Obstructive sleep apnea (OSA) is a respiratory disorder of sleep characterized by recurrent episodes of complete or partial upper airway obstruction, leading to intermittent oxygen deprivation. This results in sympathetic activation and surges in blood pressure, production of vasoactive substances, as well as activation of the inflammatory and procoagulant pathways. Epidemiological evidence indicates the prevalence of OSA is higher in patients with coronary artery disease than in the general population. The investigators recently showed that 65.7% and 41.9% of the Singapore patients admitted with myocardial infarction were found to have previously undiagnosed OSA and severe OSA, respectively. In a 10-year follow-up epidemiological study, OSA was independently associated with a higher prevalence of fatal and non-fatal cardiovascular events among the otherwise healthy general population. The investigators further showed that in patients who have undergone primary percutaneous coronary intervention for acute myocardial infarction, OSA was an independent predictor of future adverse event rates. Despite the observed association between OSA and adverse cardiovascular outcomes, the underlying pathophysiological mechanisms remain unclear. In this proposal, the investigators aim to elucidate the relationship between OSA and composition of coronary atherosclerotic plaques.

Inclusion Criteria:

• Angiogrqaphically documented coronary artery disease
• De novo lesion
• Native coronary artery

Exclusion Criteria:

• known OSA
• intubation and mechanical ventilation
• electrical instability with a high risk of malignant ventricular arrhythmia
• cardiogenic shock
• previous coronary artery bypass surgery
• chronic renal failure on dialysis
• inability to give informed consent

Patients aged 21 to 80 years who are scheduled to undergo either an elective, urgent or emergent diagnostic coronary angiography are eligible