A study conducted at St. Mary’s Hospital and 22 other sites around the world found that high-resolution CT imaging is as good as – if not better than – stress tests in assessing the risk of heart attack caused by heart arteries that have been narrowed by cholesterol and inflammation.

 Dr. Erick Avelar, a board-certified cardiologist and medical director of advanced cardiac imaging at St. Mary’s Hospital, was the lead local researcher for the study site in Athens. Dr. Avelar is a Level 3 cardiac imaging reader at Oconee Heart and Vascular Center (OHVC) with experience in conducting clinical studies. He was invited to participate in the study by Weill Cornell Medical College in New York, one of the most prestigious medical research institutions in the world.

The study was named the CREDENCE Trial (Computed tomogRaphic Evaluation of atherosclerotic DEtermiNants of myocardial isChEmia). Results were published recently in JAMA Cardiology, a journal of the American Medical Association.

“This was the first successful clinical research collaboration between OHVC, St. Mary’s and the University of Georgia, and it has brought international recognition to all three partners,” Dr. Avelar said. “Everyone wins with clinical research: clinicians, the scientific community, and – most importantly – our patients.”

The study’s goal was to see if non-invasive CT imaging of the heart’s arteries was as accurate as stress testing in detecting coronary artery blockage – the cause of most heart attacks. The study used highly accurate cardiac catheterization as the reference standard for whether CT imaging was as good as stress testing at detecting blockages. The study included 23 facilities worldwide and enrolled 612 patients as test subjects, 11 of whom were recruited at the Athens site.

“What we found is that CT is as accurate as stress testing in measuring the significance of coronary artery obstructions, if not more accurate,” Dr. Avelar said. “We also found that it can be used as the first-line cardiac imaging choice when evaluating patients with chest pain. The study demonstrates that CT is a safe and cost-effective way to diagnose coronary artery disease and produces results comparable to a functional established stress test such as a nuclear stress test, stress echo, regular EKG stress test, or stress MRI.”

Most importantly, Dr. Avelar said, the study found CT may detect potentially dangerous blockages that stress tests might miss.

"In some cases, a patient may have a significant blockage that is not detected by a stress test because adequate blood supply is still able to pass through the artery," he explained. "In those cases, the stress test is not sensitive enough to show the problem. Our study found that CT imaging was able to detect blockages that were missed by the stress test."

As a result, Dr. Avelar said, CT could play a valuable role in follow-up studies when a patient's stress test results are unclear. It might also be useful if a patient needs follow-up studies and is concerned about the risks of a cardiac catheterization test.

“Cardiac catheterization is very safe, but CT poses even less risk of external bleeding, hematoma or infection, and no risk of internal artery damage,” he said. “A catheter study takes about 45 minutes, while a CT study takes about 20 minutes, although the actual scanning time is only a few seconds. In addition, CT requires no sedation or recovery time, is virtually painless, and is less expensive. However, the CREDENCE study compared CT angiography (CTA) to stress testing, not cardiac catheterization. The CREDENCE study shows CTA provides enhanced detection that is equal to or better than stress testing, but cardiac catheterization remains the 'gold standard' for diagnosis of obstructive coronary artery disease in patients with chest pain."

Coronary artery disease is the leading cause of death in the United States, claiming about 600,000 American lives each year and generating costs of nearly $109 billion, according to the CDC. Patients with coronary artery disease experience a range of symptoms from mild angina during exertion to heart attack. Women often experience subtler symptoms than men.

Some of the biggest factors that contribute to coronary artery disease include high blood pressure, uncontrolled diabetes, a sedentary lifestyle, a high-fat diet, tobacco use, family history and aging. Most heart attacks could be prevented if people lived a heart-healthy lifestyle, according to the American Heart Association. 

Taking a closer look

All participants in the CREDENCE study were patients who were experiencing chest pain that raised concerns of obstructive coronary artery disease. All received a CT study of their coronary arteries, a stress test, and a left heart catheterization. Researchers used the results of the catheter study to see what was happening inside the patient's coronary blood vessels. They then compared the results of the CT study and the stress test to see which came closest to the results of the catheter study.

When a person has coronary artery disease, blood vessels become stiff and may develop small tears in their internal lining. Cholesterol collects at the damaged site and the body’s immune system causes swelling, creating a plaque. Eventually, the plaque may become large enough to reduce the flow of blood that serves heart tissue, causing pain on exertion. Without treatment, the plaque may go on to form a blood clot that completely blocks the vessel, causing a heart attack.

A stress test may show that a plaque is limiting blood flow, but until now, the only way to measure how much blood flow was being restricted was to insert a long, flexible tube called a catheter into the heart. Catheter studies remain the “gold standard” for diagnosing coronary blockages in patients with chest pain and heart attack risk. However, because catheter studies require puncturing an artery, sedation, hours of recovery time and are also expensive, they are usually used only after less invasive testing shows there is a need.

Until CTA receives FDA approval for this purpose, the only option for that less-invasive test is a stress test. There are several types of stress tests, all of which can signal that a blood vessel in the heart may be narrowed. But stress tests cannot visualize the blockage or measure exactly how much of the blood vessel it blocks.

CT, on the other hand, uses x-rays and contrast (a harmless solution that makes certain structures more visible on x-ray images) to create 3D images of the diseased artery. The images show the blockage and how much of the blood vessel it obstructs. Trained image readers like Dr. Avelar can use the images to measure the obstruction and its impact on blood flow.

CT angiogram testing is done on an outpatient basis and requires only a needle stick to administer the contrast. In addition, unlike stress tests, the best cardiac CT images are acquired at a low heart rate. So, medications are given by IV prior to the actual scan to achieve the optimal heart rate while the patients’ vital signs are monitored. The patient requires no sedation and is on the exam table for only a few minutes once the proper low heart rate is achieved – around 60 beats per minute or less. Unlike an exercise stress test, the patient does not have to run or bicycle as hard as they can, and unlike nuclear, echo or MRI stress tests, no medication is required to speed up the patient's heart rate.

CT testing for the study was performed on St. Mary’s 64-slice CT scanner. St. Mary’s has since upgraded its top-of-the-line scanner to a 640-slice system. A CT “slice” is like a card in a deck. A CT64 has a “deck” of 64 slices for each rotation around the patient’s body. A CT640 has a “deck” of 640 slices for each rotation, providing higher quality and more detailed images in less time.

“This advance is possible because of the highly detailed images produced by newer CT technology,” Dr. Avelar said. “The next step is for other researchers to confirm the findings of the CREDENCE trial, and then, hopefully, CT can be added to the cardiologist’s toolbox for diagnosing the risk of heart attack in patients with coronary artery disease."

The article, Stress Myocardial Perfusion Imaging vs Coronary Computed Tomographic Angiography for Diagnosis of Invasive Vessel-Specific Coronary Physiology is posted at jamanetwork.com/journals/jamacardiology.