What is the main effect of digitalis on arrhythmias?

The primary effect of digitalis on arrhythmias is its ability to increase vagal tone, which plays a critical role in controlling heart rate, particularly in certain types of arrhythmias such as atrial fibrillation or atrial flutter. Digitalis enhances the parasympathetic (vagal) influence on the heart, leading to a reduction in heart rate and a more stable rhythm. This mechanism is particularly beneficial in patients with rapid ventricular response during atrial fibrillation, as it helps to slow down the conduction through the AV node, allowing for a more controlled ventricular response.

The process involves digitalis's action on the Na+/K+ ATPase pump, resulting in increased intracellular calcium and improved contractility, but the key aspect in relation to arrhythmias is its favorable effect on vagal activity. This can help restore and maintain more regular heart rhythms, especially in scenarios where the heart's response needs to be moderated.

In contrast to other options, digitalis is not primarily used to significantly reduce blood pressure, nor does it directly decrease conduction velocity throughout all cardiac tissues. While it can impact conduction speed in specific contexts (like nodal tissue), it is not a general characteristic of its pharmacological action related to arrhythmias. Therefore,