Background A precise understanding and quantification of myocardial contraction is essential for optimising peri-operative care in high risk CABG surgery. Conventional approach has been focused on the magnitude of myocardial contraction, while its time course has received little clinical attention. This study was aimed to characterise the changes in both physiological entities early after CABG for unstable angina.
Methods 20 patients undergoing urgent CABG surgery (mean age 63 ± 7 yr, and 14 were males) were prospectively investigated. Peri-operative trans-oesophageal Echo and high fidelity LV pressures recordings was performed immediately before and 9 h after CABG.Transverse LV cavity dimension and wall thickness were derived from mid-cavity M-mode echocardiograms along with LV pressure by digitising. Cardiac output was measured by Swan-Ganz pulmonary catheter. Both the timing (with respect to the onset of QRS complex) and the magnitude of LV regional peak shortening velocity, peak systolic wall stress and peak myocardial power.
Results The mean coronary graft was 3.2 ± 0.7 and aortic cross clam time was 61 ± 22 min with blood cardioplegia. At 9 h after the operation, cardiac index (from 1.9 ± 0.5 to 2.6 ± 0.5, l/min/m2, p < 0.01); and LV stroke power index (from 0.91 ± 0.33 to 1.35 ± 0.38, W/m2, p < 0.01) both increased significantly from pre-CABG, while heart rate and LV filling pressure did not differ. Regarding regional contraction, there was a significant increase in peak shortening velocity (from 1.5 ± 0.6 to 1.9 ± 0.6 cir/sec, p < 0.01), peak myocardial power (from 22 ± 10 to 30 ± 11 mW/cm3, p < 0.01), although peak systolic wall stress did not changed. In addition, the timing of peak shortening velocity (from 214 ± 54 to 178 ± 40 msec, p < 0.01), peak stress (from 189 ± 46 to 149 ± 30 msec, p < 0.01) and peak power (from 194 ± 41 to 167 ± 33 msec, p < 0.01) all occurred significant earlier.Furthermore, the post-operative increase in cardiac index was jointly predicted by the changes in the timings of peak shortening velocity and peak power (p = 0.002, 0.027, r = 0.65).
Conclusion Early after CABG for unstable angina, there is a significant improvement in myocardial contraction at regional and global levels. This was manifested by an earlier timing and a greater magnitude of myocardial contraction. Given that the timing of contraction is the key predictor of increase in cardiac index, it should be incorporated as routine part of clinical assessment regarding peri-operative cardiac function.
- LV contraction
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