T-wave inversions in anterior precordial leads are normal
T-waves upright in most leads for first 7 days of life
T-waves typically inverted from 7 days to adolescence
Once an individual child's T-waves flip upright, they should stay that way (i.e. to become newly inverted again would be pathologic)
ECG 
Cardiac enzymes
Cardiac ultrasound
D-dimer
Transcutaneous pacing
Defibrillation
Pulmonary artery catheter
IVC ultrasound