The Chain of Survival

The chances of survival following cardiac arrest are considerably improved if there is a rapid, coordinated response to the emergency, each component of the chain being only as strong as its supporting link.

The components in the ‘chain of survival’ are:

  • early access to emergency medical services (EMS)
  • early cardiopulmonary resuscitation (CPR)
  • early defibrillation, and early advanced cardiac life support (ACLS).
  • early advanced cardiac life support


CPR (Cardiopulmonary Resuscitation)

Having recognised that a victim is in need of CPR it is most effective when it is started immediately. Early CPR provides rescue breathing and chest compressions to the victim. It will help to keep the victim’s brain and heart supplied with blood and oxygen until medical help arrives. It also increases the amount of time that an electric shock from a defibrillator can be effective.


Early defibrillation saves lives and involves trained personnel delivering an electric shock to the patient’s chest to help restore the normal function of the heart. It is the link in “The Chain of Survival” that is most likely to improve survival rates. Having a defibrillator on site within 2 minutes, there can be an 80% chance of survival. Every minute that passes survival rates are reduced by 7-10%. Studies show survival rates as high as 74% can be achieved if defibrillation is given within 3 minutes.

Automated External Defibrillators (AEDs)

An automated (more correctly ‘advisory’) external defibrillator (AED) is a small, portable piece of equipment that can deliver an electric shock in order to convert VF of the heart into its normal or usual rhythm. The AED contains computer software which analyses a cardiac rhythm and will not deliver a shock if the heart does not require it. The time to defibrillation is the single most important determinant of survival after cardiac arrest.


Effective bystander CPR, provided immediately after cardiac arrest, can double a victim’s chance of survival. CPR helps maintain vital blood flow to the heart and brain and increases the amount of time that an electric shock from a defibrillator can be effective

Approximately 95 percent of sudden cardiac arrest victims die before reaching the hospital. Death from sudden cardiac arrest is not inevitable. If more people knew CPR, more lives could be saved. Brain death starts to occur four to six minutes after someone experiences cardiac arrest if no CPR and defibrillation occurs during that time.

If bystander CPR is not provided, a sudden cardiac arrest victim’s chances of survival fall 7 percent to 10 percent for every minute of delay until defibrillation. Few attempts at resuscitation are successful if CPR and defibrillation are not provided within minutes of collapse.

What is the difference between Sudden Arrhythmic Death Syndrome (SADS) and Sudden Cardiac Death (SCD)?

Sudden Cardiac Death (SCD)

is a dramatic and/or spontaneous death that is thought to be (and usually is) caused by a heart condition and may have been brought on by exercise.

Sudden Arrhythmic Death Syndrome (SADS):

In one in every twenty cases of sudden cardiac death, no definite cause of death can be found, even after an expert cardiac pathologist has examined the heart. This is called Sudden Arrhythmic Death Syndrome. (In the past it has also been called Sudden Adult Death Syndrome or Sudden Death Syndrome but, because it affects children too, the term Sudden Arrhythmic Death Syndrome is now used.)

The Report of the Task Force on Sudden Cardiac Death

In 2004 the Department of Health set up a special taskforce to examine the issue of sudden cardiac death and its report was produced in March 2006. This report recommended increasing the numbers of people trained in CPR, a much greater provision of defibrillators in communities around Ireland and much quicker response times by emergency services. It also advised that screening should be carried out on the families of those who died and on those playing sport at a high level.

Reducing Time to Response:

Survival rates following cardiac arrest are directly related to time to resuscitation and in particular defibrillation. If defibrillated within 5 minutes, survival rates are approximately 50% and potentially higher with younger patients. If time to defibrillation is 10 minutes or more, virtually no one survives without cardiopulmonary resuscitation (CPR). This increases to 10 to 20% if CPR is used. A speedy and effective response is required if the chances of survival are to be increased.

In the absence of an effective emergency response system, survival from cardiac arrest is less than 1%. Recent data confirms that when response systems are optimised, survival rates increase. Overall survival from cardiac arrest in a Belfast study was 7.2%. Where the arrest was witnessed and the emergency medical services arrived within 7 minutes and the rhythm was VF, the survival rate rose to 41%.

In a Dublin study, the Mater Hospital Group found an overall survival to hospital discharge rate of 3.6% (13 out of 388 patients). In AED equipped sites, 7 out of 13 (54%) patients whom resuscitation was attempted survived to discharge. By contrast only 6 out of 375 (1.6%) survived arrest where an AED was not available.

These data are compatible with data from the United States where survival rates of more than 30% have been documented among cardiac arrest victims in Seattle, Washington. Taken together, the data supports the hypothesis that prompt defibrillation improves survival.

The ESC Task Force recommends a target time from call to defibrillation in out-of -hospital cardiac arrest of 5 minutes. The probability of successful defibrillation may be improved through the provision of early basic life support (BLS).