Cardiac arrest

Cardiac arrest, also known as sudden cardiac arrest, is a condition in which the heart suddenly and unexpectedly stops beating. When the heart stops, blood cannot circulate properly through the body and the blood flow to the brain and other organs is decreased. When the brain does not receive enough blood, this can cause a person to lose consciousness and brain cells begin to die within minutes due to lack of oxygen. Coma and persistent vegetative state may result from cardiac arrest. Cardiac arrest is typically identified by the absence of a central pulse and abnormal or absent breathing.
Cardiac arrest and resultant hemodynamic collapse often occur due to arrhythmias. Ventricular fibrillation and ventricular tachycardia are most commonly recorded. However, as many incidents of cardiac arrest occur out-of-hospital or when a person is not having their cardiac activity monitored, it is difficult to identify the specific mechanism in each case.
Structural heart disease, such as coronary artery disease, is a common underlying condition in people who experience cardiac arrest. The most common risk factors include age and cardiovascular disease. Additional underlying cardiac conditions include heart failure and inherited arrhythmias. Additional factors that may contribute to cardiac arrest include major blood loss, lack of oxygen, electrolyte disturbance, electrical injury, and intense physical exercise.
Cardiac arrest is diagnosed by the inability to find a pulse in an unresponsive patient. The goal of treatment for cardiac arrest is to rapidly achieve return of spontaneous circulation using a variety of interventions including CPR, defibrillation or cardiac pacing. Two protocols have been established for CPR: basic life support and advanced cardiac life support.
If return of spontaneous circulation is achieved with these interventions, then sudden cardiac arrest has occurred. By contrast, if the person does not survive the event, this is referred to as sudden cardiac death. Among those whose pulses are re-established, the care team may initiate measures to protect the person from brain injury and preserve neurological function. Some methods may include airway management and mechanical ventilation, maintenance of blood pressure and end-organ perfusion via fluid resuscitation and vasopressor support, correction of electrolyte imbalance, EKG monitoring and management of reversible causes, and temperature management. Targeted temperature management may improve outcomes. In post-resuscitation care, an implantable cardiac defibrillator may be considered to reduce the chance of death from recurrence.
Per the 2015 American Heart Association Guidelines, there were approximately 535,000 incidents of cardiac arrest annually in the United States. Of these, 326,000 experience cardiac arrest outside of a hospital setting, while 209,000 occur within a hospital.
Cardiac arrest becomes more common with age and affects males more often than females. In the United States, black people are twice as likely to die from cardiac arrest as white people. Asian and Hispanic people are not as frequently affected as white people.

Signs and symptoms

Cardiac arrest is not preceded by any warning symptoms in approximately 50 percent of people. For individuals who do experience symptoms, the symptoms are usually nonspecific to the cardiac arrest. For example, new or worsening chest pain, fatigue, blackouts, dizziness, shortness of breath, weakness, or vomiting.
When cardiac arrest is suspected by a layperson it should be assumed that the victim is in cardiac arrest. Bystanders should call emergency medical services and initiate CPR.

Risk factors

Major risk factors for cardiac arrest include age and underlying cardiovascular disease. A prior episode of sudden cardiac arrest increases the likelihood of future episodes. A 2021 meta-analysis assessing the recurrence of cardiac arrest in out-of-hospital cardiac arrest survivors identified that 15% of survivors experienced a second event, most often in the first year. Furthermore, of those who experienced recurrence, 35% had a third episode.
Additional significant risk factors include cigarette smoking, high blood pressure, high cholesterol, history of arrhythmia, lack of physical exercise, obesity, diabetes, family history, cardiomyopathy, alcohol use, and possibly caffeine intake. Current cigarette smokers with coronary artery disease were found to have a two to threefold increase in the risk of sudden death between ages 30 and 59. Furthermore, it was found that former smokers' risk was closer to that of those who had never smoked. A statistical analysis of many of these risk factors determined that approximately 50% of all cardiac arrests occur in 10% of the population perceived to be at greatest risk, due to aggregate harm of multiple risk factors, demonstrating that cumulative risk of multiple comorbidities exceeds the sum of each risk individually.

