Coronary blood flow, metabolism, and function in dysfunctional viable myocardium before and early after surgical revascularisation

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

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 (Pt(CO2)), 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 Pt(CO2) increased (+4.6 kPa; +7.8 kPa; +12.9 kPa, respectively, all P<0.05). pH and Pt(CO2) 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. Pt(CO2) 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 Pt(CO2) sensors were in agreement with established fibre-optic probes. Cardiac output was not altered.

CONCLUSIONS

Myocardial pH and Pt(CO2) 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 Pt(CO2) sensors have the potential to serve as a clinical cardiac monitoring tool during surgery and postoperatively.

Speckle-tracking imaging to monitor myocardial function after coronary artery bypass graft surgery

OBJECTIVES

The purpose of this study was to investigate the changes in myocardial function in patients after coronary artery bypass graft (CABG) surgery using longitudinal and circumferential strain on speckle-tracking imaging.

METHODS

A total of 145 patients who successfully underwent CABG surgery with a left ventricular ejection fraction (LVEF) of 50% or greater were enrolled in this study. Patients were classified into 4 groups based on age: group 1 (33-59 years), group 2 (60-64 years), group 3 (65-69 years), and group 4 (70-79 years). Routine echocardiography and longitudinal and circumferential strain measurements on speckle-tracking imaging were performed 1 week before and 1, 3, and 6 months after the CABG.

RESULTS

In all groups, longitudinal strain increased significantly at 3 and 6 months after CABG therapy compared to baseline (P < .05). A significant increase in circumferential strain was found 1 month after the CABG in groups 1, 2, and 3, and a continuous increase in the parameter was observed in all groups 3 months after therapy (P < .05). However, the LVEF, left ventricular end-diastolic dimension, and stroke volume measured by routine echocardiography were not significantly changed after successful CABG treatment in all groups during 6 months of follow-up.

CONCLUSIONS

Based on the results of our study in all age groups, speckle-tracking imaging parameters are more effective than the LVEF, left ventricular end-diastolic dimension, and stroke volume for monitoring improvement in myocardial function after CABG surgery.

Regional myocardial blood flow measured by stress multidetector computed tomography as a predictor of recovery of left ventricular function after coronary artery bypass grafting

BACKGROUND

Multidetector-row computed tomography (MDCT) applications have expanded to evaluation of myocardial blood flow (MBF) and viability. We quantified regional MBF pre- and post-coronary artery bypass grafting (CABG) using adenosine stress and cardiac 64-MDCT, and investigated whether the results predict MBF and left ventricular (LV) function recovery after CABG.

METHODS

We studied 321 regions in 19 CABG patients who underwent adenosine stress 64-row MDCT perfusion imaging and cine magnetic resonance imaging pre- and post-CABG. Myocardial blood flow was estimated from linear regression equation slopes using Patlak plot analyses and compared with LV function by measuring wall thickening (%WT) using cine magnetic resonance imaging.

RESULTS

Overall mean MBFs were 1.39 +/- 0.49 and 1.95 +/- 0.49 mL/(g min) pre- and post-CABG (P < .0001). Myocardial blood flow in revascularized areas increased significantly (pre-CABG 1.18 +/- 0.45, post-CABG 1.99 +/- 0.66 mL/[g min], P < .001), whereas nonischemic areas showed no difference (1.79 +/- 0.70 and 1.97 +/- 0.46 mL/[g min], P = .14). Revascularized areas with preoperative MBF > or = 0.9 mL/(g min) showed significantly greater MBF improvement than those with preoperative MBF <0.9 mL/(g min) (P = .04). In patients with preoperative LV dysfunction (ejection fraction <40%), %WT in revascularized areas with pre-CABG MBF > or = 0.9 mL/(g min) improved significantly after CABG (pre-%WT 40.9 +/- 22.9, post-%WT 52.8 +/- 20.6, P = .03) versus those with pre-CABG MBF <0.9 mL/(g min) (pre-%WT 53.2 +/- 35.5, post-%WT 42.5 +/- 17.0, P = .40).

