Atrial Fibrillation After CABG Surgery: Incidence and Clinical Impact
Postoperative atrial fibrillation occurs in 30-40% of patients undergoing isolated CABG surgery, with rates approaching 60% when combined with valve procedures, making it the most common complication after cardiac surgery. 1
Incidence and Timing
The reported incidence varies significantly based on detection method:
- 11% when diagnosed by intermittent 12-lead ECG 1
- >40% when continuous Holter monitoring is employed 1
- 16-30% when diagnosed based on patient symptoms 1
- Contemporary series report 30-40% for isolated CABG, rising to nearly 60% for combined CABG and mitral valve surgery 1
The arrhythmia typically occurs on postoperative days 2-3, with 70% of events occurring within the first 4 postoperative days. 1 Peak incidence is on postoperative day 2. 1 However, AF can occur at any time after surgery, including after hospital discharge, and is the leading cause of hospital readmission following early discharge. 1
Clinical Significance and Outcomes
Postoperative AF is associated with increased morbidity, prolonged hospitalization, and increased hospital costs, though it remains unclear whether preventing AF directly improves these outcomes. 1
The arrhythmia is associated with:
- Greater resource utilization 2
- Cognitive changes, renal dysfunction, and infection 2
- Increased risk of stroke and thromboembolic complications 1
- Greater in-hospital mortality and worse long-term survival 3
More than 90% of patients spontaneously return to sinus rhythm by 6-8 weeks after surgery, a higher rate of spontaneous resolution than other forms of AF. 1
Risk Factors
Non-Modifiable Risk Factors
Age is the most consistent and reproducible predictor across all studies. 1 For every 10-year increase in age, the odds ratio is 1.75 (95% CI 1.59-1.93). 2
Other established risk factors include:
- History of prior atrial fibrillation (OR 2.11; 95% CI 1.57-2.85) 2
- Chronic obstructive pulmonary disease (OR 1.43; 95% CI 1.09-1.87) 2
- Valvular heart disease 1
- Chronic lung disease 1
- Atrial enlargement and increased left atrial volume 1, 3
- Preoperative atrial arrhythmias 1
- Valve surgery (OR 1.74; 95% CI 1.31-2.32) 2
- Low ejection fraction (<35%) 3, 4
- Diastolic dysfunction 3
- Diabetes mellitus 3
Modifiable Risk Factors
Postoperative withdrawal of beta-blockers (OR 1.91; 95% CI 1.52-2.40) or ACE inhibitors (OR 1.69; 95% CI 1.38-2.08) significantly increases AF risk. 2
Postoperative factors associated with increased risk:
Pathophysiology
The mechanism involves multiple wavelets of reentry or automatic discharge requiring sufficient atrial muscle mass and regional refractoriness. 1
Multiple postoperative factors predispose to AF:
- Operative trauma from surgical dissection and manipulation 1
- Local inflammation with or without pericarditis 1
- Elevations in atrial pressure from postoperative ventricular stunning 1
- Chemical stimulation from catecholamines and inotropic agents 1
- Reflex sympathetic activation from volume loss, anemia, or pain 1
- Parasympathetic activation 1
- Fever from atelectasis or infection 1
- Inadequate atrial cardioprotection during cardiopulmonary bypass 1
Prevention Strategies
Beta-Blockers (Class I Recommendation)
Beta-blockers are the most effective prophylactic therapy, reducing AF incidence from 40% to 20% in CABG patients. 1 In a meta-analysis of 24 trials, prophylactic beta-blockade showed a summary odds ratio of 0.28 (95% CI 0.21-0.36). 1
Postoperative administration of beta-blockers reduces AF risk (OR 0.32; 95% CI 0.22-0.46). 2
Other Pharmacologic Prophylaxis
Sotalol should be considered (Class IIa recommendation) to decrease AF incidence after CABG. 1
Amiodarone should be considered (Class IIa recommendation) to decrease AF incidence after CABG. 1, 5
Statins should be considered (Class IIa recommendation) to decrease AF incidence. 1
Corticosteroids may be considered (Class IIb recommendation). 1
Additional protective factors identified:
- ACE inhibitors (OR 0.62; 95% CI 0.48-0.79) 2
- Potassium supplementation (OR 0.53; 95% CI 0.42-0.68) 2
- Nonsteroidal anti-inflammatory drugs (OR 0.49; 95% CI 0.40-0.60) 2
Intraoperative Interventions
Mild hypothermia (34°C) during cardiopulmonary bypass significantly reduces AF compared to moderate hypothermia (28°C): 21.9% vs 48.5% (p<0.02). 1
Posterior pericardiotomy significantly reduces postoperative atrial arrhythmias. 1
Evidence regarding off-pump CABG is conflicting—some studies show reduced AF (11% vs 45%), while others show no difference. 1
Management of Established AF
Rate Control
Because of high adrenergic tone postoperatively, rate control can be difficult. 1
Beta-blockers are the first-line agents for rate control, with short-acting agents particularly useful when hemodynamic instability is a concern. 1, 6
Calcium channel antagonists (diltiazem) can be used as alternative therapy. 1, 6
Digoxin is less effective when adrenergic tone is high and should be reserved for later use. 1, 6
Intravenous amiodarone has been associated with improved hemodynamics in this setting. 1
Rhythm Control
Given the self-limited course of postoperative AF, electrical cardioversion is usually unnecessary except when the dysrhythmia develops in the immediate postoperative (hypothermic) period or in highly symptomatic/poorly controlled patients. 1
Pharmacologic cardioversion options include:
Anticoagulation Strategy
If AF persists for 48 hours postoperatively, initiate warfarin therapy targeting INR 2.0-3.0, balancing stroke risk against bleeding risk from recent surgery. 1, 5, 7
High-risk patients (history of stroke/TIA, age >75 years, hypertension, heart failure, diabetes, coronary artery disease) should receive anticoagulation despite recent surgery. 1, 5
Warfarin can be started without heparin bridging to minimize bleeding complications in the immediate postoperative period. 5
Avoid anticoagulation in patients with excessive chest tube drainage, low platelet counts, or large pericardial effusions due to increased tamponade risk. 5
Continue anticoagulation for at least 30 days (minimum 4 weeks) after return to sinus rhythm due to persistent atrial mechanical dysfunction that increases thrombosis risk for several weeks. 5, 7
If AF persists beyond this period, continue long-term anticoagulation based on CHA₂DS₂-VASc score. 5
Cardioversion Without TEE Guidance
Cardioversion without TEE guidance during the first 48 hours after AF onset is Class IIb, with anticoagulation optional depending on risk assessment. 1
Recurrent AF
43% of patients who develop AF after CABG experience more than one episode. 2
Predictors of recurrent AF include:
- Older age 2
- History of congestive heart failure 2
- Left ventricular hypertrophy 2
- Aortic atherosclerosis 2
- Bicaval venous cannulation 2
- Withdrawal of ACE inhibitor or beta-blocker therapy 2
- Use of amiodarone or digoxin 2
Patients with recurrent AF have longer hospital stays and experience greater infectious, renal, and neurological complications than those with a single episode. 2
Common Pitfalls
Do not withhold anticoagulation solely due to recent surgery in high-risk patients with persistent AF >48 hours—the stroke risk often outweighs bleeding risk. 5
Do not discontinue beta-blockers or ACE inhibitors postoperatively, as withdrawal significantly increases AF risk. 2
Do not rely solely on digoxin for rate control in the immediate postoperative period when adrenergic tone is high. 1, 6
Do not assume all postoperative AF is benign—it is associated with increased stroke risk and requires appropriate anticoagulation in high-risk patients. 1, 5, 7