Electrophysiological characteristics of cardiac arrest

Cardiac arrest results either from the development of an arrhythmia which is incompatible with cardiac output, such as pulseless ventricular tachycardia, ventricular fibrillation, or asystole, or from a rhythm that is compatible with a cardiac output but in which no output occurs, termed electromechanical dissociation or pulseless electrical activity.

ECG monitoring suggests that the initiating arrhythmia in 75 per cent of cases of cardiac arrest is ventricular tachycardia or ventricular fibrillation. These malignant ventricular arrhythmias may be heralded by premature ventricular contractions or monomorphic ventricular tachycardia. With time ventricular tachycardia progresses to ventricular fibrillation and eventually to asystole, reflecting the consumption of myocardial high-energy phosphate stores, hypoxia, and progressive acidosis.

Asystole is a more common presenting rhythm in patients who are less than 17 years old, reflecting different underlying causes of cardiac arrest in this age group

(Safranek ef a/ 1.992). Asystole may also be provoked by sudden excessive vagal activity. Recognized precipitants include facial immersion in cold water, carotid sinus pressure, and stimulation of the peritoneum, cervix, or anus.

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