Sudden cardiac death (SCD) is death due to a cardiovascular cause that occurs within one hour of the onset of symptoms. A sudden cardiac arrest occurs when the heart stops beating or is not beating sufficiently to maintain perfusion and life.
Coronary artery disease is the most common cause of sudden cardiac death, accounting for up to 80% of all cases. Cardiomyopathies and genetic channelopathies account for the remaining causes. The most common causes of non-ischemic sudden cardiac death are cardiomyopathy related to obesity, alcoholism, and fibrosis.
In patients younger than 35, the most common cause of sudden cardiac death is a fatal arrhythmia, usually in the context of a structurally normal heart. In patients from birth to 13 years, the primary cause is a congenital abnormality. In patients aged 14 to 24 years, the cause of sudden cardiac death is attributed to hypertrophic cardiomyopathy (HCM), arrhythmogenic right ventricular cardiomyopathy (ARVC), congenital coronary anomalies, genetic channelopathies, myocarditis, Wolff-Parkinson-White syndrome, and Marfan syndrome.
Ischemic Heart disease
Each year, approximately 0.1% of the United States population experiences a medical services-assessed, out-of-hospital cardiac arrest. European studies have a similar incidence ranging from 0.04% to 0.1% of the population. The median age in the US is between age 66 and 68. Males are more likely to suffer from sudden cardiac arrest.
While rare, sudden cardiac death is the leading cause of nontraumatic cause of death among young athletes. In the general population, sports-related, sudden death from any cause is 0.5 to 2.1 per 100,000 yearly. Sports-related, sudden deaths are higher in elite athletes with an incidence of 1:8,253 per year per the National Collegiate Athletic Association (NCAA). NCAA Division I male basketball players have a 1:5200 incidence of sudden death.
A circadian peak of sudden cardiac death occurs between 6 am and noon, and a smaller peak occurs in the late afternoon. The overall incidence of sudden cardiac death is higher on Mondays. 
After a myocardial infarction, the risk of sudden cardiac death is highest during the first months due to fatal tachyarrhythmias, re-infarction, or myocardial rupture. 
Ventricular fibrillation (VF) and ventricular tachycardia (VT) were initially thought to be the most common causes of out-of-hospital cardiac arrest. More recent studies show pulseless, electrical activity (PEA) and asystole as more frequent. Approximately 50% of patients initially have asystole, and 19% to 23% have PEA as the first identifiable rhythm.
Immediately following OHCA the blood flow to the brain slows to essentially zero and ultimately leading to death.
Some patients experience palpitations, dizziness, or near syncope prior to sudden cardiac arrest. Almost half of the patients who have sudden cardiac arrests report no symptoms prior to collapse.
The American Heart Association recommends cardiovascular screening for high school and collegiate athletes. This includes an evaluation of the athlete's personal and family history and a physical exam.  Screening should follow the AHA guidelines:
Routine ECG testing is not recommended for student-athletes. Students found to have an abnormal exam or those with a positive personal or family history may be referred for cardiac testing including ECG and echocardiogram.
Sudden cardiac arrest patients may demonstrate brief myoclonic or seizure-like activity.
Before transportation to a hospital, emergency medical services (EMS) or lay people may utilize an automated external defibrillator (AED). Once EMS arrives cardiac monitoring via ECG should occur.
Full cardiac assessment is required for cardiac arrest survivors. The following tests should be completed to establish a cause :
ECG testing helps determine a diagnosis of ischemic heart disease, myocardial infarction, and inherited channelopathies. Echocardiograms evaluate for evidence of heart failure, cardiomyopathy, valvular heart disease, and congenital heart disease. Coronary angiography further evaluates coronary artery disease, congenital coronary anomalies, and coronary spasms. Exercise testing is helpful for diagnosis of ischemic heart disease, LQTS, and CPVT. Electrophysiology studies can detect the suspected arrhythmia. Procainamide can provoke Brugada syndrome regardless of the findings on the initial ECG. Cardiac MRI can detect ARVC, sarcoidosis (fibrotic cardiomyopathy), myocarditis, and myocardial injury from coronary spasms.
Treatment for sudden cardiac arrest should be initiated immediately by lay people and EMS. Treatment includes the use of an automated external defibrillator and cardiopulmonary resuscitation (CPR). CPR provides enough oxygen to the brain until a stable electrical rhythm can be established.
After transfer to a hospital, therapeutic hypothermia can be induced to limit neurologic injury and reperfusion injuries. Therapeutic hypothermia is more effective for the management of ventricular tachycardia and ventricular fibrillation but can also be used in PEA and asystole. Limitations to therapeutic hypothermia include a tympanic membrane temperature below 30 degrees at presentation, being comatose before the sudden cardiac arrest, pregnancy, inherited coagulation disorder, and the terminally ill patient.
If a patient survives the out-of-hospital cardiac arrest, long-term treatment is aimed at the underlying cause.
An implantable cardioverter defibrillator (ICD) is used for secondary prevention of sudden cardiac death in any person who has experienced arrhythmia-related syncope or survived sudden cardiac arrest.
Medication is targeted at the underlying cause of sudden cardiac arrest.
The overall out-of-hospital survival for sudden cardiac arrest is around 7%.
To reduce the risk of sudden death, healthcare workers should educate the family members of young sudden cardiac death victims that they may also be at an increased risk for ischemic heart disease and ventricular arrhythmias. First-degree relatives, particularly those younger than 35, should be screened. If cardiomyopathy or a genetic channelopathy is present, the evaluation of other family members should also occur. For the most part, the evaluation should be done by a cardiologist or an internist.