cardiac arrest cardiac arrest cardiac arrest is when the heart stops beating. it is a medical emergency that, without immediate medical intervention, will result in cardiac death within minutes. when it happens suddenly, it is called sudden cardiac arrest. cardiopulmonary resuscitation (cpr) and possibly defibrillation are needed until further treatment can be provided. cardiac arrest results in a rapid loss of consciousness, and breathing may be abnormal or absent. cardiac arrestother namescardiopulmonary arrest, circulatory arrest, sudden cardiac arrest (sca)cpr being administered during a simulation of cardiac arrestspecialtycardiology, emergency medicinesymptomsloss of consciousness, abnormal or no breathingcomplicationspost-cardiac arrest syndromeusual onsetolder agecausescoronary artery disease, congenital heart defect, major blood loss, lack of oxygen, electrical injury, very low potassium, heart failurediagnostic methodfinding no pulse, ekgpreventionnot smoking, physical activity, maintaining a healthy weight, healthy eatingtreatmentcardiopulmonary resuscitation (cpr), defibrillationprognosisoverall survival rate ≈10% (outside of hospital) 25% (in hospital); depends strongly on type and causefrequency13 per 10,000 people per year (outside hospital in the us)deaths> 425,000 per year (u.s.) while cardiac arrest may be caused by heart attack or heart failure, these are not the same, and in 15 to 25% of cases, there is a non-cardiac cause. some individuals may experience chest pain, shortness of breath, nausea, an elevated heart rate, and a light-headed feeling immediately before entering cardiac arrest. the most common cause of cardiac arrest is an underlying heart problem like coronary artery disease that decreases the amount of oxygenated blood supplying the heart muscle. this, in turn, damages the structure of the muscle, which can alter its function. these changes can, over time, cause ventricular fibrillation (v-fib), which most commonly precedes cardiac arrest. less common causes include major blood loss, lack of oxygen, very low potassium, electrical injury, heart failure, inherited heart arrhythmias, and intense physical exercise. cardiac arrest is diagnosed by the inability to find a pulse. cpr and defibrillation can reverse a cardiac arrest, leading to return of spontaneous circulation (rosc), but without such intervention, it will prove fatal. in some cases, cardiac arrest is an anticipated outcome of serious illnesses where death is expected. treatment for cardiac arrest includes immediate cpr and, if a shockable rhythm is present, defibrillation. two protocols have been established for cpr: basic life support (bls) and advanced cardiac life support (acls). among those whose pulses are reestablished, targeted temperature management may improve outcomes. in addition, the care team may initiate measures to protect the patient from brain injury and preserve brain function. in post-resuscitation care, an implantable cardiac defibrillator may be considered to reduce the chance of death from recurrence. in the united states, approximately 535,000 cases occur annually (about 13 per 10,000 people). of these, 326,000 (61%) experience cardiac arrest outside of a hospital setting, while 209,000 (39%) occur within a hospital. cardiac arrest becomes more common with age and affects males more often than females. the percentage of people who survive out-of-hospital cardiac arrest (ohca) with treatment by emergency medical services is about 8%. fiction has often portrayed the immediate survival rate of cardiac arrest to be unreasonably high. this may contribute to misinformed expectations of resuscitative efforts from the general public, with many studies showing the expected survival rate of resuscitative efforts after cardiac arrest exceeding 40–50%. these portrayals may also contribute to a patient's or medical decision maker's desire to pursue aggressive measures. one study suggests many of the critically ill are less likely to choose resuscitation when given accurate information about its limitations. in the event that cardiopulmonary resuscitation is successful, complete recovery is not guaranteed as many survivors experience an array of disabilities, including partial paralysis; seizures; difficulty with walking, speaking, or memory; limited consciousness; or persistent vegetative state and brain death. 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. this can present in the form of new or worsening: chest pain fatigue blackouts dizziness shortness of breath weakness vomiting when cardiac arrest is suspected by a layperson due to signs of unconsciousness and abnormal breathing, it should assumed that the victim is in cardiac arrest, and cpr should be initiated. if suspected by a trained healthcare professional, they should attempt to feel for a pulse for 10 seconds before initiating cpr. as a result of loss of cerebral perfusion (blood flow to the brain), the person will rapidly lose consciousness and can stop breathing. near-death experiences are reported by 10 to 20 percent of people who survived cardiac arrest, which demonstrates a certain level of cognitive processes that are still active during resuscitation. risk factors the risk factors for sudden cardiac arrest (sca) 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 and cardiomyopathy of cardiac disease. a prior episode of sudden cardiac arrest also increases the likelihood of future episodes. 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. previous adverse cardiac events, non-sustained ventricular tachycardia (nsvt), syncope, and left ventricular hypertrophy (lvt) have been shown to predict sudden cardiac death in children. 