The objective of the Cath will be to see directly into the arteries of your heart; if blockages are seen and your doctors think that they may correlate with your symptoms, then the options for management would be intensive medical therapy, balloon angioplasty
with stenting (if focal, few blockages are noted) or bypass surgery
(if high risk features or several blockages noted). you already have a cardiac imaging test showing abnormal perfusion, in the setting of ongoing, unclear symptoms I believe the angiogram makes sense.
Hope this helps,
Mayo Clinic Rochester