Which of the following is a bradycardia cause?

• A. Lower metabolic needs (sleep, athletic training, hypothyroidism)
• B. Hyperkalemia
• C. Pulmonary embolism
• D. Exercise-induced tachycardia

Answer: (C)

Bradycardia develops when the heart rate slows due to factors that dampen the heart’s electrical activity or reduce metabolic demand on the heart. This can happen with high vagal (parasympathetic) tone, such as during sleep or in well-trained athletes, and with hypothyroidism, where the body's metabolism slows and the heart rate drops. Electrolyte imbalances like hyperkalemia directly depress conduction and automaticity in the heart, making bradycardia more likely. On the other hand, pulmonary embolism usually triggers tachycardia as a response to hypoxia and stress on the heart, and exercise-induced tachycardia is, by definition, an increased heart rate with activity. So, the bradycardia-causing factor among these is hyperkalemia, with the other options not fitting as bradycardia triggers.