Final answer:
Hyperkalemia, which is an elevated level of potassium in the blood, causes changes in the heart's electrical activity, leading to slow repolarization observable in the ST-T segment of an ECG, and represents the best match for the described symptoms.
Step-by-step explanation:
Effects of Hyperkalemia on the Heart
Increased negativity of the resting potential and slow repolarization of the cardiac muscle, particularly in the ST-T segment, are typically indicative of hyperkalemia. Hyperkalemia is a condition characterized by an elevated potassium level in the blood, which can significantly impair the function of cardiac cells. This condition leads to partial depolarization and an inability of the cells to repolarize normally, meaning the heart muscle won't relax properly after a contraction. The slow repolarization of the cardiac muscle, manifested as changes in the ST-T segment of an ECG, implies that the heart is unable to resume its resting state efficiently, which can have severe consequences, including the heart ceasing to pump blood. Therefore, among the given options, hyperkalemia is the most likely cause of these ECG changes.