Is there a difference between focal atrial tachycardia and av nodal re-entrant tachycardia?

Svt. 2 different entities, both are different types of SVT.
Yes. Avnrt is due to an extra electrical pathway in the junction between upper and lower chambers that your born with. Whereas focal at is acquired and usually due to some scarring. Both ca be managed medically or potential cured by catheter ablation.
Yes. The mechanism by which they allow very fast heart rates differs. In focal atrial tachycardia there is one area in your upper heart chamber (atria) that is able to generate very fast heart rates. In av nodal re-entry, there is a "short-cut" or "short circuit within your av node that allows "two-way" electrical traffic that under special circumstances could allow tachycardia. See your doctor.