Transmyocardial ST changes and gas tensions in regional ischemia

This study was designed to determine changes in intramyocardial oxygen (PmO₂), carbon dioxide (PmCO₂), and ST-segment voltage (ST) with atrial pacing induced regional ischemia. PmO₂ and PmCO₂ were measured by mass spectrometry and ST with multicontact unipolar intramyocardial electrodes. In 12 open chest dogs 2 degrees of constriction of the proximal circumflex coronary artery were produced: to reduce reactive hyperemia by only 50% and to abolish reactive hyperemia without altering mean flow. Positions of the electrodes were recorded at the fraction of the distance from endocardial surface to epicardial surface. This study suggests that the significance of a given coronary constriction may be characterized with intramyocardial electrodes and atrial pacing stress; and that ST segment changes recorded in the deeper layers of the myocardium are greater than those recorded near the epicardial surface.