Cardiac arrests outside hospital

Twenty five years after the original epidemiological studies¹,² two thirds of all patients with coronary artery disease still die before reaching hospital (p 1065).³ These patients have no opportunity to benefit from the advances in hospital treatment of acute myocardial infarction, such as thrombolysis, that have dramatically reduced mortality in hospital. It is particularly sobering to see in the study by Norris et al that among patients aged under 55 who die from cardiac arrest, 91% do so outside hospital, whereas the hospital mortality from acute myocardial infarction in this age group is only 3%.³ The hospital mortality for older patients is proportionally higher, but two thirds of these patients also die before reaching hospital. Is it possible to save more of these patients who die outside hospital?

Several studies, including that by Norris et al,³ show that half these patients who die outside hospital have an unwitnessed cardiac arrest and are therefore not amenable to resuscitation. Nevertheless, half the patients in Norris et al’s study had already been diagnosed as suffering from coronary artery disease. We know from the ASPIRE study that many such patients are suboptimally treated in terms of risk factor modification and the use of prophylactic drugs.⁴ Studies such as the 4S, CARE, and LIPID studies suggest that statins may reduce mortality by 25-30% over five years in such patients,⁵ and impressive lowering of mortality, particularly in the first year after a myocardial infarction, may be achieved by the use of β blockers and angiotensin converting enzyme inhibitors. Yet many patients who have had a myocardial infarction or who have angina do not undergo even a simple exercise test to identify those at high risk who might benefit from angiography and intervention.

Prevention aside, nothing can be done for patients whose cardiac arrest is unwitnessed: only those whose arrests are witnessed stand any chance of survival. The presenting rhythm in about 85% of these patients is either ventricular fibrillation or pulseless ventricular tachycardia,⁶ both potentially reversible by defibrillation. If the arrest is witnessed the main determinant of survival is the delay from onset of the arrhythmia to electrical defibrillation of the heart. The “chain of survival” concept of early access to emergency medical services, early basic life support by a bystander, early defibrillation, and early advanced life support is well tested.⁷ In Norris et al’s study, 40% of patients who arrested in the presence of a paramedic equipped with a defibrillator survived to leave hospital—a figure comparable to those reported from cities operating rapid response emergency medical services.

In another paper in this week’s issue, Ruston et al clearly show that the lay public’s perception of a heart attack is of a patient with severe pain and often sudden collapse (p 1060).⁸ Yet this pattern occurs in only a minority of patients. They point out that the critical decision to be made by the patient and any companion is whether the symptoms might represent a heart attack. Their study suggests that those patients who are knowledgeable about the possible symptoms of a heart attack or have classic severe symptoms delay for the shortest time, those with less knowledge delay longer and try to rationalise their symptoms, and those with the least knowledge and atypical symptoms delay the longest. Other reports seem to support their conclusions and suggest that we need to educate the public, particularly patients with coronary artery disease and their companions, about the symptoms of a heart attack.^9–11

Two thirds of all patients die at home, so widespread community training in basic life support should be encouraged, though it is sensible to target people most likely to have to practise these skills. These include the close relatives and friends of patients with known coronary artery disease. Every opportunity should be used to encourage such people to learn to recognise the symptoms of a heart attack and to perform basic life support.

Basic life support performed before the arrival of a defibrillator doubles the survival rate.⁷ Calling for help activates the system, while basic life support “buys time” until the defibrillator arrives. In Britain the NHS plans to continue the single paramedic response system, prioritising emergency calls and reducing response times for life threatening emergencies from the present 14 minutes for 95% of calls in urban areas to 8 minutes for 90% of all calls in all areas.¹² The results of implementing these standards will need to be reviewed.

Some studies suggest that a two tier system involving a “first responder” with an automated external defibrillator—who can arrive within 4-5 minutes—may improve survival compared with a single tier system that aims to deliver a fully trained paramedic in 8 minutes.¹³ Innovative approaches such as the use of “intelligent” defibrillators by policemen, firemen, and other lay first responders (security guards, airline cabin attendants, and uniformed volunteer first aiders) in a medically controlled system continue to be evaluated.¹⁴ In the meantime the message seems clear: to reduce deaths outside hospital from coronary artery disease, better secondary prevention, increased public awareness of the symptoms of a heart attack, and improved activation and response times by the ambulance service are necessary.

General practice pp 1060, 1065