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Overview

Many factors determine why some people die and others live following cardiac arrest. If one knew all the factors that are associated with survival then it would be an easy matter to measure these factors and begin to understand why some communities succeed and others fail. If only it were that simple.

Factors that determine whether a person lives or dies

Hundreds of scientific articles and research studies over the past forty years shed light on the factors associated with survival from cardiac arrest. Some factors are pretty obvious such as the time from collapse to delivery of critical therapies but others may not be readily apparent. Some may come as a surprise. What does socioeconomic status have to do with cardiac arrest? Does the weather influence cardiac arrest? Can that cheeseburger really cause the heart to stop? Many of the known and speculative factors are beyond an individual's control. A person's age or sex cannot be changed to improve the likelihood of resuscitation. Some factors may be the result of pure chance. For example, was someone present to witness the collapse? But many are directly determined by personal and community decisions.

The factors, summarized in the next sections, may conveniently be grouped into 4 categories -- patient factors, event factors, system factors, and therapy factors. Patient factors are unique to that individual such as prior heart disease, weight, smoking, and genetic factors. Event factors are associated with the cardiac arrest itself. Examples are the cardiac rhythm, witnessed collapse, and bystander CPR. System factors include times from collapse to CPR and defibrillation, type of EMS system, system size, number of responders, experience of the EMS personnel, dispatcher assisted telephone CPR, quality of medical direction, organizational culture, quality of training, community CPR training and community public access defibrillation. Last, therapy factors are the actual treatments used including pharmacotherapy, hypothermia, endotracheal intubation, and quality of hospital care. The first two groupings of factors (patient factors and event factors) may be extremely important but are not influenced much by individual or community decisions. In this regard they may be called fate factors. The latter two groupings of factors (system and therapy factors) can be directly influenced by individual and community decisions. These may be called choice factors.

The table below also indicates each factor's strength of association with survival. Some factors, such as socioeconomic status, are weakly associated with survival and others, such as the time from collapse to defibrillation, are strongly associated with survival. In some instances the strength of association is unknown or the science is weak. Why even list the factor if the science is so weak? Even though the association may be based on animal studies, observational studies, or simply inferred from plausibility the fact that some data exist suggests possible avenues for future scientific inquiry. The influence of genetics is a good example. Few data exist at present to attach much important to genetic factors as an explanatory factor in resuscitation but such associations may be discovered in future years. Genetic information could conceivably guide immediate or post resuscitation therapy.

The following discussion emphasizes the direct effect these factors have on the likelihood of successful resuscitation. In some instances the factor may increase or decrease the odds of having a cardiac arrest but have no effect on the likelihood of successful resuscitation. As an example fish oils may decrease the odds of having cardiac arrest but have no influence on the outcome once the arrest happens. The goal here is to briefly summarize existing knowledge on confirmed or putative factors directly related to outcome from cardiac arrest. Many factors have little or no direct bearing on how a system can better manage cardiac arrest and so greater attention will be given to factors directly relevant to EMS providers and managers.

Type of Factor	Strength of Association with Survival From Cardiac Arrest
Patient Factors
Age	+
Sex	0
Race	++
Co-morbidity	+++
Diet	Unknown
Obesity	Unknown
Medications	+
Socioeconomic	++
Genetic	Unknown
Event Factors
Cardiac rhythm	++++
Witnessed collapse	++++
Location of collapse	++
Time of event	0
Bystander CPR	+++
Cause of cardiac arrest	++
Use of on-scene AED	++
Emesis	+
Symptoms before collapse	0
Collapse before EMS arrival	++
Agonal breathing	+++
Activities preceding collapse	Unknown
Environmental factors	0
Position of collapse	Unknown
Decision to begin resuscitation	Unknown
System Factors
Time to CPR	++++
Quality of CPR	++
Time to defibrillation	++++
Quality of defibrillation	Unknown
Interaction of CPR and defibrillation	++++
Type of EMS system	++
System size	Unknown
Number of responders	Unknown
Ratio of paramedics to population	Unknown
Dispatcher-assisted telephone CPR	+++
Quality of EMS care	+
Quality of medical direction	Unknown
On-going medical QI program	Unknown
Organizational structure and culture	Unknown
Administrative support	Unknown
Quality of training	Unknown
Community CPR training	++
Community public access defibrillation	++
Therapy Factors
Pharmacotherapy	Unknown
Defibrillator guided therapy	+
Impedance threshold device	Unknown
CPR adjuncts	0
Chest-compression only CPR	Unknown
Airway management	+
Hypothermia	++
Quality of hospital care	Unknown
Unknown, unknown association or little information 0, no or minimal association +, weak association ++ or +++, intermediate association ++++, strong association

More details about the factors are contained in Patient Factors, Event Factors, System Factors, and Therapy Factors. Viewers interested in the specific references for the various articles will find them cited in Resuscitate: Surviving Cardiac Arrest and Why Some Communities Succeed and Others Fail.