Evidence of anaerobic metabolism during low-level exercise testing in high-risk postmyocardial infarction patients

Low-level exercise testing was performed on 31 patients 7.4 +/- 2.7 days following an acute myocardial infarction. Measurements of oxygen consumption (VO2) and arterial serum lactate were made at rest and during exercise in these patients and 15 normal subjects. The patients were subdivided into finishers (F) and nonfinishers (NF) of the low-level protocol. The NF group had 2.5 +/- 6 stenosed vessels and an ejection fraction of 44 +/- 11% compared to F subjects, who had 1.4 +/- 1 vessels stenosed (p less than .001) and an ejection fraction of 54 +/- 14% (p less than .05). Finishers had significantly higher VO2 than the nonfinishers (14.5 +/- 2.5 ml/kg/min vs. 11.2 +/- 3.5 ml/kg/min p less than .01). At the end of exercise serum lactate level was 1.18 +/- .59 mM in normals, 1.43 +/- .52 mM in finishers, and 2.15 +/- .9 mM in nonfinishers. The change in serum lactate from rest to end exercise divided by the change in VO2 from rest to end exercise was .039 +/- .038 mM/ml kg per min in normals, .075 +/- .045 mM/ml kg per min in finishers (p less than .03 vs. normal), and .210 +/- .189 mM/ml kg per min for nonfinishers (p less than .001 vs. normal). These results indicate that nonfinishers produce more lactate and use less oxygen during low-level exercise, suggesting that working muscles are deriving energy by anaerobic metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)