Evaluation of the longitudinal contraction of the ventricle septum in patients undergoing off-pump coronary artery bypass graft surgery by strain rate imaging.

BACKGROUND

Strain rate (SR) imaging is an emerging technique for assessing myocardial systolic and diastolic functions. This technique can provide assessment in real time and color mapping; it also can detect ischemia at its earlier stages in comparison with visual estimation of wall motion with other techniques.

METHODS

This study group consisted of 9 patients undergoing elective coronary artery bypass graft (CABG) surgery. After general anesthesia with sevoflurane (end-tidal 1.8%) in air/oxygen mixture, a complete transesophageal echocardiography (TEE) study was performed with an ultrasound machine. Myocardial wall strain rate imaging was then preformed off-line using a customized computer software (Echopac, Windows 2000 version 2.1, General Electric) running on a Compaq P4 computer. The experimental protocol was divided into 6 parts: (1) T1: 30 minutes after general anesthesia completed, (2) T2: after opening the sternum and pericardium, (3) T3: left anterior descending coronary artery(LAD) snared for the preparation of ischemic pre-conditioning (SLAD), (4) T4: after anastomosing left internal mammary artery (LIMA) on LAD, (5) T5: before closing the sternum and pericardium and (6) T6: after closing the sternum and pericardium.

RESULTS

From strain rate imaging, peak systolic SRs were reduced or inverted over LAD perfused area during the SLAD period. In apical segments, peak systolic SR changed from -0.45 +/- 0.48 to 0.42 +/- 0.63 (P < 0.05), whereas peak diastolic SR changed from 0.34 +/- 0.61 to -0.80 +/- 1.08 (P < 0.05). In the middle septum, peak systolic SR changed from -0.67 +/- 0.51 to -0.43 +/- 0.50 (P < 0.05), while peak diastolic SR changed from 0.47 +/- 0.44 to -0.64 +/- 0.84 (P < 0.05). After LIMA grafting, peak systolic SR changed from 0.42 +/- 0.63 to -0.61 +/- 0.40 (P < 0.05), as against peak diastolic SR which changed from -0.80 +/- 1.08 to 0.21 +/- 0.44 (P < 0.05) in the apical septum. Peak systolic SR changed from -0.43 +/- 0.50 to -0.75 +/- 0.46 (P < 0.05), whereas peak diastolic SR changed from -0.64 +/- 0.84 to 0.64 +/- 0.88 (P < 0.05) in the middle septum.

CONCLUSIONS

Postsystolic shortening is a marker for both ischemia and successful myocardial reperfusion. By strain rate imaging, we could detect ischemia with a more sensitive and specific method. For anesthesiologists and surgeons, it can be an intraoperative tool for assessing ventricular function after reperfusion.