Interrupted sleep and arrhythmias
CLEVELAND, OHIO. Abnormal breathing during sleep or sleep-disordered breathing (SDB) is fairly common among older men. There are three main varieties of SDB – central sleep apnea (CSA), obstructive sleep apnea (OSA), and hypoxia. CSA is defined as cessation of airflow (breathing) for 10 seconds or longer without an identifiable respiratory effort during the period of airflow cessation. CSA occurs when the brain forgets to send a signal to the chest muscles and diaphragm, which usually forces air in and out of the lungs, and thus breathing ceases until the brain "wakes up" again. OSA is closely related to but much more common than CSA and occurs when the brain sends the signal to breathe and the muscles obey, but the flow of air is obstructed by an overly relaxed tongue or throat muscles. Snoring is often a cardinal feature of OSA. Hypoxia involves a deficiency in oxygen saturation, which can lead to SDB.

Researchers at Case Western Reserve University School of Medicine now report that there is a distinct association between arrhythmias and SDB. Their study is part of the Outcomes of Sleep Disorders in Older Men study which took place between the years 2003 and 2005 and involved 2917 men aged 65 years or older. The men all underwent in-home sleep studies using a portable polysomnography unit (Safiro, CompuMedics Ltd). The severity of SDB was expressed by the RDI (respiratory disturbance index), which is the number of OSAs, CSAs and hypoxia episodes occurring per hour of sleep.

The researchers observed a strong correlation between the occurrence of atrial fibrillation (AF) and an elevated RDI. The association was particularly evident in the case of CSA where subjects in the highest CSA quartile had a 2.7 times increased prevalence of AF. A correlation between RDI and complex ventricular ectopy (CVE) was also observed. CVE was defined as ventricular bigeminy, trigeminy, quadrigeminy or nonsustained ventricular tachycardia. Patients with high-grade OSA were 37% more likely to experience CVE than were reference patients. No significant relationship was observed between CSA and CVE frequency.

The presence of hypoxia did not correlate with AF episodes but did increase the frequency of CVEs with a 62% increased risk of CVE if 10% or more of total sleep time occurred with less than 90% oxygen saturation. The researchers found no correlation between SDB and premature atrial contractions (PACs) occurring 5 or more times an hour. They also noted that the associations between CSA and AF were significantly stronger in the 94% of patients who did not have heart failure. They conclude that the strong association between CSA and AF suggests that CSA may be a sensitive marker of underlying abnormalities in autonomic or cardiac dysfunction associated with AF.

Mehra, R, et al. Nocturnal arrhythmias across a spectrum of obstructive and central sleep-disordered breathing in older men. Archives of Internal Medicine, Vol. 169, No. 12, June 22, 2009, pp. 1147-55

Editor's comment: It is interesting that this study found only a weak correlation between OSA and afib, but quite a strong one between CSA and afib. This may explain why some afibbers using a CPAP machine have not found it helpful. Of course, if CSA and OSA coexist in the same patient, which is often the case, then a CPAP machine may be useful.