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Radiology
Multislice CT speeds the diagnosis of chest pain in the emergency room
By American College of Cardiology, Feb 21, 2007 - 8:23:54 AM

Imagine coming to the hospital with crushing chest pain, only to find that emergency room doctors are uncertain whether you’re having a heart attack. The electrocardiogram (ECG) is inconclusive and the blood tests that detect heart damage are normal. The only thing to do is wait, hour after hour, as doctors repeat the tests several times and scrutinize the results for diagnostic clues.

Soon, the wait may be much shorter. According to research reported in the February 27, 2007, issue of the Journal of the American College of Cardiology (JACC), a computed tomography (CT) scan of the heart can quickly detect whether there are fatty blockages or pockets of rock-hard calcium in the arteries of the heart—clues that coronary artery disease may be the cause of the chest pain.

"The new 64-slice CT scanners give us amazing pictures of the heart," said James A. Goldstein, M.D., F.A.C.C., Director of Research and Education in the Division of Cardiology at William Beaumont Hospital, Royal Oak, MI. "With this very simple outpatient scan, you can rapidly determine whether the arteries are normal or abnormal—and if they’re abnormal, whether the disease is mild, moderate, or severe."

Those who get a clean bill of health can safely go home from the hospital without further testing. "As a physician, it’s tremendously satisfying to tell an anxious patient, within about 30 minutes, that their heart and arteries are normal," Dr. Goldstein said.

Each year, some 6 million people in the United States are rushed to the emergency room with chest pain. At least half have inconclusive early test results; of these, approximately 65 percent are eventually found not to have suffered a heart attack—but not before racking up diagnostic costs totaling $10 billion to $12 billion annually.

Even low-risk patients with no history of heart disease can spend 18 to 24 hours in the emergency room as doctors repeat the ECG and blood tests. That’s because doctors want never to mistakenly send home a patient who is actually having a heart attack. "The consequences of missing a heart attack can be disastrous," Dr. Goldstein said. "So even if you appear to be completely healthy, if you come to the emergency room with chest pain, you’re going to go through a very laborious, expensive, and time-consuming evaluation."

Dr. Goldstein and his colleagues wanted to see whether a CT scan of the heart could make the evaluation of chest pain more efficient and less costly, allowing emergency physicians to quickly send home patients with normal coronary arteries, while accurately identifying patients with serious heart disease who needed to be admitted to the hospital.

For the study, they recruited 197 patients with heart attack-like chest pain but no history of heart disease. In all patients, the results of the ECG and the blood tests that detect heart damage were normal, both initially and after being repeated four hours later. The researchers then randomly assigned half of the patients to have a CT scan of the heart and the other half to a standard diagnostic plan, which included additional rounds of ECG and blood testing, plus a nuclear scan of the heart.

Multislice CT first uses x-rays to measure the amount of calcium in the arteries supplying blood to the heart. Then, after injection of high-contrast intravenous dye, it creates detailed pictures of the heart and coronary arteries, including any soft, cholesterol-filled blockages. The scan takes only minutes to complete.

Nuclear scanning is a two-part test that uses radioactive material to evaluate blood flow to the heart during rest and again during stress, when the heart is pumping faster as the result of exercise or medication. By definition, nuclear imaging takes longer than a CT scan. Most doctors prefer to observe the patient in the emergency room for at least eight hours before stressing the heart, just to be safe. In addition, several hours must pass between the rest and stress portions of the test to allow the radioactive material to pass through the body.

In the new study, patients with a clearly normal CT or nuclear scan were allowed to go home immediately, and those with a clearly abnormal scan were sent to the cardiac catheterization laboratory for further, invasive testing. In the CT group, patients with uncertain test results—either because the images were not clear, or because there was only a moderate amount of disease in the coronary arteries—also had a nuclear scan to help determine whether invasive testing would be needed.

