Sudden cardiac arrest is the sudden and unexpected loss of the heart’s normal pumping function, causing the victim to lose consciousness and palpable pulses.
The normal function of the heart is to pump blood throughout the body. Our hearts have a group of “pacemaker” cells in their upper right chamber that transmit electrical signals to all four chambers of the heart at a regular rate and rhythm. As the electrical signal passes through each heart chamber, it causes the muscular walls to squeeze, pushing blood forward.
Cardiac arrest can occur for many reasons, and often the cause of an arrest is not known immediately. A cardiac arrest can occur due to the sudden malfunctioning or absence of the heart’s electrical signal or the ability of the heart to pump blood despite a functioning electrical signal. For some patients, despite extensive testing after survival or autopsies for those that do not survive, we may never know the underlying reason for their cardiac arrest.
Regardless of the cause, all patients suffering from sudden cardiac arrest benefit from high-quality cardiopulmonary resuscitation starting as soon as possible.
Cardiac arrest due to malfunctioning of the electrical signal in the heart (arrhythmias called ventricular fibrillation or ventricular tachycardia) results in immediate loss of blood flow. This type of arrest can be shocked by a defibrillator to restore normal, coordinated electrical activity to trigger normal mechanical function of the heart and restore blood flow. Cardiac arrest due to a loss of mechanical activity despite normal electrical function or a complete loss of electrical signal in the heart cannot be defibrillated immediately but will benefit from cardiopulmonary resuscitation and advanced life support measures from health care professionals.
Common causes of cardiac arrest
Arrhythmias (ventricular fibrillation or ventricular tachycardia)
- Heart attack (myocardial infarction)
- Inherited conduction abnormality (channelopathy)
- Abnormal heart function (cardiomyopathy)
- Severe electrolyte abnormalities
- Hypothermia or Hyperthermia
Loss of cardiac mechanical function (pulseless electrical activity)
- Obstructing blood clots, such as a pulmonary embolism
- Severely reduced cardiac function, such as from a heart attack
- External compression on the heart (tamponade, collapsed lung)
- Severe electrolyte abnormalities
- Profound shock (infection, hemorrhage)
- A lack of oxygen (airway obstruction, overdose, drowning)
A lack of any electrical signal and mechanical activity (asystole)
- Failure of the electrical system of the heart
- Prolonged cardiac arrest from the above causes
