How can intra‑operative arrhythmias be recognized and what are their common causes?

Recognizing and Managing Intra-operative Arrhythmias

Recognition Methods

Continuous ECG monitoring is the cornerstone of intra-operative arrhythmia detection, with standard surface leads providing adequate surveillance for most cases. 1

Standard Monitoring Approach

• Monitor heart rate, rhythm regularity, P-wave presence and morphology, QRS configuration, and the relationship between atrial and ventricular activity on continuous ECG 1, 2
• Evaluate the number of P waves per QRS complex to distinguish supraventricular from ventricular rhythms 2
• Assess QRS width and configuration—narrow QRS (<120 ms) suggests supraventricular origin, while wide QRS (≥120 ms) indicates ventricular origin or aberrant conduction 1

Enhanced Detection in Cardiac Surgery

• Use temporary epicardial atrial pacing wires for superior rhythm discrimination when available, particularly for distinguishing atrial flutter from atrial fibrillation and identifying P-wave activity obscured on surface ECG 3, 4
• Record atrial electrograms (AEGs) using these wires to visualize atrial activity with much greater clarity than surface leads, especially valuable for diagnosing junctional rhythms and differentiating supraventricular tachycardias 3, 4
• In pediatric congenital heart surgery, atrial electrogram recording is especially useful for diagnosing junctional arrhythmias where P waves may be buried in the QRS complex 3

Critical Assessment Questions

• Determine immediately whether the patient is hemodynamically stable or unstable—this dictates urgency of intervention 1, 2
• Identify if the arrhythmia is dangerous (ventricular tachycardia, ventricular fibrillation, complete heart block with slow ventricular escape) versus benign (isolated premature beats, transient bradycardia) 2
• Assess whether the rhythm requires immediate treatment or can be observed while correcting underlying causes 2

Common Causes of Intra-operative Arrhythmias

Anesthetic and Surgical Factors

• Volatile anesthetic agents alter normal cardiac electrical activity and can precipitate arrhythmias through effects on automaticity and conduction 1
• Tracheal intubation triggers sympathetic stimulation and vagal reflexes that commonly cause transient bradycardia or tachycardia 2
• Surgical site manipulation, particularly thoracic, upper abdominal, and cardiac procedures, increases arrhythmia risk through direct cardiac stimulation or autonomic reflexes 2
• The oculocardiac reflex during ophthalmic surgery causes vagal-mediated bradycardia or asystole 2

Metabolic and Physiologic Derangements

• Hypoxemia and hypercarbia are leading reversible causes—verify adequate oxygenation and ventilation immediately when arrhythmia occurs 1, 2
• Hypokalemia (K+ <3.5 mEq/L) and hypomagnesemia (Mg2+ <2.0 mg/dL) predispose to both atrial and ventricular arrhythmias 1, 2
• Hypothermia during cardiac surgery increases ventricular arrhythmia risk, particularly in the immediate post-bypass period 3
• Acidosis and alkalosis alter cardiac electrophysiology and lower arrhythmia thresholds 1

Cardiac-Specific Causes

• Myocardial ischemia from hypotension, tachycardia, or coronary manipulation during surgery triggers both atrial and ventricular arrhythmias 3
• Pre-existing structural heart disease (coronary artery disease, valvular disease, cardiomyopathy) substantially increases baseline arrhythmia risk 3
• Direct cardiac manipulation during cardiac surgery—particularly during cardiopulmonary bypass, aortic cross-clamping, and coronary reimplantation—causes transient conduction abnormalities 3

Drug-Related Causes

• Sympathomimetic agents (epinephrine, dopamine, ephedrine) increase automaticity and can trigger tachyarrhythmias 1, 2
• Digitalis toxicity manifests as junctional rhythms, atrial tachycardia with block, or ventricular ectopy 3, 5
• QT-prolonging medications (certain antibiotics, antiemetics, antipsychotics) combined with electrolyte abnormalities increase torsades de pointes risk 6

Specific Arrhythmia Patterns and Their Significance

Cardiac Surgery Context

• Atrial fibrillation occurs in 28-33% of CABG patients, 33-49% of valve surgery patients, and 60% of combined CABG-valve procedures, typically peaking on postoperative day 2-4 3
• Junctional ectopic tachycardia is common in pediatric congenital heart surgery, appearing as narrow QRS tachycardia with AV dissociation, and can cause hemodynamic instability if persistent 3, 5
• Ventricular arrhythmias in the immediate post-bypass period relate to hypothermia, ischemia, and electrolyte shifts, with risk decreasing rapidly once normothermia is restored 3
• Complete AV block requiring permanent pacing occurs in 1.5% of cardiac surgery cases, with higher risk (7.2%) after valve procedures, particularly combined mitral-aortic valve replacement 3

Non-Cardiac Surgery Context

• Asymptomatic ventricular ectopy, including couplets and non-sustained ventricular tachycardia, occurs in 44% of high-risk patients but does not predict adverse cardiac outcomes and generally requires no treatment 3, 7
• Pre-existing atrial fibrillation in stable patients requires no special intra-operative management beyond standard rate control, though anticoagulation timing must be coordinated 3
• New-onset sustained ventricular tachycardia or symptomatic arrhythmias warrant investigation for acute myocardial ischemia, electrolyte abnormalities, or drug toxicity 3

Critical Pitfalls to Avoid

• Do not aggressively treat asymptomatic ventricular ectopy or non-sustained ventricular tachycardia in non-cardiac surgery—these rhythms are common (44% incidence) and not associated with increased cardiac death or MI 3, 7
• Do not mistake atrial fibrillation with rapid ventricular response (>150 bpm) for paroxysmal supraventricular tachycardia—the R-R irregularity becomes less obvious at faster rates, but atrial wires or careful surface ECG analysis reveals the irregular pattern 3
• Do not overlook temporary pacemaker malfunction as a cause of apparent bradycardia—check for lead disconnection, battery depletion, or oversensing from large P/T waves or electrical interference 3
• Do not assume junctional rhythm in children is benign—in pediatric congenital heart surgery, junctional ectopic tachycardia (120-220 bpm) can progress to heart failure if untreated, unlike the benign accelerated junctional rhythm (70-130 bpm) seen in adults 3, 5
• Do not ignore the possibility of digitalis toxicity when junctional rhythms appear—this is the most common cause of non-paroxysmal junctional tachycardia and requires immediate drug cessation 3, 5