Air Versus Oxygen In ST-elevation MyocarDial Infarction | Clinical Trial - AVOID

Description:

Supplemental oxygen is routinely used in the treatment of patients with suspected myocardial infarction (MI), and is considered a Class I indication by current guidelines. The current trial sought to compare supplemental oxygen therapy with no oxygen therapy in normoxic patients presenting with ST-segment elevation MI (STEMI).

Contribution to the Literature:  The AVOID trial showed that high-dose supplemental oxygen is not helpful and increases infarct size in normoxic patients presenting with STEMI and undergoing primary PCI.

Study Design

  • Randomized
  • Parallel

Patient Populations:

  • Paramedics assess patient
  • Symptoms of STEMI <12 hours
  • Oxygen saturation ≥94%
  • ST-elevation ≥2 contiguous ECG leads
  • Intended for PPCI

    Number of enrollees: 441
    Duration of follow-up: 6 months
    Mean patient age: 63 years
    Percentage female: 21%

Exclusions:

  • Oxygen saturation <94% on pulse oximeter
  • Oxygen administration prior to randomization
  • Altered conscious state
  • Planned transport to a nonparticipating hospital

Primary Endpoints:

  • Myocardial infarct size on cardiac enzymes
  • Mean peak creatine kinase
  • Mean peak troponin I
  • Area under curve of creatine kinase and troponin I

Secondary Endpoints:

  • ST-segment resolution (12-lead ECG)
  • Survival to hospital discharge
  • Major adverse cardiac events: death, MI, rehospitalization at 6 months
  • Myocardial infarct size on CMR at 6 months

Drug/Procedures Used:

Patients presenting with STEMI undergoing primary percutaneous coronary intervention (PPCI) and with baseline oxygen saturation of ≥94% were randomized in a 1:1 fashion to receive supplemental oxygen (8 L/min via face mask) or no oxygen. This was started in the emergency room and continued in the catheterization laboratory.

Principal Findings:

A total of 441 patients were randomized, 218 to oxygen and 223 to no oxygen. Crossover to oxygen from the no oxygen arm was observed in 7.7% (to 4 L/min). Baseline characteristics were fairly similar between the two arms. About 15% had diabetes. About 89% were Killip class I, and 35% had anterior MI on electrocardiogram (ECG). About 5% were in cardiogenic shock and 4% had experienced cardiac arrest. Oxygen saturation was higher in the oxygen therapy arm from time of arrival in the hospital to 12 hours post-procedure. A drug-eluting stent (DES) was implanted in 51% of patients, and thrombus aspiration was performed in 48%. The median door-to-balloon time was 55 minutes, and median ischemic time was 155 minutes.

Mean peak creatine kinase level was significantly higher in the oxygen arm compared with the no oxygen arm (1,948 vs. 1,543, p = 0.01, p for area under curve = 0.04). Mean troponin I levels were similarly numerically higher (57.4 vs. 48.0, p = 0.18). On cardiac magnetic resonance (CMR) at 6 months (32% subset), median infarct size was higher in the oxygen arm (20.3 vs. 13.1 g, p = 0.04; 12.6% vs. 9.0% of left ventricular mass, p = 0.08). Recurrent in-hospital MI (5.5% vs. 0.9%, p  = 0.006) and major cardiac arrhythmias (40.4% vs. 31.4%, p = 0.05) were higher, but mortality was numerically lower (1.8% vs. 4.5%, p = 0.11). At 6 months, recurrent MIs were still numerically higher (7.6% vs. 3.6%, p = 0.07), but mortality was similar (3.8% vs. 5.9%, p = 0.32).

On subgroup analysis, females had a greater evidence of harm with oxygen (relative risk 2.11, 95% confidence interval 1.42-3.14, p < 0.001).

Interpretation:

The results of this trial indicate that high-dose supplemental oxygen is potentially harmful in normoxic patients presenting with mostly low-risk STEMI. Potentially detrimental effects include increased myocardial injury and recurrent MI. This is probably due to the detrimental effects of free radicals and superoxides. These results may lead to a change in guidelines with respect to oxygen administration in patients with STEMI, although most physicians do not routinely place normoxic patients on 8 L/min oxygen as was done in this trial (typically 2 L/min). It is unclear if lower doses of oxygen would have the same toxic effects.

References:

Stub D, Smith K, Bernard S, et al., on behalf of the AVOID Investigators. Air Versus Oxygen in ST-Segment Elevation Myocardial Infarction. Circulation 2015;May 22:[Epub ahead of print].

Presented by Dr. Dion Stub at the American Heart Association Scientific Sessions, Chicago, IL, November 19, 2014.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Implantable Devices, SCD/Ventricular Arrhythmias, Acute Heart Failure

Keywords: Risk, Myocardial Infarction, Creatine Kinase, Allied Health Personnel, Area Under Curve, Drug-Eluting Stents, Heart Conduction System, Electrocardiography, Emergency Service, Hospital, Heart Arrest, Masks, Percutaneous Coronary Intervention, Shock, Cardiogenic, Superoxides, Troponin I, Thrombosis, Oxygen, Magnetic Resonance Spectroscopy, Diabetes Mellitus, AHA Annual Scientific Sessions


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