Cardiac arrest

Cardiac arrest, (also known as cardiopulmonary arrest or circulatory arrest) is the cessation of normal circulation of the blood due to failure of the heart to contract effectively. Medical personnel can refer to an unexpected cardiac arrest as a sudden cardiac arrest or SCA.

A cardiac arrest is different from (but may be caused by) a heart attack, where blood flow to the muscle of the heart is impaired.

Arrested blood circulation prevents delivery of oxygen to the body. Lack of oxygen to the brain causes loss of consciousness, which then results in abnormal or absent breathing. Brain injury is likely if cardiac arrest goes untreated for more than five minutes. For the best chance of survival and neurological recovery, immediate and decisive treatment is imperative.

Cardiac arrest is a medical emergency that, in certain situations, is potentially reversible if treated early. When unexpected cardiac arrest leads to death this is called sudden cardiac death (SCD). The treatment for cardiac arrest is cardiopulmonary resuscitation (CPR) to provide circulatory support, followed by defibrillation if a shockable rhythm is present. If a shockable rhythm is not present after CPR and other interventions, clinical death is inevitable.

Classification
Cardiac arrest is classified into "shockable" versus "non–shockable", based upon the ECG rhythm. The two shockable rhythms are ventricular fibrillation and pulseless ventricular tachycardia while the two non–shockable rhythms are asystole and pulseless electrical activity. This refers to whether a particular class of disrhythmia is treatable using defibrillation.

Signs and symptoms
Cardiac arrest is an abrupt cessation of pump function in the heart (as evidenced by the absence of a palpable pulse). Prompt intervention can usually reverse a cardiac arrest, but without such intervention it will almost always lead to death. In certain cases, it is an expected outcome to a serious illness.

However, due to inadequate cerebral perfusion, the patient will be unconscious and will have stopped breathing. The main diagnostic criterion to diagnose a cardiac arrest, (as opposed to respiratory arrest which shares many of the same features), is lack of circulation, however there are a number of ways of determining this. Near death experiences are reported by 10-20% of people who survived cardiac arrest.

Causes
Coronary heart disease is the leading cause of sudden cardiac arrest. Many other cardiac and non–cardiac conditions also increase ones risk.

Coronary heart disease
Approximately 60–70% of SCD is related to coronary heart disease. Among adults, ischemic heart disease is the predominant cause of arrest with 30% of people at autopsy showing signs of recent myocardial infarction.

Non ischemic heart disease
A number of other cardiac abnormalities can increase the risk of SCD including: cardiomyopathy, cardiac rhythm disturbances, hypertensive heart disease, congestive heart failure.

In a group of military recruits aged 18–35, cardiac anomalies accounted for 51% of cases of SCD, while in 35% of cases the cause remained unknown. Underlying pathology included: coronary artery abnormalities (61%), myocarditis (20%), and hypertrophic cardiomyopathy (13%). Congestive heart failure increases the risk of SCD by 5 fold.

Many additional conduction abnormalities exist that place one at higher risk for cardiac arrest. For instance, long QT syndrome, a condition often mentioned in young people's deaths, occurs in 1/5000-1/7000 newborns and is estimated to be responsible 3000 deaths each year compared to the approximately 300000 cardiac arrests seen by emergency services. These conditions are a fraction of the overall deaths related to cardiac arrest, but represent conditions which may be detected prior to arrest, which maybe treatable.

Non–cardiac
SCDs is unrelated to heart problems in 35% of cases. The most common non–cardiac causes: trauma, non-trauma related bleeding (such as gastrointestinal bleeding, aortic rupture, and intracranial hemorrhage), overdose, drowning and pulmonary embolism.

Risk factors
The risk factors for SCD are similar to those seen with coronary heart disease including: smoking, lack of physical exercise, obesity, diabetes, and family history.

Hs and Ts
"Hs and Ts" is the name for a mnemonic used to aid in remembering the possible treatable or reversible causes of cardiac arrest.
 * Hs
 * Hypovolemia - A lack of blood volume
 * Hypoxia - A lack of oxygen
 * Hydrogen ions (Acidosis) - An abnormal pH in the body
 * Hyperkalemia or Hypokalemia - Both excess and inadequate potassium can be life-threatening.
 * Hypothermia - A low core body temperature
 * Hypoglycemia or Hyperglycemia - Low or high blood glucose


 * Ts
 * Tablets or Toxins
 * Cardiac Tamponade - Fluid building around the heart
 * Tension pneumothorax - A collapsed lung
 * Thrombosis (Myocardial infarction) - Heart attack
 * Thromboembolism (Pulmonary embolism) - A blood clot in the lung
 * Trauma

Diagnosis
Cardiac arrest is synonymous with clinical death.

A cardiac arrest is usually diagnosed clinically by the absence of a pulse. In many cases lack of carotid pulse is the gold standard for diagnosing cardiac arrest, but lack of a pulse (particularly in the peripheral pulses) may be a result of other conditions (e.g. shock), or simply an error on the part of the rescuer. Studies have shown that rescuers often make a mistake when checking the carotid pulse in an emergency, whether they are healthcare professionals or lay persons.

