Cardiac arrest

Cardiac arrest is a sudden loss of blood flow resulting from the failure of the heart to effectively pump. Symptoms include loss of consciousness and abnormal or absent breathing. Some individuals may experience chest pain, shortness of breath, or nausea before cardiac arrest. If not treated within minutes, it typically leads to death.

Cardiac arrest is preceded by no warning symptoms in approximately 50 percent of people. For those who do experience symptoms, they will be non-specific, such as new or worsening chest pain, fatigue, blackouts, dizziness, shortness of breath, weakness and vomiting. When cardiac arrest occurs, the most obvious sign of its occurrence will be the lack of a palpable pulse in the victim. Also, as a result of loss of cerebral perfusion (blood flow to the brain), the victim will rapidly lose consciousness and will stop breathing. The main criterion for diagnosing a cardiac arrest, as opposed to respiratory arrest, which shares many of the same features, is lack of circulation; however, there are a number of ways of determining this. Near-death experiences are reported by 10 to 20 percent of people who survived cardiac arrest.

Arrhythmias that are not due to structural heart disease account for 5 to 10% of sudden cardiac arrests. These are frequently caused by genetic disorders that lead to abnormal heart rhythms. The genetic mutations often affect specialised proteins known as ion channels that conduct electrically charged particles across the cell membrane, and this group of conditions are therefore often referred to as channelopathies. Examples of these inherited arrhythmia syndromes include Long QT syndrome, Brugada Syndrome, Catecholaminergic polymorphic ventricular tachycardia, and Short QT syndrome. Other conditions that promote arrhythmias but are not caused by genetic mutations include Wolff-Parkinson-White syndrome.

The risk factors for SCD are similar to those of coronary artery disease and include age, cigarette smoking, high blood pressure, high cholesterol, lack of physical exercise, obesity, diabetes, and family history. A prior episode of sudden cardiac arrest also increases the risk of future episodes.

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. Some defibrillators even provide feedback on the quality of CPR compressions, encouraging the lay rescuer to press the person's chest hard enough to circulate blood. In addition, it has been shown that those who have arrests in remote locations have worse outcomes following cardiac arrest.

Resuscitation with extracorporeal membrane oxygenation devices has been attempted with better results for in-hospital cardiac arrest (29% survival) than out-of-hospital cardiac arrest (4% survival) in populations selected to benefit most. Cardiac catheterization in those who have survived an out-of-hospital cardiac arrest appears to improve outcomes although high quality evidence is lacking. It is recommended that it is done as soon as possible in those who have had a cardiac arrest with ST elevation due to underlying heart problems.

A study of survival rates from out-of-hospital cardiac arrest found that 14.6% of those who had received resuscitation by paramedics survived as far as admission to hospital. Of these, 59% died during admission, half of these within the first 24 hours, while 46% survived until discharge from hospital. This reflects an overall survival following cardiac arrest of 6.8%. Of these 89% had normal brain function or mild neurological disability, 8.5% had moderate impairment, and 2% had major neurological disability. Of those who were discharged from hospital, 70% were still alive four years later.