A new study by Mayo Clinic researchers has suggested that obstructive sleep apnea (OSA) - and in particular, the low nighttime oxygen saturation of the blood it causes - may be a risk factor for sudden cardiac death (SCD).
OSA is a condition that disrupts breathing during sleep and is associated with obesity. The new study identified OSA as one of two traits that increase the risk of SCD.
The other is age - patients who are 60 years old or older.
If further studies confirm these findings, OSA would join established risk factors such as smoking, obesity, high cholesterol and high blood pressure.
Doctors have suspected for years that OSA might be implicated in SCD because of evidence that low oxygen alters the blood vessels in a way that promotes heart disease.
Mayo Clinic cardiologist Apoor Gami, M.D., the lead author of the study, said that this is the first large study to rigorously test the hypothesis.
Virend Somers, M.D., Ph.D., the study's principal investigator, said: "Nighttime low oxygen saturation in the blood is an important complication of obstructive sleep apnea".
"Our data showed that an average nighttime oxygen saturation of the blood of 93 percent and lowest nighttime saturation of 78 percent strongly predicted SCD, independent of other well-established risk factors, such as high cholesterol.
These findings implicate OSA, a relatively common condition, as a novel risk factor for SCD," Somers added.
The researchers reviewed data from 10,701 consecutive adults who underwent an initial diagnostic sleep laboratory analysis session between 1987 and 2003.
During a follow-up period of up to 15 years, researchers assessed cases where patients had sudden cardiac arrest, and either died (SCD) or were resuscitated, in relationship to the presence of OSA and other data, including nighttime levels of oxygen saturation in the blood.
Results showed that during an average follow-up of 5.3 years, 142 patients had suffered SCD and either died or were resuscitated.
The study has been presented at the American Heart Association's Scientific Sessions 2008 in New Orleans.