Write-up on Cardiac Arrest

Detailed information on Cardiac Arrest:

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Cardiac arrest, also known ascardiopulmonary arrest orcirculatory arrest, is a sudden stop in effective blood circulation due to the failure of the heart to contract effectively or at all.^[1] Medical personnel may refer to an unexpected cardiac arrest as asudden cardiac arrest (SCA).

Quick facts: Classification and external resources, Specialty ...

Cardiac arrest
CPR being administered during a simulation of cardiac arrest.
Classification and external resources
Specialty	Cardiology
ICD-10	I46
ICD-9-CM	427.5
DiseasesDB	2095
MeSH	D006323

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A cardiac arrest is different from (but may be caused by) a myocardial infarction (also known as a heart attack), where blood flow to the muscle of the heart is impaired.^[2] It is different from congestive heart failure, where circulation is substandard, but the heart is still pumping sufficient blood to sustain life.

Arrested blood circulation prevents delivery of oxygen and glucose to the body. Lack of oxygen and glucose to the brain causes loss of consciousness, which then results in abnormal or absent breathing. Brain injury is likely to happen if cardiac arrest goes untreated for more than five minutes.^[3][4][5] For the best chance of survival and neurological recovery immediate treatment is important.^[6]

Cardiac arrest is a medical emergencythat, in certain situations, is potentially reversible if treated early. Unexpected cardiac arrest can lead to death within minutes: this is called sudden cardiac death (SCD).^[1] The treatment for cardiac arrest is immediate defibrillation if a "shockable" rhythm is present, whilecardiopulmonary resuscitation (CPR) is used to provide circulatory support and/or to induce a "shockable" rhythm.

Classification

Clinicians classify cardiac arrest into "shockable" versus "non–shockable", as determined by the ECG rhythm. This refers to whether a particular class ofcardiac dysrhythmia is treatable usingdefibrillation.^[7] The two "shockable" rhythms are ventricular fibrillation andpulseless ventricular tachycardia while the two "non–shockable" rhythms areasystole and pulseless electrical activity.^[8]

Signs and symptoms

Cardiac arrest is sometimes preceded by certain symptoms such as fainting, fatigue, blackouts, dizziness, chest pain, shortness of breath, weakness, and vomiting. The arrest may also occur with no warning.

When the arrest occurs, the most obvious sign of its occurrence will be the lack of a palpable pulse in the person experiencing it (since the heart has ceased to contract, the usual indications of its contraction such as a pulse will no longer be detectable). Certain types of prompt intervention can often reverse a cardiac arrest, but without such intervention the event will almost always lead to death.^[1] In certain cases, it is an expected outcome of a serious illness where death is expected.^[9]

Also, as a result of inadequate cerebral perfusion, the patient will quickly become 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.^[10]

Causes

Coronary heart disease is the leading cause of sudden cardiac arrest. Many other cardiac and non-cardiac conditions also increase one's risk.

Coronary artery disease

Approximately 60–70% of SCD is related to coronary heart disease.^[11][12] Among adults, ischemic heart disease is the predominant cause of arrest^[13] with 30% of people at autopsy showing signs of recent myocardial infarction.^{[citation needed]}

Non-ischemic heart disease

A number of other cardiac abnormalities can increase the risk of SCD including cardiomyopathy, cardiac rhythm disturbances, hypertensive heart disease,^[11] and congestive heart failure.^[14]

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%).^[15] Congestive heart failure increases the risk of SCD fivefold.^[14]

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 one of every 5000 to 7000 newborns and is estimated to be responsible for 3000 deaths each year compared to the approximately 300,000^[16] 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 and may be treatable.

Non-cardiac

About 35% of SCDs are not caused by a heart condition. The most common non-cardiac causes are trauma, bleeding (such as gastrointestinal bleeding, aortic rupture, or intracranial hemorrhage),overdose, drowning and pulmonary embolism.^[17] Cardiac arrest can also be caused by poisoning (for example, by the stings of certain jellyfish).

