A 63 year old man with a history of hypertension and ischaemic heart disease has been admitted to the intensive care unit with refractory hypotension due to severe sepsis. Inflammatory markers are raised and CXR has revealed a right lower and middle lobe pneumonia.
He has been intubated and ventilated and initiated on empirical antibiotics. Blood pressure has remained stable on a small dose of noradrenaline. On the ward round his heart rate is noted to be irregular and a 12 lead ECG shows new onset atrial fibrillation.
What are the physiological triggers for AF during critical illness?
- AF is the most frequently encountered arrhythmia in critical care. Precipitating factors are multiple and can relate to the patient, their illness, or their management.
- In the community, onset of AF is thought to be secondary to atrial remodelling via fibrosis as a result of hypertension, myocardial ischaemia, valve disease or inflammation.
- In critical illness atrial remodelling can be accelerated by persistent tachycardia and systemic inflammation. Acute imbalances in normal conduction due to electrolyte abnormalities, haemodynamic instability and sympathetic and parasympathetic activity can provide the trigger.
- Age, high BMI and disease severity factors all contribute to increased risk of developing AF in critical care.
How would you manage af occurring during critical illness?
New onset AF can lead to decompensation of the previously stable patient. Haemodynamic instability can result from impaired ventricular filling due to loss of atrial systole and/or rapid ventricular response to atrial impulses.
The Unstable Patient:
- ALS advocates synchronised DC cardioversion when new AF is identified as the precipitant of haemodynamic instability
- Markers of haemodynamic compromise are hypotension, pulmonary oedema, cardiac ischaemia and syncope
- Synchronised shock should initially be delivered at 120-150J then in increasing increments with up to 3 attempts
- Recurrence is common in the critically ill patient. Concurrent medical therapy is advised. ALS favours the use of amiodarone.
The Stable Patient:
- Discontinue precipitant medications
- Stop beta-agonists if possible
- Avoid dopamine and epinephrine
- Manage reversible triggers
- Treat electrolyte abnormalities: hypokalaemia, hypomagnesaemia
- Correct volume status, aim for euvolaemia; increased atrial size on echo has been associated with onset of AF in critical care
- Optimise ventilator synchronicity
- Treat any myocardial ischaemia
- Optimise management of underlying illness
- Acute medical management targets different phases of the cardiac cycle
- Control of rapid ventricular response:
- First line – Beta-blocker (esmolol allows easy titration and discontinuation)
- Second line – Calcium channel blockers (verapamil, diltiazem) or digoxin
- To target loss of atrial systole or if above options ineffective
- First line – Magnesium
- Second line – Amiodarone
- No changes to anticoagulation are advised during the acute phase of illness
- Control of rapid ventricular response:
What would be your approach to long term management?
- New AF will resolve in around 86% of cases prior to discharge from critical care.
- Sepsis survivors who experience new AF in critical care are more likely to go on to develop AF, and ischaemic stroke, after discharge. Suitable surveillance is advised.
- In cases of persistent AF, the CHA2DS2VASc and HAS-BLED scores can be used to calculate relative risk-benefit of anticoagulation
Take home messages from the case
- New onset AF in the critically ill patient is common
- Critical illness can accelerate atrial remodelling and trigger onset via autonomic and electrolyte imbalances
- Haemodynamic compromise can result from reduced ventricular filling. Unstable patients should be treated in accordance with ALS guidelines
- Management should focus on causative factors: correct electrolyte imbalances, treat illness, avoid volume overload, consider chronotropic effects of vasopressors
- While most cases of new AF will resolve prior to discharge, following sepsis there is a significant risk of recurrence