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Supplemental oxygen increased myocardial injury, infarct size in patients with STEMI
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CHICAGO — Patients with STEMI and normal oxygen levels who received supplemental oxygen before and during hospitalization exhibited signs of increased myocardial injury and infarct size, according to research presented at the American Heart Association Scientific Sessions.
In the multicenter, prospective AVOID trial, 638 patients were randomly assigned to 8 L/min supplemental oxygen or no supplemental oxygen. All patients were randomly assigned by paramedics before hospitalization and had symptoms indicating the presence of STEMI for fewer than 12 hours and normal oxygen levels (saturation ≥94%). Oxygen was administered before hospitalization, through the ED and treatment in the coronary cath lab. Patients in the control group did not receive oxygen unless their saturation levels fell below 94%.
The primary endpoint analysis included 441 patients with confirmed STEMI (218 received supplemental oxygen). The primary endpoint was myocardial infarct size, as indicated by creatinine kinase and troponin I levels measured during the first 3 days of admission. Secondary endpoints included improvements in ECG results, survival to hospitalization, revascularization and repeat MI. Researchers also evaluated results from cardiac MRI administered to 139 patients at 6 months.
Dion Stub
Mean peak creatinine kinase was significantly higher among patients who received supplemental oxygen (1,948 U/L vs. 1,543 U/L; P=.01), suggesting increased myocardial injury among patients who received oxygen, Dion Stub, MBBS, PhD, FRACP, of Baker IDI Heart and Diabetes Institute in Melbourne, Australia, said during a presentation. Area under the curve analysis yielded similar results (P=.04).
Mean peak troponin I did not differ significantly between the groups (oxygen, 57.4 mcg/L vs. no oxygen, 48 mcg/L; P=.18), with similar results from area under the curve analysis (P=.12).
Recurrent MI was significantly more common at discharge among patients assigned supplemental oxygen (5.5% vs. 0.9%; P=.006). The same increase was observed with cardiac arrhythmia (40.4% vs. 31.4%; P=.05). However, Stub said the AVOID trial was not sufficiently powered to assess major adverse cardiac events. Infarct size at 6 months also was greater among patients assigned supplemental oxygen who had evaluable cardiac MRI data (20.3 g vs. 13.1 g; P=.04).
Despite prior observations that oxygen administration might result in symptomatic benefits for patients, there was no difference in severity of pain or the administration of painkillers between the groups, Stub said.
“In patients with STEMI who are not hypoxic, there was the suggestion that oxygen is potentially increasing myocardial injury, recurrent MI and major cardiac arrhythmia, and may be associated with greater infarct size at 6 months,” Stub said. “These findings certainly need to be confirmed in large randomized trials that are powered for hard clinical endpoints. But the AVOID study investigators question the current practice of giving oxygen to all patients and, certainly, those who have normal oxygen levels.” – by Adam Taliercio
For more information:
Stub D. Abstract #18232. Presented at: American Heart Association Scientific Sessions; Nov. 15-19, 2014; Chicago.
Disclosure: The Alfred Hospital Foundation, FALCK Foundation and Paramedics Australia funded the study. The researchers report no relevant financial disclosures.
Perspective
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Kim Allan Williams, MD
The AVOID study results are consistent with the basic science indicating that oxygen increases vascular tone systemically and in the coronary bed. This could result in decreased blood flow delivery, such that the administered oxygen may actually result in less oxygen delivery to ischemic myocardium. If that is the case, it stands to reason that administration of oxygen tended to increase infarct size as measured by MRI and increase biomarkers associated with the infarct.
AVOID used very high-flow oxygen, estimated at 6 to 8 liters per minute. This differs from our usual clinical practice: no supplemental oxygen if the patient is normoxic, and typically using 2 to 4 liters per minute of oxygen if there is hypoxia. That lower level of oxygen administration remains to be examined.
Ultimately, I think these results are hypothesis-generating, and we would benefit from further studies. But there may indeed be a sea change, with the routine use of nasal oxygen going the way of routine use of nitroglycerin and morphine (using them very selectively since there may be harm in some patients). We look forward to more trials that specifically examine lower levels of oxygen administration, and “avoid” the high flows that are unlikely to benefit our patients.
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