Mobitz I Atrioventricular Block Following Combined Opioid and Benzodiazepine Overdose: A Case Report.

Opioids and benzodiazepines are well recognized for their depressant effects on the central nervous system, most notably respiratory depression, but atrioventricular (AV) block is an uncommon manifestation. We present the case of a 35-year-old man with polysubstance use disorder who was admitted following a combined fentanyl-benzodiazepine overdose. On admission, he was somnolent but arousable, with bradycardia and oxygen desaturation. Electrocardiogram (ECG) demonstrated Mobitz I second-degree AV block with progressive PR interval prolongation and intermittent non-conducted P waves. Laboratory evaluation revealed mild metabolic acidosis without significant electrolyte abnormalities, and toxicology was positive for fentanyl and benzodiazepines. Supportive management, including intravenous fluids, oxygen, and naloxone, led to gradual improvement. Telemetry demonstrated recovery from Mobitz I block to first-degree AV block, and ultimately restoration of normal sinus rhythm within 48 hours. Echocardiogram showed preserved left ventricular ejection fraction and no structural abnormalities. This case highlights a rare presentation of reversible Mobitz I AV block following mixed opioid-benzodiazepine intoxication. Recognition of Wenckebach as a transient conduction disturbance, consistent with guideline-directed management, prevented unnecessary pacemaker implantation. Careful monitoring is essential to detect dynamic conduction changes in drug-induced cardiac toxicity.