(HealthDay News) — ST-elevation myocardial infarction (STEMI) patients treated with oxygen endure 25–30% more cardiovascular damage than patients not given oxygen. These findings are being presented at the annual meeting of the American Heart Association, held from November 15–19 in Chicago.

For the study, researchers had paramedics in Melbourne randomly assign STEMI patients to either receive or not receive oxygen during treatment. Lanyards hung around the patients’ necks by the ambulance crews let hospital workers know who should receive oxygen during the remainder of their care, and who should not. The study included 441 STEMI patients.

In those who received oxygen, the researchers found elevated levels of creatine kinase and troponin. The levels of these enzymes were 25% higher in those who were given oxygen compared to those who didn’t get oxygen. About a third of the participants returned six months following their STEMI to undergo cardiac magnetic resonance imaging (MRI). The MRIs revealed that people who got oxygen had 30% more damage to their heart muscle than those who did not, lead investigator Dion Stub, MBBS, an interventional cardiologist at St. Paul’s Hospital in Vancouver, Canada, told HealthDay.

The researchers also found that oxygen made no difference in symptoms felt by the patients in their study – an unusual result, given that oxygen most often is provided during a STEMI because it is believed to reduce chest pain. “They certainly felt no better,” Stub said. “There was no difference in pain.” People given oxygen also had increased levels of complications, including repeat STEMIs, major bleeding, and irregular heart rhythms, he said. Death rates six months after treatment were similar – 3.8% for patients with oxygen and 5.9% for those who did not receive oxygen.

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