- Patients with any other medical conditions or who are using any medications which may interfere with the conduct of the study (including patients taking clonidine, patients with EKG conduction defects and who are taking calcium channel blockers, patients with clinically significant congestive heart failure (CHF) or bronchospasm, or patients with second- or third-degree heart block, symptomatic sinus bradyarrhythmia, or nonsinus rhythm on preoperative EKG.)