What is cardiac arrest and CPR?

Cardiac arrest is a sudden stoppage of the heart pump caused by a variety of reasons, including a heart attack. CPR or cardiopulmonary resuscitation is a life saving maneuver in cardiac arrest. CPR consists of external compression of the heart and other efforts to revive the heart, while maintaining blood supply to the organs.

Heart is a rhythmic organ, blood moves in and is pumped out in a sequence. The process moves like a metronome. On occasions, the process either completely stops or becomes a chaos, resulting in cardiac arrest. As explained in the ‘electrical wiring of the heart’, the heart pump is normally driven by electrical impulses generated in the right upper chamber. As the electrical impulses travel to the rest of the heart, the activated parts respond by squeezing, pumping the blood forward to the next chamber and then out of the heart. 

Imagine this electrical process stopping completely (asystole) or losing its ability to cause a muscle squeeze (pulseless electrical activity or PEA). Alternatively, the electrical impulses may become so chaotic that the rhythm is lost. This electrical storm, called ventricular tachycardia or fibrillation, moves so fast that it brings the heart to a standstill. 

What causes cardiac arrest? 

Cardiac arrest is most commonly caused by sudden blockage in the blood supply to the heart muscles like in heart attack. The muscles deprived of oxygen and nutrients within the heart-attack zone may act up, like salary-starved employees can strike work.  

Having a sick heart muscle, such as in heart failure, can cause the heart to be excessively sensitive to electrolyte changes. Such a sick muscle may overwhelm the electrical wiring by firing electrical impulses, like firework. 

Unusual electrical activity may also happen around a scar in the heart such as after a heart attack. The boundary between the scar and normal muscles is electrically vulnerable for such sparks. Like an active border between enemy countries, cross-fires are common. There are also other reasons for these overwhelming electrical events including certain hereditary conditions, excessive electrolyte problems such as very high blood potassium levels, inflammation of heart tissue, certain medications and illicit drugs. 


Patients usually suddenly drop or slump and remain unconscious. This is because the brain does not get enough blood supply when the heart has stopped pumping blood. 

The onset of symptoms may be sudden or may be preceded by the patient complaining of chest pain, dizziness or not feeling well in general. 

What to do? 

Time is of essence. Every second the brain cells and other organs do not get blood supply, the damage worsens, and the chances of recovery reduce significantly. 

The heart has stopped but the blood must be pumped somehow. In case of a cardiac arrest, the bystanders must initiate CPR immediately. During a cardiac arrest, CPR is a process to squeeze the heart from outside by pressing the chest. The chest must be pumped and there are many instructional videos online to train in the right technique. Everyone must know how to give CPR because it can save lives, any attempt is better than nothing. 

Calling for help is equally important, to alert the local emergency medical services. If there is an AED (automated external defibrillator) available, it should be used. Most public places have an AED or have access to one (figure 1). 

Figure 1: Identify the closest AED or ask a person who would know.

If the cause of cardiac arrest is complete electrical silence then the AED will instruct to continue CPR uninterrupted, a shock in this case will not help.  

On the other hand, if the cause of the cardiac arrest is an electrical storm, the best way to treat this hurricane is a shock which stops the storm. Imagine a stadium full of people talking, shouting and playing music. The noise is deafening. A sound over the loudspeaker draws everyone’s attention and there is silence. The shock works like that sound over the speaker. It attempts to stop electrical chaos in the heart and allow organization to return. As you can imagine, shock only works in conditions resulting in an electrical chaos. It does not work to ‘charge’ the heart in an electrical standstill as they show in the movies. 

Common myths busted 

CPR can be given by any person of any size or strength. It is also important to know your limitations and call to switch with another person. 

Mouth-to-mouth respiration is not necessary, it is however important to continue chest compressions with minimal to no interruptions. 

Have to move the patient to the closest hospital ASAP.

Don’t think, just join in saving a life. 

External sites:

  1. AHA website for basic life support training: https://cpr.heart.org/AHAECC/CPRAndECC/Training/HealthcareProfessional/BasicLifeSupportBLS/UCM_473189_Basic-Life-Support-BLS.jsp
  2. CPR training in school: https://www.youtube.com/watch?v=k1sbn84UlI8 and http://www.heart-class.com/

All opinions expressed here are those of the author and not of the employer. Information provided here is for medical education only. It is not intended as and does not substitute for medical advice. Check out the youtube channel here.

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