Obstructive sleep apnea-related factors other than apnea-hypopnea index appear to be important predictors of future CV events.
“By focusing exclusively on [apnea-hypopnea index], clinicians and researchers may have missed opportunities to better risk-stratify patients using other [obstructive sleep apnea]-related variables,” Tetyana Kendzerska, MD, MSc, of the University of Toronto, and colleagues wrote in a recent study.
The researchers conducted a historical cohort study of all adults who underwent a first diagnostic sleep study at St. Michael’s Hospital in Toronto between September 1994 and December 2010. The study included 10,149 adults (62% men; mean age, 49.9 years). Median follow-up was 68 months.
The primary outcome, a composite of MI, stroke, congestive HF, revascularization or all-cause mortality, occurred in 11.5% of participants. Apnea-hypopnea index was associated with the primary outcome in a univariate analysis (HR=1.49; 95% CI, 1.42-1.57), but after controlling for CV risk factors, the magnitude of association was attenuated and there was no difference across obstructive sleep apnea severity groups (P>.2).
The following factors were significant predictors for the primary outcome, according to a fully adjusted model:
- Time spent with oxygen saturation <90% (9 minutes vs. 0 minutes; HR=1.5; 95% CI, 1.25-1.79).
- Sleep time (4.9 hours vs. 6.4 hours; HR=1.2; 95% CI, 1.12-1.27).
- Awakenings (35 vs. 18; HR=1.06; 95% CI, 1.02-1.1).
- Periodic leg movements (13/hour vs. 0/hour; HR=1.05; 95% CI, 1.03-1.07).
- Heart rate (70 bpm vs. 56 bpm; HR=1.28; 95% CI, 1.19-1.37).
- Daytime sleepiness (HR=1.13; 95% CI, 1.01-1.28).
The identification of time spent with oxygen saturation <90% as the strongest predictor of CV is consistent with other research, Kendzerska and colleagues wrote.
“Our finding that a measure of hypoxia predicts CV risk is consistent with emerging evidence in both animal models and humans that intermittent hypoxia may be a crucial mechanistic link whereby [obstructive sleep apnea] causes oxidative stress, metabolic derangement and endothelial damage,” they wrote.
Recordings of the risk factors should not be difficult to obtain, even in home-based settings, they noted.
Disclosure: The researchers report no relevant financial disclosures.