I Have Taken An Ecg On A Paediatric Patient (16

I have taken an ecg on a paediatric patient (16 y/o) that has a shifting p-wave pattern; the p-waves move from positive to negative in AvL, and from negative to positive in the limb leads. There is some arrythmia, but the change is successive, so I do not suspect an ectopic atrial pacemaker. Could the change in p-wave configuration be because the heart shifts position in the ribcage when patient is breathing?

Best regards