Infant, cool peripheries, tachycardia (356/1700)

A 1m boy has been brought to the ED, conscious but with cool peripheries and has HR=222bpm.
He has been irritable and feeding poorly for 24h. CXR=borderline enlarged heart with clear lung
fields. ECG=regular narrow complex tachycardia, with difficulty identifying p wave. What is the
single most appropriate immediate tx?

a. Administer fluid bolus
b. Administer oxygen
c. Oral beta-blockers
d. Synchronized DC cardio-version
e. Unilateral carotid sinus massage

answer: D
Hypotension (cool peripheries) we should go for DC conversion