The antianginal effect of b-blockers may be attributed to which one of the following
**Core Concept**
The antianginal effect of beta-blockers is primarily due to their ability to reduce myocardial oxygen demand by decreasing heart rate and contractility. This is achieved through their action on beta-1 adrenergic receptors in the heart, which are responsible for regulating heart rate and contractility.
**Why the Correct Answer is Right**
Beta-blockers, such as metoprolol and propranolol, work by competitively inhibiting the binding of epinephrine (adrenaline) to beta-1 adrenergic receptors in the heart. This leads to a decrease in heart rate (chronotropy) and contractility (inotropy), resulting in a reduction in myocardial oxygen demand. As a result, the heart muscle requires less oxygen, which helps to prevent angina pectoris (chest pain) during periods of increased myocardial oxygen demand.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because calcium channel blockers (CCBs) work by inhibiting the influx of calcium ions into the cardiac muscle and vascular smooth muscle cells, leading to vasodilation and a decrease in myocardial oxygen demand. While CCBs are effective in treating angina, they do not work through the same mechanism as beta-blockers.
**Option B:** This option is incorrect because nitrates work by releasing nitric oxide, which leads to vasodilation and a decrease in preload (the initial stretching of the cardiac myocytes prior to contraction). While nitrates are effective in treating angina, they do not work through the same mechanism as beta-blockers.
**Option C:** This option is incorrect because ACE inhibitors work by inhibiting the conversion of angiotensin I to angiotensin II, leading to vasodilation and a decrease in blood pressure. While ACE inhibitors are effective in treating hypertension and heart failure, they do not work through the same mechanism as beta-blockers.
**Clinical Pearl / High-Yield Fact**
Beta-blockers are often used in combination with other medications, such as nitrates and calcium channel blockers, to achieve optimal results in the treatment of angina. Additionally, beta-blockers are often used in patients with heart failure and hypertension to reduce mortality and morbidity.
**Correct Answer:** C.