Causes and mechanisms

The underlying causes of sudden cardiac arrest can result from cardiac and non-cardiac causes. The most common underlying causes are different, depending on the patient's age. Common cardiac causes include coronary artery disease, non-atherosclerotic coronary artery abnormalities, structural heart damage, and inherited arrhythmias. Common non-cardiac causes include respiratory arrest, diabetes, medications, and trauma.
The most common mechanism underlying sudden cardiac arrest is an arrhythmia. Without organized electrical activity in the heart muscle, there is inconsistent contraction of the ventricles, which prevents the heart from generating adequate cardiac output. This hemodynamic collapse results in poor blood flow to the brain and other organs, which if prolonged causes persistent damage.
There are many different types of arrhythmias, but the ones most frequently recorded in sudden cardiac arrest are ventricular tachycardia and ventricular fibrillation. Both ventricular tachycardia and ventricular fibrillation can prevent the heart from generating coordinated ventricular contractions, thereby failing to sustain adequate blood circulation.
Less common initial arrhythmias occurring in cardiac arrest include pulseless electrical activity and asystole. These rhythms are seen when there is prolonged cardiac arrest, progression of ventricular fibrillation, or efforts like defibrillation fail to resuscitate the person.

Cardiac causes

Coronary artery disease

, also known as atherosclerotic cardiovascular disease, involves the deposition of cholesterol and subsequent inflammation-driven formation of atherosclerotic plaques in the arteries. CAD involves the accumulation and remodeling of the coronary vessels along with other systemic blood vessels. When an atherosclerotic plaque dislodges, it can block the flow of blood and oxygen through small arteries, such as the coronary arteries, resulting in ischemic injury. In the heart, this results in myocardial tissue damage which can lead to structural and functional changes that disrupt normal conduction patterns and alter heart rate and contraction.
CAD underlies 68 percent of sudden cardiac deaths in the United States. Indeed, postmortem examinations have shown that the most common finding in cases of sudden cardiac death is chronic, high-grade stenosis of at least one segment of a major coronary artery.
While CAD is a leading contributing factor, this is an age-dependent factor, with CAD being a less common cause of sudden cardiac death in people under the age of 40.

Non-atherosclerotic coronary artery abnormalities

Abnormalities of the coronary arteries not related to atherosclerosis include inflammation, embolism, vasospasm, mechanical abnormalities related to connective tissue diseases or trauma, and congenital coronary artery anomalies. These conditions account for 10-15% of cardiac arrest and sudden cardiac death.

Coronary arteritis commonly results from a pediatric febrile inflammatory condition known as Kawasaki disease. Other types of vasculitis can also contribute to an increased risk of sudden cardiac death.
Embolism, or clotting, of the coronary arteries most commonly occurs from septic emboli secondary to endocarditis with involvement of the aortic valve, tricuspid valve, or prosthetic valves.
Coronary vasospasm may result in cardiac arrhythmias, altering the heart's electrical conduction with a risk of complete cardiac arrest from severe or prolonged rhythm changes.
Mechanical abnormalities with an associated risk of cardiac arrest may arise from coronary artery dissection, which can be attributed to Marfan syndrome or trauma.
Structural heart disease

Examples of structural heart diseases include: cardiomyopathies, cardiac rhythm disturbances, myocarditis, and congestive heart failure.
Left ventricular hypertrophy is a leading cause of sudden cardiac deaths in the adult population. This is most commonly the result of longstanding high blood pressure, or hypertension, which has led to maladaptive overgrowth of muscular tissue of the left ventricle, the heart's main pumping chamber. This is because elevated blood pressure over the course of several years requires the heart to adapt to the requirement of pumping harder to adequately circulate blood throughout the body. If the heart does this for a prolonged period of time, the left ventricle can experience hypertrophy in a way that decreases the heart's effectiveness. Left ventricular hypertrophy can be demonstrated on an echocardiogram and electrocardiogram.
Abnormalities of the cardiac conduction system may predispose an individual to arrhythmias with a risk of progressing to sudden cardiac arrest, albeit this risk remains low. Many of these conduction blocks can be treated with internal cardiac defibrillators for those determined to be at high risk due to severity of fibrosis or severe electrophysiologic disturbances.
Structural heart diseases unrelated to coronary artery disease account for 10% of all sudden cardiac deaths. A 1999 review of sudden cardiac deaths in the United States found that structural heart diseases accounted for over 30% of sudden cardiac arrests for those under 30 years.