Is my sons untreated reflux triggering svt episodes?

Possibly: Supraventricular tachycardia (svt) can be triggered by emotional stress, anxiety, physical stress, medications, and pain or discomfort, among other things. Reflux may well be such a trigger fr him. Treating the reflux won't eliminate the underlying svt, of course, but it may remove one of the triggers of episodes.

Possible: Although there is not a direct correlation to date between svt episodes and GI reflux there are cases of arrhythmias being triggered by swallowing. The esophagus lies just behind the left atrial and if there is some difficulty for food passing to the stomach afib and other arrhythmias might be triggered. Empiric trial to treat the GI reflux would be reasonable. Please discuss with your doctor.

SVT: No. Reflux doesn't trigger svts.