Preventing atrial fibrillation after cardiac surgery: a single-institution cohort study after implementation of a standardized preventative protocol

Introduction

It is estimated that 300,000 cardiac surgeries are performed in the United States every year (1). These are major surgical procedures and carry significant risks for the patient. The most common complication after cardiac surgery is postoperative atrial fibrillation (POAF), which occurs in 20–50% of patients, increases the risk of stroke and ventricular dysrhythmia, and worsens hemodynamics (2-7). POAF can double the mortality rate associated with cardiac surgery. POAF also impacts hospital resources and is associated with an increased length of stay and $7,500–$11,500 in extra cost (3,5,6).

Although the exact causes of POAF are not well understood, POAF is believed to be multifactorial (5,8). Known causes include the overall inflammatory response to cardiac surgery, fluid shifts, and catecholamine release (5,6). Although temporary, the inflammatory response can last for days to weeks and is thought to be due to pericardial inflammation, autonomic imbalance, and the increased production of cytokines during the surgery (5,6,8). Additionally, there are large fluid shifts with significant third-spacing immediately after surgery. The third-spacing and vasodilation lead to an underfilled atrium and ventricle that can cause a hyperdynamic ventricle, which increases the risk of POAF (5,6). As the inflammation resolves, the interstitial fluid will reaccumulate in the vasculature. If the patient is volume overloaded, the stretch of the atrium can also lead to POAF. Additionally, these factors all lead to alterations in the refractory period of the atria and slow atrial conduction, which causes multiple re-entry wavelets. These wavelets can then lead to atrial fibrillation as well (5,6).

It is recommended that POAF prophylaxis be initiated after cardiac surgery to reduce the incidence of POAF (5-7). Different POAF-prevention strategies have been heavily studied to help reduce the incidence and severity of this complication (9). Prevention strategies have included anti-arrhythmic and anti-inflammatory medications, cardiac pacing, and active clearance chest tubes. Active clearance chest tubes were initiated in patients in light of data suggesting that they reduce atrial fibrillation, reoperation, and other postoperative complications (10,11). Individually, these interventions have shown reductions in atrial fibrillation but have not been previously established as a combined POAF-prevention algorithm. In this manuscript, we detail a POAF-prevention algorithm developed at the Charleston Area Medical Center (CAMC) Institute for Academic Medicine and study its effectiveness. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-534/rc).

Methods

Patients

We retrospectively analyzed outcomes in patients undergoing coronary artery bypass grafting (CABG) at the CAMC Institute for Academic Medicine from January 1, 2023, through June 30, 2023. The cohort was divided into two groups: pre-implementation (January–March 2023) and post-implementation (April–June 2023), based on the timing of POAF prophylactic algorithm introduction. Patients with a history of permanent atrial fibrillation were excluded. Those with paroxysmal or persistent atrial fibrillation were included as part of baseline risk characterization.

POAF prevention algorithm

The algorithm was developed based on literature review and consensus among cardiac surgeons at the CAMC Institute for Academic Medicine. Implementation began in April 2023. The initiation of active-clearance chest tubes occurred concurrently with the institutional change to enhance postoperative outcomes.

Postoperative care under the algorithm included:

• AAI (atrial pacing, atrial sensing, inhibition response to sensing) mode epicardial pacing at 90 bpm for 24 hours;
• Amiodarone (400 mg orally twice daily) beginning postoperative day (POD) 1 or continued from IV infusion started intraoperatively in high-risk patients;
• Metoprolol tartrate (12.5 mg orally twice daily) initiated on POD 1 unless contraindicated by hypotension, bradycardia, or inotrope use;
• Magnesium sulfate 4 g intravenous (IV) if magnesium <3 mEq/L postoperatively or on POD 1;
• Magnesium oxide 400 mg orally daily;
• Atorvastatin 80 mg orally daily.

