Cardiac arrest

**Cardiac arrest** happens when the heart suddenly stops beating or beats too weakly to produce a pulse. This can be caused by a heart attack in which the heart's need for oxygen is not met and the heart muscle begins to die. With cardiac arrest, normal circulation of blood stops, because of a failure of the heart to contract. This results in the body not getting enough oxygenated blood, which causes cells to start to die from oxygen starvation. Cerebral hypoxia (lack of oxygen to the brain) eventually makes a person lose consciousness and stop breathing, and this makes the heart stop completely. Unless the person is in hypothermia, brain damage usually occurs after three to five minutes. (In some cases, the person is put into hypothermia on purpose, to help the person recover better with less damage.)

Cardiac arrest is a medical emergency. If it is treated early enough, some damage done can be reversed in certain groups of patients. When cardiac arrest leads to a person's death, this is called sudden cardiac death (SCD). First aid treatment for cardiac arrest usually begins with cardiopulmonary resuscitation (CPR) to keep oxygenated blood flowing until medical treatment is available.

## Causes 
Cardiac arrest can be caused by cardiac (heart) problems, like heart attacks, and from non-cardiac problems, like breathing problems or very serious injuries. In older people, cardiac arrest is usually caused by a heart problem. In younger people, cardiac arrest is often caused by breathing problems.

### Cardiac causes 
#### Coronary artery disease 
Coronary artery disease (CAD) is disease in one or more of the coronary arteries, the main arteries that supply the heart. Over time, these arteries can form plaques— a layer of fat on the inner wall of the artery. This is more likely to happen if a person has high cholesterol. When plaques form in coronary arteries, they become partially blocked and less blood can move through them. Early on, there may be no symptoms of less blood flow through arteries— a form of disease called atherosclerosis. As coronary artery disease gets worse, the heart may not receive enough blood flow to supply the oxygen it needs to function, known as ischemia. When ischemia is happening, a person may have symptoms including chest pain. Over time, ischemia of the heart can cause damage to heart muscle and the electrical system of the heart. This damage over time causes a gradual decrease in heart function, raising a person's risk for cardiac arrest.

##### Heart attack 
Early on in CAD, coronary artery plaques only partially block arteries. While ischemia may be happening, the heart is still able to keep muscle alive. Plaques usually grow in size over time, further reducing blood flow to the heart and worsening ischemia. When ischemia becomes severe enough to cause heart muscle to die, it becomes known as a heart attack, also known as a myocardial infarction. A heart attack may also occur when a coronary artery plaque breaks away from the wall of the artery. This "ruptured" of a plaque is too bulky to travel through the heart's small blood vessels and often becomes "stuck", leading to a total blockage of that artery. Plaques damage artery walls when they break off. If this damage is severe enough to cause bleeding, artery blockage can also happen when the body forms a clot at the site of the damage.

A heart attack means ischemia is causing heart muscle to die. Sometimes, this can be seen on an electrocardiogram (ECG or EKG). In other cases, a heart attack can only be detected by a blood test that shows an elevated level of troponin, a chemical released when heart muscle dies. Because ischemia is so severe, heart attacks increase the risk of cardiac arrest much more than CAD alone.

#### Structural heart disease 
Problems with the heart's structure or movement. can also cause cardiac arrest. Heart structure problems include cardiomyopathy (abnormal heart muscle), myocarditis (infection of the heart muscle), and heart failure. 

Cardiomyopathy is a problem with the makeup, arrangement, or behavior of heart muscle. Cardiomyopathy can be caused by genes, coronary artery disease (CAD), using certain drugs, virus infections, certain cancer treatments, and severe stress. There are four main types of cardiomyopathy. Dilated cardiomyopathy (DCM) is a disease where the heart becomes too large to pump blood to the body effectively. Restrictive cardiomyopathy (RCM) is a disease where the heart muscles become too stiff to allow the heart to fill with the normal amount of blood. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic disease that causes changes in overall heart movement, changes in heart muscle tissue makeup, and arrythmias— abnormal heart rhythms.

## References