November 13, 2006
Student Scene
New CT May Separate Low- from High-risk Chest Pain Patients
Photo by Graham Ramsay Joseph Ladapo |
Patients who present to the emergency department complaining of chest pain may be the first beneficiaries of the latest in imaging technologies. Often evaluated for a suspected heart attack, these patients may soon be receiving scans using 64-slice computed tomography (CT), the newest and most advanced CT available. So called because of its 64 X-ray detectors, this CT scanner is spreading rapidly to hospitals throughout the country. Its key clinical strength is its ability to generate high-resolution images of the coronary arteries, vessels that are commonly pathological in heart disease.
Like other CTs, the 64-slice CT scanner uses X-rays to create images of internal human anatomy. Unlike older machines, however, this new technology generates images with a level of detail and precision never before seen. For this reason, it has a special application in cardiovascular health.
Plaque Detector
Patients at risk for a heart attack typically have plaque deposits in the
walls and lumens of their coronary arteries. When one of these plaques ruptures,
the resultant clot can occlude the vessel lumen, choking off downstream heart
muscle from necessary blood. Without a supply of nutrients and oxygen, these
muscles die, resulting in a heart attack. The new 64-slice CT identifies these
dangerous plaques with a high degree of accuracy.
Although the prevalence of plaque in coronary arteries is relatively high among patients with chest pain, the absence of plaque is highly predictive of a noncardiac cause of discomfort. Patients who fall into this latter category are often low risk and usually suffer from less acute conditions, such as gastric reflux or anxiety. They make up a sizeable portion of the six million people who present to the ED each year with a complaint of chest pain.
The 64-slice CT has the potential to monumentally influence how physicians care for acute chest pain patients. |
Typically, low-risk patients whose initial ED workup is indeterminate for a possible heart attack are admitted to the hospital for further evaluation. The reasons for admission are mixed, but two strong motives include the life-threatening complications associated with erroneously failing to admit a patient with a heart attack and the serious legal liability that often follows a missed diagnosis. Not surprisingly, most low-risk patients who are hospitalized for a suspected heart attack are discharged home one or two days later, without being diagnosed with this condition.
By identifying this niche group of patients, hundreds of thousands of unnecessary and expensive hospitalizations could be avoided each year. The advent of 64-slice CT brings this possibility closer to reality.
A High-tech Economy
Udo Hoffman, HMS assistant professor of
radiology, is leading a Massachusetts General Hospital study on the use of
this technology in the ED. According to Dr. Hoffman, with the exception of
64-slice CT, “There is no good instrument
right now that predicts whether [chest pain patients] will develop acute coronary
syndrome,” or ACS, a condition that encompasses both heart attacks and
unstable angina, a less acute but serious condition characterized by cardiac
ischemia.
Dr. Hoffman’s study, published in the Oct. 31 issue of Circulation, involves 103 people who presented to MGH with a chief complaint of acute chest pain. All of the patients had an initial ED workup that was negative for a heart attack, but a noncardiac cause for their chest pain could not be identified definitively. Many of them were low risk. All of them were admitted to the hospital for further evaluation after being imaged with the 64-slice CT. Only 14 were ultimately diagnosed with acute coronary syndrome.
Radiologists analyzed 64-slice CT images of their coronary arteries to identify features that distinguished patients with acute coronary syndrome from those without it. They found that all of the ACS patients had significant plaque burden in their coronary arteries, along with significant stenoses. On the contrary, most of the remaining patients either had no plaque or less significant stenoses.
“What this study shows is that when you do the MDCT [multidetector computed tomography] picture of coronary artery disease, it distinguishes between patients who appear similar at baseline,” Dr. Hoffman explained. “ACS is rare without plaque, so MDCT results may quickly identify a group of patients that can safely be discharged.”
The 64-slice CT has the potential to monumentally influence how physicians care for acute chest pain patients. Though these machines are only in a few hundred hospitals nationwide, including MGH, Brigham and Women’s Hospital, and Beth Israel Deaconess Medical Center, they are spreading rapidly to other sites. With any luck, 64-slice CT will, indeed, prove to be a technology that saves health care dollars, saves patients time, and helps physicians focus on saving the lives of patients who are truly at risk.
—Joseph Ladapo is a Harvard medical student and a PhD student in health policy.
The opinions expressed in this column are not necessarily those of Harvard Medical School, its affiliated institutions, or Harvard University.
Copyright 2006 by the President and Fellows of Harvard College