Transient Fetal Nonimmune 2:1 Atrioventricular Block Possibly Secondary to Cannabis Exposure.

Chandra A.; Waller S.; Wakai R.; Suarez V.; Strasburger J.; Moehlmann M. · CASE (Philadelphia, Pa.) · 2026

**Background & Methods** This case review examines transient fetal nonimmune 2:1 atrioventricular (AV) block in the context of maternal cannabis exposure. The authors present a clinical case and review existing literature on cannabis-induced cardiac arrhythmias in fetal, pediatric, and adult populations to establish a potential causal relationship. **Key Findings** • Transient AV block detected in utero is typically attributed to structural cardiac abnormalities or autoimmune etiologies (such as anti-Ro/SSA antibodies); however, cannabis exposure should be considered in the differential diagnosis when conventional causes have been excluded. • Pharmacological evidence demonstrates that cannabis crosses the placental barrier and directly affects cardiac electrophysiology and rhythm generation, providing a plausible mechanistic pathway for fetal arrhythmia induction. • Clinical precedent exists for cannabis-induced AV block, with documented cases of transient AV block occurring in adolescents and adults following cannabis exposure, suggesting dose-dependent or individual susceptibility-related cardiac effects. **Dosage & Administration** Not reported. The case review does not specify maternal cannabis dosage, frequency, route of administration, or timing of exposure relative to fetal cardiac manifestations. **Safety & Adverse Effects** Transient 2:1 atrioventricular block was observed as the primary cardiac manifestation. The block was reversible, consistent with the "transient" designation, though the review does not detail the resolution timeline, hemodynamic consequences, or fetal outcomes beyond arrhythmia resolution. Additional adverse effects from in utero cannabis exposure are not elaborated in the provided abstract. **Evidence Quality** This is a case review with limited evidentiary strength (Level 4-5 evidence). Significant limitations include: (1) case-based rather than controlled study design; (2) absence of epidemiological data quantifying the incidence of cannabis-related fetal AV block; (3) lack of dose-response relationships; (4) inability to definitively establish causation given the multifactorial nature of fetal arrhythmias; and (5) reliance on mechanistic plausibility rather than prospective evidence. The review contributes to clinical awareness of a potential association but does not provide high-quality evidence for a causal relationship. Further prospective studies and case series documentation are needed to establish cannabis as a confirmed etiology of fetal AV block.

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