Predicting Risk in Aortic Dissection

Thomas Tsai Photo: Martin Vloet

Each year, 10,000 Americans suffer a sudden and often lethal tear in the lining of the body’s largest blood vessel, the aorta, which carries blood from the heart to the lower half of the body.

Patients today are far more likely to survive this medical crisis, called aortic dissection, thanks to improved medical imaging and treatment. But after they leave the hospital, they face a one-in-four chance of dying within the next few years. Doctors don’t have a reliable way of predicting which patients have the highest risk of death and who might benefit most from surgery or additional treatment.

In a New England Journal of Medicine study directed by physicians in the Cardiovascular Center, researchers propose a new way to predict post-hospital death risk for aortic dissection survivors, and present a new model for the mechanism behind that risk.

The model focuses on the presence of blood clots in a channel created when the layers of the aorta separate like two layers of an onion. This channel, called the “false lumen,” runs alongside the “true” lumen — the hollow middle of the aorta, which is the pipeline for blood flowing out of the heart and down through the abdomen.

These three cross-sectional illustrations of the aorta illustrate the different states of blockage that might occur within the “false lumen” or secondary channel created by an aortic dissection. In each case, the false lumen is in purple, and the “true” aorta is red. At left, the channel is clear (also called patent), a state that was associated with lower risks of post-hospital death in the new study. In the middle, the false lumen is partially blocked by clots, a state that was associated with a much higher risk of death. At right, the false lumen is entirely thrombosed, or filled with clots. This state was associated with an intermediate risk of death. Copyright © 2007 Massachusetts Medical Society All rights reserved.

As blood enters the false lumen from the top of the torn aorta, it gets trapped inside the new channel where blood clots can form. The study showed that the risk of post-hospital death was more than two-and-a-half times greater for patients with partial clotting of the false lumen, than for those whose false lumen contained no clots. If the false lumen was completely filled with clotted blood — something that happens infrequently — the patient had an intermediate risk of death.

“This could be a predictor of patients most at risk — knowledge that might help guide decisions about when it’s wise to proceed with more aggressive treatment and when we can hold off,” says lead author Thomas Tsai (M.D. 1998), a fellow in cardiovascular medicine.

The study involved data from 201 patients with dissections in their descending aortas, who were followed for up to three years or until death, as part of IRAD — the International Registry of Acute Aortic Dissection. IRAD is headquartered at the Cardiovascular Center and includes data from 22 large medical centers in 11 countries. Kim Eagle, M.D., a director of the Cardiovascular Center, also helps direct IRAD.

—Kara Gavin

For an expanded version of the story:
www.med.umich.edu/opm/newspage/2007/aorta.htm

For patient information on aortic dissection:
www.med.umich.edu/1libr/aha/aha_aortdiss_car.htm