Abstract 2004: Controlled Myocardial Tissue Reoxygenation (PO2) with Low Flow Reperfusion Improves Post Ischemic LV Function
Reperfusion of the globally ischemic myocardium leads to a rapid increase in myocardial oxygen tension which is coupled with an early burst of reactive oxygen species (ROS). However, under CPR conditions where blood flow and thus oxygen delivery is severely curtailed, it is unclear how myocardial oxygen tension recovers during low flow and how these changes might influence the recovery of LV function.
Objective: The objective of this study was to accurately measure myocardial tissue oxygen tension changes and subsequent recovery of LV function under conditions of low flow and full flow reperfusion in the intact heart.
Methods: Isolated perfused male Sprague Dawley rat hearts were perfused at 85 mmHg with temperature-controlled (37.4 C) modified Krebs Henseleit buffer. Hearts were subjected to either 20 minutes of global ischemia with normal reperfusion of 85 mm Hg (Control Group) or 6 minutes of global ischemia followed by 14 minutes of low flow perfusion (0.5% of baseline flow) and then full reperfusion at 20 min (Low Flow Group). Lithium phthalocyanine microcrystals (40 μg) were injected into the LV wall and the perfused heart was placed in an L-band (1.2 GHz) electron paramagnetic resonance (EPR) spectrometer for continuous measurements of myocardial tissue oxygen tension. Continuous LV function was recorded using a LV balloon attached to a pressure transducer.
Results: In all hearts, myocardial tissue PO2 immediately fell to between 2–3 torr during global ischemia, with minimal increase during low flow reperfusion. During full flow reperfusion in both groups, myocardial tissue PO2 was significantly higher in the Control Group compared to the Low Flow group (p<0.001, n=4/group). Despite lower tissue PO2 in the Low Flow Group, recovery of LV function (rate pressure product, developed pressure and end diastolic function) was significantly improved in the Low Flow group compared with Control (p<0.05, n=5/group). Coronary flow was similar between groups during reperfusion when tissue PO2 differed between groups.
Conclusions: Low flow reperfusion prior to full reperfusion attenuates the recovery of myocardial tissue oxygen tension, but may paradoxically improve the recovery of LV function during full reperfusion.