Mobitz Type II AV Block 2:1 — Pacemaker Indication
medium
stethoscope Medicine
A 68-year-old man with hypertension presents with syncope. His 12-lead ECG shows a 2:1 AV block pattern with wide QRS complexes (140 ms). The rhythm strip demonstrates intermittent non-conducted P waves with a constant PR interval of 160 ms on the conducted beats, as shown in the diagram marked **A**. Which of the following is the most appropriate management?
A. Observation with serial ECG monitoring and Holter studies
B. Permanent dual-chamber pacemaker implantation
C. Intravenous atropine 0.5 mg followed by observation
D. Temporary transcutaneous pacing only, with medical optimization
Explanation
Why Permanent dual-chamber pacemaker implantation is right
The pattern shown at A is Mobitz Type II second-degree AV block with a 2:1 conduction pattern and wide QRS complex (140 ms), indicating infra-Hisian (His-Purkinje system) block. The constant PR interval on conducted beats (160 ms) with intermittent non-conducted P waves is the hallmark of Mobitz II, distinguishing it from Wenckebach (Mobitz I), which shows progressive PR prolongation. Wide-QRS Mobitz II is particularly malignant and carries high risk of progression to complete heart block with unreliable escape rhythm. According to ACC/AHA/HRS 2018 Bradycardia Guidelines, permanent pacemaker implantation is a Class I indication for Mobitz II AV block regardless of symptoms. Dual-chamber (DDD) pacing is preferred to maintain AV synchrony and reduce risk of pacemaker syndrome. This patient's syncope (Stokes-Adams attack) further reinforces the urgency of pacemaker therapy.
Why each distractor is wrong
Observation with serial ECG monitoring and Holter studies: This is appropriate for Mobitz I (Wenckebach), which is benign and AV-nodal in origin. Mobitz II is infra-nodal and carries unacceptable risk of sudden cardiac death without pacing; observation alone is contraindicated.
Intravenous atropine 0.5 mg followed by observation: Atropine may transiently improve AV-nodal block (Mobitz I) but does not reliably help Mobitz II and may paradoxically worsen block by increasing atrial rate without improving infra-Hisian conduction. It is not first-line therapy and does not address the Class I indication for pacing.
Temporary transcutaneous pacing only, with medical optimization: Temporary pacing is appropriate for acute hemodynamic compromise or symptomatic bradycardia in the immediate setting (e.g., anterior STEMI with new Mobitz II), but it is a bridge measure only. Permanent pacemaker implantation is mandatory for long-term management of Mobitz II to prevent sudden cardiac death.
High-YieldNEET PG
Mobitz II = infra-Hisian block = pacemaker Class I regardless of symptoms; wide-QRS Mobitz II is especially malignant; atropine may worsen; constant PR interval with dropped beats distinguishes it from progressive-PR Wenckebach.
ACC/AHA/HRS 2018 Bradycardia Guidelines; ESC
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