You absolutely perform a 12-lead ECG!
You can use the same rules for diagnosing acute STEMI with paced rhythm that you use for diagnosing STEMI in the presence of LBBB. This is referred to as "Sgarbossa's criteria" and it came from the GUSTO investigators.
1.) ST-elevation > 1 mm that is concordant (in the same direction as) the QRS complex
2.) ST-depression > 1 mm in the right precordial leads (V1-V3)
3.) ST-elevation > 0.2 the depth of the S-wave for QRS complexes that are negative (discordant ST-elevation).
The third criterion is a modified form of Sgarbossa's original criteria.
As for the pacemaker spikes, often they are visible as "blips" in leads V3-V5 but you can often recognize paced rhythms based on QRS morphology if you can't see the spikes.
Remember to expose the chest of every chest pain patient and look for a pacemaker/ICD can in the upper right or upper left chest as well as a surgical scar indicating prior heart surgery.
One final thought, even if you don't remember Sgarbossa's criteria, you can still identify coronary ischemia by comparing serial ECGs with LBBB and paced rhythm.
Tom