Arrhythmias

Arrhythmias in the critically unwell are very common and have significant associated morbidity and mortality.

The majority of this chapter will be based on the ALS algorithm for the management of arrhythmias.

As with any acutely unwell patients, all will need an ABCDE based assessment focusing on signs of cardiovascular instability.

All will need a 12 lead ECG (or rhythm strip in the interim if unstable). Additionally, a blood gas (and full set of bloods) will provide useful information.

Key features of instability include:

• Hypotension (SBP < 90)
• Chest Pain
• Heart Failure
• Altered Conscious State

If the patient is unresponsive and not breathing, then CPR should be commenced and the ALS algorithm followed.

The tachyarrhythmias

If the patient is unstable then synchronised DC cardioversion is recommended. This will obviously necessitate discussion with a senior clinician. Depending on the clinical situation another treatment, such as amiodarone, may be recommended.

The cause for the tachyarrhythmia needs to be considered and treated. This should include a review of the patient’s drug chart to ascertain if any regular anti-arrhythmic medication had been missed.

If patient is stable, first consider whether the QRS is broad (> 0.12 seconds) or narrow.

Broad QRS-complex tachycardias

Diagnosis

• If regular → VT
• If irregular → seek help. Possibilities include:
  1. AF with aberrancy, or
  2. polymorphic VT.
• The safest strategy if unsure, is to assume that a broad-complex tachyarrhythmia is VT until proven otherwise.

Management

Anti-arrhythmic drugs

• Amiodarone
  • Typically described as Class III anti-arrhythmic but possesses activity from all groups of the Vaughan Williams classification.
  • Accumulates in fat and muscle, and has very long half life (40-70 days). It is eliminated via tears, bile and skin with minimal renal elimination.
  • IV administration is ideally via central access, as it can cause thrombophlebitis.
  • Dosing: 5 mg/kg load (typically 300mg over 20-60 minutes) then infusion at 15mg/kg/24 hours (typically ~40mg/hr). 
    • For infusion: 450mg made up in 45mls 5% Dextrose.
  • Side Effects
    • CVS: Hypotension with IV administration, bradycardia, heart block, QTc prolongation
    • RESP: Pulmonary fibrosis and pneumonitis tend to be chronic sequelae, however rarely interstitial lung disease can present acutely.
    • GI: Jaundice, GI upset
    • ENDO: Hyper- and hypothyroidism. Hyperthyroidism is a contraindication
    • MSK: Photosensitivity, grey skin
    • OTHER: Multiple drug interactions (inhibits CYP3A4 and highly protein bound). Common drugs it can interact with include digoxin, warfarin, phenytoin.
• Other infusions used may include lignocaine and procainamide.

Electrolyte replacement

• Aim for Mg²⁺ > 1 and K⁺ > 4
  • Magnesium Sulphate can be given as 10 or 20mmol in 100mls 0.9% Normal Saline at 10 mmol / hr. Rapid administration can cause hypotension. This is the mainstay of treatment of Polymorphic VT / Torsades.
  • Potassium can be added to fluids, given as a “minibag” (10mmol in 100ml of 0.29% normal saline) or neat if central access.
    • Should be administered at 10mmol/hr with cardiac monitoring – can be given faster but should seek senior help.
    • Lignocaine (~10mg) can be added to reduce pain, as this can be a significant limiting factor of peripheral administration.
  • Both can be replaced orally.

Narrow QRS-complex tachycardias

• If regular, consider SVT (or atrial flutter with 2:1 block)
• If irregular, consider atrial fibrillation or atrial flutter
• Treatments if stable include:
  • Observation
  • Electrolyte replacement as above
  • Amiodarone
  • Digoxin
  • Beta blockade – care needed in patients with heart failure
  • Vagal manoeuvres and adenosine
• Care should be taken to consider the duration of symptoms experienced by the patient. If evidence to suggest duration longer than > 48 hours, then rhythm control may be inappropriate and rate control better depending on degree of haemodynamic stability. This should be discussed with senior colleagues if uncertain.

The bradyarrhythmias

If any features of instability or a significant bradycardia that persists (HR < 40) then first line treatment is atropine 500-600 micrograms IV. Other features that require treatment include:

• Recent Asystole
• Type II Block
• CHB with broad QRS
• Ventricular Pause > 3 seconds

Management

Atropine

• Dose: 500-600 microgram bolus
  • You can give up to 3mg total – if no improvement with this dose then unlikely to work at all.
• Competitive antagonist of post ganglionic ACh receptors. Therefore has a vagolytic action and negates the effect of the vagus nerve on cardiovascular system and allows sympathetic tone to dominate.
  • Normally the vagus nerve provides some tonic parasympathetic tone, reducing the HR from around 100bpm (if there was no parasympathetic innervation) down to 60 – 80bpm.
  • It will not work in patient’s with heart transplants – they have no vagus nerve
• Has multiple side effects: tachycardia, flushing, blurred vision, constipation, retention and confusion (most common in the elderly).

Other pharmacological treatments could include titrated adrenaline boluses +/- infusion, or isoprenaline infusion. Failure of these may necessitate pacing. This can be done transvenously or transcutaneously.

Tips for Transcutaneous Pacing

• Make sure the defibrillator can pace (some do not have pacing capability).
• This is a temporary method only and definitive treatment should be arranged simultaneously with cardiology.
• You will need both pads and ECG monitoring for the defibrillator to monitor and shock simultaneously.
• Set a desired heart rate (60-80 bpm).
• Increase current (mA) until you have both electrical capture (a broad QRS with pacing spike before) and mechanical capture (a pulse is palpable).
• Set the mA to 10 greater than the value at which you have both electrical and mechanical capture.
• Sedation likely to be required so urgent senior help needed.

References and Further Reading

Australian Resuscitation Council – Guideline 11.9: Managing Acute Dysrhythmias.

Intensive Care Network: Arrythmias in ICU – An Intensivist’s Approach

Author: George Walker