CTA necessary?

I have a CTA heart scheduled later this month and wondered if it's really necessary. Records from a CT several years ago showed atherosclerotic disease with coronary calcifications, atherosclerotic plaquing in great vessels and thoracic aorta as well as CAD (abnormal findings on diagnostic imaging of heart and coronary circulation). I also have some pulmonary issues brought about by asbestos in play. What is the CTA going to show that isn't already known? The most recent cardiologist (the one who's scheduled the CTA) hinted that a heart catherization may be called for. What are they doing then? Should I suggest skipping the CTA and getting the Cath? I certainly don't want one to have to be done after a heart attack. Very confused here.

Thank you. Concerned still, but definitely welcomed your input.