Which of the following is a common cause of complete heart block?

• A. Ischemia or infarction
• B. Hyperkalemia
• C. Hypertension
• D. Dehydration

Answer: (A)

Complete heart block happens when the electrical signal from the atria fails to reach the ventricles, so the ventricles beat at their own slower pace. The most common reason this disruption occurs is injury to the conduction system from ischemia or infarction of the heart muscle. When an MI, especially one involving the inferior wall, damages the AV node or the His-Purkinje pathway, the normal atrioventricular conduction is interrupted, leading to complete AV block with independent atrial and ventricular activity and a slower escape rhythm.

Hyperkalemia can affect conduction and sometimes cause blocks, but it’s a less frequent direct cause of complete heart block compared with ischemia or infarction. Hypertension and dehydration don’t directly injure the conduction pathways to produce a complete block, though they may influence overall cardiac risk or electrolyte balance in other contexts.