Routine oxygen therapy was not found to be associated with improved cardiovascular outcomes in normoxemic patients (ie, ≥90% oxygen [O2] saturation) with confirmed myocardial infarction (MI), according to a study published in JACC: Cardiovascular Interventions.
Oxygen therapy has been part of the standard of care for patients experiencing acute MI for decades, despite a lack of strong evidence supporting the benefits of this approach for cardiovascular outcomes. Recent guideline changes recommend O2 therapy in patients with hypoxia only. However, the optimal course of O2 therapy in patients with a low to normal saturation range (ie, 90%-94%) remains unclear.
This study is a subanalysis of the multicenter, registry-based, open-label DETermination of the role of Oxygen in suspected Acute Myocardial Infarction randomized clinical trial (DETO2X-AMI; n = 6629; ClinicalTrials.gov identifier: NCT01787110). In the DETO2X-AMI trial, patients who were normoxemic with suspected MI were randomly assigned to receive O2 therapy at 6L/min for 6 to 12 hours (n = 2485) or ambient air (n = 2525). The subanalysis examined the data of 5010 participants with confirmed MI (≥30 years; median age, 68.0 years; 72.3% men) from this trial. Participants were divided according to baseline O2 saturation into low-normal (n = 836; 16.7%) and high-normal (95%-100% O2 saturation; n = 4174; 83.3%) groups.
The primary outcome was a composite endpoint of all-cause mortality, hospitalization for heart failure (HF), or rehospitalization with MI, which was recorded after 1 year. Follow-up assessment, which occurred from 1 to 4 years, was included in the post hoc analysis to increase statistical power. Oxygen saturation was used as a covariate in the interaction analysis.
The composite endpoint (17.3% vs 9.5%, respectively; P <.001) and the individual component of hospitalization for HF (6.7% vs 2.6%, respectively; P <.01) were found to occur more often in the low- vs high-normal O2 saturation group. Participants who developed hypoxemia had the highest occurrence (23.6%) of the composite endpoint.
Irrespective of baseline saturation, O2 therapy was not associated with better outcomes when compared with ambient air for the composite endpoint (P =.79), or its individual components of all-cause mortality (P =.33), hospitalization for HF (P =.35), or rehospitalization with MI (P =.86).
Study limitations include an inability to measure the actual amount of O2 received by the patient and a possible misclassification of patients considered normoxemic.
“Oxygen saturation at baseline in the low-normal range was identified as an important independent marker of poor prognosis that was not affected by oxygen treatment,” noted the authors. They recommended that future research examine the impact of O2 therapy in specific patient groups, including those with HF or critical illness and individuals suffering cardiac arrest.
This work was supported by the Swedish Research Council [grant number VR20130307], the Swedish Heart-Lung Foundation [grant number HLF20130262, HLF20160688], and the Swedish Foundation for Strategic Research [grant number SSF KF10-0024]. Dr. Hofmann and Dr. Östlund report grants from the Swedish Research Council, and the Swedish Heart-Lung Foundation. Dr Hofmann was supported by the Stockholm County Council (clinical postdoctoral appointment). The funding agencies had no access to the study data and no role in trial design, implementation, or reporting.
James SK, Erlinge D, Herlitz J, et al; DETO2X-SWEDEHEART Investigators. Effect of oxygen therapy on cardiovascular outcomes in relation to baseline oxygen saturation [published online December 11, 2019]. JACC Cardiovasc Interv. December 2019. doi:10.1016/j.jcin.2019.09.016