Contrast enhanced CT lets doctors look at abnormal coronary arteries

Friday, July 26, 2002

JACKSONVILLE, Fla., July 26, 2002 — Physicians at Mayo Clinic in Jacksonville, Fla., are using contrast-enhanced computed tomography (CT) to look at congenital coronary artery abnormalities. The left and right coronary arteries and their smaller branches are those arteries that supply the heart muscle itself with blood. Although these abnormalities affect only about 1 percent of the population, they are a primary cause of sudden cardiac death in people under age 35.

The abnormalities, which have a different origin and course than what's considered normal, usually are not discovered until an autopsy is performed. People with a coronary artery abnormality can live a normal lifespan. However, if a coronary artery courses between the aorta and the pulmonary artery, the body's two major blood vessels, the person may die suddenly, often during exercise when the heart's blood and oxygen needs are greater. Like a straw being pinched between two fingers, the larger aorta and pulmonary artery compress the coronary artery, cutting off blood flow to a portion of the heart muscle and causing death.

Physicians might incidentally discover an abnormal coronary from a CT scan of the chest taken for another reason. More likely, though, the problem would be discovered during coronary angiography, an invasive imaging procedure used to look at blockages in the coronary arteries. But this isn't done unless physicians already suspect the patient has coronary artery problems. Angiography usually helps physicians determine if the patient needs coronary artery bypass surgery or another procedure to open a blocked artery.

These images, called angiograms, are taken during heart catheterization. Physicians make a small incision in the patient's groin, and guided by X-rays, they advance a thin catheter from the femoral artery in the leg to the aorta. A special contrast medium injected through the catheter into the coronary arteries allows physicians to look for blockages on a series of X-ray images.

However, the images obtained are two-dimensional. They may, usually unexpectedly, reveal the presence of an abnormal coronary artery but not necessarily its course. "You can quite easily and clearly tell that an abnormality is there," says Mayo Clinic cardiologist Dr. Thomas Gerber. "But it's often very hard to be absolutely sure if the abnormal artery is running between the aorta and pulmonary artery or not. That distinction is critical, because if an abnormal coronary artery were to run between the two, the patient will need bypass surgery."

If an abnormal coronary artery is discovered, a contrast-enhanced CT of the heart is ordered. Gerber and Mayo Clinic radiologist Dr. Ronald Kuzo jointly read the images. The two use a technology called contrast-enhanced multi-slice CT, the newest generation of so-called spiral CT scanners, to determine just where the abnormal coronary artery runs.

Technicians inject contrast agent - the same medium used in coronary angiography - through a simple I.V. needle in the patient's forearm vein. The contrast agent travels to the coronary arteries and distinguishes them from surrounding tissues on the CT images. The multi-slice scanner takes multiple, rapid images of the heart that can be viewed and manipulated on a computer monitor in various ways, thus allowing Gerber and Kuzo to see the course of the abnormal artery. "It takes some expertise to do this," Gerber says. "Things come together well for us here, though. Dr. Kuzo is a radiologist with an interest in the heart, and I'm a cardiologist with an interest in radiology."

Gerber says without the aid of contrast-enhanced CT, the cardiologist doing a coronary angiogram can try to track the course of an abnormal artery. However, even after threading a second catheter into the patient's pulmonary artery for an additional spatial reference and looking at multiple images taken at different angles, even very skilled cardiologists may not be able to do this with certainty.

There are numerous variations in the origin and course of the coronary arteries, but regardless of the abnormality, blood is supplied to the entire heart muscle. Gerber says it's only those 20 to 25 percent of these cases where the artery passes between the aorta and pulmonary artery that require bypass surgery.

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