Effect of Continuous Positive Airway Pressure on the Incidence of Hypertension and Cardiovascular Events in Nonsleepy Patients With Obstructive Sleep Apnea: A Randomized Controlled Trial
What is the effect of continuous positive airway pressure (CPAP) treatment on the incidence of hypertension or cardiovascular events in a cohort of nonsleepy patients with obstructive sleep apnea (OSA)?
The authors reported the results of a multicenter, parallel-group, randomized, controlled trial in 14 teaching hospitals in Spain between May 2004 and May 2006, focusing on patients with significant OSA, but without symptoms of daytime sleepiness. Subjects were free of cardiovascular disease and without daytime sleepiness (Epworth Sleepiness Scale [ESS] score of 10 or lower), referred for sleep study to evaluate observed apnea or snoring. Entry criteria were apnea-hypopnea index of 20/hour or greater. Patients were randomized to CPAP treatment or none, and the primary endpoint was incident hypertension (blood pressure >140/90 mm Hg), or cardiovascular event (nonfatal myocardial infarction, nonfatal stroke, transient ischemic attack, hospitalization for unstable angina or arrhythmia, heart failure, or cardiovascular death). Follow-up was for a median of 4 years.
Out of 725 consecutive subjects enrolled, follow-up was complete in 723, in whom there were 68 patients with new hypertension and 28 cardiovascular events in the CPAP group, and 79 patients with new hypertension and 31 cardiovascular events in the control group. This made for a hypertension or cardiovascular event incidence density rate of 9.20 per 100 person-years (95% confidence interval [CI], 7.36-11.04) in the CPAP group and 11.02 per 100 person-years (95% CI, 8.96-13.08) in the control group. The incidence density ratio was 0.83 (95% CI, 0.63-1.1; p = 0.20). For subjects with CPAP adherence >4 hours/night group versus control group, there was a significant reduction in incident hypertension and cardiovascular events with an adjusted incident density ratio of 0.69 (0.50-0.94); p = 0.02.
The authors concluded that in patients with OSA without daytime sleepiness, the prescription of CPAP compared with usual care did not result in a statistically significant reduction in the incidence of hypertension or cardiovascular events. The authors further opined that the study may have had limited power to detect a significant difference.
Although this study is reported as a ‘negative’ study, one must keep in mind three things. First, an underpowered study can fail to reach statistical significance, even though there is a benefit. The results of this study clearly trended in a positive direction. Second, there was a significant improvement in outcomes seen in the subgroup that had the most compliance with CPAP (only 4 hours per night). Third, and most frustratingly, this study used incident hypertension as an endpoint. Trying to evaluate the benefit of treating a very long-term condition (sleep apnea), on a very long-term outcome (incident hypertension) in only a 4-year study is fraught with limitations. This study’s limitations suggest that further or larger studies may be needed to determine the efficacy of CPAP in preventing cardiovascular events.
Keywords: Myocardial Infarction, Stroke, Ischemic Attack, Transient, Follow-Up Studies, Sleep Apnea Syndromes, Incidence, Snoring, Polysomnography, Heart Failure, Spain, Continuous Positive Airway Pressure, Confidence Intervals, Hypertension, Sleep Apnea, Obstructive, Patient Compliance
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