Transesophageal echo-derived left ventricular ejection fraction versus myocardial performance index in predicting outcome following coronary artery bypass grafting surgery

Abstract

BACKGROUND AND AIMS: Although left ventricular ejection fraction (LVEF) is the most commonly studied echocardiographic parameter for predicting postoperative outcome, its utility is limited by its preload dependency and ability to measure the only systolic function of the left ventricle. The myocardial performance index (MPI), a ratio obtained by summing up the time required for isovolumetric contraction and relaxation against the systolic ejection phase of the cardiac cycle, is the least studied parameter of left ventricular performance in perioperative settings. So, being a composite measure of systolic and diastolic function of the heart, we hypothesized that MPI can be a better predictor of postoperative outcome following coronary artery bypass grafting (CABG). The present study aimed at finding a correlation of LVEF and MPI with postoperative outcome indicators such as vasoactive inotropic score (VIS), the requirement of intra-aortic balloon pump (IABP) to maintain cardiac output, duration of mechanical ventilation, stay in the intensive care unit (ICU), postoperative morbidity and mortality.METHODS: A prospective, observational study was conducted on 110 subjects, scheduled for elective CABG. Transesophageal echocardiography (TEE) was performed after induction of anesthesia and before coronary grafting. Patients with no or grade I mitral regurgitation (vena contracta-VC <0.3 cm, effective regurgitant orifice area <0.2 cm2) and those in normal sinus rhythm were included. Patients with arrhythmia and MR of more than grade I (VC >0.3 cm, EROA >0.2 cm2) were excluded. Pre-CABG LVEF was measured using Simpson's biplane method. MPI was measured using Pulsed-wave Doppler across mitral inflow and left ventricular outflow tract. Subjects were labeled as “good” and “poor” outcomes based on standard criteria for defining the immediate postoperative outcome. Pre-CABG MPI and LVEF were correlated with these postoperative outcome variables following CABG.RESULTS: Of 110 subjects, 14 were excluded due to the presence of more than grade I MR (n = 8) and arrhythmias (n = 6) before CABG. Out of 96 subjects, 66% (n = 63) had “good” outcome and 34% (n = 33) had a “poor” outcome. Pre-CABG MPI and LVEF were (0.51 ± 0.12 and 47.2% ± 8.8%) in subjects with “good” compared to (0.57 ± 0.13 and 42.00% ± 8.70%) (P = 0.032 and 0.007 respectively) “poor” outcome following CABG. A higher pre-CABG MPI (0.57 ± 0.13) alone significantly correlated with increased VIS (r = 0.325, P = 0.001) in contrast to lower LVEF (42% ± 8.7%) (r = −0.181, P = 0.077). Both, lower precardiopulmonary bypass LVEF (40.46% ± 8.81%) and higher MPI (0.6 ± 0.11) were significantly correlated with increased ICU stay in days (r = −0.218 and r = 0.287, respectively). The mean MPI was 0.57 ± 0.08 and LVEF was 39.55% ± 4.05% in those subjects who succumbed in the postoperative period following CABG.CONCLUSION: MPI was a relatively better predictor of postoperative outcome following CABG. Increased Pre-CABG MPI was more consistent with the postoperative inotropic and vasopressor requirement. The requirement of an IABP to maintain cardiac output following CABG and mortality was correlated well with both low preoperative LVEF and higher MPI values.