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Do You Prefer One Shock or Three?

The Changing Role of Defibrillation in Cardiopulmonary Resuscitation


Updated January 15, 2007

People like defibrillation.

Shocking a stopped heart to get it started again is a technological example of life-saving medical care that can be administered by almost anyone.

Besides, defibrillation is sexy.

The young, handsome doctor holds the shiny paddles up and briskly rubs them together.


The nurses working on the patient stop suddenly and take a step back. The doctor brings the paddles down on the patient's chest and fires a jolt of electricity through his lifeless body. The patient's back arches as his heart springs back to life. The quiet that follows is broken by a faint beep-beep-beep.

While there is a bit of exaggerated truth to the scenario, real cardiac arrest victims don't move nearly as much from defibrillation as actors playing them do. Not only that, hardly anyone uses paddles anymore since adhesive patches became available. Technically, defibrillators don't actually start the heart; they stop the heart, to let it start again on its own.

The American Heart Association is constantly amending the guidelines for cardiopulmonary resuscitation (CPR) and emergency cardiac care. After years of placing the focus of cardiac arrest resuscitation on defibrillation, the association restructured its guidelines in 2005 to put the focus back on CPR. Defibrillation still happens, but not as often.

2005 Changes to Defibrillation Guidelines

  • Perform CPR for about two minutes prior to defibrillation on all unwitnessed cardiac arrest victims

  • One initial shock instead of three

  • No assessment after shock - begin CPR immediately

  • Two minutes of CPR between shocks instead of one

Research has shown that performing CPR on a cardiac arrest victim prior to shocking makes the heart much more likely to respond. The only exception to this rule is if the defibrillator is with the victim when the heart stops.

Research also indicates that cardiac arrest victims are unlikely to respond to a second or third successive shock if the first doesn't work. They are, in fact, much more likely to respond to a repeat shock after two minutes of CPR.

CPR supplies oxygen to the brain as well as the heart muscle. Dfibrillation, if successful, simply lets the heart start beating again. Once restarted, the heart often needs a minute or two to adequately begin pumping blood. CPR gives the heart a little boost while it gets back into the rhythm (pun intended).

Each change to the cardiac arrest resuscitation guidelines seeks to increase survival for cardiac arrest victims. The changes are not arbitrary. The next page in this series examines how some of these changes came to be made.

Read: Changing Defibrillation: Why Humans are Smarter than Computers

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