Sleep Disorder May Cause Heart Attacks

ROCHESTER, Minn., Feb. 11, 2003 -- An interruption in normal breathing patterns during sleep which is often seen in heart failure patients may contribute to heart failure rather than just being a result, according to findings of a Mayo Clinic collaborative study published this week in Circulation: Journal of the American Heart Association.

"The goal of medicine is to not just treat symptoms of illness, but to find underlying causes," says Virend Somers, M.D. Ph.D., a Mayo Clinic cardiologist and one of the study's authors. "In this instance we are now finding that central sleep apnea, which has been previously understood as a symptom of heart failure, may contribute to the development of heart failure in people at risk."

Heart failure is the most common cause of hospitalization in people over age 65, and people who reach age 40 have a 1-in-5 chance of eventually developing heart failure. Symptoms include fatigue, shortness of breath and swelling in the legs and abdomen.

Sleep apnea is an interruption of airflow for 10 seconds or more during sleep, which can cause significantly lower oxygen levels in the bloodstream. Patients with severe apnea have 30 or more of these episodes per hour, while those with mild apnea stop breathing at least 15 times. In obstructive sleep apnea (OSA) the chest and abdomen move normally, but a blocked airway prevents the patient from breathing. Central sleep apnea (CSA) differs in that the patient's airway is not obstructed, but the body's breathing reflex is periodically interrupted so there is no chest and abdomen movement.

The Mayo Clinic study, conducted in cooperation with Paola Lanfranchi, M.D., and colleagues at the Fondazione Salvatore Maugeri in Veruno, Italy, evaluated sleep patterns in 47 patients whose heart pumping function was impaired but who had not yet progressed to full-blown heart failure. Over half (55 percent) had CSA (36 percent severe) and another 5 percent had OSA. Those with CSA also had more evidence of heart arrhythmias than patients with normal breathing patterns.

"Previous studies had shown that heart failure patients often have central sleep apnea, and that those with central apnea are more likely to develop abnormal and dangerous heart rhythms," says Dr. Somers. "Now we know many patients have central apnea and associated heart rhythm abnormalities long before they develop any outward manifestation of heart pumping dysfunction."

Dr. Somers says with the identification of CSA as a possible risk factor for heart failure, further research is needed to develop effective treatments. "We have good treatments for obstructive apneas to help keep the airway open, but central apnea treatments are still mostly experimental. Studies of those therapies are under way, however, and these findings are a good first step that should spur efforts to diagnose and treat central apneas, and hopefully prevent further damage in patients like these."