalization is not required for a cardiac PET scan.

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