Reduction of infarct size by oxygen inhalation following acute coronary occlusion

This study was carried out in order to determine the effects of the inspiration of O2-enriched air on the size of myocardial infarction. In 15 anesthetized dogs, epicardial electrograms were recorded from 10 to 14 sites on the anterior surface of the left ventricle before and after intermittent occlusion of the left anterior descending coronary artery or one of its major branches. In each dog, one occlusion was carried out while the fraction of inspired oxygen (FIO2) was 0.20 and the other while the FIO2 was 0.40. With an FIO2 of 0.20 the average ST-segment elevation (ST) was 4.0 +/- 0.6 mV (SEM) and the number of sites exhibiting ST-segment elevations exceeding 2 mV (NST) 15 minutes following occlusion was 6.2 +/- 0.7 sites; comparable values following occlusion with an FIO2 of 0.40 were 1.8 +/- 0.4 mV (P less than 0.01) and 2.7 +/- 0.7 sites (P less than 0;01), reflecting reduction in acute myocardial ischemic injury; An FIO2 of 1.0 did not decrease myocardial injury further. In 24 other dogs, occlusion was maintained for 24 hours. In nine dogs in which FIO2 was increased from 0.20 to 0.40 30 minutes after occlusion, myocardial creatine phosphokinase activity (CPK) was less depressed in sites having comparable levels of ST-segment elevation at 15 minutes than in dogs that respired an FIO2 of 0.20 during the entire 24 hours. All (54) sites with ST-segment elevations greater than 3 mV in the 0.20 FIO2 group showed early signs of myocardial infarction, while only 49% of such specimens showed infarction in the 0.40 FIO2 group. Thus it is concluded that 0.40 FIO2 following an experimental coronary artery occusion decreases acute ischemic injury and reduces the eventual development of necrosis, as evaluated by enzymatic and histological techniques.