CONCLUSIONS

Our results demonstrated more significantly increased MBF post-CABG than pre-CABG, particularly in revascularized areas. Regional MBF before CABG may predict MBF and LV function recovery, in the short term, after CABG.

Metabolomic profiling reveals distinct patterns of myocardial substrate use in humans with coronary artery disease or left ventricular dysfunction during surgical ischemia/reperfusion

BACKGROUND

Human myocardial metabolism has been incompletely characterized in the setting of surgical cardioplegic arrest and ischemia/reperfusion. Furthermore, the effect of preexisting ventricular state on ischemia-induced metabolic derangements has not been established.

METHODS AND RESULTS

We applied a mass spectrometry-based platform to profile 63 intermediary metabolites in serial paired peripheral arterial and coronary sinus blood effluents obtained from 37 patients undergoing cardiac surgery, stratified by presence of coronary artery disease and left ventricular dysfunction. The myocardium was a net user of a number of fuel substrates before ischemia, with significant differences between patients with and without coronary artery disease. After reperfusion, significantly lower extraction ratios of most substrates were found, as well as significant release of 2 specific acylcarnitine species, acetylcarnitine and 3-hydroxybutyryl-carnitine. These changes were especially evident in patients with impaired ventricular function, who exhibited profound limitations in extraction of all forms of metabolic fuels. Principal component analysis highlighted several metabolic groupings as potentially important in the postoperative clinical course.

CONCLUSIONS

The preexisting ventricular state is associated with significant differences in myocardial fuel uptake at baseline and after ischemia/reperfusion. The dysfunctional ventricle is characterized by global suppression of metabolic fuel uptake and limited myocardial metabolic reserve and flexibility after global ischemia/reperfusion stress in the setting of cardiac surgery. Altered metabolic profiles after ischemia/reperfusion are associated with postoperative hemodynamic course and suggest a role for perioperative metabolic monitoring and targeted optimization in cardiac surgical patients.

Metabolism of hibernating myocardium assessed by microdialysis during surgical revascularization: report of a case

We present an 80-year-old woman with hibernating myocardium in the left anterior descending coronary artery (LAD) territory who underwent surgical revascularization and metabolic evaluation of the dysfunctioning segments by microdialysis (microD) technique. Myocardial lactate, pyruvate, and glucose did not show obvious changes throughout the procedure. Conversely, myocardial glycerol and glutamate concentrations markedly increased early after cardioplegic arrest and subsided after weaning from cardiopulmonary bypass (CPB) and recovery of myocardial function. Intraoperative myocardial microD may add relevant pathophysiologic information on hibernating myocardium undergoing coronary flow restoration and, eventually, improve patient care.

Dobutamine Stress Echocardiography Is Highly Accurate for the Prediction of Contractile Reserve in the Early Postoperative Period, but May Underestimate Late Recovery in Contractile Reserve After Revascularization of the Hibernating Myocardium

OBJECTIVE

We sought to investigate the accuracy of dobutamine stress echocardiography to predict the degree and timing of recovery in resting function and contractile reserve (CR) after revascularization of the hibernating myocardium.

METHODS

In all, 24 patients with ischemic cardiomyopathy (ejection fraction < 40%) underwent dobutamine stress echocardiography 1 week before and 6 weeks, 3 months, and 6 months after coronary artery bypass grafting.

RESULTS

Recovery rates at 6 weeks, 3 months, and 6 months postoperation were 21%, 33%, and 45% (P < .01) for resting function and 55%, 65%, and 74% (P < .01) for CR. Positive and negative predictive values for recovery of resting function and CR at 6 months postrevascularization were 66% vs 97% (P < .001) and 78% vs 48% (P < .001), respectively. Positive and negative predictive values were both high for recovery of CR at 6 weeks postrevascularization (89% and 78%).

CONCLUSIONS

Dobutamine stress echocardiography can predict early recovery in CR postrevascularization with an excellent accuracy but may underestimate the degree of late recovery in CR.