Thanks for posting your query.
T wave inversion in defined leads may be a normal variant or part of inferolateral ischemia
(as per defined leads).
T wave inversion more than or equal to 3 mm is highly suggestive of ischemic changes.
As such there is no correlation between gastroenteritis
and persisting t wave inversion.
You should go for serum electrolytes, stress test
Stress test will guide for the utility of coronary angiography
and 2 D echo.
Electrolytes imbalance may also cause T wave inversion.
You can go for repeat ECG after recovery from gastroenteritis.
Dr. Mayank Bhargava