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. functional changes in the heart such as reduced ejection fraction or cardiac arrhythmia have been shown to increase the risk of cardiac arrest and act independently from the aforementioned risk factors. conditions that produce these functional changes can be acquired following previous cardiac injury or inherited through familial history of arrhythmogenic disorders.: 828 causes and mechanisms conduction of the heart. changes in this pattern can result from injury to the cardiac muscle and lead to non-conducted beats and ultimately cardiac arrest. ekg depiction of ventricular fibrillation (no organized rhythm) sudden cardiac arrest (sca), or sudden cardiac death (scd), occurs when the heart abruptly begins to beat in an abnormal or irregular rhythm (arrhythmia). without organized electrical activity in the heart muscle, there is no consistent contraction of the ventricles, which results in the heart's inability to generate an adequate cardiac output (forward pumping of blood from the heart to the rest of the body). there are many different types of arrhythmias, but the ones most frequently recorded in sudden cardiac arrest are ventricular tachycardia and ventricular fibrillation. less common causes of dysrhythmias in cardiac arrest include pulseless electrical activity (pea), bradyarrhythmias, or asystole. such rhythms are seen when there is prolonged cardiac arrest, progression of ventricular fibrillation, or efforts like defibrillation executed to resuscitate the person. the rhythm changes also appear to correlate with the underlying cause of cardiac injury when present (ischemic vs. nonischemic causes).: 831 sudden cardiac arrest can result from cardiac and non-cardiac causes including the following: coronary artery disease normal vs blocked coronary artery coronary artery disease (cad), also known as ischemic heart disease, is responsible for 62 to 70 percent of all sudden cardiac deaths. cad is a much less frequent cause of sudden cardiac death in people under the age of 40. cases have shown that the most common finding at postmortem examination of sudden cardiac death is chronic high-grade stenosis of at least one segment of a major coronary artery, an artery that supplies the heart muscle with its blood supply. this stenosis is often the result of narrowing and hardening of the arteries following deposition of cholesterol plaques and inflammation over several years. this accumulation and remodeling of the coronary vessels along with other systemic blood vessels characterizes the progression of atherosclerotic cardiovascular disease. when a stable plaque ruptures, it can block the flow of blood and oxygen through small arteries resulting in ischemic injury as a result. the injury to tissue following ischemia can lead to structural and functional changes preventing the heart from continuing normal conduction cycles and altering heart rate.: 829 : 829 non-atherosclerotic coronary artery abnormalities abnormalities of the coronary arteries not related to atherosclerosis include congenital coronary artery anomalies (most commonly anomalous origin of the left coronary artery from the pulmonary artery), inflammation known as coronary arteritis, embolism, vasospasm, and mechanical abnormalities related to connective tissue diseases or trauma. these conditions account for 10-15% of cardiac arrest and sudden cardiac death.: 829 coronary arteritis commonly results from a pediatric febrile inflammatory condition known as kawasaki disease. other vasculitides 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.: 829 structural heart disease short axis view of the heart demonstrating wall thickening in left ventricular hypertrophy structural heart diseases unrelated to coronary artery disease account for 10% of all sudden cardiac deaths. examples of these include: cardiomyopathies (hypertrophic, dilated, or arrhythmogenic), cardiac rhythm disturbances, myocarditis, hypertensive heart disease, and congestive heart failure. ekg depiction of left ventricular hypertrophy left ventricular hypertrophy is thought to be 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 caused a maladaptive change to the wall of the heart's main pumping chamber, the left ventricle. increased blood pressure means the heart must pump harder to adequately circulate blood throughout the body. if the heart does this for a prolonged period of time due to uncontrolled hypertension, the left ventricle can experience hypertrophy (grow larger) in a way that decreases the heart's effectiveness. left ventricular hypertrophy can be demonstrated on an echocardiogram and electrocardiogram (ekg). 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. a study of military recruits ages 18-35 found that this accounted for over 40% of sudden cardiac deaths. congestive heart failure increases the risk of sudden cardiac death fivefold. structural abnormalities of the cardiac conduction system (notably the atrioventricular node and his-purkinje 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.: 833 inherited arrhythmia syndromes arrhythmias 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 specialized proteins known as ion channels that conduct electrically charged particles across the cell membrane, and this group of conditions is therefore often referred to as channelopathies. examples of these inherited arrhythmia syndromes include long qt syndrome (lqts), brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and short qt syndrome. many are also associated with environmental or neurogenic triggers such as response to loud sounds that can initiate lethal arrhythmias.: 833 other conditions that promote arrhythmias but are not caused by genetic mutations include wolff-parkinson-white syndrome. long qt syndrome, a condition often mentioned in young people's deaths, occurs in one of every 5000 to 7000 newborns and is estimated to be responsible for 3000 deaths annually compared to the approximately 300,000 cardiac arrests seen by emergency services. these conditions are a fraction of the overall deaths related to cardiac arrest but represent conditions that may be detected prior to arrest and may be treatable. the symptomatic expression of long-qt syndrome is quite broad and more often presents with syncope rather than cardiac arrest. the risk of cardiac arrest is still