Which changes occur on ECG with hypokalemia?

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Potassium levels shape how the heart repolarizes after each beat. In hypokalemia, repolarization is slowed, so the ECG shows flattened or inverted T waves, a prominent U wave after the T wave, ST-segment depression, and a longer QT interval. This combination reflects delayed ventricular repolarization and creates a substrate for dangerous arrhythmias like torsades de Pointes. The pattern described in the other choice—tall, peaked T waves with ST elevation—fits hyperkalemia, not hypokalemia, and QT shortening is not a feature of hypokalemia.