Published: Apr. 27, 2004
Updated: Nov. 3, 2004
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By Duke Medicine News and Communications
HONOLULU. -- Coronary artery bypass patients are twice as likely to suffer a later major cardiac event if they experience abnormalities in the motion of the walls of the main pumping chamber of their heart during surgery, according to Duke University Medical Center researchers. According to the researchers, their findings suggest that such patients should be followed closely after discharge.
Using transesophageal echocardiography (TEE), which provides high-quality images of the heart, the researchers correlated abnormal movements in the walls of the left ventricle during surgery with subsequent heart attacks, death or the need for another bypass surgery or angioplasty procedure within two years.
The researchers said that the findings of their analysis can help physicians predict which of their bypass patients are at the higher risk of adverse outcomes after surgery. They also said the findings further confirm the utility of using TEE during surgery, an approach that is routine at Duke University Hospital and is becoming the standard of care nationally.
"One small study in 1989 demonstrated that abnormal wall motion seen by intraoperative TEE was predictive of adverse outcomes for patients while still in the hospital," said Duke cardiothoracic anesthesiology fellow Daniel DeMeyts, M.D., who presented the results of the Duke study April 27, 2004, at the annual scientific session of the Society of Cardiovascular Anesthesiologists.
"Ours was the first large-scale study to examine whether or not new wall motion abnormalities detected during surgery were predictive of long-term outcomes," DeMeyts continued. "The results of our analysis do clearly show that the presence of new abnormal movements in the walls of the left ventricle put bypass patients at a higher risk of future adverse outcomes."
During a TEE examination, a small probe is placed down the esophagus to a location behind the heart. From this vantage point, it captures moving images of the heart -- and especially the left ventricle. It has been used routinely as a diagnostic tool to assess valve function and areas of heart muscle that have been damaged or killed by past heart attacks.
The routine use of TEE during bypass surgery is gaining wider acceptance, the researchers said.
Physicians at Duke have employed TEE on all bypass procedures performed since the early 1990s. For their analysis, the researchers identified 1,543 bypass patients who underwent bypass surgery since 2000, of which 221 suffered a major cardiac event within two years.
For each patient, the researchers studied 16 distinct areas of the muscle wall of the left ventricle. For each area, the movement of the wall was given one of four scores: normal (1) and three degrees of abnormal, weak movement (2), no movement (3) or erratic movement (4). The individual scores for each region were added together and then divided by 16 to yield a composite score.
"We found that there was a significant statistical association between the higher post-bypass scores and the occurrence of adverse events," DeMeyts said. "As the score increased, so did the risk even after accounting for other risk factors such as age and diabetes."
Both DeMeyts and senior member of the research team, Joseph Mathew, M.D. said that while there is not an immediate clinical application of the new findings, the occurrence of wall motion abnormalities during surgery should spur physicians to follow these patients more closely after discharge. Most of these patients will be treated aggressively, and will be prescribed drugs, such a beta blockers, which are known to have a protective benefit.
A key question to be answered, they continued, is what causes the wall motion abnormalities. They could be the result of the existing heart disease, the time the heart is stopped to allow the surgery to occur, the actual surgery itself, or a combination of factors.
"The main problem is that we don't have the technology to adequately measure the patency of the grafted arteries while we're in the operating room," Mathew said. "When we have that we can really make a difference by identifying any problems in the operating room and fixing them. The current technologies are fine at imaging blood flow in the larger vessels, but no technique is good at looking at blood flow in the smaller vessels."
The researchers are currently investigating another ultrasound technique using TEE that may allow them to evaluate small vessel blood flow before the patient leaves the operating room.
While the current study used aggregate scores from the 16 different regions of the left ventricle, the researchers are now focusing on dividing the left ventricle into three regions based on supply from the three main coronary arteries to see if the abnormal wall motions in specific regions confer more risk than other areas. They are also studying the effects of these new wall motion abnormalities on length of hospitalization.
The analysis was supported by Duke's Department of Anesthesiology.
Other members of the Duke team were Madhav Swaminathan, M.D., Mihai Podgoreanu, M.D., John Booth, M.D., Richard Morris, Ph.D., Fiona Clements, M.D., Hilary Grocott, M.D., and Mark Newman, M.D.