Abstract
Since weakening of the heart muscle leads to incomplete emptying and progressive dilatation, which in turn results in impaired conduction, arrhythmias, and auricular fibrillation, it is conceivable that these conditions would be improved by increasing the force of the heart and slowing its rate by digitalis, or by relieving its load.
In order to accomplish the latter we have bled 5-10 cc. per kg. or changed the distribution of the blood in the active circulation by snake venom (Lachesis colatitudes), histamine, peptone and nitrites.∗ These drugs were injected into the femoral vein of cats previously anesthetized with urethane. Respiration and blood pressure curves were taken and checked up by simultaneous electrocardiograms.
After a normal tracing and electrocardiogram were taken, cardiac arrhythmias were produced by chloral or aconitine, mostly the former because of its more uniform results. Fifty mg. of chloral hydrate per kg. was the initial dose used. Occasionally this was sufficient to cause an irregular heart, but as a rule it had to be repeated 2 or 3 times. As soon as the tracing showed an irregularity, an electrocardiogram was taken, and then the therapeutic drug was injected. The electrocardiograms before the injection revealed numerous right and left ventricular extra-systoles, auricular extra-systoles, nodal rhythm, or partial heart block. Some of these electrocardiograms showed a single irregularity, while others showed combinations of several irregularities. In untreated animals the arrhythmia lasted for 15 to 45 minutes. A few animals died within 15 minutes, the irregularity persisting till death.
The first drug used was Lachesis lanceolatus, 0.025 mg. per kg., and, as a rule, in about one minute the heart became regular, as shown by the tracing and the electrocardiogram.
Histamine 0.03 mg. per kg., peptone 100 mg. per kg., nitroglycerine 0.4 mg. per kg., withdrawal of about 10 cc. of blood per kg., or pressure on the Inferior Vena Cava gave similar results.
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