by Dr. Stefano Sdringola, MD, MHA
It is a common experience for many families to have a loved one affected by heart disease or stroke (cardiovascular diseases), which could lead to sudden death or long-term disability. Cardiovascular diseases, particularly heart disease, remain by far the leading cause of death, hospitalization, and cost of healthcare in the United States for both men and women. Approximately every 40 seconds an American will have a heart attack. It is estimated that such conditions and events are highly preventable, up to 90% of the time. Early detection and treatment of coronary artery disease could prevent unnecessary tragedies. It is therefore essential to have a strategy of aggressive risk factor modification and the use of the right technology at the right time, to detect the presence of heart disease and guide therapy.
What Is PET?
PET stands for Positron Emission Tomography and is currently the most accurate non-invasive technology for visualizing blood flow in the heart muscle supplied by the coronary arteries. Pictures of the myocardial blood flow are taken before and after pharmacologic stress instead of exercise to determine if maximum blood flow is restricted by the narrowing of the coronary arteries. PET can be the first step for risk assessment of coronary heart disease or an excellent alternative to invasive tests such as cardiac catheterization when results of other tests are equivocal or inconclusive. The test also helps physicians determine when more invasive procedures such as coronary artery stents or coronary artery bypass surgery are absolutely necessary to relieve symptoms, prevent the progression of heart disease, or decrease the risk of a heart attack. Most recently, the development of dedicated software to provide quantitative measurement of coronary blood flow continues to improve the utility of PET in guiding the long-term management of coronary heart disease. Such comprehensive features provide precise quantitative information on the health conditions of the heart and, in particular, of the essential system that supplies the necessary energy for the vital function of the heart muscle (coronary arteries system).
What Is a Cardiac Stress PET Study?
A cardiac PET study is a stress test used to check blood flow to your heart. During the test, a small amount of radioactive material called “radioactive tracer” is injected into a vein. The tracer most commonly used is Rubidium-82. It is not a dye or contrast and will decay in a few minutes while not risking damage to your kidneys. The tracer will deposit in the heart muscle in an amount proportional to the blood flow. The different regions of the heart will “light up” with an intense color if the coronary arteries are fully patent and with a gradually less intense, cooler, color if there are “blockages” causing an impediment to proper blood flow in the coronary arteries. A special camera, called a cardiac PET scanner, detects the radiation released by the tracer and creates accurate computer images of your heart muscle. The imaging test is performed at rest and under “stress,” combined with a medication to maximally open your blood vessels circulation (vasodilator). The medication stimulates the effects of exercise. The test with the medication helps your doctor to find out if your heart is getting enough blood while you are maximally active compared to when you are resting.
The test is also used to:
- Find out how much heart damage you have after a heart attack
- Find out how well your cardiac treatment plan is working
Why Should a Cardiologist be Ordering a PET vs. Traditional Nuclear SPECT Imaging?
There are multiple reasons:
1. The first is accuracy. The traditional SPECT nuclear stress test study is based on an older, simpler, technology that does not have a high spatial, contrast, or temporal resolution of the images, resulting often in “blurry” or “grainy” images that are difficult to interpret and can provide a false-positive or falsely negative results due to the artifact intrinsic in a less than optimal image. The advantage of PET is in the higher quality and diagnostic accuracy; it works as an efficient gatekeeper, avoiding unnecessary invasive angiographic procedures in patients when revascularization is not indicated.
2. The second is safety. When we perform imaging (X-rays, CT, nuclear, or invasive angiogram) of the heart, we have to accept some low levels of radiation exposure. Thanks to the very short half-lives (70 seconds for Rb-82) and rapid clearance from the blood of the nuclear tracer utilized, PET provides a much lower radiation exposure to patients, technologists, and physicians compared to SPECT radiotracers or CT angiograms. The radiation exposure for a rest/stress Rb-82 PET is approximately equivalent to the natural background exposure of living one year in Denver. In fact, PET is recommended by the current guidelines as a preferred stress imaging technique when necessary to study coronary artery disease in young persons.
3. The third reason is that PET is patient-centered, providing efficient and timely care. A rest/stress PET test can be completed and a report can be generated in less than 45 min. This saves a lot of the patient’s time compared to the 3-4 hours necessary for a traditional SPECT stress test.
4. Fourth: PET it is equitable. In fact, PET can be used with similar accuracy in men, women, or people who are of larger or smaller sizes, since, at the contrary to SPECT, the quality of the images is not significantly affected by breast size or body habitus.
5. The fifth, last but not least, major reason is the unique capacity of the PET to measure absolute blood flow going to the heart muscle. This is called with technical terms: coronary flow reserve and coronary flow capacity. This allows us to know not only if the test is normal or abnormal but to quantify in great detail (milliliters of blood per gram of heart muscle per minute) of how healthy or unhealthy the coronaries system actually is. This type of information cannot be obtained even in the catheterization lab with an invasive coronary angiogram.
What Type of Patients Benefit Most from Cardiac PET?
Because of the peculiar advantages of PET with the high-quality images, accuracy, and capacity to quantitatively assess coronary blood flow in the different coronary arteries territories, PET is particularly helpful in patients who had equivocal results with other imaging techniques. This includes those patients who are obese and/or have large breasts, patients with complex coronary artery disease (like those who already had a coronary artery bypass or coronary stents) in whom a diagnostic error can carry the worst clinical consequences, and when absolute flow information is essential to exclude balanced and diffuse coronary artery disease or microvascular disease, which may not be identified with the other imaging technologies available. Furthermore, PET is strongly preferred in patients who are unable to exercise on a treadmill or are young (less than 50 years old) and likely to require further medical radiation exposure during their lifetime. Finally, if a revascularization procedure is planned, PET imaging is likely to indicate with precision which area is most likely to benefit from coronary stent/angioplasty or bypass surgery.
Why Is Cardiac PET Heart Imaging Not More Widely Utilized?
There are a number of reasons but the main one has been the cost. Although cardiac PET has been used for more than 40 years, it has been limited to research institutions due to the cost of the machine (several times more expensive than the SPECT machine seen in the usual cardiology hospital divisions or cardiologist offices) and the cost for the production of the sophisticated nuclear tracer. Currently, the fixed costs are still relatively high, but more affordable by a large cardiology practice. The second reason is education, since only a few of the currently practicing cardiologists have been lucky enough to be exposed and trained with such sophisticated technology. The lack of knowledge and awareness of the benefit that cardiac PET brings makes its use not yet widespread. However, it is rapidly becoming more popular, and embracing this technology to best serve our patients will be inevitable.
Can PET Assist in Preventing Disease and Save Money?
A PET study can detect coronary atherosclerosis early on. We can measure the health of your coronaries like we would measure blood pressure or blood sugar. Therefore, we can intervene early on and we can monitor the effect of risk factor modification interventions with follow-up studies, as clinically indicated, to evaluate the progression or regression of coronary heart disease. We can detect disease well before patients become symptomatic or have a heart attack. In addition, PET rest/stress can identify those patients and coronary territories that will benefit the most from revascularization procedures avoiding unnecessary costly invasive coronary angiograms or procedures with questionable health benefits.
If you experience any of the usual telltale symptoms of heart disease, heart attack, or other heart conditions, be sure to discuss your options with your doctor as quickly as possible, as these tests can help prevent major, life-threatening cardiac events. At Vital Heart & Vein, we provide a wide array of cardiac testing including PET scans. Learn more about our diagnostic testing by visiting us online or scheduling an appointment.