The Effects of Digitalis on the Heart, June 25, 1986

The Effects of Digitalis on the Heart, June 25, 1986

Small doses of digitalis can increase the heart’s excitability and conductivity, but as the dose increases, it begins to have a suppressive effect. Regardless of the dose, digitalis slows down the conduction system of the atrioventricular node, thereby prolonging the PR interval; higher doses can even cause conduction block. Digitalis inhibits the heart’s conduction system, which consists of both vagal and non-vagal pathways. At low doses, the vagal pathway predominates; at high doses, the non-vagal pathway predominates. Digitalis shortens the refractory periods of the atrium and ventricle while prolonging the refractory period of the atrioventricular node; it also promotes the autonomy of the atrium, ventricle, atrioventricular node, and bundle branches.

Digitalis’s diuretic effect: primarily due to increased cardiac output, coupled with increased renal blood flow and glomerular filtration rate. In addition, digitalis can directly act on the distal renal tubules to promote sodium and water loss, while also counteracting aldosterone to enhance diuresis.