Okay, let's tackle this question about the ECG features of hyperkalemia. First, I need to recall what hyperkalemia does to the heart's electrical activity. High potassium levels affect the resting membrane potential of cardiac cells. Normally, potassium is inside the cells, and when levels are high, the resting potential becomes less negative, leading to partial depolarization.

So, what ECG changes are associated with this? I remember that the classic signs start with peaked T waves. Then, as potassium levels get higher, the PR interval might prolong, the QRS complex widens, and eventually, the P wave can flatten or disappear. In severe cases, there might be sine wave patterns and even ventricular fibrillation or asystole.

The options given are A to D, but the user didn't list them. But since the correct answer is supposed to be one of the ECG features, the most common ones are peaked T waves, which are often the earliest sign. Other features include prolonged PR, widened QRS, and loss of P waves. So the correct answer should be peaked T waves.

Now, for the incorrect options, if they were, say, ST depression, that's more common in ischemia, not hyperkalemia. U waves are associated with hypokalemia. If any option mentioned these, they'd be incorrect. Also, if an option said "normal T waves," that's wrong because hyperkalemia specifically causes peaked T waves.

I need to structure the explanation into the required sections. Core concept would be about the effect of potassium on cardiac cells. Then explain why peaked T waves are correct, then each wrong option. The clinical pearl would be to remember the order of ECG changes with hyperkalemia. The correct answer is D. Peaked T waves.

**Core Concept** Hyperkalemia (elevated serum potassium) alters cardiac cell membrane potential, leading to characteristic ECG changes. Potassium affects repolarization and conduction velocity, with early signs including peaked T waves and late features like widened QRS and sine-wave morphology.

**Why the Correct Answer is Right** Peaked T waves are the earliest and most specific ECG finding in hyperkalemia. Elevated potassium enhances phase 2 (plateau phase) of cardiac action potential, increasing repolarization duration and heightening T waves. As severity progresses, PR prolongation, QRS widening, and loss of P waves occur due to impaired impulse conduction through the AV node and ventricles.

**Why Each Wrong Option is Incorrect**
**Option A:** *ST depression* is seen in ischemia or hypokalemia, not hyperkalemia.
**Option B:** *U waves* are classic for hypokalemia, not hyperkalemia.
**Option C:** *Flattened T waves* occur in hypokalemia or hypomagnesemia.

**Clinical Pearl / High-Yield Fact** Remember the "Peaked T, Wide QRS, No P" sequence for hyperkalemia. Treat with calcium gluconate (stabilizes myocardium), insulin/glucose (shifts potassium intracellularly), and diuretics/bind resins (removes potassium). ECG changes correlate with potassium levels: >6.5 mEq/L is critical for cardiac toxicity.

**Correct Answer: D. Peaked

✓ Correct Answer: B. Wide QRS complex