Epidemiological aspects

Cardiac arrest is the absence of cardiac pumping activity, characterized by the clinical features of pulselessness and loss of consciousness. It can be the common endpoint of many primary and/or secondary conditions affecting the heart.

Sudden unexpected cardiac arrest in adults has an incidence of 0.1 to 0.2 per cent in the general population, with 80 per cent of cases due to coronary heart disease. The incidence of cardiac arrest increases exponentially with age, reflecting the escalating frequency of coronary heart disease, but at all ages men are at greater risk than women. For coronary heart disease populations, hereditary factors producing hypertension, diabetes, lipid abnormalities, and male-pattern baldness predispose to cardiac arrest. Racial characteristics are important, with increased risks in colored populations, although the reasons for this are unclear. Cigarette smoking is the major acquired (and preventable) risk factor, although sedentary occupation and diet also play significant roles.

Although acute and chronic alcohol abuse is associated with an increased frequency of arrhythmias, moderate intake may have a protective effect on coronary heart disease and cardiac arrest by increasing 'protective' lipid concentrations. Other poorly understood factors may be involved in cardiac arrest. There is a circadian variation, with an excess of events occurring in the early morning (MullerandMangel 1994). Mental and/or physical stress effected through autonomic activity, along with altered platelet activity, is suggested as a cause. Holter monitoring shows an increased incidence of ST depression (implying ischemia) between 12 midnight and 12 noon. There is some evidence to suggest that this can be prevented or modified with b-blockers and/or aspirin. A linkage between stress and cardiac arrest is popular in the media but the evidence is tenuous, although the 1994 Northridge earthquake reportedly caused an excess of sudden cardiac deaths, with a reduction in the following week, suggesting that emotional stress (independent of physical exertion) can be a triggering factor in predisposed individuals.

Causes of cardiac arrest that are unrelated to coronary heart disease include many disparate conditions, but drugs, trauma, infections, and cardiomyopathies are the principal causes. These conditions are relatively more common in younger patients and provoke cardiac arrest by producing increased susceptibility to malignant ventricular arrhythmias. Cocaine, a 'recreational' drug that increases myocardial sensitivity to catecholamines by blocking their presynaptic uptake, is one example.

Non-penetrating blunt myocardial injury, such as being struck on the chest by cricket balls, baseballs, or ice-hockey pucks, can lead to cardiac arrest without producing identifiable cardiac structural damage or in the absence of pre-existing pathology (commotio cordis). The etiology is believed to involve arrhythmias induced by relatively minor myocardial trauma occurring at an electrically vulnerable phase of ventricular excitability.

The cardiac causes of sudden death are listed in Table 1,.

Table 1 Cardiac causes of sudden death

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