DALLAS – New-onset postoperative atrial fibrillation following cardiac surgery occurs in two distinct phases, with different risk factors for each.
That’s the key finding in an analysis of the recent experience at the University of Alabama, Birmingham, where new-onset postoperative AF occurred in 27% of 1,583 consecutive patients who underwent coronary artery bypass graft and/or valve surgery.
The first peak in the onset of postoperative AF occurred in the first 3 hours after surgery. This was followed by a sharp decline in incidence over the next 24 hours. The second peak happened at postoperative day 2, followed by a more gradual tail off, Dr. Spencer J. Melby reported at the American Heart Association scientific sessions.
Ninety-six percent of all cases of postoperative AF in this retrospective chart review began within the first 7 days after surgery. Of the 423 patients who developed this common and vexing condition, 16% did so within the first 24 hours, 48% had their onset at 24-72 hours, and 36% did so after 72 hours, according to Dr. Melby, a cardiothoracic surgeon at the university.
Dr. Spencer J. Melby
In a multivariate analysis, the most potent risk factor for onset of postoperative AF during the first phase was mitral valve repair or replacement, which was associated with a 2.5-fold increased risk. The other significant risk factors for early-onset AF were older age – with 70-year-olds having a 1.6-fold greater risk than 50-year-olds – and longer ischemic time, with patients whose cross-clamp time was 70 minutes having a 1.3-fold greater risk compared with those who had a cross-clamp time of 35 minutes.
Advanced age was also a risk factor for late-phase onset of AF, but it was a stronger risk factor there than for early onset AF, with 70-year-olds being at threefold greater risk than 50-year-olds – nearly twice as great a risk as for early-onset postoperative AF. The other significant risk factors for late-phase postoperative AF in a multivariate analysis were white race, with a 1.9-fold increased risk, and heavier body weight, with patients weighing 100 kg being at 1.6-fold greater risk than those tipping the scales at 70 kg.
"We believe that these different risk factors at each time phase are indicative of change over time in the mechanisms that drive postoperative atrial fibrillation," the surgeon said.
The first peak may be the result of tissue trauma, which is typically greater with more complex operations having longer cross-clamp times. And mitral valve procedures often entail contact with the left atrium.
"We’ve found that in patients with onset in the second peak there’s a polymorphonuclear leukocyte riot going on in the pericardial space after surgery. Inflammation is high, oxidative stress is high. Troponin levels are extremely high in the pericardial fluid, so there are problems in the heart muscle itself. The body is trying to heal and may be overdoing it as reflected by the inflammation in that space," Dr. Melby explained.
Dr. Brendan M. Everett, session cochair, noted that postoperative day 2 is when a host of process-of-care issues potentially relevant to postoperative AF come into play.
"Postop day 2 is when pain control begins to slip a bit. Patients are mobilized, chest tubes are pulled. A lot of factors are going on that are very important overall to getting a patient up and out of the hospital but are serious stimuli – adrenergic and otherwise – that may force a patient to go into atrial fibrillation," observed Dr. Everett, director of the general cardiology inpatient service at Brigham and Women’s Hospital, Boston.
Audience members praised Dr. Melby’s study as having "tremendous implications" for clinical practice, especially with regard to patient management guidelines. Dr. Melby noted that postoperative AF is a costly matter: It increases hospital length of stay by 1-2 days at a cost of roughly $10,000 per episode. Nationally, postoperative AF costs $4 billion per year.
Dr. Melby reported having no financial conflicts regarding his study.