**Core Concept**
The early changes in hyperkalemia on an electrocardiogram (ECG) are due to the effects of elevated potassium levels on cardiac membrane excitability. Hyperkalemia disrupts the normal functioning of cardiac ion channels, leading to alterations in the ECG waveform.

**Why the Correct Answer is Right**
The first change seen in hyperkalemia on an ECG is the appearance of **peaked T waves**. This occurs due to the increased potassium ion concentration, which affects the repolarization phase of the cardiac action potential. Potassium ions prolong the repolarization phase, resulting in a taller and more peaked T wave. This change is often seen before any other alterations in the ECG, such as the widening of the QRS complex or the appearance of sine wave activity.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a recognized early change in hyperkalemia on an ECG.
* **Option B:** While changes in the ST segment can occur in hyperkalemia, they are not typically the first change observed on an ECG.
* **Option D:** This option is incorrect as the widening of the QRS complex is not the first change seen in hyperkalemia on an ECG.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize the early changes in hyperkalemia on an ECG, as they can be an indicator of impending cardiac arrest. The appearance of peaked T waves should prompt immediate action to correct the hyperkalemia.

**Correct Answer: C. peaked T waves**