Temporal Relationships of Myocardial Lactate Metabolism, Left Ventricular Function, and S-T Segment Depression During Angina Precipitated by Exercise

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Abstract
Continuous monitoring of myocardial lactate metabolism and the electrocardiogram in association with an assessment of left ventricular function were carried out in a group of 14 patients before, during, and after a period of supine leg exercise. Of the 12 patients who were shown to have coronary artery disease, seven experienced exertional angina whereas five remained free of pain. Marked increases in arterial and coronary sinus lactate concentrations were observed in all subjects early in exercise although arterial lactate levels were higher in the angina group. In the normal subjects and in the non-angina group, myocardial lactate extraction increased to 36.7 and 28.5%, respectively, during exercise. In the angina group, however, lactate extraction remained abnormal during exercise, increasing to only 8.8%, but in this group only two patients showed myocardial lactate production. Left ventricular end-diastolic pressure was consistently elevated during exertional angina and showed a close temporal relationship to ischemic S-T segments. Left ventricular stroke work was unchanged at these elevated filling pressures indicating impaired left ventricular contractility. While correlation of exertional angina, S-T segment depression, and hemodynamic abnormalities was close, it was not possible to relate these changes to metabolic evidence of ischemia since this was obscured by the elevated arterial lactate concentrations.