Owing to the inaccuracy in this method of diagnosis, some bodies such as the European Resuscitation Council (ERC) have de-emphasised its importance. The Resuscitation Council (UK), in line with the ERC's recommendations and those of the American Heart Association, have suggested that the technique 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 such as agonal respiration.

Various other methods for detecting circulation 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, colour, twitching and movement. However, in face of evidence that these guidelines were ineffective, the current recommendation of ILCOR is that cardiac arrest should be diagnosed in all casualties who are unconscious and not breathing normally.

Prevention
With positive outcomes following cardiac arrest unlikely, an effort has been spent in 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.

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".

Extensive research has shown that 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 carry out measurement of 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 to this, many hospitals now have increased training for ward based staff. A number of "early warning" systems also exist which aim to quantify the risk which patients are at of deterioration based on their vital signs and thus provide a guide to staff. In addition, specialist staff are being utilised more effectively in order to augment the work already being done at ward level. These include:
 * Crash teams (or code teams) - These are designated staff members who have particular expertise in resuscitation, who are called to the scene of all arrests within the hospital. This usually involves a specialized cart of equipment (including defibrillator) and drugs called a "crash cart".
 * Medical emergency teams - These teams respond to all emergencies, with the aim of treating the patient in the acute phase of their illness in order to prevent a cardiac arrest.
 * Critical care outreach - As well as providing the services of the other two types of team, these teams are also responsible for educating non-specialist staff. In addition, they help to facilitate transfers between intensive care/high dependency units and the general hospital wards. This is particularly important, as many studies have shown that a significant percentage of patients discharged from critical care environments quickly deteriorate and are re-admitted - the outreach team offers support to ward staff to prevent this from happening.

Implantable cardioverter defibrillators
A technologically based intervention to prevent further cardiac arrest episodes is the use of an implantable cardioverter-defibrillator (ICD). This device is implanted in the patient and acts as an instant defibrillator in the event of arrhythmia. Note that standalone ICDs do not have any pacemaker functions, but they can be combined with a pacemaker, and modern versions also have advanced features such as anti-tachycardic pacing as well as synchronized cardioversion. A recent study by Birnie et al. at the University of Ottawa Heart Institute has demonstrated that ICDs are underused in both the United States and Canada. An accompanying editorial by Simpson explores some of the economic, geographic, social and political reasons for this. Patients who are most likely to benefit from the placement of an ICD are those with severe ischemic cardiomyopathy (with systolic ejection fractions less than 30%) as demonstrated by the MADIT-II trial.

Management
Sudden cardiac arrest may be treated via attempts at resuscitation. This is usually carried out based upon basic life support (BLS) / advanced cardiac life support (ACLS), pediatric advanced life support (PALS) or neonatal resuscitation program (NRP) guidelines.

Cardiopulmonary resuscitation
CPR is a critical part of the management of cardiac arrest. It should be started as soon as possible and interrupted as little as possible. The component of CPR which seems to make the greatest difference is the chest compressions. Tracheal intubation has not been found to improve survival rates in cardiac arrest cases. A 2009 study has found that assisted ventilation may worsen outcomes over placement of an oral airway with passive oxygen delivery. Intubation in the prehospital environment has been found to decrease survival. Correctly performed bystander CPR has been shown to increase survival; it is performed in less than 30% of out of hospital arrests.

Defibrillation
Clinicians distinguish shockable and non–shockable causes of cardiac arrest - based on the presence or absence of ventricular fibrillation or pulseless ventricular tachycardia. The shockable rhythms are treated with CPR and defibrillation. Most out-of-hospital cardiac arrests occur following a myocardial infarction (heart attack), and present initially with a heart rhythm of ventricular fibrillation. The person is therefore likely to respond to defibrillation, and this has become the focus of interventions.

In addition, there is increasing use of public access defibrillation. This involves placing automated external defibrillators in public places, and training staff in these areas how to use them. This allows defibrillation to take place prior to the arrival of emergency services, and has been shown to lead to increased chances of survival. Some defibrillators even provide feedback on the quality of CPR compressions, encouraging the lay rescuer to press the patient's chest hard enough to circulate blood. In addition, it has been shown that those who suffer arrests in remote locations have worse outcomes following cardiac arrest: these areas often have first responders, whereby members of the community receive training in resuscitation and are given a defibrillator, and called by the emergency medical services in the case of a collapse in their local area.

Medications
Medications, while included in guidelines, have been shown not to improve survival to hospital discharge post cardiac arrest. This includes the use of epinephrine, atropine, and amiodarone. The study, however, only refers to the ineffectiveness of these drugs in reference to out-of-hospital cardiac arrests. Though in their 2010 guidelines, the American Heart Association has singled out atropine, indicating that "Available evidence suggests that the routine use of atropine during PEA or asystole is unlikely to have a therapeutic benefit."

