Cardiodepression in Organophosphate Poisonings

During clinical epidemiological investigation of acute human organophosphate intoxication a cardiodepressive form of poisoning was recognised. It had a bad prognosis with a high incidence of lethality. The cardiodepressive form involved mechano- and electrodepression which were manifested in cardiogenic shock and sudden atrioventricular block or both associated with ventricular asystole early in the course of the disease. Experimentally the phenomenon is reproducible in dimethoate poisoned guinea-pigs. Mechanodepression is due to the deterioration of myocardiac contractility both in human intoxication and animal experiments. Electrodepression probably results from a decrease in excitability. The above pathological phenomena show poor correlation with the degree of cholinesterase enzyme inhibition. On the other hand, a close relationship between cardiodepression and myocardiac dimethoate concentration was found in animal experiments, while clinically good correlation could be observed between cardiac failure and QT-lengthening in the electrocardiogram.