present, and people with family histories of sudden cardiac arrests should be screened for lqts and other treatable causes of lethal arrhythmia. higher levels of risk for cardiac arrest are associated with female sex, more significant qt prolongation, history of unexplained syncope (fainting spells), or premature sudden cardiac death.: 833 additionally, individuals with lqts should avoid certain medications that carry the risk of increasing the severity of this conduction abnormality, such as certain anti-arrhythmic, anti-depressant, and quinolone or macrolide antibiotics. non-cardiac causes non-cardiac causes account for 15 to 25% of cardiac arrests. the most common non-cardiac causes are trauma, major bleeding (gastrointestinal bleeding, aortic rupture, or intracranial hemorrhage), hypovolemic shock, overdose, drowning, and pulmonary embolism. cardiac arrest can also be caused by poisoning like the stings of certain jellyfish or through electrocution like lightning. reversible causes other non-cardiac causes of cardiac arrest may result from temporary disturbances in the body's homeostasis. this may be the result of changes in electrolyte ratios, oxygen saturation, or alterations of other ions influencing the body's ph. mnemonic for reversible causes main article: hs and ts "hs and ts" is a mnemonic used to remember the treatable or reversible causes of cardiac arrest. note: this mnemonic includes causes of cardiac and non-cardiac origin, but all are reversible with appropriate and time-sensitive treatment. hs hypovolemia – a lack of blood volume hypoxia – a lack of oxygen hydrogen ions (acidosis) – an abnormal ph in the body hyperkalemia or hypokalemia – an increased or decreased blood potassium hypothermia – a low core body temperature hypoglycemia or hyperglycemia – a low or high blood glucose ts tablets or toxins, such as drug overdose cardiac tamponade – fluid building up around the heart tension pneumothorax – a collapsed lung thrombosis (myocardial infarction) – a heart attack thromboembolism (pulmonary embolism) – a blood clot in the lung traumatic cardiac arrest children in children, the most common cause of cardiopulmonary arrest is shock or respiratory failure that has not been treated. heart arrhythmia is not the most common cause in children. when there is a cardiac arrhythmia, it is most often asystole or bradycardia, in contrast to ventricular fibrillation or tachycardia as seen in adults. other causes can include drugs such as cocaine and methamphetamine or overdose of medications such as antidepressants in a child who was previously healthy but is now presenting with a dysrhythmia that has progressed to cardiac arrest. common causes of sudden unexplained cardiac arrest in children include hypertrophic cardiomyopathy, coronary artery abnormalities, and arrhythmias. mechanism ventricular fibrillation the definitive electrical mechanisms of cardiac arrest, which may arise from any of the functional, structural, or physiologic abnormalities mentioned above, are characterized by tachyarrhythmic or bradyarrhythmic events that do not result in systole.: 837–838 the tachyarrhythmias can be further classified as ventricular fibrillation (v-fib) and pulseless or sustained ventricular tachycardia (v-tach), both of which are rapid and erratic arrhythmias that alter the circulatory pathway such that adequate blood flow cannot be sustained and is inadequate to meet the body's needs.: 837–838 the mechanism responsible for the majority of sudden cardiac deaths is ventricular fibrillation. ventricular fibrillation is a tachyarrhythmia characterized by turbulent electrical activity in the ventricular myocardium leading to a heart rate too disorganized and rapid to produce any meaningful cardiac output, thus resulting in insufficient perfusion of the brain and essential organs. in ventricular tachycardia, the heart also beats faster than normal, which may prevent the heart chambers from properly filling with blood. some of the electrophysiologic mechanisms underpinning ventricular fibrillations include ectopic automaticity, re-entry, and triggered activity. structural changes in the diseased heart as a result of inherited factors (mutations in ion-channel coding genes, for example) cannot explain the suddenness of sudden cardiac death. both ventricular fibrillation and ventricular tachycardia can result in the heart ineffectively pumping blood to the body. ventricular tachycardia is characterized by an altered qrs complex and a heart rate greater than 100 beats per minute. when v-tach is sustained (lasts for at least 30 seconds), inadequate blood flow to heart tissue can lead to cardiac arrest. bradyarrhythmias occur following dissociation of spontaneous electrical conduction and the mechanical function of the heart resulting in pulseless electrical activity (pea) or through complete absence of electrical activity of the heart resulting in asystole. similar to the result of tachyarrhythmias, these conditions lead to an inability to sustain adequate blood flow as well, though in the case of bradyarrhythmias, the underlying cause is an absence of mechanical activity rather than rapid beats leading to disorganization.: 837–838 diagnosis medical personnel checking the carotid pulse of a (simulated) patient cardiac arrest is synonymous with clinical death. historical information and a physical exam can diagnose cardiac arrest and provide information regarding the potential cause and prognosis. the provider taking the person's clinical history should aim to determine if the episode was observed by anyone else, what time the episode took place, what the person was doing (in particular if there was any trauma), and if there were involvement of drugs. the physical examination portion of diagnosing cardiac arrest focuses on the absence of a pulse. in many cases, lack of a carotid pulse is the gold standard for diagnosing cardiac arrest. lack of a pulse in the periphery (radial/pedal) may also result from other conditions (e.g. shock) or simply an error on the part of the rescuer. studies have shown that rescuers may often make a mistake when checking the carotid pulse in an emergency, whether they are healthcare professionals or lay persons. point-of-care ultrasound (pocus) is a tool that can be used to examine the movement of the heart and its force of contraction at the patient's bedside. pocus can accurately diagnose cardiac arrest in hospital settings, overcoming some of the shortcomings of diagnosis through checking the central pulse (carotid arteries or subclavian arteries), as well as detecting movement and contractions of the heart. using pocus, clinicians can have limited, two-dimensional views of different parts of the heart during arrest. these images can help clinicians determine whether electrical activity within the heart is pulseless or pseudo-pulseless, as well as help them diagnose the potentially reversible causes of an arrest. published guidelines from the american society