False Lumen Status Predicts Mortality Risk After Type B Aortic Dissection

ANN ARBOR, Mich., July 26 -- Partial thrombosis of the false lumen created after a dissection in the descending aorta is a strong predictor of death after hospital discharge, researchers found.

Risk of death is more than two-and-a-half times higher in patients with a partial thrombosis of the channel created along the true lumen of the aorta after vessel dissection - the false lumen - than risk in patients with patent false lumens, according to a study published in the July 26 issue of the New England Journal of Medicine.

Patients with completely occluded false lumens have an intermediate risk of death, wrote Thomas T. Tsai, M.D., M.Sc., of the University of Michigan at Ann Arbor, and colleagues.

Patients with a dissection confined to the descending aorta (a type B dissection) have better in-hospital survival than those with dissections of the ascending aorta. But post-discharge survival rates vary widely -- from 56% to 92% at one year, and 48% to 82% at five years.

Patency of the false lumen has been suggested as a predictor of outcomes. To explore that link, the researchers examined data from the International Registry of Acute Aortic Dissection (IRAD). The study period was 1996 through 2003 and included 201 patients with type B aortic dissection who survived to hospital discharge.

Of these, 114 patients (56.7%) had a patent false lumen, 68 patients (33.8) had a partial thrombosis of the false lumen and 19 patients (9.5%) had complete thrombosis of the false lumen.

"In our study, partial thrombosis of the false lumen was defined as the concurrent presence of both flow and thrombus in the false lumen; this condition was not considered a distinct physiological state in most previous studies and has not been previously associated with increased mortality," the investigators explained.

The mean three-year mortality rate with a patent false lumen was 13.7%, with a partially thrombosed false lumen it was 31.6%, and it was 22.6% with a complete thrombosis of the false lumen.

Independent predictors of death after discharge were partial thrombosis, with a relative risk of 2.69, a history of aortic aneurysm, with a relative risk of 2.05 and a history of atherosclerosis, with a relative risk of 1.87.

"One potential explanation [for the higher mortality with a partially thrombosed false lumen] relates the pressure within the false lumen to the presence of partial thrombosis," Dr. Tsai's team proposed.

"Whereas a patent false lumen may be perfused by a proximal entry tear and decompressed through distal reentry tears, formation of a partial thrombus may occlude these distal tears, impeding outflow and, in the most extreme situation, resulting in a blind sac?," they said.

"Complete thrombosis of the false lumen excludes the false lumen from the circulation and is thought to be a prerequisite for complete healing," they added.