WASHINGTON (Reuters) - A drug once commonly used for emphysema and other forms of chronic obstructive pulmonary disease may raise the risk of heart death by a third, U.S. researchers reported on Tuesday.

The drug, called ipratropium, is made by Boehringer Ingelheim Pharmaceuticals Inc under the brand names Atrovent and Combivent. It has largely been replaced by Pfizer Inc's Spiriva. It prevents bronchospasms, attacks in which the airways narrow, making breathing difficult.

"This medication may be having some systemic cardiovascular effect that is increasing the risk of death in COPD patients," said Todd Lee of Northwestern University in Chicago, who led the study.

Lee's team found that military veterans with recently diagnosed COPD who used Atrovent or Combivent were 34 percent more likely to die of a heart attack or arrhythmia than COPD patients using only a similar product called albuterol, or those who did not take any drugs.

Writing in the Annals of Internal Medicine, the researchers said they looked at the cause of death of 145,000 veterans with newly diagnosed COPD from 1999 to 2003.

Lee said doctors and patients should be aware of the potential risk.

COPD is an umbrella term for respiratory diseases including emphysema and chronic bronchitis and is mostly caused by smoking. An estimated 12 million people in the United States have COPD, the fourth-leading cause of death.

"The safety of drugs for COPD patients has flown under the radar," Lee said.

In March the U.S. Food and Drug Administration said another COPD drug called Spiriva, marketed by Pfizer Inc and Boehringer Ingelheim, may increase the risk of stroke.

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