The Effects of Trans Venous Cardiac Pacing on Coronary Microvascular Function and Hemodynamics

Inclusion Criteria: All patients 19 years of age or older with clinical evidence of coronary ischemia undergoing coronary angiogram, and who have a pacemaker. Exclusion Criteria: * Acute ST segment myocardial infarction * Known sensitivity or contraindication to the agents planned for administration during coronary angiography * Pacemaker dependent patients * Pregnancy * Hypotension (a systolic blood pressure lower than 90mmHg) that would preclude the administration of adenosine * Severe renal dysfunction, defined as a estimated glomerular filtration (eGFR) less than 30ml/min, confirmed by recent testing * Study subject has any underlying disorder that, in the opinion of the investigator, precludes them from giving informed consent at the time of enrollment