Sirolimus for symptomatic cardiac rhabdomyoma in infants: outcomes, recurrence, and safety.

Sirolimus is increasingly used for symptomatic or large cardiac rhabdomyoma, but the risk of recurrence remain unclear. We evaluated clinical response, tumour regression, recurrence, and safety in infants treated with sirolimus. This retrospective study included all infants with symptomatic or large cardiac rhabdomyoma treated with sirolimus between January 2022 and June 2025. Sirolimus was initiated at 1 mg/m2/day and titrated to maintain trough levels of 5-15 ng/mL. Serial echocardiography and electrocardiography monitored obstruction, cardiac function, arrhythmias, and tumour regression or recurrence. For the 11 infants included, sirolimus was initiated at a mean age of 19.4 ± 8.9 days. Indications overlapped and included heart failure (n = 5), ventricular outflow tract obstruction (n = 4), clinically significant arrhythmias (n = 4), and the presence of a large tumour (n = 7). TSC1/TSC2 mutations were identified in 5 infants, and another 5 had extracardiac features of tuberous sclerosis complex. The mean tumour size reduced by 32% at 1 month and 77% at final follow-up, with complete disappearance in 64%. Arrhythmias resolved except in one infant with persistent congenital complete heart block present at baseline. The mean time to achieve a complete clinical response was 19.3 ± 3.98 days of sirolimus therapy. The mean duration of sirolimus therapy was 215 ± 103 days with a maximum of 385 days. Mild hypertriglyceridaemia (n = 2) was the only adverse effect, but it did not warrant discontinuation of sirolimus therapy. Three (27%) infants had tumour regrowth after treatment cessation; all responded promptly to re-initiation of sirolimus. Sirolimus is a safe and effective for symptomatic cardiac rhabdomyoma in infants, producing rapid clinical stabilisation and tumour regression. The optimal duration of therapy is uncertain, and the risk of tumour regrowth after cessation warrants longer follow-up.