Cardiac arrest

Cardiac arrest
Specialty	Cardiology, emergency medicine

A cardiac arrest is the cessation of normal circulation of the blood due to failure of the ventricles of the heart to contract effectively during systole. 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 stop breathing.

Cardiac arrest is a medical emergency that, if left untreated, invariably leads to death within seconds to minutes. The primary first-aid treatment for cardiac arrest is cardiopulmonary resuscitation (commonly known as CPR).

Etiology

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%. Other causes of cardiac arrest include electrocution and near-drowning, as well as other cardiac conditions such as the cardiomyopathies.

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

Every fatal injury or illness ultimately terminates in cardiac arrest, which is a natural part of the processes of death.

Treatable causes

There are 8 reversible causes of cardiac arrest, known as the "4Hs and 4Ts". 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 hypovolemia due to external bleeding), and so can offer only supportive treatment pending the arrival of emergency medical services.

4 Hs:-

• Hypoxia - A lack of oxygen to the brain and other vital organs. This is treated by providing the patient with oxygen, either through a bag-valve-mask device, or 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 - direct pressure for external bleeding, or emergency surgery (usually an immediate emergency thoracotomy on the ward, to clamp off the descending aorta and achieve haemostasis, the bleed is then repaired properly once the patient has regained circulation) 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 or injected into the body can lead to cardiac arrest. This can be evidenced by items found on or around the patient, 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 angioplasty] or surgical embolectomy.

In addition to the specific treatments for the causes of cardiac arrest, full resuscitation (using advanced life support protocols) is be offered to all 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 defined as a heartbeat which does not result in efficient pumping of blood. 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.

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 identify cardiac arrest in a number of ways. In the USA, most lay rescuers are trained to check for a carotid pulse, whereas in the UK, 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 (formerly called electromechanical dissociation) - where the heart's electrical system is working normally but there is a problem with mechanical function (so the rhythm on the heart monitor appears normal, but no pulse)
• ventricular fibrillation - A quivering of the ventricles
• ventricular tachycardia - The ventricles pumping too fast

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.

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

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 undignified and simply adds to the suffering of a victim with a terminal illness who wishes to die peacefully.

It is not surprising that some people with a terminal illness choose to avoid such "heroic" 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 death and hospice.