Myocardial oxygenation during high work states in hearts with postinfarction remodeling

Abstract

Background - Postinfarction left ventricular remodeling (LVR) is associated with reductions in myocardial high-energy phosphate (HEP) levels, which are more severe in animals that develop overt congestive heart failure (CHF). During high work states, further HEP loss occurs, which suggests demand-induced ischemia. This study tested the hypothesis that inadequate myocyte oxygen availability is the basis for these HEP abnormalities. Methods and Results - Myocardial infarction was produced by left circumflex coronary artery ligation in swine. Studies were performed in 20 normal animals, 14 animals with compensated LVR, and 9 animals with CHF. Phosphocreatine (PCr)/ATP was determined with 31P NMR and deoxymyoglobin (Mb-δ) with 1H NMR in myocardium remote from the infarct. Basal PCr/ATP tended to be decreased in postinfarct hearts, and this was significant in animals with CHF. Infusion of dobutamine (20 μg · kg-1 · min-1 IV) caused doubling of the rate-pressure product in both normal and LVR hearts and resulted in comparable significant decreases of PCr/ATP in both groups. This decrease in PCr/ATP was not associated with detectable Mb-δ. In CHF hearts, rate- pressure product increased only 40% in response to dobutamine; this attenuated response also was not associated with detectable Mb-δ. Conclusions - Thus, the decrease of PCr/ATP during dobutamine infusion is not the result of insufficient myocardial oxygen availability. Furthermore, in CHF hearts, the low basal PCr/ATP and the attenuated response to dobutamine occurred in the absence of myocardial hypoxia, indicating that the HEP and contractile abnormalities were not the result of insufficient oxygen availability.