While observing continuously the string of the electrocardiograph in an experiment on animals, after digitalis had been injected, we noted that a normal sinus rhythm was present when the animal was quiet, and that ventricular ectopic beats appeared temporarily after a struggle. This phenomenon recurred many times in the same animal. When the dose was increased, ectopic beats appeared and were uninfluenced by struggling. In another experiment, ectopic beats appeared spontaneously after an injection of digitalis and disappeared when the animal struggled. Struggling obviously calls forth a variety of agencies acting on the heart. Some of these agencies depend on the connection of the heart with the central nervous system, such as reflexes from various organs; others may produce their effects on the heart even after it has been isolated from the central nervous system, such as dynamic changes in the circulation or chemical factors in the blood, for example,
GOLD H, LIEBERSON A, GELFAND B. MECHANISM OF PRODUCTION OF SUBAURICULAR BEATS BY DIGITALIS BODIES. Arch Intern Med (Chic). 1931;48(2):262–285. doi:10.1001/archinte.1931.00150020093006
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