Tricuspid accessory valve-induced hemodynamic deterioration in a Noonan syndrome neonate with myocardial hypertrophy.

UNLABELLED: While accessory mitral valves have been reported in association with ventricular outflow obstruction of Noonan syndrome, accessory tricuspid valves remain extremely rare. To the best of our knowledge, this is the first well-documented case report of this unique combination. We report a 2-month-old male infant with myocardial hypertrophy, who presented with progressive right ventricular outflow tract obstruction (RVOTO) caused by accessory tricuspid valve tissue. At referral, echocardiography revealed severe RVOTO due to the prolapse of accessory tricuspid valve tissue during systole. Cardiac catheterization revealed suprasystemic right ventricular pressure. Surgical resection of the accessory tissue led to immediate resolution of the RVOTO. Postoperatively, the patient was successfully managed with beta-blockers and discharged in stable condition. Although the combination of myocardial hypertrophy and accessory tricuspid valve tissue is rare, clinicians should be aware that it may lead to dynamic and potentially life-threatening hemodynamic deterioration due to RVOTO. LEARNING OBJECTIVE: In neonates with Noonan syndrome, an accessory tricuspid valve leaflet can cause right ventricular outflow tract obstruction, and early surgical resection can prevent fatal hemodynamic deterioration.