Study objectives: To evaluate the frequency of sleep-disordered breathing (SDB) in patients presenting with acute cardiovascular events.
Design: Repeat observational study.
Setting: Coronary care unit of a university hospital.
Patients: A total of 26 patients presenting with unstable angina, myocardial infarction, or left ventricular failure.
Measurements: Level 3 portable sleep study performed at the time of acute presentation (study 1; 26 patients) and again ≥ 6 weeks later (study 2; 18 patients).
Results: SDB (apnea-hypopnea index ≥ 15) was identified in 13 of 26 patients (50%) during study 1. One patient had central sleep apnea. Of the 18 who completed the two studies, SDB was confirmed in 10 of 18 patients (56%) during study 1 but in only 5 of 18 patients (28%) during study 2. All five of those patients had obstructive sleep apnea (OSA). Six patients were deemed to have false-positive results for SDB at follow-up, and one patient was deemed to have a false-negative result. Detailed analysis suggested that supine posture during study 1 may have contributed to the high false-positive rate, even though only three of six patients fulfilled the criteria for positional OSA.
Conclusions: SDB occurs commonly in patients presenting with an acute cardiovascular event. Consideration of the diagnosis of SDB is an important strategy for secondary prevention. However, our findings indicate that SDB abnormalities may be transient. Sleep studies to investigate SDB as a potential risk factor for cardiovascular morbidity should be carried out when the patient is clinically stable.