Final answer:
Alpha agonists decrease SA node conduction velocity by inhibiting sympathetic stimulation and activating alpha-1 adrenergic receptors.
Step-by-step explanation:
Alpha agonists decrease SA node conduction velocity by inhibiting sympathetic stimulation and activating alpha-1 adrenergic receptors. Sympathetic stimulation releases norepinephrine (NE), which binds to the beta-1 receptors in the SA node, increasing heart rate. Alpha agonists, on the other hand, bind to the alpha-1 adrenergic receptors and cause vasoconstriction, reducing sympathetic stimulation. This results in decreased heart rate and conduction velocity at the SA node.