Healthwatch: Defibrillators

Heartening Findings - Automated External Defibrillators in Public Places Can Save Lives

Evra Taylor Levy and Eddy Lang

Special to the Gazette

Monday, July 07, 2008

HealthWatch runs every other week as a regular Gazette feature where medical journalist Evra Taylor Levy and emergency physician Eddy Lang help make sense of sometimes contradictory medical research.

Following a swim at the Pointe Claire Aquatic Centre, Montreal dentist Mark Lazare suffered what could have been a fatal cardiac arrest. Fortunately, thanks to some quick-thinking lifeguards and an on-site automated external defibrillator used to shock his heart, Lazare is alive and well today and advocating for the widespread availability of these devices.

Incredible as such stories are, they also raise questions. Where should these devices be located and who can and should use them? In this edition of HealthWatch, we review the findings of a British study that compares two approaches to using these devices in sudden cardiac arrest.

Understanding cardiac arrest

Sudden cardiac arrest kills 35,000 to 45,000 Canadians annually, many of whom believed themselves to be healthy, unaware they were harbouring heart disease. The most common immediate cause of sudden cardiac death is ventricular fibrillation - a fatal cardiac rhythm that prevents the heart from pumping blood effectively.

How can you survive a cardiac arrest?

Defibrillation, done by "shocking" the heart with a measured dose of electricity, can restore a functional heart rhythm; in fact, it is the primary treatment for ventricular fibrillation. Your chances of surviving a cardiac arrest are typically less than five per cent. Worse yet, a high percentage of survivors suffer permanent brain damage and can remain in a vegetative state for years. The likelihood of surviving a cardiac arrest rises significantly if someone witnesses the event, cardiopulmonary resuscitation (CPR) is performed quickly, and the fatal heart rhythm is ended, restoring the normal beat.

What are automated external defibrillators and how do they work?

Automated external defibrillators are laptop computer sized units that are attached to the bare chest of the victim through adhesive pads.

The machine automatically analyzes the heart rhythm, determines if a shock to the heart is necessary, and then with a touch of a button by the rescuer, the lifesaving electrical jolt is delivered.

Although the most common place for sudden cardiac arrest to occur is in the home, most advocates for the widespread accessibility of automated external defibrillators are targeting such busy public places as casinos, airports and shopping centres as sites in which these units should be installed - even though only 15 to 20 per cent of cardiac arrests occur in such places.

Speed makes all the difference

The impact of early defibrillation is dramatic: for every minute of delay in defibrillation, the survival rate of a cardiac arrest victim decreases by seven to 10 per cent. Effective CPR and defibrillation can restore blood flow to the brain and other vital organs, making the heart more responsive to shocks. Since the time interval from collapse to the arrival of an ambulance is generally seven to eight minutes or longer, the victim is dependent on the quick actions of bystanders and local rescuers to perform CPR and, if possible, early defibrillation.

The study

MC Colquhoun et al. A national scheme for public access defibrillation in England and Wales: Early results. Resuscitation 2008.

What was the goal of study?

The purpose was to report the effectiveness of the United Kingdom's program for placing AEDs in high-traffic areas like rail stations and busy workplaces. While the devices have already been shown to save lives under well-controlled study conditions, these researchers set out to show how this kind of program would play out in real life.

They also compared two aspects of the same global program. The first involved a team of community first responders like firefighters, who were trained and equipped with a mobile AED unit and could respond more quickly than ambulances to calls for distress. The other component of the program involved strategically placed AEDs in areas where there was already evidence that the likelihood of cardiac arrest was high. Local programs that encouraged employees to take the four-hour basic training course in CPR and AED use were crucial for this part.

What did the study show?

The authors report the outcomes of more than 1,500 resuscitation attempts initiated by laypersons and community first responders equipped with an AED, from 1999 to 2005. Not all the people involved received a shock. Of those who did, 18 per cent survived and were discharged from the hospital, a dramatic improvement over previous survival rates.

Equally dramatic was the study's comparison between attempts by first responders and by the general public using on-site AEDs: Only three per cent of patients given CPR by first responders survived their episode in a way that allowed them to leave the hospital alive, compared with 26 per cent of victims resuscitated by bystanders.

This striking difference most probably was the result of getting the AED pads attached to the victims in less than half the time when the device was available as part of the on-site strategy than when it had to be transported to a patient.

So, what should you do?

AEDs are a major advance in cardiovascular medicine, but their effectiveness depends on their availability and on bystanders who have received the minimal training required to use them.

These devices probably don't make sense for use in the home because the chances that they would ever be used there are miniscule - a notion supported by another recent study. However, AEDs should definitely be considered in busier places frequented by lots of middle-aged or older individuals. Does your gym, shopping mall or busy workplace keep a readily visible AED for use in a medical emergency? Would you know how to use one and potentially save a life?

Take a CPR course to learn how easy it is to operate an AED, which, incidentally, has been successfully taught to Grade 4 students. Find out where the AEDs are stored in the busy places that you frequent. If there's no AED in a location that should have one, a little advocacy can go a long way toward getting one installed.

Healthwatch wishes to thank Eli Segal, emergency physician at the SMBD Jewish General Hospital and research director at Urgences Santé for his contribution to this column.