Cardiac PET Scan and CAD Diagnosis

A cardiac PET scan is a powerful nuclear medicine imaging test used to examine the heart muscle.

With superior ability to accurately measure blood flow between the coronary arteries and heart muscle, PET has become a leading tool for detecting, assessing, and treating conditions of the heart, such as coronary artery disease (CAD). It is also used to detect dead or injured tissue following a heart attack.

To better understand the role cardiac PET scans play in heart disease risk assessment, evaluation, and treatment, we spoke with cardiac imaging expert, Dr. Peggy Chan. From how cardiac PET is performed to what types of patients can benefit from the test, Dr. Chan shares valuable advice to help patients navigate this complex medical scan.

[DocPanel] How is a cardiac PET scan performed?

[Dr. Chan]

During a cardiac PET scan, a small amount of radioactive tracer is injected into a vein using Rubidium-82 or Ammonia N-13 tracer. The test is performed at rest or with pharmacological stress (a diagnostic test used to evaluate blood flow to the heart).

A cardiac PET scanner detects the radiation released by the tracer and creates computer images of your heart. (The tracer is not a dye or contrast.) ECG will be placed on your chest while the PET scanner detects signals from the tracer. The test is combined with a medication to open your blood vessels (vasodilator). The medication simulates the effects of
exercise on your cardiovascular system, and is used if you are unable to exercise on a treadmill or stationary bike.

[DocPanel] What are the uses and benefits of a cardiac PET scan?

[Dr. Chan]

There are two types of myocardial perfusion imaging (MPI) techniques: positron emission tomography (PET) and single-photon emission computed tomography (SPECT). While SPECT is the less expensive option, cardiac PET imaging is more accurate, less risky, and more efficient. It has a major in that

A noninvasive test, a cardiac PET scan can detect whether areas of your heart muscle are receiving enough blood, which aids in the diagnosis and management of patients with known or suspected coronary artery disease. On the flip side – cardiac PET can measure coronary flow reserve to exclude high risk coronary artery disease, which is a huge advantage over Technitium SPECT imaging.

A cardiac PET scan is also used to find out how well your cardiac treatment plan is working. For patients who have had, or may have had, a heart attack, cardiac PET is used to check for damaged or scarred tissue in the heart. The capability also allows doctors to assess for heart failure, cardiomyopathy, and other heart conditions.

Cardiac PET scans utilizing F-18 FDG is the most sensitive modality to detect hibernating viable myocardium and predict left ventricular functional recovery after revascularization. Performance of the F-18 FDG tracer also provides excellent accuracy when evaluating infections and inflammatory diseases, making it a very powerful tool when compared to other tests.

[DocPanel] What types of patients can benefit from a cardiac PET scan?

[Dr. Chan]

A cardiac PET scan is used for both the detection of present abnormalities, as well as risk assessment for various conditions of the heart. Many patients may benefit from a cardiac PET scan.

Your doctor may ask you to get a cardiac PET scan for the following indications:

Detection of coronary artery disease (CAD) in the symptomatic patient with acute chest pain.

Detection of CAD/risk assessment without ischemic equivalent (chest/breathing symptoms):

• Asymptomatic high-risk patient for CAD
• New-onset or newly diagnosed heart failure with LV systolic dysfunction without ischemic equivalent
• Ventricular tachycardia
• Syncope with intermediate or high CAD risk
• Troponin elevation without additional evidence of acute coronary syndrome

Risk assessment – prior test results and/or known chronic stable CAD:

• Equivocal, borderline, or discordant stress testing where obstructive CAD remains a concern
• New or worsening symptoms – abnormal coronary angiography or abnormal prior stress imaging study
• Coronary stenosis or anatomic abnormality of uncertain significance
• Asymptomatic, high CHD risk, Agatston score (coronary calcium score) between 100-400
• Asymptomatic, Agatston score greater than 400
• Asymptomatic, intermediate-to-high risk Duke Treadmill score on exercise stress test

Risk assessment – preoperative evaluation for non-cardiac surgery without active cardiac conditions:

• Intermediate-risk surgery.
• Vascular surgery

Risk assessment for patients within 3 months of acute coronary syndrome:

• ST-elevation MI
• Unstable angina /non-ST elevation MI

Risk assessment – post revascularization (PCI or CABG):

• Symptomatic
• Asymptomatic- incomplete revascularization or greater than or equal to 5 years post CABG

Assessment of viability/ischemia:

• Ischemic cardiomyopathy
• Assessment of viability for patient eligible for revascularization

Evaluation of left ventricular function in:

• the absence of recent reliable diagnostic information from another imaging modality
• baseline and serial measures after key therapeutic milestones or evidence of toxicity from potentially cardiotoxic therapy

[DocPanel] What advice do you have for patients who get a cardiac PET scan?

[Dr. Chan]

While the capabilities of a cardiac PET scan make it the preferred modality in many cases – it’s a complex scan that requires expertise. My advice is to ensure your scan is administered at an accredited imaging facility and interpreted by a radiologist who specializes in cardiac imaging and nuclear medicine. There are many nuances in these scans, so you want to be sure it is reviewed by someone with extensive knowledge and experience.

Getting a second opinion from a service such as DocPanel is a great way to ensure your scan has been reviewed by a radiologist well-suited for your particular condition. It can also help ensure your doctors get the most information out of the exam. Even if you have two specialists review your scan, their reports may slightly differ. Having more than one opinion can help strengthen the accuracy of the final diagnosis/interpretation.

[DocPanel] What preparation is necessary for cardiac PET scans?

[Dr. Chan]

In preparation for a cardiac PET scan, patients are instructed to not eat or drink anything except water for 4 to 6 hours before the test. They should also not have anything that contains caffeine for 24 hours before the test. This includes coffee, tea, cola, and other sodas,
chocolate, and strawberries (these contain a small amount of caffeine). It also includes products labeled decaffeinated and caffeine-free (these contain small amounts of caffeine as well). Like caffeine, nicotine also affects the test results. No smoking is allowed on the day of the test.

Patients should tell their health care provider if:

• You are afraid of close spaces (have claustrophobia). You may be given medicine to help you feel sleepy and less anxious.
• You are pregnant or think you might be pregnant.
• You have any allergies to injected dye (contrast).
• You take insulin for diabetes. You will need special preparation.

[DocPanel] Do any medications interfere with the tracer used in a cardiac PET scan?

[Dr. Chan]

Yes – patients should bring a list of all medications and supplements they take, including those that are non-prescription (over-the-counter).

Patients will need to make sure they do not take any over-the-counter medication that contains caffeine (such as Excedrin) for 24 hours before the test. If they have asthma, do not take theophylline for 48 hours before the scan and bring your asthma inhaler with you.

Patients who use Dipyridamole (Persantine) should stop taking it 48 hours before the test. If you take insulin for diabetes, you will need special preparation.

[DocPanel] Are there any risks associated with a cardiac PET scan?

[Dr. Chan]

The amount of radiation used in a PET scan is low. It is about the same amount of radiation as in most CT scans. Also, the radiation does not last for very long in your body. However, women who are pregnant or are breastfeeding should let their provider know before having this test.
Infants and babies developing in the womb are more sensitive to the effects of radiation because their organs are still growing.

It is possible, although very unlikely, to have an allergic reaction to the radioactive substance. Some people have pain, redness, or swelling at the site of the injection.

A cardiac PET scan is a powerful tool that helps doctors not only detect disease at a late stage and treat it with expensive procedures and care.

While there are a number of diagnostic tests for the heart, a cardiac PET scan combined with subspecialty interpretation is among the most powerful. With superior image quality, it plays an important role in patient outcomes.