Direct-acting vasodilators have which of the following effects on the heart rate?
A. Heart rate decreases.
B. Heart rate remains significantly unchanged.
C. Heart rate increases.
D. Heart rate becomes irregular.
Correct Answer: A. Heart rate decreases.
Heart rate decreases in response to decreased blood pressure caused by vasodilation. Hydralazine and minoxidil act by dilating resistance arterioles, thus reducing peripheral resistance, with no dilating effect on the venous side of the circulation. There is a baroreflex-mediated venoconstriction, resulting in an increase in venous return to the heart, along with a direct catecholamine-mediated positive inotropic and chronotropic stimulation of the heart.
Option B: In general, Vasodilators dilate or prevent constriction of the blood vessels, which allow greater blood flow to various organs in the body. Many vasodilators bind to receptors on endothelial cells of the blood vessel, which stimulate calcium release.
Option C: Anticholinergics are used to increase heart rate through vagolytic effects, causing increase in cardiac output. These agents are indicated when symptoms of hypoperfusion exist. They are thought to work centrally by suppressing conduction in the vestibular cerebellar pathways. They may have an inhibitory effect on the parasympathetic nervous system.
Option D: Antiarrhythmic medications have several areas of concern. First and foremost, most agents also have some degree of proarrhythmic potential. Practically speaking, while trying to suppress arrhythmias with the medications, the medications themselves, can lead to other (potentially more dangerous) arrhythmias.
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