WEDNESDAY, Oct. 24 (HealthDay News) -- In a surprising finding, people with sleep apnea appear to suffer less heart damage during a nonfatal heart attack than those without the condition, researchers report.

In obstructive sleep apnea, a person's breathing is disrupted during sleep because their airway becomes narrowed or blocked, causing pauses or decreases in air flow.

Although the new findings do not contradict the widely accepted view that sleep apnea is a risk factor for heart disease that can lead to a heart attack, they do suggest that obstructive sleep apnea can provide some heart protection in the event of a heart attack, explained lead investigator Dr. Neomi Shah, associate director of the pulmonary sleep lab at Montefiore Medical Center in New York City.

One heart expert called the finding "intriguing."

"It is counter-intuitive to what we would expect," said Dr. Howard Weintraub, a clinical associate professor in the department of medicine at NYU Langone Medical Center, in New York City. He theorized that sleep apnea might reduce the damage from heart attack "due to patients [with apnea] being accustomed to lower levels of oxygen in their blood during apneic periods."

In the study, the Montefiore team looked at more than 130 heart attack patients. Their median age was 58, and 35 percent had obstructive sleep apnea.

People with the condition were significantly older than those without it (62 years versus 52 years, on average), the study authors noted in a Montefiore news release.

Patients with obstructive sleep apnea had lower blood levels of Troponin-T, a marker for heart cell death that accurately predicts heart attack severity, and lower levels of an enzyme that indicates injury or stress in heart muscle, the investigators found.

The study was published Oct. 24 in the journal Sleep and Breathing.

Although the study found an association between having sleep apnea and experiencing less heart damage during a nonfatal attack, it did not prove a cause-and-effect relationship.

Another cardiologist believes the study might have some weaknesses.

"Of the patients screened for the study, only about 1 percent ... were enrolled in the registry; this is a very low number for most studies," noted Dr. Stephen Green, associate chairman of the department of cardiology at North Shore University Hospital in Manhasset, N.Y.

He also pointed out that the study "says that patients with sleep apnea have smaller heart attacks than those without sleep apnea. It does not say that people with sleep apnea have less heart attacks, and cannot say this."

Weintraub agreed.

"Sleep apnea may potentially result in more frequent, but less damaging, heart attacks," he said. Therefore, he added, "even in light of this information, I would strongly endorse appropriate treatment of sleep apnea."

Green also noted that "the diagnosis of [heart attack] was made by Troponin levels, which may be oversensitive, and especially in patients having breathing problems. It is not clear that heart doctors would consider all of the Troponin elevations to be heart attacks."

More information

The U.S. National Heart, Lung, and Blood Institute has more about sleep apnea.