Aortic dissection patients may have new hope

New way to predict post-hospital death risk

Survivors of aortic dissection may improve their odds of long-term survival with more aggressive follow-up care and more targeted discharge instructions, based on the findings of a new study in the New England Journal of Medicine.1

An international team of researchers, led by University of Michigan Cardiovascular Center experts, propose a new way to predict post-hospital death risk for aortic dissection patients, and a new model for the mechanism behind that risk. Their research focused on partial clotting in what is known as a "false lumen" — the channel created when the layers of the aorta separate like two layers of an onion. This channel runs alongside the "true" lumen, which is the hollow middle area of the aorta that acts as the pipeline for blood to flow out of the heart and down through the abdomen.

What made the researchers suspect partial clotting in the false lumen? "At our hospital we follow these patients in our clinic, and [some of these clots] just take a more aggressive course — the clot gets bigger much faster than others," explains Thomas Tsai, MD, MSc, of the University of Michigan Cardiovascular Center in Ann Arbor and lead author of the article. "We noticed the [MRI] scans would show partial clotting and that caught our eye, so we decided to investigate." No other researchers "had really looked at this before," he asserts.

The study involves data from 201 patients with dissections in their descending aortas, who were discharged from the hospital after treatment and followed for up to three years or until death as part of IRAD, the International Registry of Acute Aortic Dissection. (IRAD, which is headquartered at the University of Michigan Cardiovascular Center and supported in part by the university's medical school, the Mardigian Foundation, and the Varbedian Fund for Aortic Research, includes data from 22 large medical centers in 11 countries.)

The paper is based on retrospective clinical data from 114 patients who had a patent false lumen when they were admitted to an IRAD hospital, 68 patients who had a partially thrombosed (clot-filled) false lumen, and 19 who had a completely thrombosed false lumen.

By the end of the three-year follow-up period, nearly 25% of the patients had died. However, the researchers found a significant difference in death risk:

  • 13.7% of the patients with patent (clear) false lumen had died, compared with 31.6% of the partially thrombosed patients and 22.6% of the completely thrombosed patients. This difference held up after other factors were corrected for.

A matter of survival

This research — and the findings — were of great import because of the high mortality rates among these patients, notes Tsai. "With aortic dissection of this type [Type B, in the descending aorta], most survive discharge, but once they leave the management is unclear as to what mode of action is best," he says. "The current protocol is to follow with imaging, and once the aorta becomes large enough [just how large, he says, is undefined] you may operate on it or take some other action."

With a three-year mortality rate of 25%, finding more targeted methods of follow-up could clearly make a big difference, he continues. "Our findings provide the possibility for physicians to look for other factors in the imaging tests above and beyond just how big the dissection is — like other features that either show the need for earlier surgery, or the safety of holding off."

A more sophisticated mode of treatment, he adds, would home in on the status of the false lumen. "At present we are not looking specifically at each lumen, whether it is false or true," says Tsai. "We should challenge ourselves to look at what happens within the false lumen: Is it clotted? Is it partially clotted? Where are the tears? We need a better understanding about the anatomy of dissection."

Current scanning technology enables such studies, he asserts, "but we still need experts who will be looking for this; most radiologists now will look at the size and don't know to look at anything else. You have to specifically ask for what you want, but if you do, they can do it correctly and get that information."

Should discharge instructions change?

While noting that the team's findings are "not yet completely substantiated," Tsai says it's not too soon to be considering an adjustment to discharge instructions and patient follow-up.

"Currently the implication is that we as physicians should be cognizant of what the anatomy of the dissection is when the patient leaves," he says. "If you see a partial thrombosis when the patient is leaving the hospital, you may say to them, 'Your dissection may be more risky for getting larger; we should make sure to image you again in one month,' and make sure to ask the radiologist what is going on with the false lumen."

Discharging physicians will recommend "frequent follow-up imaging," which could be every three, six, or nine months. "In addition to looking at more than just size, we should potentially try to refine how frequently we do follow-up imaging," Tsai suggests. "However, radiation exposure does not come without cost, so we need to better refine just what we are looking for."

Reference

1. Tasi TT, Evangelista A, Nienaber CA, et al. Partial Thrombosis of the False Lumen in Patients with Acute Type B Aortic Dissection. N Engl J Med 357:49, July 26, 2007.

[For more information, contact:

Thomas Tsai, MD, MSc, University of Michigan Cardiovascular Center, 1500 E. Medical Center Drive, Ann Arbor, MI 48109-5853. Phone: (734) 945-9408. E-mail: hsianshi@umich.edu.]