When to use the defibrillator? Let's discover the shockable rhythms
A heart attack is an extreme situation that requires preparation and timing. A cornerstone of intervention lies in the concept of shockable rhythms
Ventricular fibrillation and pulseless ventricular tachycardia are shockable rhythms
When can the defibrillator be used? Let’s delve into this together.
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Sinus rhythm
When at rest, the heart beats at a regular rhythm between 60 and 100 beats per minute: this is the sinus rhythm.
When an alteration of the normal heart rhythm occurs, it is called an arrhythmia.
In most cases, arrhythmia does not pose a serious danger, but some malignant arrhythmias can alter the circulation so profoundly that they cause cardiac arrest.
Cardiac arrest is a dramatic and sudden event that today causes the death of 60,000 people every year in Italy.
Its severity, combined with the speed with which it strikes, leaves little room for intervention by anyone in the vicinity.
For this reason, cardiac arrest is also called Sudden Cardiac Arrest or Sudden Cardiac Death, precisely because it occurs without warning and unexpectedly.
But what happens with cardiac arrest? The heart begins to beat at a dangerously high speed to the point of vibrating and stops pumping blood to the body and brain.
This leads to a rapid loss of consciousness and breathing: these are the two symptoms associated with cardiac arrest.
If action is not taken within a few minutes with cardiopulmonary resuscitation and a semi-automatic external defibrillator, the affected person will die.
However, the use of the AED is not always indicated, as not all cardiac rhythms associated with cardiac arrest are shockable
Shockable rhythms are characterised by alterations in rhythm that cause the heart’s pumping activity to be absent.
In these cases, the only effective treatment is electrical defibrillation.
The defibrillatable heart rhythms are ventricular fibrillation and ventricular tachycardia.
Ventricular fibrillation (VF) is an arrhythmia characterised by rapid, ineffective and irregular contractions of the ventricles.
Without a proper contraction capable of pumping blood into the circulation, there is a risk of severe impairment of cardiac output.
This is why ventricular fibrillation is considered one of the main causes of cardiac arrest.
This arrhythmia can be fatal if action is not taken within a few minutes with a defibrillator: the defibrillator, by means of two pads placed on the chest, delivers an electric shock that attempts to restore the heart’s normal beat.
Ventricular tachycardia (VT) is an arrhythmia characterised by a high heart rate (greater than 100 beats per minute).
The arrhythmia may last for only a few beats, but if it lasts longer, it represents a real medical emergency, as the heart is unable to pump blood adequately.
Ventricular fibrillation and ventricular tachycardia are the most frequent initial rhythms in out-of-hospital cardiac arrest (70-90%) and their only effective treatment is defibrillation.
Indeed, cardiopulmonary resuscitation succeeds in bringing oxygen to the brain cells and can prolong the duration of defibrillable rhythms.
However, it cannot convert a defibrillatable rhythm into a valid rhythm: only a manual or semi-automatic defibrillator can use electric shocks to restore normal rhythm.
The prognosis in the case of a shockable rhythm is therefore much more favourable than for non-shockable rhythms.
However, action must be taken as soon as possible because the chances of rescue decrease with time (7-10% every minute) and a shockable rhythm quickly degenerates into a non-shockable rhythm.
Asystole and pulseless electrical activity are Non-Shockable Rhythms
Non-Shockable rhythms are Asystole and Pulseless Electrical Activity.
These two arrhythmias are usually caused by acute situations of extreme severity and are difficult to treat.
Ventricular asystole represents the total absence of ventricular electrical activity corresponding to the absence of contraction of the ventricles.
There is no blood supply to the brain and, if resuscitation manoeuvres have no effect, it leads to death.
Pulseless electrical activity (PEA) is a cardiac arrest situation in which electrical activity is present in the heart (visualised on the ECG electrocardiogram) but any palpable pulse is absent.
With this arrhythmia, some mechanical contractions of the heart may occur, but these are too weak for an effective cardiac output.
In both cases, analysis of the heart rhythm (which with a semi-automatic defibrillator is provided by the device itself) will indicate that shock is not advised and that cardiopulmonary resuscitation should be initiated immediately.
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