Risk factors

The risk factors for SCD are similar to those of coronary heart disease and include smoking, lack of physical exercise, obesity, and diabetes, as well as family history.^[18]

Hs and Ts

Main article: 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.^[7][19]

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
• Traumatic cardiac arrest

Diagnosis

Cardiac arrest is synonymous withclinical death.

A cardiac arrest is usually diagnosed clinically by the absence of a pulse. In many cases lack of carotid pulse is thegold standard for diagnosing cardiac arrest, but lack of a pulse (particularly in the peripheral pulses) may result from 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^[20] or lay persons.^[21]

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,^[19]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.^[7]

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.^[19] These signs included coughing, gasping, colour, twitching and movement.^[22] 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.^[19]

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 ahealthy diet, exercise, and smoking cessation are important. For people at risk of heart disease, measures such asblood pressure control, cholesterollowering, and other medico-therapeutic interventions are used.^[1]

Code teams

In medical parlance, cardiac arrest is referred to as a "code" or a "crash". This typically refers to "code blue" on thehospital 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.^[7][23]This has been attributed to a lack of knowledge and skill amongst ward-based staff, in particular a failure to carry out measurement of therespiratory rate, which is often the major predictor of a deterioration^[7] 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 with 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" or "crash trolley".
• 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.

In some medical facilities, the resuscitation team may purposely respond slowly to a patient in cardiac arrest, a practice known as "slow code", or may fake the response altogether for the sake of the patient's family, a practice known as "show code".^[24] This is generally done for patients for whom performing CPR will have no medical benefit.^[25] Such practices are ethically controversial,^[26] and are banned in some jurisdictions.

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 apacemaker, 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.^[27] An accompanying editorial by Simpson explores some of the economic, geographic, social and political reasons for this.^[28] 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.^[29]

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),^[19] pediatric advanced life support (PALS)^[30] or neonatal resuscitation program (NRP) guidelines.

Cardiopulmonary resuscitation

Cardiopulmonary resuscitation (CPR) is an important part of the management of cardiac arrest. It is recommended that it be started as soon as possible and interrupted as little as possible. The component of CPR which seems to make the greatest difference in most cases is the chest compressions. Correctly performed bystander CPR has been shown to increase survival; however, it is performed in less than 30% of out of hospital arrests as of 2007.^[31]If high-quality CPR has not resulted in return of spontaneous circulation and the person's heart rhythm is in asystole, discontinuing CPR and pronouncing the person's death is reasonable after 20 minutes.^[32] Exceptions to this include those with hypothermia or who havedrowned.^[32] Longer durations of CPR may be reasonable in those who have cardiac arrest while in hospital.^[33]

Tracheal intubation has not been found to improve survival rates in cardiac arrest^[31] and in the prehospital environment may worsen it.^[34] A 2009 study found that assisted ventilationmay worsen outcomes over placement of an oral airway with passive oxygen delivery.^[35]

CPR which involves only chest compressions results in the same outcomes as standard CPR for those who have gone into cardiac arrest due to heart issues.^[36] A 2013 review found some evidence that mechanical chest compressions (as performed by a machine) are better than manual chest compressions^[37] while a 2011 and 2012 review considered the evidence insufficient.^[38][39] It is unclear if a few minutes of CPR before defibrillation results in different outcomes than immediate defibrillation.^[40]

Defibrillation

Shockable and non–shockable causes of cardiac arrest is based on the presence or absence of ventricular fibrillation or pulseless ventricular tachycardia. The shockable rhythms are treated with CPR and defibrillation.

