Cardiac arrest is when our heart stops beating, and there is no contraction of the heart muscle (although there may be electrical activity still present in the heart [pulseless electrical activity/PEA]).
It is a medical emergency as it can lead to irreversible brain damage within <5 minutes of the arrest this is why we need to perform CPR immediately to prevent ischaemia to the brain. It is much more fatal than a myocardial infarction and has a very poor survival rate in the community (2-8%). In-hospital CA has a 1-year survival of 15%.
Pathophysiology
The causes of cardiac arrest are very wide and vast. However, it is simply down to an impairment in the intrinsic cardiac nervous system leading to abnormal heart rhythms such as ventricular tachycardia and ventricular fibrillation. They may also be due to bradycardia.
Some causes include:
- Scarring of cardiac tissue - due to prior heart attack, trauma etc.
- Cardiomyopathy
- Medication - especially antiarrhythmics and diuretics.
- Electrical abnormalities such as WPW syndrome, long QT syndrome
- Vascular abnormalities
- Recreational drugs
Cardiac arrest may be reversible or irreversible. There is an important set of 4 H’s and 4 T’s to remember the causes of reversible cardiac arrest:
H’s | T’s |
Hypoxia | Tension pneumothorax |
Hypovolaemia | Tamponade (cardiac) |
Hypokalaemia | Toxins |
Hyperkalaemia | Thromboembolism |
Hypothermia |
😷 Presentation
- Loss of consciousness abruptly
- Absent pulse
- Absent breathing
- Sudden collapse
Patients may have some symptoms prior to a sudden cardiac arrest:
- Chest discomfort
- SOB
- Weakness
- Palpitations
🔍 Investigations
Once again it is a life-threatening medical emergency. We assess and diagnose using the ABC system and immediately get to treatment.
🧰 Management
- CPR is the first line treatment as it needs to be carried out immediately on recognition of a patient who has had cardiac arrest. We manually do chest compressions and hope that we get return of spontaneous circulation (ROSC).
We can also pass large electrical currents through the heart to depolarise it completely. It will be followed by a brief period of asystole and after which we hope to see a return of the sinus rhythm.
It all depends if the rhythm is shockable or non-shockable:
Shockable rhythms
- Ventricular fibrillation
- Pulseless ventricular tachycardia
A single person should continue chest compressions uninterrupted while everyone else prepares the defibrillator.
Once the defibrillator is charged and ready, and the safety check performed, the shock should be delivered.
CPR should continue immediately.
Medication should be delivered after 3 shocks.
Non-shockable rhythms
- Pulseless electrical activity - this means that the electrical activity should be producing a pulse but simply isn’t’. It is most commonly due to hypovolaemia.
- Asystole
For these, CPR should be continued and IV access obtained, after which IV adrenaline 1mg should be administered.
Reversible causes should be considered as well.
The shock can be given by defibrillation (an unsynchronised shock). Cardioversion is the other form of shock therapy that is given in the elective setting, for significant (yet not immediately life-threatening) arrhythmias (AF, narrow complex tachycardias etc.).
In the case of cardioversion, digoxin should be withheld for 24 hours before treatment as it increases the risk of arrhythmias after cardioversion.
- IV adrenaline 1mg every 3-5 minutes (or every 2 shocks).
- If shockable, give 300mg IV amiodarone after 3 defibrillation attempts. After 5 attempts another 150mg may be administered. Lidocaine is an alternative.
If it is a witnessed cardiac arrest while on a monitor, give up to three successive shocks before CPR.