The mechanism of postoperative AF is complex and not fully understood, but almost certainly multifactorial. Noninvasive signal-averaged electrocardiography suggested a preoperative conduction abnormality that predisposes some patients to AF in the postoperative setting. One of the most likely triggering mechanisms is the heightened adrenergic present in the postoperative state. Other factors that play a role include pericarditis, atrial ischemia, electrolyte abnormalities, atrial myopathy, and others. Patients with concomitant valve surgery are at an even greater risk.

Most Atrial Fibrillation Cases are Short Term Episodes 

The clinical pattern of atrial fibrillation can be highly variable. Unpublished observations from our clinical registry suggests that most patients have paroxysmal AF, i.e., episodes that self- terminate. Our experience suggest that the great majority of patients who experience AF do so in a self- limited way, not requiring active intervention. A minority experience prolonged AF, symptoms, hemodynamic instability, or complications that require a more active approach.

If AF is recurrent or prolonged, there is certainly a risk of cardioembolic stroke. Acute and post-discharge anticoagulation is critical. The period of risk likely expires a few weeks after surgery.

AF Treatment Modalities: Two Approaches 

A number of treatment modalities have been proposed as a preventative measure for postoperative AF. These include both antiarrhythmic drugs and atrial pacing.

AThe largest experience with prophylactic medical therapy is with beta-blockers. A number of clinical trials using a wide variety of beta-blockers have been published. Patients who have used preoperative beta-blockers that are withdrawn after surgery seem to be at particularly high risk of AF. Reinstitution of beta-blockers after surgery has been associated with a reduction of postoperative AF in most clinical trials.

A recent meta analysis suggest that AF is reduced by approximately 40% i.e. from an incidence of 30% to 20%. No one beta-blocker is superior to another.

A class III antiarrhythmic drug, sotalol, that also has beta blocking properties, has been tested in a small number of trials. Sotalol has consistently and successfully reduced the AF incidence, but probably no greater than that observed for more conventional beta-blockers.

Amiodarone, a highly effective class III antiarrhythmic drug available in intravenous and oral formulation, has also been tested in a small number of trials. Reduction of AF incidence may be slightly greater than that for beta-blockers and sotalol, perhaps in the range of about 50% risk reduction. The nature of administration of amiodarone has varied quite a bit in clinical trials, ranging from preoperative oral loading to postoperative IV infusion.

The newest promising technique is epicardial atrial pacing. Because during cardiac surgery epicardial-pacing electrodes can easily be placed, and then controlled by an external temporary pacemaker, this is a relatively simple extension of standard surgical technique

The concept underlying atrial pacing is to maintain stable atrial activation patterns avoiding premature beats, pauses, and dispersion of atrial conduction and/or refractoriness. Similar efforts have been made to prevent AF outside the surgical setting. A very small number of controlled trials have tested right atrial, left atrial, and biatrial pacing. Overall, there appears to be a favorable trend in the atrial-paced patients, regardless of the pacing agorithm utilized.

Minimal Effect on Length of Stay 

Although a variety of methods have successfully been employed to reduce AF incidence, successful reduction in length of hospital stay has been consistently absent. In essence, none of these pharmacologic or pacing modalities have had an impact on length of stay, which remains stubbornly increased by the presence of atrial fibrillation.

Overall, the meta analysis suggested AF prophylaxis reduces length of stay by only about one half of one day. Length of stay likely remains prolonged because of symptoms and complications of AF, necessity to apply pharmacologic or cardioversion interventions, adverse effects of medications, and intentional clinical observation. The data also suggests that there is no reduction in stroke risk due to any of the effective prophylactic treatments of AF.

In Summary 

In summary, beta-blockers represent the simplest and most cost-effective prophylactic treatment of postoperative AF, and are easy to employ in a patient population that requires betablockers for other purposes as well. Alternative antiarrhythmia drug therapy includes amiodarone and sotalol, and atrial pacing is promising, but not yet of proven benefit. The interventional approach to the patient experiencing postoperative AF must be individualized.

References:
Steinberg JS, ed. ³Atrial Fibrillation After Cardiac Surgery². Kluwer Academic Publishers, Norwell, MA 1999

Crystal E et al. Interventions for Prevention of Postoperative Atrial Fibrillation in Patients Undergoing Heart Surgery: A Meta Analysis. Circulation 2002; 106:75-80.

Reproduced with permission. Published by the Arrhythmia Service of St. Luke's-Roosevelt Hospital Center, New York, New York.