Imaging Test May Enable Doctors to Better Predict Heart Attacks By Kevin Self Reviewed by Elizabeth Klodas, MD, FACC  and    Positron emission tomography (PET) scans are commonly used to detect cancer, but increasingly, they are also being used to detect heart disease. A new study shows that PET evaluations may enable doctors to accurately predict whether a serious heart event will occur within 3 years of undergoing the test.

Coronary artery disease (CAD), which affects thousands of Americans each year, is a heart condition that results from the buildup of plaque inside heart arteries, causing a reduction in blood flow to heart muscle. Although much is known about the condition, it is still difficult to assess the risk of a serious heart problem (such as a heart attack or the need for bypass surgery) occurring in affected patients.

Research conducted at the University of Zurich, however, suggests that utilizing a new imaging technique may offer doctors a way to predict — or increase early detection of — patients who are at greater risk of suffering a heart attack or even death as a result of their current heart condition.

For years the detection and severity of CAD was primarily determined with an imaging technique that used single-photon emission computerized tomography, or SPECT. This test is commonly referred to as a “thallium test” or a “cardiolyte study”. Increasingly, research suggests that PET is more accurate than SPECT because it is able to measure coronary flow reserve (CFR) — an important indicator of heart artery health.

The present study was designed to measure how accurate PET — using the tracer ¹³N-ammonia — and CFR are at predicting the outcomes of patients with known or suspected coronary artery disease. A tracer is a radioactive compound, administered in very low doses through an IV, which can track various physiologic activities within the body.  13N- ammonia tracks blood flow to the heart.

Researchers found that patients with abnormal 13N-ammonia PET scans were significantly more likely to suffer a major heart event or death than those with normal PET results. Similarly, patients with abnormal CFR had a dramatically higher rate of heart problems — suggesting a significant predictive value for both PET and CFR. However, the study proved that CFR was consistently the most accurate factor in predicting future adverse events over the entire follow up period.

“Also significant was that normal CFR in normal PET perfusion images indicates good outcomes, which offers patients essentially a warranty period of three years,” says Dr. Philipp Kaufmann, one of the authors of the study. “This is important because it is a safe, non-invasive and reliable test and therefore can be repeated after the end of the warranty period to help continually monitor heart health.”

Kaufmann acknowledges some of the limitations of the study and suggests further tests be conducted with tracers other than 13N-ammonia. Currently, 13N- ammonia is only available in very specialized centers and requires a complex infrastructure to produce.  Nevertheless, it is expected that cardiac PET testing will continue to shed new light on heart disease and be more widely available over time.

The study findings are published in the July 7, 2009 issue of the Journal of the American College of Cardiology.

Source:  

Herzog BA et al. Long-Term Prognostic Value of 13N-Ammonia Myocardial Perfusion Positron Emission Tomography. Added Value of Coronary Flow Reserve. Journal of the American College of Cardiology, 2009

Dr. Philipp Kaufmann, Cardiovascular Center at the University Hospital Zurich, Switzerland.