Rare supraventricular tachycardias
Pulmonary vein tachycardia has positive P waves in V2 to V6 as the atrial activation starts posteriorly and moves towards the recording electrodes. Tachycardia originating from the right atrial appendage may have negative P waves in chest leads.
Atrial fibrillation is extremely rare in a new born because it needs a larger atrium for maintenance. If atrial fibrillation is seen in a new born, it indicates atrial enlargement as in ventricular dysfunction and could be due to conditions like ALCAPA.
On the contrary, AVRT is quite likely in newborns as accessory pathways are congenitally present. In fact many of them disappear later on due to apotosis. Accessory pathways are just modified strands of atrial musculature connecting the atria and ventricles electrically across the mitral or tricuspid annulus, which acts as an electrical barrier for direct transmission of impulses from the atria to the ventricles.