A 29-day-old newborn weighing 4,100 kg was brought by his parents to the health centre for evaluation for facial rash. On examination, his paediatrician observed tachycardia and tachypnoea, and pulse oximetry showed a heart rate of 255 bpm and O2 Sat: 97%, so he was referred to hospital. Until then, he tolerated feeding well and showed good weight gain.
Pregnancy and delivery were normal, being full term with Apgar 8/9, birth weight 3,250 g, length 51.5 cm and head circumference 31.8 cm. No family history of interest was noted.
On arrival at the emergency department, he had a good general appearance with good colour, tachypnoea and subcostal tugging, a heart rate of over 250 beats per minute (bpm) with an O2 Sat of 97%. A few minutes later he presented with worsening general condition, coldness and acral cyanosis and facial pallor. The ECG showed supraventricular tachycardia morphology with narrow QRS complexes, retrograde P waves and a heart rate of 288 bpm.

Vagal manoeuvres were performed (ice on the face) with no effect, so 1 intravenous (IV) bolus of 50 µg/kg of adenosine was administered without response and 3 minutes later a second bolus of 100 µg/kg was administered, the tachycardia subsided and reverted to sinus rhythm with a heart rate of 168 bpm, with improvement in skin colouring and general appearance.
Since we have 2 ml ampoules of Adenocor® with 6 mg of drug available in our environment, dilutions were necessary. In our case, we took 0.5 ml (1.5 mg) diluted with 14.5 ml of saline, obtaining a concentration of 100 µg/ml. An initial dose of 2 ml (50 µg/kg) is then administered and in the absence of response a second dose of 4 ml (100 µg/kg) is administered.
After resolution of the tachycardia, the patient was transferred to the paediatric intensive care unit (PICU) of the referral hospital for follow-up and evaluation. During the following 24 hours, he presented a new episode of supraventricular tachycardia, also resolved with adenosine, and subsequently remained asymptomatic. Normal echocardiography was reported. To date, he has not presented any recurrence, maintaining prophylactic treatment with propranolol.

