Which of the following anti hypertensives act by decreasing heart rate only?
**Core Concept**
Beta-blockers are a class of antihypertensive medications that primarily exert their effect by reducing heart rate and myocardial contractility, thereby decreasing cardiac output and blood pressure.
**Why the Correct Answer is Right**
Beta-blockers act by selectively inhibiting the beta-1 adrenergic receptors in the heart, which are responsible for increasing heart rate and contractility in response to sympathetic stimulation. This results in a decrease in heart rate, cardiac output, and subsequently, blood pressure. The primary mechanism of beta-blockers is through negative chronotropy, meaning they slow the heart rate.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because ACE inhibitors primarily work by inhibiting the conversion of angiotensin I to angiotensin II, leading to vasodilation and decreased aldosterone secretion, which in turn decreases blood pressure.
* **Option B:** This option is incorrect because calcium channel blockers primarily work by inhibiting the influx of calcium ions into vascular smooth muscle cells, leading to vasodilation and decreased peripheral resistance.
* **Option D:** This option is incorrect because diuretics primarily work by increasing sodium and water excretion in the urine, leading to decreased blood volume and subsequently, blood pressure.
**Clinical Pearl / High-Yield Fact**
Beta-blockers are particularly useful in patients with heart failure or post-myocardial infarction, as they reduce the risk of sudden death and improve survival.
**Correct Answer:** C.