Adjunctive therapies included stress-dose hydrocortisone (50 mg IV every 6 hours for four doses), based on clinical indicators such as inflammatory markers [e.g., leukocytosis, elevated C-reactive protein (CRP)], presence of vasoplegia (persistent hypotension despite fluid resuscitation requiring vasopressors), and suspected adrenal insufficiency (e.g., prior steroid use or low random cortisol levels).

Posterior pericardiotomy was performed selectively at the discretion of the operating surgeon. Ranolazine and omega-3 fatty acids were part of the optional adjunct list but were not used during the study period (Table 1).

Statistical analysis

The primary outcome was the incidence of POAF within 30 days of surgery. Baseline characteristics were summarized using means and standard deviations for continuous variables, and frequencies and percentages for categorical variables. Differences between cohorts were compared using t-tests or Chi-squared tests as appropriate. All statistical analyses were conducted using IBM SPSS Statistics for Windows, Version 28.0 (IBM Corp., Armonk, NY, USA).

Artificial intelligence or machine learning tools were not used in this study.

IRB statement

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Charleston Area Medical Center (CAMC)/West Virginia University Charleston Division IRB as exempt under “Category 2: Research that includes interactions involving educational tests” (IRB #17-348) and individual consent for this retrospective analysis was waived.

Results

We conducted a comparative analysis of all patients undergoing cardiac surgery at CAMC during two timeframes: January–March 2023 (pre-algorithm implementation) and April–June 2023 (post-algorithm implementation). A total of 218 patients were included with 92 patients in the pre-implementation cohort and 126 patients in the post-implementation cohort. Baseline demographic and clinical characteristics were well matched across groups (Table 2), with no significant differences in age, sex, ejection fraction, or comorbidities such as chronic obstructive pulmonary disease (COPD), diabetes, or hypertension.

The incidence of POAF decreased significantly following implementation of the prevention algorithm. In the pre-intervention group, POAF occurred in 31.5% of patients, compared to 23% in the post-intervention group—a relative risk reduction of 27% and an absolute risk reduction of 8.5%. The number needed to treat (NNT) to prevent one case of POAF was 12 (Table 3). This outcome suggests the bundled strategy was clinically meaningful despite using interventions with previously established efficacy.

When evaluating POAF onset timing, the majority of cases occurred between postoperative days 1 and 3 in both groups. Given that the algorithm initiated prophylactic pacing, amiodarone, magnesium correction, and metoprolol during this early postoperative phase, the observed reduction in POAF was most likely due to interventions acting during this window.

Subgroup analysis indicated that age over 70 years, history of COPD, and lower preoperative ejection fraction were associated with a higher likelihood of POAF in both cohorts (Table 4). Notably, despite similar risk distributions between groups, the intervention cohort had lower POAF incidence across all subgroups (Table 5).

A per-protocol adherence review confirmed high compliance with pacing and amiodarone administration; however, the use of corticosteroids was selective and based on inflammatory or vasoplegic status. Polyunsaturated fatty acids (PUFAs) were not administered to any patient during the study period (Table 6).

Discussion

This single-center, before-and-after cohort study demonstrates that implementing a standardized, protocol-driven POAF prevention algorithm significantly reduced POAF incidence following cardiac surgery. The absolute reduction of 8.5% and NNT of 12 support the effectiveness and practicality of a bundled prophylactic strategy, even when comprised of previously studied individual interventions.

Importantly, this study emphasizes the value of targeted timing. Most POAF cases occurred between postoperative days 1–3, and our algorithm was designed to aggressively manage this early window with epicardial pacing, amiodarone, and magnesium. These components align with known contributors to atrial arrhythmogenesis—electrolyte imbalance, autonomic fluctuations, and inflammation.

Despite this, the NNT did not improve beyond that seen in prior monotherapy trials. Several explanations may contribute; overlapping mechanisms among the bundled interventions, clinical variation in steroid use, or selection bias for higher-risk patients in the algorithm cohort may have attenuated the potential benefit.