Therapeutic hypothermia
Cooling a person after cardiac arrest with return of spontaneous circulation (ROSC) but without return of consciousness improves outcomes. This procedure is called therapeutic hypothermia. The first study conducted in Europe focused on people who were resuscitated 5–15 minutes after collapse. Patients participating in this study experienced spontaneous return of circulation (ROSC) after an average of 105 minutes. Subjects were then cooled over a 24 hour period, with a target temperature of 32 - 34 C. 55% of the 137 patients in the hypothermia group experienced favorable outcomes, compared with only 39% in the group that received standard care following resuscitation. Death rates in the hypothermia group were 14% lower, meaning that for every 7 patients treated one life was saved. Notably, complications between the two groups did not differ substantially. This data was supported by another similarly run study that took place simultaneously in Australia. In this study 49% of the patients treated with hypothermia following cardiac arrest experienced good outcomes, compared to only 26% of those who received standard care.

ECMO
Sporadic reports of resuscitation with extracorporeal membrane oxygenation devices have appeared in recent years.

Chain of survival
Several organisations promote the idea of a "chain of survival". The chain consists of the following "links":


 * Early recognition - If possible, recognition of illness before the patient develops a cardiac arrest will allow the rescuer to prevent its occurrence. Early recognition that a cardiac arrest has occurred is key to survival - for every minute a patient stays in cardiac arrest, their chances of survival drop by roughly 10%.
 * Early CPR - improves the flow of blood and of oxygen to vital organs - an essential component of treating a cardiac arrest. In particular, by keeping the brain supplied with oxygenated blood, chances of neurological damage are decreased.
 * Early defibrillation - is effective for the management of ventricular fibrillation and pulseless ventricular tachycardia If defibrillation is delayed the rhythm is likely to degenerate into asystole for which outcomes are worse.
 * Early advanced care - Early Advanced Cardiac Life Support is the final link in the chain of survival.

If one or more links in the chain are missing or delayed, then the chances of survival drop significantly.

These protocols are often initiated by a Code Blue, which usually denotes impending or acute onset of cardiac arrest or respiratory failure, although in practice, Code Blue is often called in less life-threatening situations that require immediate attention from a physician.

Prognosis
Out-of-hospital cardiac arrest (OHCA) has a worse survival rate (2-8% for discharge and 8-22% for admission), than an in-hospital cardiac arrest (15% for discharge). The principal determining factor is the initially documented rhythm. People with ventricular fibrillation or pulseless ventricular tachycardia have 10-15 times greater chance of surviving than those suffering from pulseless electrical activity or asystole.

Since mortality in case of OHCA is high, programs were developed to improve survival rate. Although mortality in case of ventricular fibrillation is high, rapid intervention with a defibrillator increases survival rate.

Survival is mostly related to the cause of the arrest (see above). In particular, patients who have suffered hypothermia have an increased survival rate, possibly because the cold protects the vital organs from the effects of tissue hypoxia. Survival rates following an arrest induced by toxins is very much dependent on identifying the toxin and administering an appropriate antidote. A patient who has suffered a myocardial infarction due to a blood clot in the left coronary artery has a lower chance of survival.

A study of survival rates from out of hospital cardiac arrest found that 14.6% of those who had received resuscitation by ambulance staff survived as far as admission to hospital. Of these, 59% died during admission, half of these within the first 24 hours, while 46% survived until discharge from hospital. This gives us an overall survival following cardiac arrest of 6.8%. Of these 89% had normal brain function or mild neurological disability, 8.5% had moderate impairment, and 2% suffered major neurological disability. Of those who were discharged from hospital, 70% were still alive 4 years later.

A specific pattern of the brain damage in cardiac arrest survivors revealed by MRI study has been known as a delayed T1-hyperintensity localized in the striatum, cerebral cortex, thalamus, and/or substantia nigra (Fujioka, M. et al. Stroke. 1994;25:2091-2095.; Fujioka, M. et al. Neuroradiology. 1994;36:605-607.). The MRI volumetric study demonstrated that the human hippocampus showed its selective atrophy in a delayed fashion after cardiopulmonary resuscitation (Fujioka, M. et al. Cerebrovasc Dis. 2000;10:2-7.).

A review into prognosis following in-hospital cardiac arrest found a survival to discharge of 14% although the range between different studies was 0-28%.

Epidemiology
Based on death certificates sudden cardiac death accounts for about 15% of all death in Western countries (330,000 per year in the United States). The lifetime risk is three times greater in men (12.3%) than women (4.2%) based on analysis of the Framingham Heart Study. However this gender difference disappeared beyond 85 years of age.

Ethical issues
Some people choose to avoid aggressive measure at the end of life. A do not resuscitate (DNR) in the form of an advance health care directive makes it clear that in the event of cardiac arrest the person does not wish cardiopulmonary resuscitation. Other directive may be made to stipulate the desire for intubation in the event of respiratory failure or if confort measures are all that are desired by stipulating "allow natural death".