Evaluation of Left Ventricular Myocardial Work Performance in Patients Undergoing Coronary Artery Bypass Surgery: A Pilot Study

Objectives: The estimation of the left ventricular (LV) function is crucial for the follow-up and the prognosis of patients undergoing coronary artery bypass grafting (CABG) surgery.

LV function can be quantified with echocardiography by measuring the strain experienced by individual segments during the heart cycle. Automated Functional Imaging (AFI) employs speckle tracking to allow the quantification of LV strain.

Myocardial Work augments AFI by taking dynamic LV pressure into account, adding an important dimension to the assessment of LV function and facilitating interpretation of strain traces in relation to LV pressure dynamics.

Methods: We prospectively evaluated 50 patients undergoing CABG surgery with heart lung machine and anterograde Bretschneider cardioplegia. Patients had transthoracic echocardiography exams prior to surgery and one week postoperatively as well as concurrently systolic arterial blood pressure measurements at rest. We quantified the myocardial work index (MWI), global longitudinal strain (GLS) and ejection fraction (EF). We used the GE Vivid E90 with the EchoPac software. MWI was calculated as the area of the LV pressure-strain loop. Empirical cut-off values were set to identify segmental systolic dysfunction for MWI (<1,700 mm Hg %) and strain (more than −14%).

Results: Postoperative GWI was significantly reduced compared to preoperative values (1,594.2 ± 567.4 mm Hg% vs. 967.9 ± 460.3, p < 0.0001), as well as EF (p < 0.001) and GLS average (p < 0.0001). We could not detect a correlation between preoperative GLS, GWI, and EF values with postoperative complications and ICU stay. Cardiopulmonary bypass time did not affect the postoperative GWI, GLS, and EF. Our pilot study demonstrated that during the early postoperative period all the echocardiographic parameters of the global LV Function/total work index are reduced. It though seems that while global work is reduced, the segmental work index reaction is differing between the myocardial segments. Noticeably there are segments acting counterbalancing after CABG surgery with a corresponding increased segmental myocardial work index.

Conclusions: We suggest that the evaluation of global LV function after CABG surgery should be judged with late postoperative period follow-up while the echocardiographic measurements of early postoperative LV function are declined and consequently not representative.