Mediastinal Air Entrapment During Extravascular ICD Implantation: A Preventable Cause of Elevated Shock Impedance

Elevated shock impedance during extravascular implantable cardioverter-defibrillator (EV-ICD) implantation may preclude defibrillation threshold (DFT) testing despite appropriate retrosternal lead position. We describe suspected mediastinal air entrapment as a reversible mechanism and a simple preventive strategy.

During early EV-ICD implantation experience, two patients developed shock impedance > 200 Ω immediately after retrosternal lead placement, with associated sensing abnormalities. Lead repositioning did not normalize impedance, no pneumothorax was identified, and DFT testing was deferred. Shock impedance normalized spontaneously within 1-2 days, permitting successful DFT testing without lead revision. Transient mediastinal air entrapment along the defibrillation vector was suspected. A procedural modification was adopted in which 5-10 cm H₂O positive end-expiratory pressure was applied immediately before retrosternal introducer removal, followed by prompt EV-ICD lead advancement. Among five consecutive subsequent implantations using this approach, initial shock impedance remained within the expected range, permitting immediate DFT testing without lead repositioning or delay.

Transient mediastinal air entrapment may cause elevated shock impedance during EV-ICD implantation. Positive end-expiratory pressure during introducer removal may mitigate this complication and facilitate reliable intraoperative DFT testing.