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Cardiac arrest: overview of shockable and non-shockable rhythms

By Cristiano Antonino On May 17, 2023

The rhythms associated with cardiac arrest are divided into defibrillatable and non-defibrillatable: in the case of defibrillatable rhythms, it will be possible to beat cardiac arrest

Cardiac arrest is among the leading causes of death in Western countries.

At the onset of the first symptoms of cardiac arrest, early intervention will be crucial to prevent death

The likelihood of survival will be higher the earlier the intervention.

It will be essential to intervene first with cardiac massage and then by using the defibrillator; a defibrillator that can also be used by ordinary citizens, since a doctor will not be needed to decree cardiac arrest.

The defibrillator, when the pads are applied, will be able to analyse the heart rhythm by means of EGC and will only allow a discharge if the detected heart rhythm is compatible with defibrillation.

In the event of cardiac arrest, the success of the manoeuvre will depend on the heart rhythm.

Rhythms will be divided into defibrillable and non-defibrillable rhythms

Defibrillable cardiac rhythms will be characterised by alterations in rhythm that will see the absence of pumping activity of the heart muscle.

The only effective treatment will be defibrillation.

Ventricular fibrillation and pulseless ventricular tachycardia belong to this category.

Ventricular fibrillation is a cardiac arrhythmia characterised by a very rapid and irregular activation of the ventricles.

The heart will no longer be able to generate a valid contraction and the cardiac output will stop.

Pulseless ventricular tachycardia is extremely risky, it presents an extremely accelerated heartbeat that may reach up to 180-250 beats per minute; the heart will then not be able to fill up sufficiently and send blood to the brain.

In this case, ventricular fibrillation and cardiac arrest may develop.

In these two rhythms, the only effective treatment will be the use of a defibrillator; the likelihood of defibrillation will decrease over time because the defibrillatable rhythms may degenerate into non-defibrillatable rhythms.

Cardiac massage will slow down brain damage by prolonging the duration of defibrillator rhythms while waiting for the defibrillator, but it will not be possible to establish a normal rhythm.

Therefore, in the presence of a cardiac arrest caused by a defibrillatable rhythm, the chances of resuscitating the subject will be greater.

Non-defibrillable rhythms are represented by asystole and pulseless electrical activity

In the case of asystole, the blood circulation will be blocked, which could lead to death in a very short time.

Asystole, and thus lack of electrical activity of the heart, will be caused by pulmonary embolism, myocardial infarction, hypoglycaemia, etc.

Pulseless electrical activity is a circulatory collapse that will occur despite the presence of recordable electrical activity on the electrocardiogram.

The causes may be varied: pump failure due to myocardial dysfunction, fluid loss, massive pulmonary embolism, cardiac tamponade, and so on.

It will be more complicated to resolve such a cardiac arrest as the defibrillator will not deliver the shock but will suggest not to stop the cardiac massage.

In the case of a non-defibrillable rhythm arrest, performing CPR manoeuvres will therefore be vital, while the use of a defibrillator will prove useless.