Guidelines Miss Aortic Dissections

DALLAS -- Most patients who present with type A acute aortic dissection have an aortic diameter below the threshold at which preventive aneurysm surgery is recommended in current surgical guidelines, Dr. Linda A. Pape said at the annual scientific sessions of the American Heart Association.

"We have the problem of diameter not appearing to be a very good predictor of dissection risk," observed Dr. Pape of the University of Massachusetts, Worcester.

She reported on 591 patients with type A acute aortic dissection enrolled in the International Registry of Acute Aortic Dissection. All patients had measurements of their aortic diameter at dissection via MRI, transesophageal echo, CT, and/or angiography.

Current guidelines recommend preventive surgery when the maximum ascending aortic diameter reaches 5.5 cm in patients without Marfan syndrome and 5 cm in those with Marfan. That's the threshold at which the risk of dissection or rupture becomes sufficient to outweigh the morbidity of major surgery.

But in the first-ever study of its kind to examine the issue in a large unselected patient population, Dr. Pape found fully 59% of patients had a maximum ascending aortic diameter less than the 5.5-cm cutoff. "A surprisingly high 40% of patients dissected at diameters less than 5 cm," he added.

Patients who dissected at less than 5.5 cm had higher rates of reported back pain, radiating pain, abrupt onset of pain, and more neurologic deficits than did patients with an aortic diameter of 5.5 cm or greater at dissection, but rates of such complaints were high in both groups. Interestingly, the 5% of patients with Marfan syndrome were more likely to present with a diameter greater than 5.5 cm. Overall, mortality was 27%.

"Aortic size is not a sufficient marker of risk for dissection. In order to prevent aortic dissection and its potentially catastrophic outcome, we need better methods--genetic, biomarkers, or aortic functional studies--to identify patients at risk," Dr. Pape said.

"Aortic diameter has been considered the best predictor of risk for rupture in the descending thoracic and abdominal aorta," said Dr. Frank Pomposelli, clinical chief, division of vascular surgery, Beth Israel Deaconess Medical Center, Boston, when asked to comment on this presentation.

"This appears to not be the case for the ascending aorta and likely reflects the different pathology involved in ascending aneurysms.

"The conclusion arising from this study is that smaller aneurysms should be repaired, but this must be tempered by the significant morbidity and mortality risk involved in ascending AA repair by traditional surgery.

"Thoracic stent grafts are now being used to repair ascending and arch aneurysms with lower morbidity than traditional surgery and may play an increasingly important role in their treatment especially for smaller, uncomplicated aneurysms," he added.