New Light Shed On Atrial Fibrillation After Bypass Surgery
DURHAM, N.C. -- An analysis of 4,657 patients undergoing coronary artery bypass surgery has shown that discontinuing certain heart medications such as beta blockers and ACE inhibitors can lead to abnormal accelerations in heart pumping known as atrial fibrillation, while those and other agents can offer protection.
Since an estimated one in three bypass patients will suffer at least one episode of atrial fibrillation in the days and weeks following surgery, these and additional findings from a new international study have important clinical implications, said principal investigator and Duke anesthesiologist Joseph Mathew, MD. Past studies have shown that atrial fibrillation can lead to heart failure, kidney damage or stroke, and can prolong hospitalization after surgery while the irregular heart rhythm is controlled.
The researchers also found that more than 40 percent of patients who experience atrial fibrillation after surgery have more than one episode, and that it is these patients who are responsible for the bulk of increased complications and lengthened hospital stays.
According to the researchers, no large-scale international study has systematically evaluated the preoperative risk factors for atrial fibrillation, as well as the potential risk factors during surgery and during the recovery period after surgery. The results of the first such analysis were published March 14, 2004, in the Journal of the American Medical Association.
"Based on the results of our analysis, we now have a risk index that should be better able to not only predict which heart surgery patients are at higher risk for atrial fibrillation, but what actions we can take to prevent it from occurring," Mathew said. "The incidence of atrial fibrillation has remained fairly constant over the past two decades; we hope this new risk index can improve outcomes for bypass surgery patients."
Atrial fibrillation arises from abnormal electrical discharges in the heart, which cause the upper pumping chambers, the atria, to beat much faster than normal. This abnormal beating causes the lower pumping chambers, the ventricles, to pump erratically and inefficiently, leading to an inadequate amount of blood being pumped throughout the body.
For their analysis, the international team followed 4,657 patients treated at 70 centers in 17 countries. The data collected on two-thirds of the patients were used to identify the risk factors that were used to develop the index. The predictive value of that index was then validated against the other one-third of patients.
According to the researchers, this was the first study to actually capture the precise day of onset of atrial fibrillation and the postoperative complications. These data allowed the researchers to examine the relationship between the two, as well as the effect of recurrent atrial fibrillation on postoperative outcomes.
The study was supported by the Ischemia Research and Education Foundation, San Francisco, a non-profit research organization. Also collaborating in the study were investigators of the Multicenter Study of Perioperative Ischemia Research Group.
"This is also the first analysis that not only enrolled such a large number of patients, but looked at treatment practices in many different countries," Mathew said. "Given that the incidence of atrial fibrillation was consistent across the major regions of the world, we feel that we have an accurate and representative sample of patients upon which to base a predictive index."
Of the patients in the study, 32.3 percent suffered at least one episode of atrial fibrillation as measured by an electrocardiogram (EKG). The risk factors most associated with atrial fibrillation were advancing age, a past history of the disorder, and chronic obstructive pulmonary disease. Additionally, there were strong associations between the incidence of atrial fibrillation and the discontinuation of beta blockers and ACE inhibitors immediately after surgery, Mathew said.
Significantly, the administration of beta blockers and ACE inhibitors, as well as non-steroidal anti-inflammatory drugs (NSAIDS) and potassium, appeared to reduce the risk of atrial fibrillation for those who were not taking the drugs.
"It has been long assumed that patients are too sick after surgery to continue to receive beta blockers or ACE inhibitors, so many physicians stopped their use," Mathew said. "This same assumption used to hold true for heart failure patients. However, studies have since shown that heart failure patients actually benefited, especially the high-risk ones. So based on the results of this study, the discontinuation of beta blockers and ACE inhibitors would be unwise and their use appears to be protective."
More research needs to be done, however, to determine if continuation of these medications will be safe for all patients undergoing heart surgery, Mathew said.
Additionally, the researchers found that 43 percent of patients suffered more than one episode of atrial fibrillation. Significant risk factors for recurrent atrial fibrillation included older age, history of heart failure, aortic atherosclerosis and the withdrawal of beta blockers and ACE inhibitors.
"Patients with recurrent atrial fibrillation had longer hospital stays and experienced greater infectious, kidney and neurological complications than those with a single episode," Mathew said. "For that reason, these patients should be treated the most aggressively."
The majority of the initial episodes of atrial fibrillation occurred within the first three days after surgery. However, 60 percent of patients with more than one episode had another episode within the first two days.
The research team plans to analyze blood samples of more than 1,000 of these patients to determine whether or not there is a genetic marker that would help predict which patients are most at risk. They also plan to follow these patients long-term to see what happens to them after they leave the hospital.