Patients with ascending aneurysms strongly protected from atherosclerosis

Ascending thoracic aortic aneurysms (ATAAs), which can lead to fatal bleeding if ruptured, remain a leading cause of death worldwide. A team led by Yale School of Medicine researchers finds patients with ATAAs are also protected against the development of atherosclerotic plaque, a leading cause of heart attack and stroke.

In a new review, senior author John Elefteriades, MD, and colleagues collect their results from several studies. "Previously, we published each building block of evidence separately," Elefteriades says. "In the current article, we bring together all the avenues by which this protection is manifest, syntheiszing prior findings into a unified concept."

Researchers say the walls of ascending aneurysms are generally smooth and free of atherosclerotic plaque.

"The coronary arteries, which feed the heart, are clean," Elefteriades says. "The peripheral (e.g. femoral) arteries are soft and smooth, like a teenager's." A series of studies established that compared with controls, patients with ATAA have, on average:

• Lower thickness of arterial walls (.131mm lower carotid intima-media thickness),
• Lower plasma levels of low-density lipoprotien (LDL), a major marker and risk factor for atherosclerosis,
• Lower calcification scores for the coronary arteries and the aorta (6.53 vs 9.36),
• Significantly reduced chance of coronary artery disease (61 vs 140) and heart attack (11 vs 83).

"With genetically based ascending aorta aneurysm, it is hard to develop or die from atherosclerosis," says Elefteriades. "It is overwhelmingly likely that your arteries are clean." But only aneurysms in the ascending aorta - the portion rising upward from just above the heart - offer protection. "Patients with aneurysms in the lower part of the aorta (e.g. the abdominal aorta) have increased atherosclerosis."

Researchers are now working to uncover what causes the protective effect. One theory is that the enzymes and growth factors causing aneurysm disease "digest" atherosclerotic plaques as a side effect. The team says genetic factors could be at play, too. "The aneurysm gene may prevent the smooth muscle cells in the aortic wall from "going rogue" to form atherosclerotic plaques," Elefteriades suggests.