Obstructive sleep apnea and risk of cardiovascular events and all-cause mortality: a decade-long historical cohort study

Background — Obstructive sleep apnea (OSA) has been reported to be a risk factor for cardiovascular (CV) disease. Although the apnea-hypopnea index (AHI) is the most commonly used measure of OSA, other less well studied OSA-related variables may be more pathophysiologically relevant and offer better prediction. The objective of this study was to evaluate the relationship between OSA-related variables and risk of CV events.

Methods and Findings — A historical cohort study was conducted using clinical database and health administrative data. Adults referred for suspected OSA who underwent diagnostic polysomnography at sleep laboratory at St. Michael’s Hospital (Toronto, Canada) between 1994 and 2010 were followed through provincial health administrative data (Ontario, Canada) until May 2011 to examine the occurrence of a composite outcome (myocardial infarction, stroke, congestive heart failure, revascularization procedures, or death from any cause). Cox regression models were used to investigate the association between baseline OSA-related variables and composite outcome controlling for traditional risk factors. The results were expressed as hazard ratios (HRs) and 95% CIs; for continuous variables, HRs compare the 75th and 25th percentiles. Over a median follow-up of 68 months, 1,172 (11.5%) of 10,149 participants experienced our composite outcome. In a fully adjusted model, other than AHI OSA-related variables were significant independent predictors: time spent with oxygen saturation <90% (9 minutes vs. 0; HR=1.5, 95% CI: 1.25–1.79), sleep time (4.9 vs. 6.4 hours; HR=1.2, 95% CI: 1.12–1.27), awakenings (35 vs. 18; HR=1.06, 95% CI: 1.02–1.10), periodic leg movements (13 vs. 0/hour; HR=1.05, 95% CI: 1.03–1.07), heart rate (70 vs. 56 bpm; HR=1.28, 95% CI: 1.19–1.37), and daytime sleepiness (HR=1.13, 95% CI: 1.01–1.28). The main study limitation was lack of information about CPAP adherence.

Conclusion — OSA-related factors other than AHI were shown as important predictors of composite CV outcome and should be considered in future studies and clinical practice.