Which of the following conditions can lead to a bradyarrhythmia in infants?

The correct choice is electrolyte imbalance, as several electrolyte disturbances can significantly affect the electrical activity of the heart, leading to bradyarrhythmias in infants. Key electrolytes like potassium, calcium, and magnesium play crucial roles in maintaining normal cardiac rhythms. For instance, hyperkalemia (high potassium levels) can slow down the heart rate and eventually cause bradycardia. Conversely, hypocalcemia (low calcium levels) can also disrupt normal heart function. Since infants have less physiological reserve, even minor changes in electrolyte levels can lead to pronounced cardiac effects such as bradyarrhythmia.

While hypoglycemia, hyperthermia, and dehydration can cause various health issues, they are less directly linked to the electrical conduction system of the heart when compared to electrolyte imbalances. Hypoglycemia can lead to altered mental status and irritability but is less commonly associated with bradycardia in infants. Hyperthermia often results in tachycardia instead. Dehydration can lead to cardiovascular compromise but primarily leads to decreased perfusion and subsequent tachycardia as the body attempts to maintain blood flow. Thus, electrolyte imbalance is the most pertinent condition for causing bradyarrhythmia in infants.