Cardiac arrest

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For other uses, see Cardiac arrest (disambiguation).

A cardiac arrest, or circulatory arrest, is the abrupt stop of normal circulation of the blood due to failure of the heart to contract effectively during systole.^[1]

The resulting lack of blood supply results in cell death from oxygen starvation. Cerebral hypoxia, or lack of oxygen supply to the brain, causes victims to lose consciousness and to stop breathing, which in turn causes the heart to stop. Brain damage is likely to occur after 3-5 minutes, except in cases of hypothermia. To improve survival and neurological recovery immediate response is paramount.^[2]

Cardiac arrest is a medical emergency that, in certain groups of patients, is potentially reversible if treated early enough. When cardiac arrest leads to death this is called sudden cardiac death (SCD).^[1] The primary first-aid treatment for cardiac arrest is cardiopulmonary resuscitation (commonly known as CPR) to provide circulatory support until availability of medical treatment.

Etiology

Ventricular fibrillation (VF) constitutes the most common electrical mechanism in cardiac arrest, and is responsible for 65 to 80% of occurrences. Another 20-30% is caused by severe bradyarrhythmias, pulseless electrical activity (PEA) and asystole. Other conditions are associated with impaired circulation due to a state of shock. ^[1]

Among adults ischemic heart disease is the predominant cause.^[3] At autopsy 30% of victims show signs of recent myocardial infarction. Other conditions include structural abnormalities, arrhythmias and cardiomyopathies. Secondary cardiac arrest may be elicited by non-cardiac conditions such as hypoxia from a variety of causes,^[4] overwhelming infection (sepsis), massive pulmonary embolus, arrythmias, cardiac tamponade, shock, pneumothorax, ventricular rupture, as well as other conditions such as electrocution and near-drowning. Non-cardiac conditions constitute the principal cause of cardiac arrest in in-hospital patients.^[5]

Coronary heart disease (CHD) -also known as coronary artery disease, or (CAD)- is the predominant disease process associated with sudden cardiac death in the United States and elsewhere in the developed world. The incidence of CHD in individuals who suffer sudden cardiac death is between 64 and 90%.

In children, cardiac arrest is typically caused by hypoxia from other causes such as near-drowning. With prompt treatment survival rates are high.

Treatable causes

There are 8 reversible causes of cardiac arrest, known as the "4Hs and 4Ts".^[5] They are looked for and treated by ambulance technicians/paramedics or by medical staff at the hospital while undertaking advanced life support, protocols for which will be used alongside any specific treatments for each of the causes. Lay rescuers performing basic life support can generally neither identify nor treat them (with the exception of hypoxia due to choking), and so can offer only supportive treatment pending the arrival of emergency medical services.

 

4 Hs

• Hypoxia - A lack of oxygen to the heart, brain and other vital organs. This is treated by providing the patient with oxygen, either through a bag-valve-mask device, or through mechanical ventilation by inserting an endotracheal tube (intubation)

• Hypovolemia - A lack of circulating body fluids, principally blood. This is usually (though not exclusively) caused by some form of bleeding. Peri-arrest treatment includes giving IV fluids and blood transfusions, and controlling the source of any bleeding - by direct pressure for external bleeding, or emergency surgical techniques such as esophagogastroduodenoscopy (i.e. esophageal varices) and thoracotomy for internal bleeding.

• Hypo/Hyper-metabolic disorders - An abnormally high or low level of electrolytes such as potassium and calcium circulating the body. An arterial blood gas and blood electrolyte test are performed to find the problem, then IV crystalloids are given to correct it.

• Hypothermia - A low core body temperature, defined clinically as a temperature of less than 35 degrees Celsius. The patient is re-warmed either by using a cardiac bypass or by irrigation of the body cavities (such as thorax, peritoneum, bladder) with warm fluids; or warmed IV fluids. CPR only is given until the core body temperature reached 30 degrees Celsius, as defibrillation is ineffective at lower temperatures. Patients have been known to be successfully resuscitated after periods of hours in hypothermia and cardiac arrest, and this has given rise to the often-quoted medical truism, "You're not dead until you're warm and dead."

