Association between R-wave amplitude of the electrocardiogram and myocardial function during coronary artery bypass grafting

The recovery of R-wave amplitude in the V₅lead of the electrocardiogram (ECG) was recently found to be worse in nonsurvivors than in survivors after coronary artery bypass grafting (CABG). On the contrary, an increase in R-wave amplitude has been found to reflect myocardial dysfunction in exercise testing. The purpose of this study was to examine whether the changes in R-wave amplitude are associated with changes of myocardial function during CABG. A prospective clinical study. Cardiothoracic division of surgery in a university hospital. Ten consecutive patients undergoing CABG. R-wave amplitude was measured at eight different time points. Left ventricular end-systolic wall tension, wall stress at isovolumic contraction (afterload), end-diastolic wall stress (preload), end-systolic wall stress per end-systolic area (contractility), and stroke work were calculated using transesophageal echocardiography and arterial pressure. Linear regression was calculated between changes in R-wave amplitude and echo parameters. A weak positive association within subjects was noted among R amplitude and all measured cardiac function parameters except preload. R² value varied from 0.101 to 0.266, and R² for preload was 0.017. These results suggest that only 10% to 27% of variation in R-wave amplitude can be explained by left ventricular function indices measured by echocardiography in patients with CABG. Thus, R-wave amplitude changes in an individual patient undergoing CABG have very limited utility as a noninvasive measure of left ventricular function.