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graphWhen a person’s heart stops beating, it is known as sudden cardiac arrest. When it occurs outside of the hospital, it is termed an “out-of-hospital cardiac arrest.” In either case, the patient is most likely to survive if they experience an electrical or rhythm disturbance known as ventricular fibrillation (VF). When this happens, the squeezing of the heart muscle changes from the coordinated pumping action that keeps blood flowing throughout our bodies to a disorganized state of seemingly random contraction that stops all blood flow.

The successful treatment of cardiac arrest depends upon the four key components described in the American Heart Association’s “Chain of Survival”: early access, early CPR, early defibrillation, and early advanced care. For patients in VF, early and appropriately timed use of a defibrillator is of critical importance.

about2For years, it has been thought that the success of emergency medical services (EMS) systems' treatment of cardiac arrest patients was dependent upon how quickly they could get a defibrillator to a patient and provide a “shock” to the heart. This shock is designed to “reset” the heart so that the native, coordinated electrical activity that was mentioned above can restore itself.

What is now known is that early use of a defibrillator may not be the best treatment for every patient. For those patients who have been in VF for several minutes, their chances of survival may be improved by delivering a brief period of CPR prior to any “shocks.”

For this reason, the American Heart Association and other international groups who develop the treatment guidelines for resuscitation have allowed, at the discretion of each EMS system’s medical direction, the option of providing a period of CPR prior to defibrillator use, particularly when the patient may have been in ventricular fibrillation for more than four to five minutes.

The problem is trying to determine which patients need immediate defibrillator use and which patients need an initial period of CPR. In many cities like New York, the agency responsible for EMS dispatch attempts to identify people who are both suffering from cardiac arrest and those whose symptoms suggest that a patient is about to experience cardiac arrest. These patients are given the highest priority and the resources necessary to treat a cardiac arrest are sent.

Although this approach is best to ensure that patients who are in cardiac arrest are given the appropriate EMS resources, it does present some difficulties in trying to determine the amount of time that has passed between the patient’ actual cardiac arrest and the arrival of the first EMS providers.

For reasons such as this, and in an attempt to develop a more accurate and patient-specific way of making such decisions, a computer analysis has been developed that a defibrillator can use to decide if a patient needs CPR or immediate defibrillation – this technology is called SMART CPR.  

Read more about Defibrillators.

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