HsHypovolemia – A lack of blood volume
Hypoxia – A lack of oxygen
Hydrogen ions (acidosis) – An abnormal pH in the body
Hyperkalemia or hypokalemia – Both increased and decreased potassium can be life-threatening
Hypothermia – A low core body temperature
Hypoglycemia or hyperglycemia – A low or high blood glucoseTsTablets or toxins such as drug overdose
Cardiac tamponade – Fluid building up around the heart
Tension pneumothorax – A collapsed lung
Thrombosis (myocardial infarction) – A heart attack
Thromboembolism (pulmonary embolism) – A blood clot in the lung
Traumatic cardiac arrest

Children
In children, the most common cause of cardiopulmonary arrest is shock or respiratory failure that has not been treated. Heart arrhythmia is not the most common cause in children. When there is a cardiac arrhythmia, it is most often asystole or bradycardia, in contrast to ventricular fibrillation or tachycardia as seen in adults. Other causes can include drugs such as cocaine, methamphetamine, or overdose of medications such as antidepressants in a child who was previously healthy but is now presenting with a dysrhythmia that has progressed to cardiac arrest. Common causes of sudden unexplained cardiac arrest in children include hypertrophic cardiomyopathy, coronary artery abnormalities, and arrhythmias. Mechanism
The definitive electrical mechanisms of cardiac arrest, which may arise from any of the functional, structural or physiologic abnormalities mentioned above are characterized by tachyarrhythmic or bradyarrhythmic events that do not result in systole.
Implantable cardioverter defibrillator
An implantable cardioverter defibrillator (ICD) is a battery-powered device that monitors electrical activity in the heart and when an arrhythmia is detected is able to deliver an electrical shock to terminate the abnormal rhythm. ICDs are used to prevent sudden cardiac death (SCD) in those that have survived a prior episode of sudden cardiac arrest (SCA) due to ventricular fibrillation or ventricular tachycardia (secondary prevention). ICDs are also used prophylactically to prevent sudden cardiac death in certain high risk patient populations (primary prevention).Numerous studies have been conducted on the use of ICDs for the secondary prevention of SCD. These studies have shown improved survival with ICDs compared to the use of anti-arrhythmic drugs. ICD therapy is associated with a 50% relative risk reduction in death caused by an arrhythmia and a 25% relative risk reduction in all cause mortality.Primary prevention of SCD with ICD therapy for high-risk patient populations has similarly shown improved survival rates in a number of large studies. The high-risk patient populations in these studies were defined as those with severe ischemic cardiomyopathy (determined by a reduced left ventricular ejection fraction (LVEF)). The LVEF criteria used in these trials ranged from less than or equal to 30% in MADIT-II to less than or equal to 40% in MUSTT. Management
Sudden cardiac arrest may be treated via attempts at resuscitation. This is usually carried out based upon basic life support, advanced cardiac life support (ACLS), pediatric advanced life support (PALS), or neonatal resuscitation program (NRP) guidelines.