Reproducible Bradycardia After Flumazenil Reversal of Midazolam-Propofol Intravenous Sedation in a Patient With Klinefelter Syndrome: A Case Report.

Klinefelter syndrome (KS) is the most common sex chromosome aneuploidy in males and is associated with metabolic, cardiovascular, and neurodevelopmental features. Some individuals with KS have also been reported to exhibit altered heart rate (HR) regulation, although cardiovascular responses associated with intravenous sedation (IV-S) have not been well documented. We report a 14-year-old boy with KS, intellectual disability, and autism spectrum disorder who underwent multiple dental treatments under IV-S with midazolam and propofol. During three consecutive sessions at approximately two-week intervals, flumazenil administration at the end of each session was followed by reproducible declines in HR of 13-21 beats per minute, while blood pressure and oxygen saturation showed no marked deterioration. The post-flumazenil HR was lower than both the pre-sedation baseline HR and the lowest HR recorded during dental treatment in each session. The patient had no history of structural heart disease, and post-procedure chest radiography and transthoracic echocardiogram showed no significant abnormalities. These observations raise the possibility that the abrupt pharmacologic transition associated with flumazenil reversal, together with KS-related vulnerability in HR regulation, contributed to the reproducible post-reversal bradycardia. Careful monitoring during reversal and emergence may be warranted when flumazenil is used in patients with KS.