Part III Intercollegiate exam / Management of Atrial Fibrillation

Post-operative Atrial Fibrillation (AF)

You have been asked to see a 79 male who has had left hemicolectomy 3 days ago. The nurse is concerned because his heart rate has jumped from 70-80/min to > 130/min. His BP is 110/70 and he is afebrile. What do you think has happened?

Possible reasons for his tachycardia can be:

Hypoxia
Dehydration and hypovolaemia
Sepsis
Pain
Cardiac arrhythmia

His heart rhythm is irregular. What is the most common arrhythmia seen in post-op patients?

Atrial fibrillation (AF). AF affects > 4% of patients following non-cardiothoracic surgery (4).

How do diagnose AF?

ECG findings:

Irregular rhythm: irregular & frequently rapid ventricular response resulting in irregular heart rhythm.
Absent p wave: p wave is replaced by rapid, irregular, fibrillatory waves that vary in size, shape, and timing. (1)

What triggers AF in post-operative patients?

Post-operative AF is believed to be triggered by systemic inflammatory response and is most often seen in 1^st – 4 post-op days (4). Following factors have been seen to be associated with risk of new onset post-op cardiac arrhythmia:

Sepsis: most common source of sepsis – intra-abdominal collection, anastomotic leak & chest infection
Biochemical and metabolic derangements: eg hypokalaemia or hyponatraemia – electrolyte derangement is considered to be a contributing factor rather than sole precipitant of sepsis.
Hypoxia
Anaemia
Cerebrovascular accident
Pre-operative risk factors: cardiac co-morbidity eg, H/O myocardial infarction, age, male gender, asthma, H/O cardiac arrhythmia, hyperthyroidism. (4)

How will you manage this patient?

A: ensure airway is patent. Start O2 with mask.
B: breathing is OK. Check O2 sats and Chest examination

· C: Check for BP. And follow the algorithm (NICE Guidelines- “Unless contraindicated, post-operative AF following non-cardiothoracic surgery should be managed as for acute-onset AF with any other precipitant”.) (2)

· Unstable hypotensive patient with fast AF is a medical emergency & needs urgent help from a cardiologist to consider electric cardioversion.(2)

Chart review: is he known to have AF?
If recent onset AF, identify & correct the precipitating cause: in post operative patients there may be a precipitating cause eg, hypoxia, hypothermia, electrolyte imbalance, sepsis or post-operative pain. Treatment of underlying cause often restores normal rhythm.(3)

Pharmacological rate control:

Intravenous treatment should be with one of the following:

· beta-blockers eg, metaprolol or esmolol(CI: Asthma, heart failure, heart block or WPW syndrome)

· rate-limiting calcium antagonists (CI: heart failure, heart block or WPW syndrome)

· amiodarone, where beta-blockers or calcium antagonists are contraindicated or ineffective (2)

Please note: digoxin is no more favoured by NICE for rate control(2). However, few still believe in its use. Digoxin acts via vagal inhibition and is effective in controlling resting ventricular rate where as ß-blockers & Ca++ channel blockers are more effective in rate control in patients with high sympathetic drive eg, pyrexia, thyrotoxicosis or sepsis.(1)

Pharmacological cardioversion:

· Where there is a delay in organising electrical cardioversion, intravenous amiodarone should be used.

· In those with known WPW syndrome, flecainide may be used as an alternative.

· atrioventricular node-blocking agents such as diltiazem, verapamil or digoxin should not be used. (2)

References:

1. Emergency management of AF (free download, registration required)

2. NICE guidelines - management of AF

3. ACC/ESC guidelines - management of AF

4. Postoperative arrhythmias in general surgery patients: Annals of Royal College of Surgeons of England (March 2007)

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