A 68-year-old man presents for routine ECG screening. The tracing shows the pattern marked **A** in the diagram — a PR interval of 240 ms with every P wave followed by a QRS complex. He is asymptomatic with no chest pain, dyspnea, or syncope. His medications include metoprolol for hypertension and diltiazem for rate control. Which of the following is the MOST appropriate next step in management?

Question

Accepted Answer

C. Obtain serum electrolytes, TSH, and troponin; review medications for offending agents. ## Why "Obtain serum electrolytes, TSH, and troponin; review medications for offending agents" is right

The pattern marked **A** defines first-degree AV block: PR interval >200 ms with every P wave conducted to a QRS complex. According to ACC/AHA/HRS 2018 Bradycardia Guidelines, asymptomatic first-degree AV block (especially with PR <300 ms) requires no acute intervention. The appropriate management is to identify and address reversible causes: review medications (this patient is on two AV-nodal-blocking agents: metoprolol and diltiazem), check electrolytes (hyperkalemia, hypermagnesemia can prolong PR), TSH (hypothyroidism), and exclude ischemia (troponin/ECG changes). Discontinuation or dose reduction of offending drugs is the first-line intervention in asymptomatic patients.

## Why each distractor is wrong

- **"Discontinue metoprolol and diltiazem, and reassess PR interval in 2 weeks"**: While medication review is correct, this option omits the essential diagnostic workup (electrolytes, TSH, troponin, ischemia assessment) that must accompany medication adjustment. The question asks for the MOST appropriate NEXT STEP, which is comprehensive evaluation, not immediate drug withdrawal alone.
- **"Initiate atropine 0.5 mg IV and prepare for transcutaneous pacing"**: Acute interventions (atropine, pacing) are NOT indicated for asymptomatic first-degree AV block. These are reserved for symptomatic bradycardia or higher-degree blocks with hemodynamic compromise. This patient has no symptoms and every P is conducted.
- **"Implant a dual-chamber permanent pacemaker immediately"**: Pacemaker implantation is only considered for SYMPTOMATIC marked first-degree AV block (PR >300 ms with pseudo-pacemaker syndrome symptoms). This patient is asymptomatic with PR 240 ms and has not yet had reversible causes addressed. Premature pacing would be inappropriate.

**High-Yield:** First-degree AV block (PR >200 ms, every P conducted) in asymptomatic patients = observation + identify reversible causes (drugs, electrolytes, ischemia); pacemaker only for symptomatic marked PR prolongation (>300 ms) with pseudo-pacemaker syndrome.

[cite: ACC/AHA/HRS Bradycardia Guidelines 2018]

Answer

A. Discontinue metoprolol and diltiazem, and reassess PR interval in 2 weeks

Answer

B. Implant a dual-chamber permanent pacemaker immediately

Answer

D. Initiate atropine 0.5 mg IV and prepare for transcutaneous pacing

Explanation

Why "Obtain serum electrolytes, TSH, and troponin; review medications for offending agents" is right

Why each distractor is wrong

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