Holter monitor identifies sleep apnea
Sleep apnea may be diagnosed simply by using a Holter monitor during the night. Sleep-disordered breathing (sleep apnea syndrome) is fairly common, especially among patients with coronary heart disease or hypertension (high blood pressure). Sleep apnea is, unfortunately, not simple to diagnose and it is estimated that 80-90% of all cases remain undiagnosed. This is clearly a problem as sleep apnea has been linked to an increased risk of heart attack, stroke, angina, ventricular arrhythmias, hypertension, and decreased heart rate variability. The interrupted sleep pattern characterizing sleep apnea can result in an increased risk of accidents, depression, anxiety, memory loss, and diminished sexual function.Diagnosis involves as overnight stay in a sleep-testing laboratory where the patient is hooked up to a polysomnograph during sleep. The polysomnograph continuously records such variables as brain waves, eye movements, muscle activity, heart rate, and blood oxygen level. Some equipment even produces a snoring index.
Researchers at the Washington University School of Medicine now propose that a relatively simple Holter monitor recording done overnight may be useful as a screening tool for sleep apnea. Their study involved 57 patients 33 of which had been diagnosed with sleep apnea through polysomnography. By examining the patients' Holter monitor recordings the researchers were able to identify all patients who DID NOT have sleep apnea (100% sensitivity). They also found that all patients, whose change in heart rate during an apnea episode were equal to or exceeded 20 beats/minute for at least 20% of the total recording time, had significant obstructive sleep apnea. Overall, they were able to identify correctly 33% of all patients with a polysomnographic diagnosis of sleep apnea.The researchers believe that nighttime Holter monitor recordings may be useful in screening for sleep apnea and other sleep-related disorders such as restless leg syndrome. They do point out that test results may be misleading for patients with major autonomic dysfunction as well as for those who take beta-blockers or have frequent arrhythmias.