An uncommonly used surgical procedure that bypasses a narrowed aortic valve, rather than replacing it, effectively restores blood flow from the heart to the rest of the body and gives high-risk patients a safe alternative to conventional valve surgery. That is the finding of a study conducted at the University of Maryland Medical Center in Baltimore. The researchers conclude that the procedure, called aortic valve bypass, is an important treatment option for high-risk elderly patients with a narrowed aortic valve, a condition called aortic stenosis.
The bypass procedure can be performed in a minimally invasive way without stopping the heart. Many of the patients in the study had previously been considered too frail to benefit from surgery. The study will appear in the September 30, 2008 print issue of Circulation and is now online.
"Because of the possible risks associated with aortic valve replacement in the elderly, almost 60 percent of patients with symptoms related to aortic stenosis are never referred to surgery," says the study's principal investigator, James S. Gammie, M.D., associate professor of surgery at the University of Maryland School of Medicine and cardiac surgeon at the University of Maryland Medical Center.
Survival for these patients without surgery is poor; only 20 percent are alive three years after diagnosis. "But our research and five years of experience with the bypass procedure suggests there is a group of patients, typically considered inoperable because they are at the upper level of the risk spectrum, who could benefit from aortic valve bypass," says Dr. Gammie.
The aortic valve controls the flow of blood from the heart's main pumping chamber, the left ventricle, to the aorta, the artery that supplies blood to the rest of the body. In aortic stenosis, calcium deposits narrow the valve and impair the heart's ability to pump blood. Aortic stenosis is the most common heart valve disease of the elderly in the United States. More than 50,000 people in the United States require surgery for aortic stenosis each year.
During conventional valve replacement, the surgeon opens the chest, stops the heart for about 90 minutes, opens the aorta just above the aortic valve, cuts out the old valve and sews in a new one. While valve replacement has benefited millions of patients with good outcomes, in elderly patients, particularly those with other health conditions, the death rate can exceed 10 percent.
The bypass procedure
In order to bypass the narrowed aortic valve, surgeons at the University of Maryland Medical Center have refined a procedure, originally called an apicoaortic conduit, which was developed in the 1970s and initially used for children. During the procedure, most of the blood flow from the heart is diverted through a tube containing a standard replacement valve that is placed near the apex of the left ventricle, the pointed tip at the bottom of the heart, to the aorta, the main blood vessel at the back of the chest.
The surgeons work through an incision between two ribs on the left side of the chest. During the first cases, a large incision was needed. However, the procedure was modified this year, so that only a small, three-inch opening between the ribs is required. "We are excited because for the first time we can surgically treat a narrowed aortic valve through a minimally-invasive approach with the heart beating, compared to the traditional breastbone-splitting approach," says Dr. Gammie.
Between 2003 and 2007, the surgeons treated 31 high-risk aortic stenosis patients with aortic valve bypass surgery. Many of the patients also had other conditions ranging from chronic obstructive pulmonary disease to kidney disease, or had a history of heart attack or diabetes. The average age was 81, and nearly half had been refused conventional surgery. Early in the series, four of the 31 patients did not survive the procedure, yet there were no deaths among the most recent 16 consecutive patients.
The procedure was as effective as conventional aortic valve replacement surgery at relieving the obstruction of blood leaving the heart. Stroke and kidney problems were uncommon. Because the impaired aortic valve was left in place, some blood flow continued through that valve. But postsurgical blood flow measurements indicated that in most patients, approximately 70 percent of cardiac output flowed through the new bypass.
The study results suggest that continued improvements in technology and surgical technique may warrant extending aortic valve bypass surgery to moderate-risk patients with aortic stenosis. In addition to the 31 patients who received an aortic valve bypass, the University of Maryland Medical Center performed 438 other aortic valve procedures during the same time period.
Gammie JS, Krowsoski LS, Brown JM, Odonkor PN, Young CA, Santos MJ, Gottdiener JS, Griffith BP. Aortic Valve Bypass Surgery: Mid-term Clinical Outcomes in a High-Risk Aortic Stenosis Population. Circulation. Published online ahead of print, September 15, 2008.