Transmural gradients in myocardial gas tensions in regionally ischemic canine left ventricle

Previous studies from this laboratory have demonstrated the usefulness of myocardial gas tensions as measured by mass spectrometry for the quantitative assessment of regional myocardial ischemia (Khuri et al., 1975a). Progressive increases in myocardial carbon dioxide tensions were noted when progressive reduction in coronary blood flow was created by means of a variable constrictor. The present study was designed to determine if changes in myocardial oxygen and carbon dioxide tension were greater in deep, compared to more superficial, myocardial layers. In eight anesthetized dogs, progressive reduction in circumflex coronary flow was associated with a progressive reduction in myocardial oxygen tension and a progressive increase in myocardial carbon dioxide tension and intramyocardial ST-segment voltage. Evidence of a transmural gradient in the severity of ischemia was present at all degrees of flow reduction. These results confirm the findings of previous metabolic studies, which demonstrated gradients in lactate and high-energy phosphates. Myocardial carbon dioxide tension, which can be monitored continuously by mass spectrometry, would appear to provide a useful means of quantitatively assessing changes in regional myocardial metabolism.