CT Scans after Bypass Surgery

(LifeWire) - "Bypass surgery" -- or, more formally, coronary artery bypass graft surgery (CABG) -- helps prevent a first (or subsequent) heart attack by grafting replacement sections of blood vessel and rerouting blood around dangerously blocked coronary arteries.

But how can doctors tell if the surgery has worked -- that the bypass grafts are still open and providing the heart muscle with an adequate supply of oxygen-rich blood? Computed tomography (CT) scanning is a new, noninvasive and effective way of doing so. However, CT scanning (using available technology) is not risk-free, and further, more invasive measures will often be needed if such scanning identifies graft problems.

Heart disease is the leading cause of death in the U.S., taking more than 650,000 lives annually. Heart attacks, generally triggered by blocked coronary arteries, account for a major part of this toll. Of the 860,000 Americans who have heart attacks each year, about 157,000 -- more than one in six -- die.

It's no wonder that much medical research has focused on ways to prevent heart attacks by treating blocked coronary arteries. CABG, performed on nearly 300,000 Americans annually, is one of the most common surgical remedies.

Bypass surgery not only restores the flow of oxygen-rich blood to the heart but also improves a patient's quality of life. However, up to 10% of bypass grafts close during or shortly after surgery. Moreover, about 60% of grafts taken from veins elsewhere in the body close within 10 years, as do 17% of grafts taken from arteries.

An angiogram, or angiography, is one method doctors use to tell whether bypass grafts are functioning properly. It involves threading a catheter (usually from the groin) up an artery to the heart and injecting a contrast dye so any blockage will show up in an x-ray.

But angiograms are invasive, while CT scans are not. On the other hand, CT testing exposes patients to roughly four times more radiation than angiography -- which can measurably increase the individual's lifetime cancer risk.

Moreover, if CT indicates a likely blockage, a catheter angiogram will still be needed before any corrective procedure -- to fully map and define the coronary arteries. Doctors attempt to balance the advantages and disadvantages of each test, including relative accuracy, cost and safety.

In CT scanning, a patient is placed on a table, inside a device that resembles a large doughnut (after removing jewelry or other items that could interfere with the scan).

The patient is in sight of the technician who performs the scan, and the two can communicate through an intercom system. During the scan itself, the patient will be asked to hold his breath for a few moments while the cylindrical scanner rotates, taking low-dose x-ray images.

Under typical circumstances, fasting or sedation isn't needed before the test. Afterward patients can immediately resume normal activities.

The scanner provides cross-sectional images, or slices, of different organs or areas of the body. CT images have proven more accurate than angiograms in detecting bypass graft problems, while angiography is more accurate in detecting blockages in the original vessels.

Patrizia Malagutti, M.D., the lead author of a 2006 study on the subject, writes that CT scans "may be of particular practical use when knowledge about [the] previous surgery is incomplete." That study concluded that CT scans were 99% accurate in identifying bypass graft problems.

Another study, in the American Journal of Roentgenology, showed that -- in some patients -- beyond simply checking bypass graft function, CT scans also uncovered other conditions, for example, lung cancer, pulmonary embolism and pneumonia.

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