: 837–838  The tachyarrhythmias can be further classified as Ventricular fibrillation (V-fib) and pulseless or sustained Ventricular tachycardia (V-tach), both of which are rapid and erratic arrhythmias that alter the circulatory pathway such that adequate blood flow cannot be sustained and is inadequate to meet the bodys needs. : 837–838 The mechanism responsible for the majority of sudden cardiac deaths is ventricular fibrillation. Ventricular fibrillation is a tachyarrhythmia characterized by turbulent electrical activity in the ventricular myocardium leading to a heart rate too disorganized and rapid to produce any meaningful cardiac output, thus resulting in insufficient perfusion of the brain and essential organs. In ventricular tacycardia, the heart also beats faster than normal, which may  prevent the heart chambers from properly filling with blood. Some of the electrophysiologic mechanisms underpinning ventricular fibrillations include ectopic automaticity, re- entry, and triggered activity. Structural changes in the diseased heart as a result of inherited factors (mutations in ion-channel coding genes for example) cannot explain the suddenness of sudden cardiac death.Both ventricular fibrillation and ventricular tachycardia can result in the heart ineffectively pumping blood to the body. Ventricular tachycardia is characterized by an altered QRS complex and a heart rate greater than 100 beats per minute. When V-tach is sustained (lasts for at least 30 seconds), inadequate blood flow to heart tissue can lead to cardiac arrest.Bradyarrhthmias occur following dissociation of spontaneous electrical conduction and the mechanical function of the heart resulting in pulseless electrical activity (PEA) or through complete absence of electrical activity of the heart resulting in asystole.
In children 2 to 4 J/Kg is recommended.The defibrillation is made by an automated external defibrillator (AED), a portable machine that can be used even by any user because it produces voice instructions that guide the process, automatically checks the victims condition, and applies the correct electric shocks. Some defibrillators even provide feedback on the quality of CPR compressions, encouraging the lay rescuer to press the persons chest hard enough to circulate blood.In addition, there is increasing use of public access defibrillation. This involves placing an automated external defibrillator in public places, and training staff in these areas how to use them. This allows defibrillation to take place prior to the arrival of emergency services and has been shown to lead to increased chances of survival. It has been shown that those who have arrests in remote locations have worse outcomes following cardiac arrest. Medications
As of 2016, medications other than epinephrine (adrenaline), while included in guidelines, have not been shown to improve survival to hospital discharge following out-of-hospital cardiac arrest. This includes the use of atropine, lidocaine, and amiodarone. Epinephrine in adults, as of 2019, appears to improve survival but does not appear to improve neurologically normal survival. It is generally recommended every five minutes. Epinephrine acts on the alpha-1 receptor, which in turn increases the blood flow that supplies the heart. This would assist with providing more oxygen to the heart.