The conventional echocardiography parameters of the rabbits before and after coronary artery ligation as well as after reperfusion were shown in table 1. LVEF decreased significantly after ligation, and there were no significant differences in the remaining parameters.
The normal longitudinal strain curve was mainly a negative wave below the baseline, arranged neatly, and the peak time was concentrated (Fig. 1A). After 45 min ligation, the longitudinal strain was distorted. GLSsys and GLSp decreased significantly, and the peak was shifted back (Fig. 1B). After 120 min reperfusion, GLSsys and GLSp increased to varying degrees in I-PostC group, ATP-V-PostC group and ATP-A-PostC group (Fig. 1C). The results were shown in Table 2.
After 45 min ligation, the curves of strain and strain rate in the segments with LV dysfunction of rabbits were disordered, LSsys and LSp decreased significantly, and the peak shifted. After 120 min reperfusion, the parameters increased significantly in segments with LV dysfunction in I-PostC group, ATP-V-PostC group and ATP-A-PostC group. The peak time moved forward. LSp increased significantly in ATP-V-PostC group compared with that in I-PostC group (p < 0.01). The peak time of LSsys and LSp increased significantly in ATP-A-PostC group (p < 0.01).
Circumferential strain curves of normal rabbits were wide negative single peak, the strain curves of every segment were arranged neatly, the peak time was concentrated, and the shape of curves was consistent (Fig. 2A). After 45 min ligation, the circumferential strain curves were flat, the form of the waves was disordered, and the peak times were not concentrated (Fig. 2B). After 120 min reperfusion, the parameters were recovered to varying degrees. The results were shown in Table 3.
After 45 min ligation, GCSsys and GCSp decreased significantly. Most of the peak times shifted. The curves of strain and strain rate in the segments with LV dysfunction of rabbits were low and most of them were distributed in the middle and apical segments of each chamber wall. GCSsys and GCSp increased to some extent in I-PostC group, ATP-V-PostC group and ATP-A-PostC group after 120 min reperfusion. Peak time moved forward. Parameters were increased slightly in I/R group (Table 3). Both the strain peak and the strain rate rose to varying degrees, and the reverse motion of the systolic and diastolic compressive strain curves disappeared (Fig. 2C and 2D).
The normal radial strain curve was a wide single-peak forward wave. The strain rate curve was a positive wave during the systolic phase and the diastolic phase was a negative wave. The peak time of each curve was concentrated and arranged neatly (Fig. 3A). After 45 min ligation, the curves of radial strain and strain rate in dysfuncted segments were low and disordered (Fig. 3B). The absolute value of RSsys and RSp of every segment decreased significantly and the peak time delayed distinctly. After 120 min reperfusion, the reverse motion of RSsys curve disappeared in I-PostC group, ATP-V-PostC group, and ATP-A-PostC group. RSsys and RSp increased significantly in ATP-V-PostC group and ATP-A-PostC group after reperfusion (p < 0.01) and the delay phenomenon in peak time of systolic strain relieved (Fig. 3C). RSp was higher in I-PostC group and ATP-PostC group than that in I/R group (Table 4).
Evaluation Of Torsion Function
Rotation curves of normal rabbits LV (ROT) were wide and counterclockwise with single peak, arrived peak at the end of systolic phase and descended in diastolic phase (Fig. 4A). Rotation rate curves of normal rabbits LV (ROTR) were positive rotation peak in systolic phase and high negative untwiSTEng peak in diastolic phase (Fig. 4B). After 45 min ligation, the absolute values of Ptw, PTV and PUV of LV decreased significantly (p < 0.01), the peak time delayed, HTU increased (Fig. 4C), ROTR curve in diastolic period had a notch (Fig. 4D). After 120 min reperfusion, the reverse motion of the torsion curves disappeared in I-PostC group, ATP-V-PostC group and ATP-A-PostC group. Ptw, PTV, and PUV significantly increased, and the peak time delay of the peak of the torsion angle was alleviated (Fig. 4E and 4F). The results were shown in Table 5.
Sensitivity and specificity of STE technique in detecting MI rabbits
The area under the ROC curve AUC, cutoff value, sensitivity and specificity results were shown in Table 6. For LSp, the sensitivity and the specificity of the MI rabbits were 89.3% and 85.7%, respectively. The AUC of RSp was 0.858, and the cutoff value of 22.67%. The sensitivity and specificity were 88.1% and 81.5%, respectively. The AUC of CSp and GLSp were 0.856 and 0.848. The sensitivity was − 15.33% and − 13.89%, respectively. The AUC of Ptw was 0.810, and the sensitivity and specificity were 79.2% and 75%, respectively. The sensitivity and specificity of PTV in detecting MI rabbits were lower and statistically significant.
As shown in the table 7, AST, CK, CK-MB and LDH increased significantly in all groups after ligation. After reperfusion, AST and CK-MB further increased in I/R group, and other parameters had no changes. After reperfusion, myocardial enzyme values in I-PostC group, ATP-V-PostC group and ATP-A-PostC group were lower than those in I/R group to varying degrees.
Myocardial Infarct Size
The myocardium supplied by the occluded LV branch of LAD exhibited an irregular dark area distributed mainly over the lateral, posterior, and inferior walls of the LV and the apex. The percentage of AR (AR/LV) had no difference among the four groups before reperfusion. The percentage of AN (AN/AR) was obviously larger in I/R group than that in the other three groups (p < 0.05) after reperfusion. The infarct size in I/R group were higher than those in other three groups (Table 8).
The Changes In Cell Apoptosis
After staining with the TUNEL assay kit, the normal nucleus was blue and the nucleus of the apoptotic cells was brown. The cells were arranged disorderly and the nucleus was unevenly deformed in I/R group (Fig. 5A). The cardiomyocyte nuclei were all in blue in I-PostC group, the cells were arranged neatly, and the nucleus was elliptical. Few brown nuclei were in the ATP-PostC group. The percentages of apoptotic cells in I/R group were higher than those in other three groups (Table 8). The Bax content in the normal tissues of four experimental groups was basically the same. After ischemia and reperfusion, the Bax in the ischemic tissue and infarcted tissue increased. The Bax content decreased in the I-PostC group and APT-PostC group (Fig. 5B). All the levels of Bcl-2 in the normal tissues were basically the same. After ischemia and reperfusion, the content of Bcl-2 in the ischemic and infarcted tissues decreased, the Bcl-2 increased after ischemic postconditioning and post-drug adaptation treatments (Fig. 5C).