**Core Concept**
Low QRS voltage on an electrocardiogram (ECG) refers to a reduced amplitude of the QRS complex, which is the segment of the ECG that represents the depolarization of the ventricles. This phenomenon is often associated with conditions that affect the volume of the ventricles or the conduction of electrical impulses through the heart.

**Why the Correct Answer is Right**
Low QRS voltage can be caused by conditions that reduce the volume of the ventricles, such as pericardial effusion or cardiomyopathy. In these cases, the reduced volume of the ventricles results in a decrease in the amplitude of the QRS complex. Additionally, conditions that affect the conduction of electrical impulses through the heart, such as bundle branch block or ventricular hypertrophy, can also cause low QRS voltage.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because it does not provide a specific condition or mechanism that would cause low QRS voltage.
**Option B:** This option might be a distractor that seems plausible but is not the best answer. For example, hypokalemia can cause changes to the ECG, but it is not the most direct cause of low QRS voltage.
**Option C:** This option is likely incorrect because it is too vague and does not provide a specific condition or mechanism that would cause low QRS voltage.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that low QRS voltage can be a sign of cardiac tamponade, a life-threatening condition that requires immediate medical attention.

**Correct Answer: D. Cardiomyopathy.**