of echocardiography, american college of emergency physicians, european resuscitation council, and the american heart association, as well as the 2018 preoperative advanced cardiac life support guidelines, have recognized the potential benefits of using pocus in diagnosing and managing cardiac arrest. owing to the inaccuracy of this method of diagnosis, some bodies like the european resuscitation council (erc) have de-emphasized its importance. instead, the current guidelines prompt individuals to begin cpr on any unconscious person with absent or abnormal breathing. the resuscitation council in the united kingdom stands in line with the erc's recommendations and those of the american heart association. they have suggested that the technique to check carotid pulses should be used only by healthcare professionals with specific training and expertise, and even then that it should be viewed in conjunction with other indicators like agonal respiration. various other methods for detecting circulation and therefore diagnosing cardiac arrest have been proposed. guidelines following the 2000 international liaison committee on resuscitation (ilcor) recommendations were for rescuers to look for "signs of circulation" but not specifically the pulse. these signs included coughing, gasping, color, twitching, and movement. per evidence that these guidelines were ineffective, the current ilcor recommendation is that cardiac arrest should be diagnosed in all casualties who are unconscious and not breathing normally, a similar protocol to that which the european resuscitation council has adopted. in a non-acute setting where the patient is expired, diagnosis of cardiac arrest can be done via molecular autopsy or postmortem molecular testing, which uses a set of molecular techniques to find the ion channels that are cardiac defective. this could help elucidate the cause of death in the patient. other physical signs or symptoms can help determine the potential cause of the cardiac arrest. below is a chart of the clinical findings and signs/symptoms a person may have and potential causes associated with them. physical findings related to potential causes location findings possible causes general pale skin hemorrhage decreased body temperature hypothermia airway presence of secretions, vomit, blood aspiration inability to provide positive pressure ventilation tension pneumothorax airway obstruction neck distension of the neck veins tension pneumothorax cardiac tamponade pulmonary embolism trachea shifted to one side tension pneumothorax chest scar in the middle of the sternum cardiac disease lungs breath sounds only on one side tension pneumothorax right mainstem intubation aspiration no breath sounds or distant breath sounds esophageal intubation airway obstruction wheezing aspiration bronchospasm pulmonary edema rales aspiration pulmonary edema pneumonia heart decreased heart sounds hypovolemia cardiac tamponade tension pneumothorax pulmonary embolus abdomen distended and dull ruptured abdominal aortic aneurysm ruptured ectopic pregnancy distended and tympanic esophageal intubation rectal blood present gastrointestinal hemorrhage extremities asymmetrical pulses aortic dissection skin needle tracks drug abuse classifications clinicians classify cardiac arrest into "shockable" versus "non-shockable", as determined by the ekg rhythm. this refers to whether a particular class of cardiac dysrhythmia is treatable using defibrillation. the two "shockable" rhythms are ventricular fibrillation and pulseless ventricular tachycardia, while the two "non-shockable" rhythms are asystole and pulseless electrical activity. prevention with the lack of positive outcomes following cardiac arrest, efforts have been spent finding effective strategies to prevent cardiac arrest. with the prime causes of cardiac arrest being ischemic heart disease, efforts to promote a healthy diet, exercise, and smoking cessation are important. for people at risk of heart disease, measures such as blood pressure control, cholesterol lowering, and other medico-therapeutic interventions are used. a cochrane review published in 2016 found moderate-quality evidence to show that blood pressure-lowering drugs do not reduce the risk of sudden cardiac death. exercise is an effective preventative measure for cardiac arrest in the general population but may be risky for those with pre-existing conditions. the risk of a transient catastrophic cardiac event increases in individuals with heart disease during and immediately after exercise. the lifetime and acute risks of cardiac arrest are decreased in people with heart disease who perform regular exercise, perhaps suggesting the benefits of exercise outweigh the risks. diet according to a study published in the journal of the american heart association in 2021, diet may be a modifiable risk factor that leads to a lower incidence of sudden cardiac death. the study found that those who fell under the category of having "southern diets" representing those of "added fats, fried food, eggs, organ and processed meats, and sugar‐sweetened beverages" had a positive association with an increased risk of cardiac arrest, while those deemed following the "mediterranean diets" had an inverse relationship regarding the risk of cardiac arrest. the american heart association also has diet recommendations aimed at preventing cardiovascular disease. additionally, marine-derived omega-3 polyunsaturated fatty acids (pufas) have been promoted for preventing sudden cardiac death due to their postulated ability to lower triglyceride levels, prevent arrhythmias, decrease platelet aggregation, and lower blood pressure. according to a systematic review published in 2012, omega-3 pufa supplementation is not associated with a lower risk of sudden cardiac death. code teams in medical parlance, cardiac arrest is referred to as a "code" or a "crash". this typically refers to "code blue" on the hospital emergency codes. a dramatic drop in vital sign measurements is referred to as "coding" or "crashing", though coding is usually used when it results in cardiac arrest, while crashing might not. treatment for cardiac arrest is sometimes referred to as "calling a code". patients in general wards often deteriorate for several hours or even days before a cardiac arrest occurs. this has been attributed to a lack of knowledge and skill amongst ward-based staff, in particular, a failure to measure the respiratory rate, which is often the major predictor of a deterioration and can often change up to 48 hours prior to a cardiac arrest. in response, many hospitals now have increased training for ward-based staff. a number of "early warning" systems also exist that aim to quantify the person's risk of deterioration based on their vital signs and thus provide a guide to staff. in addition, specialist staff are being used more effectively to augment the work already being done at the ward level. these include: crash teams (or code teams) – these are