Additionally, POAF still occurred in 23% of patients despite prophylaxis, underscoring the need for further refinement. Our analysis did not identify a specific “resistant phenotype”, but age, COPD, and lower ejection fraction were consistent risk factors. Future iterations of the protocol may consider more personalized thresholds for steroid initiation, further integration of anti-inflammatory markers, or evaluating newer prophylactic agents.

Nonetheless, our findings support the feasibility and effectiveness of a multi-pronged prevention strategy in real-world practice. Adoption of similar algorithms at other institutions may improve outcomes while minimizing variation in postoperative management.

Risk factors for POAF

There are preoperative, intraoperative, and postoperative risk factors for POAF (Table 7). Preoperatively, risk factors include age over 70 years, male sex, previous history of atrial fibrillation, heart failure with reduced ejection fraction, left atrial enlargement, right-sided heart disease, COPD, chronic kidney disease, diabetes, obesity, and rheumatic heart disease (5-8,12,13). Our population was indeed at high risk with the average age of 71 years, more than 60% male sex, 40% with obesity, 35% with diabetes, 25% with a prior history of atrial fibrillation, and nearly 20% with heart failure with reduced ejection fraction among other risk preoperative risk factors. Intraoperatively, risk factors include valve surgery, atrial injury, prolonged ischemia time, acute volume changes, pulmonary vein vent, and venous cannulation (5-8). Postoperatively, risk factors include volume overload, hypotension, prolonged ventilation, and increased afterload (5-7). Intraoperative and postoperative risk factors in our population were also prevalent with 28% demonstrating volume overload, 22% undergoing valve surgery, and 16% with prolonged mechanical ventilation; only 10% had prolonged ischemia time.

Specific markers of inflammation, such as CRP, leukocytosis, and albumin can also provide clues of increased risk of POAF. CRP is commonly used as an indicator of inflammation, and elevated CRP levels have been correlated with an increased risk of POAF (14-17). Additionally, increased capillary leak index (CRP levels divided by albumin levels), has been correlated with POAF when examined both preoperatively and postoperatively. Leukocytosis and demargination of neutrophils are common postoperatively due to an increase in stress and cortisol release. This is seen as neutrophilia without bandemia (6,14-16).

The occurrence of POAF has a bimodal distribution. There is a peak of incidence immediately following surgery that lasts for the first 18 hours (6). Risk factors for this initial peak include increased ischemic time, advanced age, and mitral valve surgery. The second peak begins on POD 2, with 70% of POAF cases occurring in the first 4 days after surgery and 94% in the first 6 days (5,6,8). Complications associated with POAF lead to an estimated 5-day increase in hospital length of stay and a $7,500–$11,500 increase in costs (3,5,6).

Interventions

Multiple interventions, including rhythm modification through pharmacological interventions or pacing, have been shown to reduce the incidence of atrial fibrillation. We incorporated many of these interventions into our POAF-prevention algorithm (Table 6).

Beta blockers have the largest impact in the reduction of POAF and, therefore are the number one choice for POAF prevention. This is reflected in the fact that the use of beta blockers to prevent POAF was a class I recommendation in American College of Cardiology Foundation (ACCF)/American Heart Association (AHA) practice guidelines (9). In patients who were taking beta blockers before surgery, restarting beta blockers significantly reduced the incidence of POAF. This effect was present but decreased if the patient was not on beta blockers before surgery (5). Metoprolol and carvedilol remain the most commonly prescribed beta-blockers. Sotalol is a beta-blocker that is also an antiarrhythmic and was found to reduce POAF to a greater extent than other beta blockers but also was associated with more hemodynamic compromise and bradycardia (2-4,6-8).

Atrial pacing decreases POAF by suppressing atrial overdrive and reducing bradycardia-induced dispersion of repolarization (2-4,7). Amiodarone is a class III antiarrhythmic and has been shown to decrease POAF, especially if started in the preoperative period and continued postoperatively. The use of amiodarone was classified as a class IIa recommendation in ACCF/AHA practice guidelines (9). However, IV doses were associated with an increased risk of bradycardia and hypotension, especially if more than 1 g/day was administered (2-4,6-8).

