Background Supraventricular tachycardia (SVT) is the most common arrhythmia in infants.

Aim To study the clinical presentation and outcome of narrow complex cardiac arrhythmias in infants

Methods All infants diagnosed with narrow complex arrhythmias in children less than 1 year of age between 2007 and 2013 at Addenbrooke’s hospital were included in the study.

Results 34 infants diagnosed with narrow complex arrhythmias were identified. Eighteen (53%) infants presented within first 7 days after birth, 8 (24%) between 1–4 weeks and the remaining 8 (24%) presented after 4 weeks of age.

Only 3 infants had antenatal diagnoses of arrhythmia. SVT was diagnosed in 27 infants (80%). Other types of arrhythmias included atrial flutter (2) and automated atrial tachycardia (5). Eight infants had underlying significant congenital heart disease.

Fifteen infants were excluded from study as 3 died of other serious underlying conditions, 5 transferred to other hospitals and 7 did not require maintenance therapy.

Of the 19 infants diagnosed with SVT needing maintenance therapy, 6 (32%) are still on maintenance therapy while in 13 (68%) infants maintenance therapy was stopped. Ten had no recurrences after stopping maintenance while three had recurrences needing re-starting treatment.

The average duration of medical treatment was 8 months. Maintenance medications used included propranolol, flecainide and amiodarone. 63% cases had monotherapy while 37% needed multi-drug therapy.

Conclusion Narrow complex tachycardia carries good prognosis in infants without any underlying morbidities. About two thirds infants are managed on single medication for an average duration of 8 months.