## **Core Concept**
Hypertrophic obstructive cardiomyopathy (HOCM) is a condition characterized by thickening of the heart muscle that can obstruct blood flow. Management involves avoiding drugs that worsen obstruction or increase contractility.

## **Why the Correct Answer is Right**
The correct answer, **D. Isoproterenol**, is a beta-adrenergic agonist that increases heart rate, contractility, and consequently, the obstruction in HOCM. Isoproterenol can worsen symptoms in patients with HOCM by increasing the contractility of the heart muscle, thereby increasing the dynamic obstruction of the left ventricular outflow tract.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Atenolol is a beta-blocker. Beta-blockers are often used in the management of HOCM as they decrease contractility and heart rate, which can reduce obstruction.
* **Option B:** Verapamil is a calcium channel blocker that can be used in HOCM for patients who do not respond to or cannot tolerate beta-blockers. It helps by reducing contractility and heart rate.
* **Option C:** Digoxin increases the contractility of the heart. However, its use in HOCM is generally avoided because it can worsen obstruction, similar to isoproterenol. However, among the options provided, digoxin is not as directly harmful as isoproterenol in the context of HOCM.

## **Clinical Pearl / High-Yield Fact**
In HOCM, drugs that increase contractility (positive inotropes) or heart rate are generally avoided as they can exacerbate the obstruction. Beta-blockers and sometimes calcium channel blockers are preferred for managing symptoms.

## **Correct Answer:** . Isoproterenol