Key result
Phase 4 His-Purkinje block triggers unpredictable syncope and ventricular standstill requiring permanent pacemaker implantation.
Case Report (n=1)
Phase 4 block causes unpredictable syncope in His-Purkinje disease, requiring permanent pacemaker implantation.
Phase 4 block may explain unpredictable syncope in conduction disease; hypothesis-generating and should not yet change practice.
CASE SUMMARY: A 66-year-old man with prior atrial fibrillation ablation presented after nearly drowning due to abrupt syncope without prodrome. He reported recurrent monthly episodes for 2 years. Baseline electrocardiogram showed sinus rhythm with left bundle branch block; echocardiography was normal. Telemetry captured a premature atrial beat precipitating ventricular standstill consistent with a phase 4 infranodal block in a diseased His-Purkinje system. Recovery showed transient high-grade Mobitz II block with dynamic QRS changes, indicating diffuse conduction disease. Permanent pacemaker implantation was performed. TAKE-HOME MESSAGES: Phase 4 block causes unpredictable syncope in His-Purkinje disease. Dynamic QRS changes suggest advanced conduction system involvement requiring pacing.
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Ahmad et al. (2026) conducted a case report in Recurrent syncope and ventricular standstill (n=1). Permanent pacemaker implantation was evaluated. Phase 4 His-Purkinje block caused unpredictable syncope and ventricular standstill in a 66-year-old man, requiring permanent pacemaker implantation.
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