Antithrombotics

Why do patients fitted with drug-eluting stents require antiplatelet treatment for 12 months while those on who have bare metal stents fitted require only 28 days' treatment. Plus what drug is used in drug-eluting stents?

Is it safe for a patient suffering from atrial fibrillation taking aspirin 75mg to prevent blood clots to stop taking the asprin seven days before planned spinal surgery?

Please indicate how the risk factors may be evaluated for such a patient.