Postoperative Arrhythmia

Postoperative arrhythmia is any new or worsened disturbance of cardiac rhythm after surgery, from benign sinus tachycardia and ectopics to life threatening ventricular and conduction disorders.

Epidemiology. Minor arrhythmias occur in most patients on continuous monitoring. Significant arrhythmias needing treatment occur in about 1% to 5% (an imprecise estimate), with higher rates after cardiac and thoracic surgery.

Causes.

• Electrolyte disturbance: potassium, magnesium and calcium.
• Hypoxia, hypercapnia, pain, anxiety, hypovolaemia, anaemia, sepsis.
• Myocardial ischaemia and heart failure.
• Drugs: beta agonists, aminophylline, adrenaline, neostigmine, digoxin toxicity, and QT-prolonging agents such as ondansetron, droperidol, amiodarone, haloperidol and macrolides.
• Vagal stimulation, cardiac manipulation, central line tip position.
• Thyrotoxicosis, phaeochromocytoma, alcohol or beta blocker withdrawal.
• Raised intracranial pressure (bradycardia).

Pathophysiology.

Arrhythmias arise from abnormal automaticity, triggered activity or re-entry. Catecholamines, ischaemia, electrolyte disturbance and drug effects alter conduction and refractoriness.

QT prolongation predisposes to torsades de pointes.

Palpitations, dizziness, syncope, chest pain, dyspnoea, hypotension, or detection on the monitor.

Red flags.

• Instability (shock, heart failure, chest pain, reduced consciousness).
• Ventricular tachycardia, ventricular fibrillation or torsades.
• Complete heart block or pauses over 3 seconds.
• Ischaemic ECG change.
• QTc over 500 ms.

• 12-lead ECG with rhythm strip.
• Potassium (target 4.0 to 5.0 mmol/L), magnesium (1.0 mmol/L or more), calcium, glucose, haemoglobin, blood gas, troponin and thyroid function.
• QTc: over 450 ms in men or over 460 ms in women is prolonged.
• Review drugs and echocardiography if structural disease is suspected.

Differential diagnosis.

• Sinus tachycardia from pain, hypovolaemia or fever.
• Atrial fibrillation or flutter.
• Supraventricular tachycardia.
• Ventricular tachycardia versus aberrancy.
• Heart block.
• Artefact.

Assess for instability first, treat the cause, and then treat the rhythm.

Unstable tachycardia. Synchronised cardioversion: 120 to 150 J biphasic for broad complex tachycardia or atrial fibrillation, 70 to 120 J for narrow regular tachycardia or flutter, with sedation. Pulseless: CPR and defibrillation at 150 to 200 J biphasic.

Stable regular narrow complex tachycardia. Vagal manoeuvres, then:

• Adenosine: 6 mg rapid IV followed by 20 mL saline flush, then 12 mg, then 12 mg after 1 to 2 minutes if needed; maximum 30 mg; continuous ECG; use 3 mg via a central line, with dipyridamole, carbamazepine or after heart transplant; avoid in severe asthma.

Stable ventricular tachycardia.

• Amiodarone: 300 mg IV over 20 to 60 minutes, then 900 mg over 24 hours; maximum 1.2 g in 24 hours; monitor ECG, blood pressure, liver and thyroid function; central line preferred; caution in hepatic impairment; avoid verapamil in broad complex tachycardia.

Torsades de pointes. Stop QT-prolonging drugs and correct potassium and magnesium.

• Magnesium sulphate: 2 g IV over 10 minutes, repeated once if needed; maximum 4 g for this indication; monitor reflexes, respiratory rate and levels; reduce in renal impairment. Use overdrive pacing or isoprenaline for recurrent pause dependent torsades.

Bradycardia with adverse signs.

• Atropine: 500 microgram IV, repeated every 3 to 5 minutes; maximum 3 mg; monitor heart rate; caution in glaucoma and ineffective in transplanted hearts, Mobitz II and complete block.
• Then transcutaneous pacing or adrenaline infusion 2 to 10 microgram/min, titrated to heart rate; monitor blood pressure; central access preferred.

Pulseless arrest. Cardiopulmonary resuscitation, adrenaline 1 mg IV every 3 to 5 minutes, amiodarone 300 mg after the third shock then 150 mg after the fifth; correct reversible causes. After cardiac surgery, early resternotomy is part of arrest management.

Prevention. Continue beta blockers, maintain potassium 4.0 to 5.0 mmol/L and magnesium 1.0 mmol/L or more, and avoid unnecessary QT-prolonging combinations.

Monitoring. Continuous ECG, electrolytes, QTc and haemodynamics.

Referral and escalation. Urgent cardiology or electrophysiology for ventricular tachycardia, high grade block, recurrent arrhythmia or need for pacing.