Which of the following is NOT a common cause of 3rd degree AV block?

• A. Acute myocardial infarction
• B. Digitalis toxicity
• C. Uncontrolled hypertension
• D. Heart surgery

Answer: (C)

Third-degree atrioventricular (AV) block, also known as complete heart block, occurs when there is a complete failure of electrical conduction between the atria and ventricles. This results in a dissociation between atrial and ventricular activity. The common causes of third-degree AV block predominantly involve structural or ischemic changes that affect the conduction system of the heart.

Acute myocardial infarction can lead to ischemic damage to the conduction pathways, particularly in the presence of inferior wall myocardial infarctions where the AV node may be compromised. Digitalis toxicity can affect cardiac conduction and lead to AV block due to its effects on the nodal tissue. Heart surgery, especially procedures involving the heart valves or coronary arteries, can result in injury to the conduction system, hence contributing to the development of AV block.

Uncontrolled hypertension, while it poses various risks to cardiovascular health, is less directly associated with the specific disruption of conduction pathways that is characteristic of third-degree AV block. Hypertension can lead to heart muscle hypertrophy and other changes over time but does not typically result in the acute disruptions seen with the other conditions listed. Therefore, it is not recognized as a common direct cause of third-degree AV block. This distinguishes it clearly from the other factors, making