How do the symptoms differ in anxiety vs long qt syndrome?

They are different: Long qt syndrome usually doesn't have symptoms. If you have chest pain, palpitations or especially if you faint, see your regular doctor first. If you're ok then see a psychiatrist as palpitations and chest pressure can be symptoms of panic. But heart health always comes first.

See MD: Prolonged qt is a rare, but very serious medical disorder. Symptoms can be dizziness, lightheadedness and passing out. Anxiety symptoms can be similar, but increased heart rate, sweating, shortness of breath, etc. Anyone having symptoms like these should see their doctor for a full evaluation.