What effect do Class IV antidysrhythmics have on the heart rate?

Class IV antidysrhythmics, which include calcium channel blockers such as verapamil and diltiazem, primarily exert their action by inhibiting calcium influx during depolarization of cardiac and vascular smooth muscle. This leads to several important effects on cardiac function.

One of the primary impacts of Class IV agents is their ability to slow down conduction through the atrioventricular (AV) node. By blocking calcium channels, these medications reduce the rate of depolarization in both the atria and AV node. Consequently, this slows down the overall heart rate, especially in conditions of tachycardia, where the heart rate is already elevated. This mechanism is particularly beneficial in managing certain types of supraventricular tachycardia by effectively reducing the frequency of impulses that can lead to a rapid heart rate.

Moreover, the decreased heart rate contributes to other therapeutic effects such as reducing myocardial oxygen demand and promoting better filling of the ventricles, which can be crucial in various clinical scenarios like atrial fibrillation with rapid ventricular response or other tachyarrhythmias.

Given these pharmacological effects, the correct understanding of Class IV antidysrhythmics is that they primarily decrease the heart rate, which is why the answer is accurate.