CABG patchy for AF prevention

New risk assessment index pinpoints patients at risk of atrial fibrillation after bypass surgery

By Samuel Munson

Coronary artery bypass graft (CABG) surgery is one of the most common major surgeries in Canada � over 50,000 are performed each year. Unfortunately, along with the health benefits, the operation comes with an unwelcome aftereffect � the chaotic movement of the atria. The quivering motion of atrial fibrillation (AF) can set the stage for the formation of a blood clot. In about 10% of Canadians over 70, this can spell subsequent trouble in the form of a stroke.

Knowing who's at risk of developing AF would be useful, since the condition may be reversible. This goal is in sight with the recent publication of a paper in the April 14 issue of Journal of the American Medical Association. Dr Joseph Matthew at Duke University in Durham, North Carolina and his colleagues reported that they've developed a predictive index for AF.

Over 4,600 CABG patients from 17 countries and 70 medical centres around the globe were studied. Of these, 1,503 (32.3%) developed AF after the surgery, most within the first three days post CABG. The incidence "was remarkably consistent across most regions of the world," the authors noted. Not surprisingly, AF was associated with longer stays in the hospital, particularly in the intensive care unit, and with an increased death rate. Moreover, for 43% of the patients with AF, this was only the beginning as the initial fibrillation was followed by repeated episodes.

The researchers were able to come up with a model to assess the risk for AF, based on different factors. The final plus-minus balance sheet could be tallied up and graded to see whether a patient had a low- or high-risk of post-CABG AF.

Old age, a past history of AF or chronic obstructive pulmonary disease, and valve surgery, were all found to be risk factors for both an initial bout of fibrillation and for subsequent atrial malfunctions. Further, problems like left ventricle malfunction, hardening of cardiac arteries and the insertion of a cannula into a heart valve were also associated with increased danger of repeated bouts of AF. Finally, those lucky patients who received beta-blockers, ACE-inhibitors, or anti-inflammatory drugs generally faired better, and weren't as likely to develop AF. Disconcertingly, however, the authors noted that "only 52% of the patients were treated with beta-blockers post-operatively; and in 24%, beta-blockers were actually withdrawn from therapy."

The study's conclusion may mean that the number of patients on beta-blockers goes up and the number with post-CABG AF comes down. In any event, flagging patients who are likely to have AF after surgery is definitely good news.