Can you tell me the difference between atrial tachycardia and junctional tachycardia?

Very little!: Rapid heart rhythm can have many causes. The most important difference is between those starting in the ventricles, v tach or v fib, which are often rapidly lethal, and those starting in the atria and/or av junction, which cause symptoms but are rarely fatal. The regular rapid rhythms atrial tachycardia or av junctional tachycardia can be hard to separate and are treated similarly.

Atach vs J tach : The source of atach is in the upper chamber the attia. Junctional tach arises from a location midway between the atria and ventricle.