## Diagnosis: First-Degree AV Block ### Clinical Presentation The patient has a prolonged PR interval (0.24 seconds; normal <0.20 seconds) with 1:1 AV conduction — every P wave is followed by a QRS complex. This is the defining feature of first-degree AV block. ### Key Diagnostic Features **Key Point:** First-degree AV block is characterized by: - PR interval >0.20 seconds (200 ms) - 1:1 AV conduction maintained - All P waves conducted to the ventricles - Usually asymptomatic ### Pathophysiology The conduction delay occurs at the AV node (most commonly) or occasionally in the His bundle. In this patient's context of recent inferior MI, AV nodal ischemia is the likely cause. ### Clinical Significance **Clinical Pearl:** First-degree AV block in the setting of acute inferior MI is typically benign and resolves spontaneously as the ischemia improves. It does not require pacing unless symptomatic. ### Comparison with Other AV Blocks | Feature | First-Degree | Mobitz I (2°) | Mobitz II (2°) | Third-Degree | |---------|--------------|---------------|----------------|---------------| | PR interval | Prolonged (>0.20 s) | Progressive lengthening | Constant | Variable/absent | | P waves conducted | All (1:1) | All but last | Some dropped | None | | QRS width | Normal | Normal | Wide (often) | Variable | | Prognosis | Benign | Usually benign | May progress to 3° | Requires pacing | | Location | AV node | AV node | His bundle/below | Variable | **High-Yield:** In inferior MI, first-degree AV block and Mobitz I (Wenckebach) are common and usually resolve. Mobitz II in inferior MI is rare and suggests extensive conduction system disease. ### Management No specific treatment is required. Continue monitoring and reassess after recovery from the acute MI phase.
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.