Study On The Evaluation Of Myocardial Ischemia By Optical Coherence Tomography In Vitro And In Vivo

Objective: To study the feasibility of evaluating myocardial ischemia by optical coherence tomography. Methods: Acute myocardial ischemia model was replicated by ligatting the left anterior descending coronary artery(LAD) of SD rates. In vitro studies: SD rats in experimental group sacrificed before the ligation and in the following periods: 10 min, 20 min, 30min, 40min, 50min, 60min, 90min, 120min after ligatting LAD, SD rats in control group sacrificed before and after Sham operation on each set time the same as above. The hearts were protected by ice after blood was drawn, and serum troponin-I(CTNI),creatine kinase isoenzyme quantitation(MMB),creatine kinase (CK),creatine kinase isoenzyme (CK-MB), and lactate dehydrogenase (LDH) were tested on each set time in both experimental group and control group. OCT images were obtained from the ischemic region located in anterior wall of left ventricular, and then the heart was removed for pathology study. In vivo studies: In both experimental group and control group, ECG and OCT images of left ventricular anterior wall were studied on each set time the same as in vitro study.MATLAB soft ware was used to extract and analyze scattering coefficient (μs) from the OCT images. Results: (1)In vitro studies: The ST segment elevation in experimental group≧0.1mV after ligatting; compared with the control group, there were significant differences (P<0.01).The serum CTNI, CK, CK-MB, LDH in experimental group kept increasing with the ischemic time extending, compared to the control group, there were significantly different (P<0.01).However,the serum MMB values showed no distinct change and has no significant differences between experimental group and control group (P>0.05). The scattering coefficient obtained from OCT images of the experimental group kept decreasing with ischemic time extending following the ligation, there were significantly different compared to the control group(P<0.01). Histological examination: With the liggating time extending in experimental group, HE stain study showed the myocardial injury was gradually aggravated; however, there was no obvious pathological change in the myocardium of control group. Compared the injury score between the experimental group and the control group, there was significantly different (P<0.01). TUNEL showed the apoptosis index(AI) in experimental group kept increasing with ischemic extending, and there were significant differences between those two groups(P<0.01).(2) In vivo studies: Comparing the ST segment elevation of the experimental group with the control group, there were significant differences (P<0.01), and comparing theμs obtained from OCT images of experimental group with that in control group, there were also significant differences(P<0.01).(3)Correlation analysis: In vitro studies, compared myocardial tissueμs with serum CTNI, CK, CK-MB, LDH, myocardial injury score and AI, there were highly negatively correlated (P<0.01),but no correlation with the serum MMB (P> 0.05). Comparedμs obtained from OCT images between in vivo and in vitro study, there were highly positively correlated (P<0.01). Conclusion: In vitro study,μs obtained from OCT images show a high degree of relevance with histological study and serological test, that means the OCT images have highly relevant with the extent of myocardial ischemia. Meantime, OCT images between in vivo and in vitro study also show a high degree of relevance. All of these evidences prove that OCT technique in evaluating the myocardial ischemia is feasible.