Linda123,
Your welcome, again.
SVT stands for "supraventricular tachycardia", which means any fast heart rhythm originating above the ventricles. Atrial tachycardia is a form of SVT, just like vanilla is a form of ice cream.
Atrial tachycardia does not necessarily imply "damage". Atach can be technically more challenging to ablate than extra pathways (called accessory pathways), but sometimes may be easier as well.
Atach ablation in the US is fairly advanced, but the success depends on the particulars of the given person's atach. Also, I don't know the level of sophistication of the UK interventional electrophysiologists -- in general, the UK tends to be less procedure oriented than the US.
Most anti-depressants have the potential to affect the heart, but some certainly more than others. The SSRI class (prozac, zoloft, celexa, etc) is generally considered safer than the tricyclics (like amitriptyline), but this is not always the case -- so amitriptyline might make more sense for you. Talk to your doctor.
Hope that helps.
Best Wishes