To investigate if the index of myocardial performance (IMP) is valid under acutely changing hemodynamic surgical conditions by comparing it to changes in cardiac index (CI) measured by thermodilution pulmonary artery catheter (PAC). Echocardiographic doppler derived IMP has proved useful in following long term outcome in patients with left ventricular (LV) dysfunction. IMP encompasses important periods of LV systolic contraction, ejection, and diastolic relaxation. IMP is independent of heart rate (HR), mean blood pressure (MBP), central venous pressure (CVP)and ventricular geometry. IMP in healthy subjects is upto 0.55 seconds, and prolonged (>0.55 seconds) in diminished LV function.
We prospectively studied 70 adult male patients who underwent elective coronary artery bypass graft (CABG) surgery. IMP was measured with the aid of transesophageal echocardiography (TEE) [Figure 1]. Measurements were made at five points during each case [following anesthetic induction, following sternotomy, after narcotic administration, after preload correction, and after completion of CABG surgery] by the first investigator. Five corresponding CI, HR, MBP, and CVP measurements were made with the aid of the PAC, radial arterial line, and central venous line by the blinded second investigator.
1) There is stastically significant (r=0.57; p<0.0001) negative linear relationship between IMP and CI measurements. 2) Changes in HR (r=0.00; p=0.980), MAP (r=0.07; p=0.510), and CVP (r=0.00; p=0.99) do not affect IMP. Data was analyzed by a linear regression method and Bayes’ Rule for probability calculation.CONCLUSIONS: 1) This study establishes that improvement in CI (or LV function) is associated with IMP shortening or vice versa under acutely changing hemodynamic cardiac surgery conditions. 2) IMP is independent of changes in HR, MBP, and CVP.CLINICAL APPLICATIONS: The TEE doppler derived IMP is a useful, and reproducible index of global LV function.This index can be used to follow acute changes in LV function during and after myocardial revasculariztion. As compared to other indices of systolic and diastolic funtion, IMP is independent of changes in HR, MBP, and CVP.
A.D. Sharma, None.