Oxygen consumption of the normal and failing heart during left heart bypass

In order to determine whether myocardial oxygen consumption (MOC) is decreased during left heart bypass (LHB), two groups of 6 dogs each were subjected to 2 hours of heparinless LHB. Group 2 differed from Group 1 in that cardiogenic shock was induced by temporary coronary artery occlusion prior to LHB. In Group 1 animals (normal dogs), MOC decreased significantly during the surgical preparation but did not change appreciably during subsequent LHB. Upon completion of LHB, MOC increased slightly in all animals. This increase in MOC was insignificant, however, when adjusted to changes in mean aortic blood pressure (MAP). A highly positive linear correlation between MOC and MAP was noted regardless of whether the animals were on or off bypass. In Group 2 animals, MOC was markedly decreased after the iduction of cardiogenic shock but gradually increased during the 2 hours of LHB. Upon completion of bypass, MOC of the damaged heart increased to a remarkable degree, but not to initial control levels. However, the linear correlation between MOC and MAP, noted before the induction of cardiogenic shock, disappeared after shock and was not restored after 2 hours of apparently successful bypass. We have concluded that MOC is decreased surgical stress and is further decreased by temporary coronary artery occlusion. MOC is not, however, reduced by nearly total or total LHB in normal hearts. MOC is markedly decreased by cardiac damage but gradually increases in damaged hearts by the use of LHB.