 

4 Ts

• Tension pneumothorax - A rush of air into one of the pleural cavities which is not able to escape compresses the lungs and causes the trachea to deviate away from the mid-line, often putting pressure on the heart so it is not able to beat effectively. This is relieved in an emergency by inserting a needle into the 2nd intercostal space at the mid-clavicular line, releasing the air and the pressure on the thoracic organs.

• Tamponade (Cardiac) - Blood or other fluids building up in the pericardium can put pressure on the heart so that it is not able to beat. This is treated in an emergency by inserting a needle into the pericardium to drain the fluid (pericardiocentesis), or if the fluid is too thick then an emergency thoracotomy is performed to cut the pericardium and release the fluid.

• Toxins - Toxic substances which have been ingested, injected, absorbed or inhaled into the body can lead to cardiac arrest. This may be evidenced by items found on or around the patient, the patient's medical history (i.e. drug abuse, medication) taken from family and friends, checking the medical records to make sure no interacting drugs were prescribed, or sending blood and urine samples to the toxicology lab for report. Treatment is mainly supportive, unless there is an antidote which can be administered.

• Thrombosis - Blood clots in the heart (myocardial infarction) or lungs (pulmonary embolism) are both well known causes of cardiac arrest. Treatment includes thrombolysis, and possibly surgical interventions such as percutaneous transluminal coronary angioplasty (PTCA), coronary bypass or surgical embolectomy.

In addition to the specific treatments for the causes of cardiac arrest, full resuscitation (using advanced life support protocols) is offered to patients as soon as possible, and continues until the patient is either declared dead or regains a pulse and stable heart rhythm.

Diagnosis

Cardiac Arrest is an abrupt cessation of pump function (evidenced by absence of a palpable pulse) of the heart that with prompt intervention could be reversed, but without it will lead to death.^[1] In many cases, lack of carotid pulse is the gold standard for diagnosing cardiac arrest, but pulselessness (particularly in the peripheral pulses) may be a result of other conditions (i.e. shock, or other conditions leading to poor circulation)

In a hospital or ambulance, cardiac arrest is identified by the lack of a pulse (or lack of heartbeat if listened to through a stethoscope), and advanced life support is given.

Out of hospital, lay rescuers are now being taught to identify cardiac arrest in as simple a manner as possible. With the latest standard as set by the ILCOR, lay rescuers are taught that a lack of normal breathing is evidence of cardiac arrest, and they begin CPR without checking a pulse.

An ECG clarifies the exact diagnosis and guides treatment, but basic life support should begin without awaiting an ECG. The ECG may reveal:

• Asystole (known colloquially as a flatline) - a complete stoppage of the heart
• Pulseless electrical activity - The ECG shows electrical activity that could be consistent with a palpable pulse but no pulse is palpable. It can be because of electromechanical dissasociation(EMD) or because the cardiac output is so poor as to not be palpable.
• ventricular fibrillation - A quivering of the ventricles
• ventricular tachycardia - The ventricles contract so rapidly that they do not refill fully between beats, so they do not pump enough blood to maintain circulation.

Treatment

First aid

First aid treatment of cardiac arrest varies from country to country, but the general principles of the guidelines in all locales are to summon help (in the form of an ambulance) and then begin CPR.

Other prehospital care

In many situations in the UK and USA, lay people are trained in the use of an automated external defibrillator, which analyzes the heart rhythm and delivers a controlled electric shock to the heart if indicated.

Jurisdictions are beginning to purchase automated CPR machines, such as AutoPulse, to assist first responders. Such machines are proving superior in cardiac arrest support over manual CPR, providing for greater circulation and, thus, lower rates of morbidity and mortality when used in a timely fashion. The ASPIRE Trial - a multicenter investigational trial of the AutoPulse - published its results and stated that the AutoPulse resulted in worse neurological outcome than manual compression CPR.

Hospital treatment

Treatment within a hospital usually follows advanced life support protocols. Depending on the diagnosis, various treatments are offered, ranging from defibrillation (for ventricular fibrillation or ventricular tachycardia) to surgery (for cardiac arrest which can be reversed by surgery - see causes of arrest, above) to medication (for asystole and PEA). All will include CPR.

