Left ventricular filling during coronary artery bypass grafting

Left ventricular (LV) filling, determination of preload, right ventricular end-diastolic volumes, volume contributions during early (E) and atrial (A) phases of LV filling and mitral valve opening areas were studied in 75 patients scheduled for elective coronary artery bypass grafting (CABG).

The purposes of the study were: (1) To evaluate changes in LV filling judged as peak velocity E/A ratios determined by Doppler transesophageal echocardiography during and in the early phase after CABG. (2) Validation of clinical determination of LV dimension before and after cardiopulmonary bypass (CPB) by comparing two measures of preload: (i) inspection of the line of contact between the heart (margoacutus) and the diaphragmatic pericardium and (ii) the end-diastolic LV cross-sectional area determined by two-dimensional transesophageal echocardiography. (3) To determine the right ventricular end-diastolic volume by fast response thermodilution using the relation of the acute margin of the heart to the diaphragm as an endpoint when transfusing the patients during weaning from CPB. (4) To validate the volume contribution during early and atrial phases of left ventricular filling assessed by Doppler transesophageal echocardiography by comparing it with nuclear cardio-angiography during CABG. (5) To measure the mean and maximum cross-sectional area of the mitral valve by two-dimensional transesophageal echocardiography during the early and atrial phases of left ventricular filling.

Results: (1) There was an altered diastolic filling pattern in the immediate phase after CABG, with a gradual recovery of the peak velocity E/A ratio from 0.46+0.06 to0.87+0.08 during the first 6 hours in the intensive care unit. (2) A clinical measure, inspection of the line of contact between the heart and the diaphragm provided reliable information on LV preload during weaning from CPB. There was a strong correlation, r 0.88, between left ventricular end-diastolic area before and after CPB. (3) The clinical measure of preload was determined more by the left ventricle than the right and there was a weak correlation, r=0.54, between right ventricular end-diastolic volume before and after CPB. (4) There was a good agreement between Doppler echocardiographic and nuclear angiocardiographic methods regarding volume contributions during the E, r=0.98, and A, r=0.88, phases of left ventricular filling. (5) The mean opening area of the mitral valve, determined by echocardiography, during the E and A phases was the same and recordings of the mitral velocity time integral therefore reflect volumetric flow. Myocardial ischemia during aortic occlusion,increased heart rate, and decreased VTI E/A ratio, did not alter the area.