Cardiac disease accounts for more than 50% of out-of-hospital cardiac arrests and death is usually caused by a lethal tachy-arrhythmia, which in turn is usually precipitated by anterior myocardial infarction (AMI) (Rosen et al. 2001). Tachyarrhyth-mias are fast unstable heart rhythms which may also be caused by electrolyte imbalance, drug toxicity and cardiomyopathies though these are much less common (Engdahl et al. 2002).
The true incidence of cardiac arrests presenting with ventricular fibrillation (VF) is unknown; however, a great deal of data suggest it is over 80% (Norris 1998). It is also known that the chances of successfully defibrillating the patient fall by between 7% and 10% per minute if defibrillation is delayed (Resuscitation Council UK 2000).
Survival is greater amongst patients who suffer their arrest in public places rather than at home, which is where such events more commonly occur. In one UK study 80% of instances of advanced life support (ALS) provided by paramedics were in the casualty's home (Dowie et al. 2003).
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