SAN FRANCISCO — Chest pain represents one of the most common presenting symptoms in the emergency department, and it also represents a diagnostic challenge: Is it a pulmonary embolism? Is it an aortic dissection? Is it coronary artery disease? Or is it nothing?
Now, new CT technology promises to revolutionize this diagnosis, giving the ability to rule out all three conditions with a single 15-second scan.
In theory, this scan can replace stress testing for coronary artery disease, echocardiography or CT for aortic dissection, and CT pulmonary angiography or a ventilation-perfusion scan for pulmonary embolism, Dr. Matthew J. Budoff, M.D., said at a cardiovascular imaging conference sponsored by the American College of Cardiology.
Although no diagnostic or prognostic studies on the triple rule out have yet been published, there's some indication that the single scan will have 90% accuracy or better for each of the three conditions, said Dr. Budoff of Harbor-UCLA Medical Center in Torrance, Calif.
The technology involves a 64-slice CT scan from the apex to the base of the lungs.
Patients will have to hold their breath for 20–30 seconds as contrast is injected and the images are acquired. Acquisition of the slices will be gated to the heart's rhythm, allowing for stable, high-resolution images of the heart and lungs. The slice thickness will be 0.625 mm.
Software and a sophisticated workstation will allow the clinician to construct three-dimensional images of the heart, lungs, or aorta, and to manipulate three-dimensional and two-dimensional images in a variety of ways.
In addition to aortic dissection, pulmonary embolism, and coronary artery disease, the technique will allow clear views of the pericardium, permitting the diagnosis of calcified or thickened pericardium and sometimes pericarditis.
In addition, “you might pick up pneumonia, and you might pick up pulmonary adhesions or even pericardial adhesions,” Dr. Budoff said.
“There are a lot of things you could possibly see. And it could be done during the chest pain episode, which is a great advantage over some of the other modalities where you'd want to wait until their chest pain is quiescent.”
Dr. Budoff described the case of an elderly woman who complained of chest pain and shortness of breath.
Because of her age, he was reluctant to order a stress test. The CT angiography showed that her coronary arteries were normal and that her ejection fraction was acceptably high. When he examined the lung images closely, however, he discovered several pulmonary emboli.
“We admitted her to the hospital, put her on heparin, and it all cleared up,” he said.
Despite its promise, the triple rule out does have some limitations. For one thing, it subjects patients to a relatively high dose of radiation—in the neighborhood of 24–30 millisieverts, equivalent to 240–300 chest x-rays.
Because it's a gated study, more contrast must be used and the injection time is longer than for a standard CT. Some patients may have trouble holding their breath for 20–30 seconds.
Then there's the issue of who is going to read these images when a patient presents to the emergency department at 3 a.m. The radiologist staffing the emergency department may not be facile with cardiac CT angiography. Although the images could be transferred over data lines, the cardiologist is not likely to have a workstation with the proper software at home. In all likelihood, someone will have to come to the hospital to read the study.
Still, Dr. Budoff expects the triple rule out to become a routine test in the emergency department, a prospect he greets with mixed emotions.
“We really need to see how this is going to pan out, and work out the reading issues before we start applying this to everybody who comes in with a twinge in their chest or shortness of breath,” he said. “I'm a little leery … to say just because we can do it we should.”
On the left: an aortic dissection appears as a long, thin dissection flap in the descending aorta. In the center: an endoscopic view of the aortic dissection shows the true lumen (larger area) and false lumen. On the right: a high-grade stenosis is shown in the mid-left anterior descending artery. Photos courtesy Dr. Matthew J. Budoff
