What ventricular arrhythmias are common after Coronary Artery Bypass Graft (CABG)?

Ventricular Arrhythmias After Coronary Artery Bypass Graft

Ventricular tachycardia (VT) and ventricular fibrillation (VF) are the most common life-threatening ventricular arrhythmias after CABG, occurring in approximately 5-10% of patients, with the majority (60-90%) developing within the first 48 hours postoperatively. 1

Incidence and Types of Ventricular Arrhythmias

The spectrum of ventricular arrhythmias after CABG includes:

• Non-sustained monomorphic VT: Most common at 17.6% incidence 2
• Sustained monomorphic VT: Occurs in 5.5% of patients 2
• Ventricular fibrillation: Occurs in 2.7% of patients 2
• Sustained polymorphic VT: Least common at 0.8% 2

The overall incidence of sustained VT/VF ranges from 5-10% across multiple studies, with some reporting rates as high as 8.5% 1, 3, 2, 4. Simple ventricular arrhythmias (premature ventricular contractions) are common but benign and do not affect prognosis 5.

Temporal Pattern

The critical monitoring period is the first 48 hours after surgery, when 60-92% of all ventricular arrhythmias occur. 1, 2

• 61% of ventricular fibrillation episodes occur within the first 48 hours 2
• 90-92% of all malignant ventricular arrhythmias occur within 48 hours of PCI in the acute MI setting 1
• The risk of sudden cardiac death is highest in the first month post-surgery 1

Risk Factors for Post-CABG Ventricular Arrhythmias

High-risk patients can be identified by the combination of reduced left ventricular ejection fraction (LVEF ≤38%), presence of ventricular late potentials on signal-averaged ECG, and reduced heart rate variability (SDNN ≤28 ms). 3

Independent Predictors:

Cardiac Function:

• LVEF <40% or ≤35% (strongest predictor) 1, 3, 2
• Presence of ventricular late potentials (91% of patients with VT vs 9% without) 3
• Reduced SDNN <28 ms 3

Perioperative Factors:

• Postoperative myocardial infarction (total CK >1,000 or MB-CK elevation) 2, 4
• Hemodynamic instability requiring intra-aortic balloon pump 2, 4
• Electrolyte imbalance (84.6% of VT patients vs 45.6% without) 2, 4
• Need for three or more bypass grafts 4

Baseline Characteristics:

• Severe three-vessel coronary artery disease (91.7% of VT patients) 4
• History of heart failure 1
• Hypotension, tachycardia, or shock 1
• Low TIMI flow grade 1

Mechanisms

The mechanisms underlying post-CABG ventricular arrhythmias include 1:

• Continuing myocardial ischemia
• Hemodynamic abnormalities
• Electrolyte disturbances
• Reentry circuits (particularly for sustained VT)
• Enhanced automaticity

CABG is more effective at reducing ventricular fibrillation than ventricular tachycardia, because VT typically involves reentry through scarred endocardium rather than acute ischemia. 1

Clinical Significance and Outcomes

Sustained VT/VF after CABG carries a high mortality rate and significantly increases in-hospital mortality (16.3% vs 3.7% in patients without arrhythmias). 1, 5

• Recurrence rates are highest in the ventricular fibrillation group (52%) 2
• Sustained VT/VF occurring >48 hours after reperfusion are associated with increased risk of death 1
• Simple ventricular arrhythmias do not affect prognosis and require no specific treatment 5

Monitoring Recommendations

Continuous arrhythmia monitoring should be initiated immediately and continue uninterrupted for at least 48-72 hours after CABG. 1

• For high-risk patients (advanced age, history of atrial fibrillation, valvular disease), monitoring should continue until hospital discharge 1
• The need for monitoring should be reassessed every 24 hours with a goal of continued monitoring until the patient has been event-free for 12-24 hours 1

Management Approach

First-line treatment consists of immediate defibrillation for VF, correction of precipitating factors (ischemia, electrolytes, hemodynamics), and beta-blocker therapy. 1

Acute Management:

• Immediate defibrillation for VF 1
• Correct myocardial ischemia 1, 5
• Correct electrolyte abnormalities 1
• Stabilize hemodynamics 1
• Beta-blocker therapy 1

Long-term Considerations:

ICD implantation should be delayed for at least 3 months after CABG to allow time for LV recovery, as routine early ICD implantation has not improved survival. 1

• Patients with persistent LVEF ≤35% at 3 months post-CABG may benefit from prophylactic ICD (31% reduction in all-cause mortality) 1
• Wearable cardioverter-defibrillator use in the first 90 days showed no significant reduction in sudden death but may benefit compliant patients 1
• Electrophysiologically guided therapy and ICD implantation should be considered for survivors of sustained VT/VF 5

Common Pitfalls

• Do not implant prophylactic ICDs within 40 days of CABG, as this has not been associated with improved survival and may increase non-arrhythmic deaths 1
• Do not assume all ventricular arrhythmias require intervention—simple ventricular ectopy is common and benign 1, 5
• Do not discontinue monitoring at 24 hours in high-risk patients (low LVEF, three-vessel disease, perioperative MI) as late arrhythmias can occur 1, 2
• Ensure adequate screening for myocardial viability before ICD implantation, as LV function may recover after revascularization 1