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As described in the “About SMART CPR” section, cardiac arrest is the term used to describe the loss of the heart’s ability to maintain blood flow throughout the body and has been defined as the “abrupt cessation of heartbeat.”
Normally, our hearts contract in such a way that blood is squeezed from the heart and out to the body. That wave of blood being pushed from the heart causes a pressure change within the arteries into which the blood moves, resulting in what we feel as a pulse.
The list of things that can cause the heart to suddenly stop pumping our blood is a long one. It includes things like disturbances in our electrolytes (salts such as potassium and calcium), a variety of injuries, blood loss, oxygen deprivation, infections, structural heart defects, and blood clots. But the most common cause of cardiac arrest among adults is myocardial ischemia – more commonly referred to as a “heart attack.”
Regardless of the cause of the cardiac arrest, the most important initial actions that impact the likelihood that the patient will survive include the early recognition of the arrest and activation of the 911 system, as well as the provision of CPR in the following moments before the arrival of the EMS providers.
Those patients most likely to survive are estimated to have a 7-10% decrease in their chances to survive for each minute between the time that their cardiac arrest begins and the arrival of EMS . If a friend, co-worker, family member, or other bystander is willing to do CPR until EMS arrives, that decrease is significantly lessened to 2-3% per minute. (Click here to learn more about CPR and how you could help save someone’s life.)
Once EMS providers arrive on the scene, the treatment of the patient begins with a short period of CPR followed by an analysis of the electrical activity within the heart. This analysis may be performed either by an automated external defibrillator (or AED) with a built-in computer analysis or by paramedics who are trained to interpret the electrical patterns seen on the monitor screen. At this point, the electrical activity within the heart may be classified into two groups – “shockable” and “non-shockable.”
The treatment of “non-shockable” rhythms includes the delivery of chest compressions and artificial ventilation, the search for a reversible cause, and the delivery of specific medications and interventions targeting those reversible causes. Overall, this group’s survival rate is much lower than those who present with a “shockable” rhythm.
For patients who present in a “shockable” rhythm, the initial treatment includes the delivery of chest compressions and artificial ventilation, as well as the use of a defibrillator. (Click here to learn more about defibrillators.) While it was long believed that the earlier the use of the defibrillator, the better the patient’s chances of survival, it now appears that there exist two groups of patients who present with “shockable” rhythms – those who will benefit from immediate defibrillator use and those who would benefit from a short period of CPR prior to any defibrillator use.
At present, it is unclear just how these two groups of “shockable” rhythms can be identified. Studies suggest that the time that has passed from the onset of the cardiac arrest until the arrival of EMS may serve as a marker that could be used to define the two groups. The problem for systems that aggressively dispatch EMS personnel to patients both in cardiac arrest and those who may be showing signs that they are about to suffer cardiac arrest is that this interval becomes more difficult to define.
Several studies have shown that the mathematical properties of those shockable rhythms may provide a more reliable means of determining whether a patient is likely to respond favorably to immediate defibrillator use or whether they may need a period of CPR prior to initial defibrillator use. This type of technology is the focal point of this study.