Can scar tissue from pericarditis cause a blockage and be the reason for my positive ischemia stress test result even though cac score from cta scan 0?

This would be an unlikely scenario or cause for an abnormal stress test as the pericardium would have to compress a coronary artery or branch. On the other hand, you're age and CAC would make coronary blockage unlikely unless spasm or endothelial dysfunction occurred. Did you have a nuclear stress study or echo study? I vote for a nuclear study& hope a CT angiogram or catheterization won't be need