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.^[41] In addition, it has been shown that those who have arrests in remote locations have worse outcomes following cardiac arrest.^[42]

Medications

Medications, while included in guidelines, have been shown not to improve survival to hospital discharge following out-of-hospital cardiac arrest. This includes the use of epinephrine,atropine, and amiodarone.^[43][44]Vasopressin overall does not improve or worsen outcomes but may be of benefit in those with asystole especially if used early.^[45]

Epinephrine does appear to improve short-term outcomes such as return of spontaneous circulation.^[46] Some of the lack of long-term benefit may be related to delays in epinephrine use.^[47]

The 2010 guidelines from the American Heart Association no longer contain the association's previous recommendation for using atropine in pulseless electrical activity and asystole due to the lack of evidence for its use.^[48] Evidence is insufficient for lidocaine, and amiodarone may be considered in those who continue in ventricular tachycardiaor ventricular fibrillation despite defibrillation.^[49] Thrombolytics when used generally may cause harm but may be of benefit in those with a pulmonary embolism as the cause of arrest.^[50]

Targeted temperature management

Cooling a person after cardiac arrest who has a return of spontaneous circulation (ROSC) but no return ofconsciousness improves outcomes.^[51][52] This procedure is calledtargeted temperature management(previously known as therapeutic hypothermia). People are typically cooled for a 24-hour period, with a target temperature of 32–34 °C (90–93 °F). Death rates in the hypothermia group are 35% lower than in those with no temperature management.^[51][53]Complications are generally no greater in those who receive this therapy.^[51][54]

A November 2013 trial found that actively cooling to a temperature of 36 °C (97 °F) results in the same outcomes as 33 °C (91 °F).^[52][55] This may be because preventing fever, rather than the hypothermia itself, is more important.^[52][56] Other possible reasons could be the long time of >8 hours needed to cool in the 33 °C group and the very high rate of bystander of CPR compared to usual international rates.^[57][58]

Earlier versus later cooling may result in better outcomes.^[59] A trial that cooled in the ambulance, however, found no difference compared to starting cooling in-hospital.^[59] A registry database found poor neurological outcome increased by 8% with each five-minute delay in initiating TH and by 17% for every 30-minute delay in time to target temperature.^[60]

Do not resuscitate

Some people choose to avoid aggressive measures at the end of life. Ado not resuscitate order (DNR) in the form of an advance health care directivemakes it clear that in the event of cardiac arrest, the person does not wish to receive cardiopulmonary resuscitation.^[61] Other directives may be made to stipulate the desire forintubation in the event of respiratory failure or, if comfort measures are all that are desired, by stipulating that healthcare providers should "allow natural death".^[62]

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%.^[7]
• 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 fibrillationand pulseless ventricular tachycardia^[7]
• Early advanced care
• Early post-resuscitation care

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 acode 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.^{[citation needed]}

Other

Resuscitation with extracorporeal membrane oxygenation devices has been attempted with better results for in-hospital cardiac arrest (29% survival) than out-of-hospital cardiac arrest (4% survival) in populations selected to benefit most.^[63] Cardiac catheterizationin those who have survived an out-of-hospital cardiac arrest appears to improve outcomes although high quality evidence is lacking.^[64]

The precordial thump may be considered in those with witnessed, monitored, unstable ventricular tachycardia (including pulseless VT) if a defibrillator is not immediately ready for use, but it should not delay CPR and shock delivery or be used in those with unwitnessed out of hospital arrest.^[65]

Prognosis

The survival rate to hospital discharge of people who receive initial emergency care by ambulance is 2%, with 15% experiencing return of spontaneous circulation.^[66] However, with defibrillation within 3–5 minutes, the survival rate increases to 30%.^[67][68]Since mortality in case of out-of-hospital cardiac arrest 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.^[13][69]

A 1997 review into outcomes following in-hospital cardiac arrest found a survival to discharge of 14% although the range between different studies was 0-28%.^[70] In those over the age of 70 who have a cardiac arrest while in hospital, survival to hospital discharge is less than 20%.^[71] How well these individuals are able to manage after leaving hospital is not clear.^[71]

Survival is mostly related to the cause of the arrest (see above). In particular, people who have suffered hypothermiahave 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.^{[citation needed]}

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 reflects 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 four years later.^[72]

Epidemiology

Based on death certificates, sudden cardiac death accounts for about 15% of all death in Western countries^[11](330,000 per year in the United States).^[31] The lifetime risk is three times greater in men (12.3%) than women (4.2%) based on analysis of theFramingham Heart Study.^[73] However this gender difference disappeared beyond 85 years of age.^[11]