Key Point

Sleep-disordered breathing is common in those presenting with an acute cardiovascular event. Patients with obstructive sleep apnea-hypopnea syndrome are at increased risk for cardiac rhythm disturbances and ST-segment depression.

DUNEDIN, NEW ZEALAND, AND MADRID—Two studies in Chest have once again shown an association between sleep-disordered breathing and acute cardiovascular episodes. In one of the studies, D. Robin Taylor, MD, and colleagues found that sleep-disordered breathing was common in 26 patients admitted to the coronary care unit with unstable angina, acute myocardial infarction, or left ventricular or congestive heart failure.¹

Based on conservative diagnostic criteria, sleep studies completed soon after coronary care unit admission revealed a 50% rate of sleep-disordered breathing in the study population. However, a second round of sleep studies performed at least six weeks later showed a substantially lower but still disturbingly high 28% rate.

“That is because we had a significant number of false-positive results in the first round, at least as far as chronic sleep-disordered breathing was concerned,” explained Dr. Taylor in an interview with Pulmonary Reviews. “Because of that possibility, the results of sleep studies should not be relied upon in patients like ours when they are acutely ill,” recommended Dr. Taylor, Professor of Respiratory Medicine at Dunedin School of Medicine in New Zealand.

The second study, by Alonso-Fernández and colleagues, detected higher rates of cardiac rhythm disturbances and ST-segment depression in 21 patients with obstructive sleep apnea-hypopnea syndrome (OSAHS) than in 12 snorers without hypersomnolence and 15 healthy controls.² Moreover, added the investigators, ST-segment changes are related to sympathetic tone and sleep fragmentation, “whereas most of the rhythm disturbances in patients with OSAHS are associated with sleep fragmentation, nocturnal hypoxemia, and catecholamine excretion.”

DIAGNOSE WITH MORE RIGOROUS CRITERIA

After stabilization, Dr. Taylor’s patients underwent an overnight, in-hospital sleep study with a portable device that has been validated against full polysomnography for the diagnosis of OSAHS.³ The sleep study was repeated at home in 18 patients a mean of 74 days later.

Sleep-disordered breathing, when conservatively defined as an apnea-hypopnea index score of 15 or greater, was identified in 13 of the 26 patients in the first sleep study; the investigators diagnosed obstructive sleep apnea in 12 of these cases and central sleep apnea in one. The second sleep study confirmed sleep-disordered breathing in only five of 18 patients, and the diagnosis was obstructive sleep apnea each time.

When sleep-disordered breathing was defined as an apnea-hypopnea index score of 5 or greater, the incidence in the first and second studies rose dramatically to 73% and 83%, respectively. Thus, concluded Dr. Taylor’s group, “it is probably wiser to arrive at a diagnosis and to offer treatment based on the more rigorous criteria.”

OSAHS AND ARRHYTHMIAS

The conclusions of Dr. Alonso-Fernández and colleagues were based mainly on the findings of three tests: overnight polysomnography, 24-hour Holter monitoring, and serial analysis of urine catecholamines. Testing indicated that nocturnal and daytime sinus bradycardia, pauses, premature supraventricular beat, supraventricular tachycardia, couplets, bigeminy, ST-segment depression, and daytime sinus tachycardia were more likely in the OSAHS patients than in the snorers or controls.

In the OSAHS group, statistical analysis associated ST-segment depression with the arousal index and daytime urine epinephrine levels, while nocturnal sinus bradycardia and supraventricular tachycardia were related to minimum arterial oxygen saturation. Urine epinephrine and norepinephrine levels correlated with sinus and supraventricular arrhythmias.

“As arrhythmias described in patients with OSAHS are generally benign, it is difficult to evaluate the implications of these findings,” the investigators pointed out. “There are no data evaluating mortality in patients with OSAHS and bradyarrhythmias, nor is there any information on the natural course or evolution of heart blockage in this group.”

Further studies will be required to determine the cardiovascular morbidity and mortality rates of untreated and undertreated patients with OSAHS-related cardiac arrhythmias, added the investigators. “However, arterial hypertension … in addition to rhythm disturbances, may be the most deleterious cardiovascular effects of OSAHS,” they suggested.

—Timothy Begany

References
1. Skinner MA, Choudhury MS, Homan SDR, et al. Accuracy of monitoring for sleep-related breathing disorders in the coronary care unit. Chest. 2005;127:66-71.
2. Alonso-Fernández A, García-Río F, Racionero MA, et al. Cardiac rhythm disturbances and ST-segment depression episodes in patients with obstructive sleep apnea-hypopnea syndrome and its mechanisms. Chest. 2005;127:15-22.
3. Dingli K, Coleman EL, Vennelle M, et al. Evaluation of a portable device for diagnosing the sleep apnoea/hypopnoea syndrome. Eur Respir J. 2003;21:253-259.

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