Which AV conduction abnormality is commonly seen after an inferior myocardial infarction and can progress to more serious AV block?

Which AV conduction abnormality is commonly seen after an inferior myocardial infarction and can progress to more serious AV block?

• A. Second Degree Heart Block Type I (Wenckebach)
• B. First Degree Heart Block
• C. Second Degree Heart Block Type II
• D. Third Degree Heart Block

Answer: (B)

Inferior myocardial infarction often involves the AV node because the AV nodal artery is usually a branch of the right coronary artery. When the AV node becomes ischemic, conduction from the atria to the ventricles slows, showing up on ECG as a prolonged PR interval. This pattern—constant P waves followed by a consistently longer-than-normal PR interval with every beat—is the first-degree AV block. It is commonly seen after inferior MI and is usually reversible with reperfusion or improved perfusion, but the ischemia can sometimes worsen, allowing progression to a higher-grade block with more significant bradycardia or instability.

In contrast, a second-degree block type II or a complete (third-degree) block reflects more extensive disease of the His-Purkinje system and is more typical of extensive anterior infarction or severe conduction system damage; these are less common after an inferior MI. Wenckebach-type (second-degree AV block Type I) can occur with nodal disease as well, but the scenario described—inferior MI with potential progression from a nodal conduction delay—most characteristically points to first-degree AV block.