In the past, numerous definitions made it difficult to determine which cardiac arrest patients were likely to die suddenly. 

Clear definitions have been developed:

• Sudden death: death within 1 hour of collapse
• Cardiac arrest: sudden loss of cardiac activity, signaled by loss of consciousness, ineffective breathing, and nonpalpable pulse
• Sudden cardiac death (SCD): unexpected death within 1 hour of cardiac arrest.

Causes 

While it is common to think that death from cardiac arrest is from coronary artery disease (CAD), other causes include noncoronary cardiac disease (e.g., congenital heart disease, valvular heart disease) and noncardiac disease (pulmonary, vascular, and neurologic). Up to 30% of deaths may be due to noncardiac disease, and many patients never have a diagnosis. To prevent death, responders must quickly determine and manage the underlying causes.

Cardiac Disease Deaths

The exact number of sudden deaths from cardiac causes is unknown. However, atherosclerosis is the most common cause of sudden death from SCD. Up to 50% of men who died with CAD had a thrombus or narrowing of the coronary arteries. Most patients with sudden death have coronary disease, even if a significant number (50% of men and 65% of women) have no prior symptoms. Autopsies reveal that up to 75% of SCD is caused by CAD and acute coronary syndrome (ACS), while the remainder are due to valvular disease (10%) and cardiomyopathy (15%). Additionally, congestive heart failure (CHF) is being recognized as a cause for SCD, and one-third of CHF patients will die from ACS. Similar to risk factors for CAD, risk factors for SCD include male sex, increasing age, dyslipidemia, hypertension, smoking, and left ventricular hypertrophy.

Atherosclerosis is the build-up of cholesterol, fats, and other substances in the artery walls.

Non-Cardiac Disease Deaths

It is important to remember there are other etiologies of sudden death, even if cardiac disease is present. By maintaining a high index of suspicion, responders can quickly address other causes to reduce the patient’s risk of death.

Preventing Death 

It is critical to focus on prevention to reduce the population of cardiac patients and make the most significant long-term impact. Individuals at risk should be sure to seek primary prevention, while healthcare providers must treat survivors to prevent a recurrence. Once cardiac arrest occurs, CPR responders and EMS personnel are the first line of defense and must be adequately trained.