Peri-arrest period

The period (either before or after) surrounding a cardiac arrest is known as the peri-arrest period. During this period the patient is in a highly unstable condition and must be constantly monitored in order to halt the progression or repeat of a full cardiac arrest. The preventative treatment used during the peri-arrest period depends on the causes of the impending arrest and the likelihood such an event occurring.

Prognosis

The out-of-hospital cardiac arrest (OHCA) has a worse survival rate (2-8% at discharge and 8-22% on admission), than an in-hospital cardiac arrest (15% at discharge). The principal determining factor is the initially documented rhythm. Patients with VF/VT have 10-15 times more chance of surviving than those suffering from Pulseless electrical activity or Asystole (as they are sensitive to defibrillation, whereas asystole and PEA are not).^[4]

Since mortality in case of OHCA is high, programs were developed to improve survival rate. A study by Bunch et al showed that, although mortality in case of ventricular fibrillation is high, rapid intervention with a defibrillator increases survival rate to that of patients that did not have a cardiac arrest.^[3][6]

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 as it cuts of the blood supply to most of the left ventricle (the chamber which must pump blood to the whole of the systemic circulation).

Cobbe et al (1996) conducted a study into survival rates from out of hospital cardiac arrest. 14.6% of those who had received resuscitation by ambulance staff survived as far as admission to an acute hospital ward. Of these, 59.3% died during that admission, half of these within the first 24 hours. 46.1% survived to hospital discharge (this is 6.75% of those who had been resuscitated by ambulance staff), however 97.5% suffered a mild to moderate neurological disability, and 2% suffered a major neurological disability. Of those who were successfully discharged from hospital, 70% were still alive 4 years after their discharge. ^[7]

Ballew (1997) performed a review of 68 earlier studies into prognosis following in-hospital cardiac arrest. They found a survival to discharge rate of 14% (this roughly double the rate for out of hospital arrest found by Cobbe et al (see above)), although there was a wide range (0-28%). ^[8]

Several high profile organisations (such as St John Ambulance and the British Heart Foundation) have promoted the "Chain of Survival", which is made up of 4 links, as a way to maximise prognosis following arrest:

• Early Access - Identifying patients at risk of cardiac arrest early is the best way of improving prognosis, as it is often possible to prevent the arrest. Similarly, if the arrest is witnessed there is a much greater chance of survival, as treatment can begin straight away before tissue hypoxia sets in.

• Early CPR - CPR is unlikely to revive the patient, but it does buy some time by keeping a (limited) circulation going until it is possible to reverse the arrest, thereby increasing the chances of this reversal being successful, and minimising the risk of cerebral hypoxia (which can lead to neurological impairment following return of circulation).

• Early defibrillation - Patients who present with VF/VT can be defibrillated, and the earlier this happens the better, as VF/VT often degenerate into asystole (which is unshockable).

• Early hospital care - Many patients suffer further arrests within the first 24 hours of admission, so it is better that they are in hospital where their chances of survival are a little higher.

Ethical Issues

Cardiopulmonary resuscitation and advanced cardiac life support are not always in a person's best interest. This is particularly true in the case of terminal illnesses when resuscitation will not alter the outcome of the disease. Properly performed CPR often fractures the rib cage, especially in older patients or those suffering from osteoporosis. Defibrillation, especially repeated several times as called for by ACLS protocols, may also cause electrical burns. Internal cardiac massage, an ACLS procedure performed by emergency medicine physicians requires splitting open the rib cage, which is painful during the weeks of recovery. While such treatment is worthwhile when it saves a life, it is sometimes perceived as undignified and adding to the suffering of a victim with a terminal illness who wishes to die peacefully.

Some people with a terminal illness choose to avoid such measures and die peacefully.

People with views on the treatment they wish to receive in the event of a cardiac arrest should discuss these views with both their doctor and with their family.

It is also important that these views are written down somewhere in the medical record. In the event of cardiac arrest, health professionals need to act quickly on the information that is available to them. As cardiac arrest often happens out of regular hours, the resuscitation team rarely includes anybody who actually knows the patient.

A patient may ask their doctor to record a do not resuscitate (DNR) order in the medical record. Alternatively, in many jurisdictions, a person may formally state their wishes in an "advance directive" or "advance health directive".

See also

• Asystole
• Death
• Defibrillation
• Myocardial infarction
• Near-death experience
• Ventricular fibrillation

References