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TIME-COURSE OF SLEEP DISORDERED BREATHING IN PATIENTS WITH ACUTE CORONARY SYNDROMES
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Ahmed S BaHammam, FRCP, FCCP, Associate Professor Sleep Disorders Center, College of Medicine, King Saud University, Riyadh, Saudi Arabia, Abdullah Al-Mobeireek,FRCPC, FCCP
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ashammam{at}awalnet.net.sa Ahmed S BaHammam, FRCP, FCCP, et al.
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To the Editor: We read with great interest the article by Skinner and colleagues (1) (January 2005). The time-course of sleep disordered breathing (SDB) in patients with acute coronary syndromes (ACS) has not been explored systematically before. The study revealed that patients with ACS had high prevalence of SDB despite low body mass index (BMI) and low Epworth sleepiness scale (ESS). Moreover, the study demonstrated high false- positive results at 6 weeks follow up. We studied 50 consecutive patients with first-ever acute myocardial infarction or unstable angina admitted to CCU once the patient’s condition was stable. All patients underwent full overnight polysomnography (PSG) 3.1 ± 2.4 days after the acute event. Patients with an AHI>10 hour (n=21), then underwent repeat PSG in the sleep disorders center (SDC), 6 months later. BMI and ESS of the studied group were comparable to that of Skinner et al 1, 26.9 ± 0.8 kg/m2 and 4.2 ± 0.6 respectively (mean ± SE). Fifty six percent of the studied group had an AHI>10 hour, 44% had an AHI>20/hour and 34% had an AHI>30 hour. AHI was 23.1 ± 3.6/hour. AHI was divided into obstructive apnea index (OAI) and central apnea index (CAI). OAI was 20.3 ± 3.2 and CAI was 3.9 ± 0.8. Cheyne-Stoke respiration (CSR) lasting more than 10% of total sleep time was documented in 6 patients. Ejection fraction was significantly lower in the group who had CSR compared to those who did not. Interestingly, AHI, OAI and the mean duration of obstructive apneas did not change significantly over the 6 months. On the other hand, CAI and central apnea duration were significantly lower in the second assessment. Our results concur with Skinner et al (1) and others (3-6) who demonstrated that ACS patients show a high prevalence of SDB. Moreover, the finding that obstructive apneic episodes persisted at 6 months after the acute cardiac event, when patients were clinically stable, suggests that such episodes occurred in these patients prior to the onset of the acute event, whereas central apnea and CSR may be a consequence of ACS. Few possible explanations may clarify the differences between our results and Skinner et al (1). The authors already mentioned some the possibilities for the false positive results in their paper like the fact that patients are more likely to lie supine in the CCU setting compared to their own home. We controlled for this factor by performing the repeat study in the SDC. Another possible confounder is the administration of drugs that may affect respiration like narcotics and hypnotics. While we used a drug free period of at least 48 hours, Skinner et al (1) used 12 hours only. Thirdly, EEG monitoring was not done in Skinner et al paper (1). Therefore, sleep efficiency could not be assessed. Finally, studies like ours may have the risk of “regression towards the mean” phenomenon (7), which means that if a subgroup with a higher AHI is tested a second time, it is likely that the AHI may be lower at the second investigation. Obviously, more studies with larger number of patients and stringent control for possible confounders are required to clarify the relationship between ACS and SDB. References: 1. Skinner MA, Choudhury MS, Homan SDR, Cowan JO, Wilkins GT, Taylor DR. Accuracy of monitoring for sleep-related breathing disorders in the coronary care unit. Chest 2005; 127: 66-71. 2. BaHammam A, Al-Mobeireek A, Al-Nozha M, Al-Tahan A, Bin Saeed A. Behavior and Time-Course of Sleep Disordered Breathing in Patients with Acute Coronary Syndromes. Int J Clin Pract 2005; 59 (in press). 3. Hung J, Whitford EG, Parsons RW, et al. Association of sleep apnea with myocardial infarction in men. Lancet 1990; 336: 261-264. 4. Moruzzi P, Sarzi-Braga S, Rossi M, Contini M. Sleep apnoea in ischemic heart disease: differences between acute and chronic coronary syndromes. Heart 1999; 82: 343-347. 5. De Olazabal JR, Miller Mj, Cook WR, Mithoefer JC. Disordered breathing and hypoxia during sleep in coronary artery disease. Chest 1982; 82: 548- 552. 6. Mooe T, Rabben T, Wiklund U, Franklin KA, Eriksson P. Sleep-disordered breathing in men with coronary artery disease. Chest 1996; 109: 659-663. 7. J M Bland, D G Altman. Statistic Notes: Regression towards the mean. BMJ 1994;308:1499. |
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