Muscle damage will not show up on an angiogram.
Troponin can be found in a blood test and is an indicator for myocardial injury.
Pre-stenting elevation of troponin levels indicate that your heart was suffering from the blockages/ischemia.
Post-stenting elevation of troponin levels can be a late effect from the pre-stenting situation or it can be an indication that your heart suffered some injury from the PCI procedure.
It is not uncommon that during the PCI procedure, when balloon catheters temporarily block the blood supply through your coronary arteries, (minor) injury to the heart happens.