Reperfusion with venous blood after cardioplegic arrest during bypass surgery results in faster microbubble transit rates compared to arterial blood: Evidence for less endothelial injury?

During cardiopulmonary bypass, both delivery of cardioplegic solutions and reperfusion result in endothelial dysfunction. It has been previously shown that sonicated albumin microbubbles adhere to injured endothelium and that the transit rate of these microbubbles can be measured using myocardial contrast echocardiography (MCE). We, therefore, hypothesized that endothelial dysfunction caused by cardioplegia and reperfusion can be detected using MCE. The myocardial transit rate of microbubbles injected into the aortic root was measured in 12 dogs and 12 patients during cardioplegia delivery and reperfusion with arterial and venous blood after cardioplegic arrest. The myocardial transit rates of ^99mTc-labeled red blood cells and similarly labeled 5% human albumin were also measured and the cardioplegic solutions were sampled for biochemical analysis. In comparison to the red blood cell and albumin transit rates which remained constant at a given flow rate regardless of the composition of the cardioplegic solution infused, microbubble transit rates were markedly slower during delivery of crystalloid cardioplegic solutions (p< 0.001). They increased significantly when blood was added to these solutions (p<0.001). Reperfusion with venous blood after cardioplegic arrest was associated with faster transit rates compared to arterial blood (p<0.001). The transit rates did not correlate with perfusate pH, pO₂, pCO₂, or K⁺. These results indicate that endothelial dysfunction during cardioplegic arrest and after reperfusion may be ameliorated with use of cardioplegic solutions containing venous rather than arterial blood. They also imply that MCE could be used to assess endothelial function on-line in the operating room.