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Gated SPECT Is Best for Heart Disease Assessment

A study comparing the ability of various medical techniques to accurately determine the extent of heart disease and stratify patients according to disease severity found that myocardial perfusion testing with gated SPECT was the best predictor of prognosis in chronic ischemic heart disease. According to the American Heart Association, it is the leading cause of death in the United States and the European Union.

“The prognostic value of stress testing with myocardial perfusion imaging [gated SPECT] has been investigated for several years,” says Alessia Gimelli, MD, of the Clinical Physiology Institute CNR, G. Monasterio Foundation in Pisa, Italy. “However, substantial changes in nuclear cardiology have occurred over the past two decades that have led to improved techniques. The clinical profile of patients with ischemic heart disease has also changed, with patients often being older and affected by more diseases than in the past. We were therefore surprised to see that gated SPECT remains the best predictor of future cardiac events in patients with ischemic heart disease.”

Gated SPECT is uses a small amount of radioactive material that, after injection, circulates in the bloodstream to show whether the heart muscle is receiving adequate blood supply under stress and/or rest conditions. SPECT imaging performed after stress reveals the distribution of the radiopharmaceutical and, therefore, the relative myocardial perfusion to the different regions of the heart muscle. The resulting set of SPECT images provides quantitative information regarding myocardial perfusion after stress and at rest, as well as the heart as it contracts.

Since its introduction in the late 1980s, gated SPECT has become one of the most commonly performed cardiology procedures in nuclear medicine departments. The automation of image processing and quantification has made the technique highly reproducible, practical, and user friendly in clinical settings. It is similar to a standard SPECT study except that more images are acquired. Diagnosis is made by comparing stress images with an additional set of images obtained at rest. It is sensitive to even the most modest changes in blood flow and can determine whether the heart is receiving enough blood and oxygen. In this way, gated SPECT provides information regarding the presence of myocardial infarction and myocardial ischemia, explains Gimelli.

For the study, published in the April issue of the Journal of Nuclear Medicine, researchers selected a group of patients with known or suspected, albeit stable, ischemic heart disease. Those with previous coronary artery bypass surgery, chronic kidney failure, and hyperthyroidism were excluded, leaving 492 study subjects aged 55 to 75. Each patient underwent a complete diagnostic workup that included a medical history, physical examination, blood tests, electrocardiography at rest, 2D echocardiography, and gated SPECT after stress and at rest.

Study patients also underwent coronary arteriography, the standard clinical procedure for diagnosing ischemic heart disease, according to the American Heart Association. A contrast dye is then injected, and x-rays record areas where narrowing or blockage in one or more coronary arteries has occurred.

For 37 months, patients returned for periodic examinations in an outpatient setting. Armed with the resulting data, the researchers determined that of the techniques investigated, including coronary arteriography, gated SPECT is the best predictor of future cardiac events. Although left ventricular ejection fraction is more commonly used in clinical practice to predict patient outcome, this study reveals that the extent of damage to the heart muscle, as shown in the SPECT images, is a better prognosticator of how patients will fare. This ability to identify individuals at risk for future cardiac events, such as heart attacks, has considerable appeal because the early initiation of preventive therapies may alter the course of the disease, the researchers note.

“Risk stratification allows us to categorize patients according to the severity of their disease and risk of future cardiac events,” says Gimelli. “As a result, we are able to allocate resources where needed and treat the sickest patients more aggressively.”

— Source: Society of Nuclear Medicine