Magnesium, a calcium channel antagonist, causes a reduction in intracellular calcium and a decrease in energy demands. It is also a cofactor in Na-K-ATPase channel which stabilizes the myocytes. Hypomagnesemia has been associated with an increased risk of tachyarrhythmias and increasing to supratherapeutic levels has been shown to decrease POAF (2,3,7,8). Ranolazine is a sodium channel blocker typically used as a chronic angina medication. Ranolazine has antiarrhythmic properties that block early and delayed after depolarization, leading to a reduction of POAF (2,18).

Because inflammation is an underlying mechanism driving POAF, several anti-inflammatory agents have been used in POAF-prevention strategies. High-dose statins have demonstrated anti-inflammatory effects in patients with coronary artery disease and postoperatively in patients who undergo cardiac surgery, especially when started preoperatively (2,6). Omega-3 PUFAs reduce POAF with similar effectiveness as beta blockers and amiodarone (2,19). Non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids have also been shown to reduce POAF without an increased risk of morbidity (2,6).

Additional measures that can reduce the incidence of POAF include active-clearance chest tubes and posterior pericardiotomy. Active-clearance chest tubes have a wire that sits within the chest tube and can be moved within the chest tube using a magnet. This helps clear the chest tube more efficiently and without the high negative pressure associated with stripping the chest tube using a manual technique of squeezing and pulling along the tube to dislodge clots. Studies have shown a reduction in POAF with the use of active chest-tube clearance (10,11). Posterior pericardiotomy is an intraoperative procedure where a 4-cm longitudinal incision is made along the posterior pericardium parallel to the phrenic nerve. This allows drainage of blood and fluid, which can cause irritation and pressure leading to atrial fibrillation, out of the pericardium (3).

Study limitations

There are limitations to this study. The study was non-randomized and observational in design. Although baseline characteristics were balanced, residual confounding factors cannot be excluded. Additionally, because multiple interventions (e.g., POAF-prevention algorithm, active-clearance chest-tube use) were started at the same time, we cannot say for certain which intervention was the most influential or if all interventions are needed. Although it appears that the POAF-prevention algorithm significantly reduced relative risk, the direct outcomes of the protocol can only be inferenced. Further prospective studies should be considered to evaluate the effects of multimodal strategies to determine the true impact on outcomes. Adherence to the protocol was high but not universal—particularly for corticosteroids, which were administered selectively. Data on compliance with each component of the prevention algorithm was not available because of the complexities of defining compliance when medications can be started and discontinued multiple times within the postoperative course or can be used selectively (e.g., corticosteroids). Also, because of the retrospective nature of this study, information regarding the timing of the onset of atrial fibrillation during the hospitalization was not available nor was information on how the prevention algorithm may have affected this timing. And finally, we lacked continuous rhythm monitoring beyond discharge, so late POAF incidence was not assessed.

Furthermore, this study was limited by its sample size, which may have been underpowered to detect smaller differences in POAF incidence with high statistical confidence. Our cohort included all eligible patients within a defined 6-month period; however, a formal a priori sample size calculation was not performed. Future studies with larger cohorts are warranted to validate these findings in a more statistically robust manner.

Conclusions

Given the observed 27% relative risk reduction and NNT of 12 with no obvious increased risk to the patient, this POAF-prevention algorithm may reduce atrial fibrillation rates post-cardiac surgery, reduce length of stay, and reduce the morbidity associated with POAF. Additional studies evaluating this prevention strategy in a prospective manner and evaluating its cost-effectiveness should be considered.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-534/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-534/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-534/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-534/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Charleston Area Medical Center (CAMC)/West Virginia University Charleston Division IRB as exempt under “Category 2: Research that includes interactions involving educational tests” (IRB #17-348) and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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