Postoperative atrial fibrillation (POAF) is a minor and transient complication, occurring in one in three patients undergoing cardiac surgery. Initially viewed as a benign adverse event, numerous studies have shown that it increases hospital stay by 1 to 6 days and raises the incidence of postoperative and long-term stroke. The exact mechanism triggering this arrhythmia remains unclear, although it is associated with a combination of preoperative and postoperative risk factors. These range from degenerative changes in the atrial myocardium due to age and the patient’s inherent lesion mechanisms to postoperative changes that promote POAF, including left atrial refractory period dispersion, increased phase 3 depolarization, heightened automaticity, extended interatrial conduction time, reduced conduction velocity, transmembrane potential alterations, and various electrolyte imbalances.

The study analyzed in this article aims to evaluate POAF characteristics and outcomes, as well as the effect of posterior pericardiotomy on its prevention. Using PALACS study data, a post hoc analysis was performed, describing clinical and hemodynamic characteristics, including data on onset, duration, rapid ventricular response (>100 bpm), antiarrhythmic use, electrical cardioversion, and systemic anticoagulation.

Among the 420 patients analyzed, 25% developed POAF. The median time to arrhythmia onset was 50.3 hours, with 71% of cases occurring within the first 3 days. More than half of the cases presented with a rapid ventricular response, and in 8.7% of patients, POAF led to hemodynamic instability. The majority of patients (97%) received some form of antiarrhythmic therapy; 20% required electrical cardioversion, and 40% received oral anticoagulation. The median duration of POAF was approximately 24 hours, with 71% resolving within the first 36 hours. This accounted for around 16% of the patient’s total hospital stay. All patients showed sinus rhythm at follow-up. Experiencing POAF extended hospital stay by one day (p < .001) without a clear increase in morbidity or mortality. Posterior pericardiotomy reduced the incidence of POAF by nearly half (17.7% vs. 31.3%; p < .001), with this effect observed after the second postoperative day. Age was confirmed to be associated with POAF, while female sex, coronary artery bypass grafting, beta-blocker therapy, and posterior pericardiotomy provided protection against it.

The study authors concluded that, despite advances, POAF remains a common postoperative complication. Although rarely causing hemodynamic instability, it frequently presents with a rapid ventricular response requiring electrical cardioversion. The arrhythmia typically resolves within the first month post-surgery, with posterior pericardiotomy notably reducing POAF incidence, especially beyond the second postoperative day.

COMMENTARY:

The PALACS study was a single-center, prospective, randomized trial aimed at assessing the efficacy of posterior pericardiotomy in preventing POAF. Patients were randomized into groups with and without posterior pericardiotomy. The study included patients undergoing coronary artery bypass grafting, aortic valve replacement, ascending aortic repair, and combined surgeries. Mitral and tricuspid valve surgeries were excluded. Continuous postoperative telemetry monitoring was employed, with POAF defined as an irregular rhythm without detectable P waves lasting more than 30 seconds. The duration of POAF episodes was recorded to calculate total time in POAF if multiple episodes occurred. An independent committee comprising two cardiologists and a cardiac surgeon evaluated all arrhythmic events. The clinical trial demonstrated that posterior pericardiotomy significantly reduced POAF incidence (OR 0.44; p < .005).

The quest for an effective drug or maneuver to prevent POAF is longstanding in cardiac surgery. Various agents, such as beta blockers, sotalol (a class III antiarrhythmic with beta-blocking activity), amiodarone, atrial pacing, and even antioxidant vitamins, have been used with varying success. Many other drugs, like digoxin, class I antiarrhythmics, calcium channel blockers, intravenous magnesium, ACE inhibitors, statins, N-acetylcysteine, colchicine, naproxen, and glucocorticoids, have proven ineffective. Posterior pericardiotomy is particularly appealing as a relatively simple procedure with minimal side effects compared to the extensive list of medications attempted.

A major strength of the PALACS study is its precise definition of POAF and the use of telemetry for its diagnosis. Despite its frequency, POAF has multiple definitions depending on the source—be it the Society of Thoracic Surgeons, the Heart Rhythm Society, or the American Association for Thoracic Surgery. This lack of consensus complicates the comparison of findings across different studies. Moreover, many studies rely on clinical diagnoses, underestimating the true incidence of the arrhythmia.

Posterior pericardiotomy creates a communication between the pericardial cavity and the left pleura. Its association with reduced POAF incidence provides insight into the pathophysiology of this arrhythmia and its relationship with postoperative pericardial effusion. POAF occurring within the first 48 hours is more likely linked to the patient’s preexisting arrhythmogenic substrate. Given the minimal invasiveness of added left posterior pericardiotomy, this procedure could be considered in all patients undergoing median sternotomy.

The findings from this post hoc analysis should be interpreted cautiously. These results stem from a single-center study with a relatively high POAF incidence, even in low-risk patients, and are not generalizable to patients with mitral or tricuspid pathology. Potassium and magnesium levels at POAF onset were not recorded, nor was the number of episodes per patient, with only cumulative arrhythmia time provided. There is no data beyond 30 days post-discharge, limiting late-onset POAF analysis.

In summary, this study provides intriguing and promising insights into POAF characteristics and how posterior pericardiotomy might influence its onset. Future studies are warranted to explore the pathophysiologic underpinnings of this frequent complication.

REFERENCE:

Perezgrovas-Olaria R, Chadow D, Lau C, Rahouma M, Soletti GJ, et al. Characteristics of Postoperative Atrial Fibrillation and the Effect of Posterior Pericardiotomy. Ann Thorac Surg. 2023 Sep;116(3):615-622. doi:10.1016/j.athoracsur.2022.11.007.