Abstract
Previous studies have shown that the “Q-T” interval of the human electrocardiogram is related to the duration of the cardiac cycle (“R-R” interval) 1 and that the “Q-T” interval is lengthened in relation to the cardiac cycle in cases of heart failure. 2 Since digitalis is the drug most successfully used in combating cardiac insufficiency, a study of the effect of this drug was made. It was found that adequate doses of digitalis almost uniformly produce a relative shortening of the “Q-T” interval and that a change in the same direction occurs in normal individuals 2 as well as in cardiac patients. Moreover, this effect of digitalis is seen at least as early as any other known change produced by its administration. A discussion with further details will be given in the complete paper.
The accompanying table gives a few examples of this effect of digitalis. Several hundred records, including those of 5 normal individuals, have been studied. In the table “K” is a constant in the formula, “Q-T” interval = K “R-R” interval, so that “K” is an index of the ratio, “Q-T” interval: cycle length.
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