Antitussive agents should be used with caution in patients who have a history of addiction.

Choice A rationale

Unstable angina is characterized by sudden, severe chest pain that occurs at rest or with minimal exertion and is not relieved by nitroglycerin. It represents an imminent risk of myocardial infarction.

Choice B rationale

Ischemic heart disease can cause various types of angina, including stable, unstable, and Prinzmetal’s angina. The term “ischemic” refers to a lack of blood flow to the heart muscle, but this choice is too broad.

Choice C rationale

Stable angina occurs when there is an imbalance between myocardial oxygen supply and demand, typically during physical exertion or emotional stress. It is characterized by predictable chest pain that is relieved by rest or nitroglycerin.

Choice D rationale

Prinzmetal’s angina, also known as variant angina, is caused by a spasm in the coronary arteries, which leads to a temporary reduction in blood flow. It can occur at rest and is not necessarily related to the imbalance of myocardial supply and demand.

Choice A rationale

Cardiac glycosides are not known for increasing heart rate. Instead, they tend to decrease heart rate by enhancing vagal tone and increasing the refractory period of the atrioventricular node, which helps in controlling heart rate, especially in atrial fibrillation.

Choice B rationale

Cardiac glycosides actually increase the force of myocardial contractions. They inhibit the sodium-potassium ATPase pump, which leads to an increase in intracellular sodium and calcium levels in the myocardial cells, thus increasing the force of contraction.

Choice C rationale

Cardiac glycosides do not significantly decrease conduction velocity. They primarily affect the contractility and heart rate but their influence on conduction velocity is relatively mild.

Choice D rationale

Cardiac glycosides improve renal blood flow and increase urine output by increasing the cardiac output and reducing the activation of the renin-angiotensin-aldosterone system. This helps in relieving symptoms of heart failure.