Hi, a CT angiogram is noninvasive as compared to the traditional angiogram and is usually the preferred mode of investigation. CT angiograms will expose you to a small amount of radiation. If you have known coronary artery disease, a traditional coronary angiogram may be a better option, since you can also receive treatment for your artery blockages during a traditional coronary angiogram. Since you are symptomatic but do not have known coronary artery disease, you can go ahead with the CT scan, based on these findings further therapy can be planned. Regards.
Personally I would have the gold standard Angiogram with catheter simply because they can usually fix the problem during the same procedure if the disease isn't too severe. If this is heart disease, I can't emphasise enough how the smoking will harm you and make it worse. If you stop smoking, after just a few hours your blood oxygen will start to rise gradually and you will feel a huge benefit after 24-48 hours. A friend of mine has heart disease and smokes. When he gets angina, he stops smoking to feel better and gets an Angiogram done, usually with stenting. Then he's back to the smoking again straight after. I've told him a million times if he stays off the cigs, he will not likely need more stents.