Myocardial tissue CO2 tension detects coronary blood flow reduction after coronary artery bypass in real-time

Abstract

Background. Coronary stenosis after coronary artery bypass grafting (CABG) may lead to myocardial ischaemia and is clinically difficult to diagnose. In a CABG model, we aimed at defining variables that detect hypoperfusion in real-time and correlate with impaired regional ventricular function by monitoring myocardial tissue metabolism. Methods. Off-pump CABG was performed in 10 pigs. Graft blood flow was reduced in 18 min intervals to 75, 50, and 25% of baseline flow with reperfusion between each flow reduction. Myocardial tissue PCO2 (PtCO2), PO2, pH, glucose, lactate, and glycerol from the graft supplied region and a control region were obtained. Regional cardiac function was assessed as radial strain. Results. In comparison with baseline, myocardial pH decreased during 75, 50, and 25% flow reduction (-0.15; -0.22; -0.37, respectively, all P<0.05) whereas PtCO2 increased (+4.6 kPa; +7.8 kPa; +12.9 kPa, respectively, all P<0.05). pH and PtCO2 returned to baseline upon reperfusion. Lactate and glycerol increased flow-dependently, while glucose decreased. Regional ventricular contractile function declined significantly. All measured variables remained normal in the control region. PtCO2 correlated strongly with tissue lactate, pH and contractile function (R=0.86, R=-0.91, R=-0.70, respectively, all P<0.001). New conductometric PtCO2 sensors were in agreement with established fibre-optic probes. Cardiac output was not altered. Conclusions. Myocardial pH and PtCO2 monitoring can quantify the degree of regional tissue hypoperfusion in real-time and correlated well with cellular metabolism and contractile function, whereas cardiac output did not. New robust conductometric PtCO2 sensors have the potential to serve as a clinical cardiac monitoring tool during surgery and postoperatively.