Syncope and New-Onset Bifascicular Block Associated With Intravenous Immunoglobulin in a Patient With Chronic Inflammatory Demyelinating Polyneuropathy.

Chronic inflammatory demyelinating polyneuropathy (CIDP) is an immune-mediated neuropathy often treated with intravenous immunoglobulin (IVIG), which is generally well-tolerated but has occasionally been associated with rare cardiovascular side effects. We present the case of an 84-year-old male with CIDP, maintained on biweekly IVIG infusions, who experienced a syncopal episode with documented bradycardia of 30 beats per minute (bpm) during an infusion. Upon evaluation in the emergency department, the patient was found to have a new bifascicular block requiring pacemaker placement. This case underscores a rare adverse reaction associated with IVIG infusion, highlighting the importance of careful cardiac monitoring in older patients with CIDP and underlying or potential cardiac risk factors.