The researchers found that CT alone was able to determine that heart disease was the cause of chest pain—or reliably rule out that possibility—in 75 percent of patients. The remaining 25 percent of patients had a nuclear scan in addition to CT. Even so, both the cost and the time it took to reach a diagnosis were significantly lower in the CT group. Costs averaged $1,586 for patients who had a CT scan, as compared to $1,872 for patients who had a standard diagnostic evaluation (p<0.001). Similarly, the time it took to make a diagnosis averaged 3.4 hours with CT, as compared to 15 hours with the standard diagnostic approach (p<0.001).

"We were able to show a dramatic reduction in the time it took to reach a definitive diagnosis, even though in this small study we did not have the scanner operating 24 hours a day, seven days a week," Dr. Goldstein said. "For both individual patients and society, the use of CT to evaluate chest pain in the emergency room could have tremendous implications for the costs and efficiency of care."

"CT angiography has produced very impressive images of the coronary arteries without the need for catheterization, but where, when and how to use this information is uncertain," said Anthony N. DeMaria, M.D., F.A.C.C., Editor-in-Chief of JACC. "These data demonstrate a potential application of CT angiography for the rapid assessment of chest pain in the emergency room. However, it must be acknowledged that the patient population was limited, confined to low risk individuals based upon initial evaluation, and that the primary benefit was in detecting abnormalities sooner and more inexpensively, but not more accurately. The effect of the earlier diagnosis upon outcome also remains to be determined."

A large randomized controlled trial will put CT to a demanding test. Dubbed CT-STAT, the Coronary Computed Tomography for Systematic Triage of Acute Chest Pain Patients to Treatment trial will involve 750 low-risk patients evaluated for heart attack-like chest pain at 15 hospitals across the United States. Patient recruitment will begin soon.

CT does have limitations, Dr. Goldstein said. For example, if a patient is already known to have coronary artery disease, CT is less helpful. That’s because it can’t determine whether a moderate blockage is substantial enough to interfere with blood flow to the heart, thereby causing chest pain. In addition, it often fails to produce clear images in very obese patients—although this barrier may fall as manufacturers work on new imaging methods.

Another concern is radiation exposure, noted Pim J. de Feyter, M.D., Ph.D., F.A.C.C., University Hospital Rotterdam, the Netherlands, in an accompanying editorial in the Feb. 27, 2007, issue of JACC. This is particularly true for patients with moderate arterial narrowings or unclear CT images. They receive one dose of radiation during CT scanning, a second dose of radiation during follow-up nuclear scanning, and in some cases, a third dose during cardiac catheterization. "If multislice CT does not give a definitive diagnosis, alternative diagnostic strategies that avoid radiation exposure…should be investigated," Dr. de Feyter said.

Dr. Goldstein reports no potential conflicts of interest regarding this topic.

Also in this issue of JACC

A report from Queen’s University, Kingston, Ontario, Canada, describes the development of new standards for identifying metabolic syndrome in adolescents. Metabolic syndrome is defined by a cluster of unhealthy characteristics that hike the risk of cardiovascular disease, including a large waist measurement, high blood pressure, high blood sugar, high blood levels of fats known as triglycerides, and low blood levels of "good" cholesterol, or HDL cholesterol.

In adults, the cut-off points for identifying metabolic syndrome—just how large a waist circumference, or how high the blood pressure reading—are well established and considered valid. Until now, the cut-off points used in adolescents have been arbitrary and have varied from one research study to the next. The Canadian research group created a more reliable set of standards by starting with the already validated adult cut-off points for 20-year-old women and men, then performing a statistical analysis to work backward to age 12. They displayed the data for each of the characteristics of metabolic syndrome as an age-related growth curve, just like the ones pediatricians routinely use in evaluating a child’s age-related height and weight.

"Our goals were to provide age-appropriate and health-based metabolic syndrome component cut-points for adolescents…that could be used consistently in clinical and research settings," the researchers noted. "In light of the increasing prevalence of obesity and other metabolic syndrome indicators in the pediatric population, it seems urgent to address this problem in this age group."


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