Which statement about dromotropic agents is correct?

• A. They primarily affect myocardial contractility
• B. They affect conduction speed of the AV node, and subsequently the rate of electrical impulses in the heart
• C. They primarily affect heart rate
• D. They alter vascular tone

Answer: (B)

Dromotropic effects describe how an agent changes the speed of electrical conduction through the heart, especially through the AV node. The correct idea is that dromotropic agents influence how quickly impulses travel across the AV node and, as a result, affect the overall rate at which impulses reach the ventricles. Positive dromotropes speed AV nodal conduction, potentially increasing ventricular rate, while negative dromotropes slow conduction, reducing the rate. The other options describe different cardiac properties: contractility (inotropy) affects how hard the heart muscle squeezes; heart rate (chronotropy) refers to how fast the heart beats; and vascular tone relates to the constriction or dilation of blood vessels. Thus, the statement focusing on AV nodal conduction and the resulting impulse rate best captures what dromotropic agents do.