| Objective:To investigate the correlation between left ventricular myocardial strain and myocardial infarction size and time,as well as the pathological characteristics of left ventricular remodeling after myocardial infarction,the changes of magnetic resonance related parameters and corresponding indicators of pathological changes in rabbits’ model of myocardial infarction(MI)were observed.Methods and Materials:Forty-three adult male rabbits were divided into sham operation group(8 rabbits)and myocardial infarction group(35 rabbits).A rabbit myocardial infarction model was established by ligation of the left ventricular branch of the coronary artery.Thirty-two models were successfully constructed,with a success rate of 74.42%.3.0T cardiac magnetic resonance(CMR)scans were performed at 1w,2w,4 w,8w,16 w postoperatively,respectively.Cardiac markers were also acquired at the corresponding time points.The CMR scan sequences include: Fast Imaging Employing Steady State Acquisition(FIESTA)sequence,and reverse recovery fast gradient echo sequence.Post processing obtains left ventricular functional parameters,mainly including left ventricular ejection fraction(LVEF),left ventricular stroke volume(SV),left ventricular cardiac output per minute(CO),left ventricular end systolic volume(ESV),and left ventricular end diastolic volume(EDV);the global and segmental strain values of the left ventricle mainly include the longitudinal,circumferential,and radial peak strain parameters(PLS,PCS,PRS)of the global,basal,mid-ventricular,and apical layers of the short and long axes;left ventricular Late Gadolinium Enhancement(LGE)parameters mainly include overall enhancement volume,overall enhancement mass,and enhancement volume percentage.The measurement data between groups were compared using Mann Whitney U test/independent sample t test,and the comparison between multiple groups was performed using Kruskal Wallis test/one-way analysis of variance(ANOVA).Multiple comparisons were performed using Postmortem test and Bonferroni correction.To investigate the correlation between left ventricular global and segmental strain indicators and left ventricular LGE area in rabbits with myocardial infarction using univariate logistic regression analysis.Results:(1)Multi-parameter comparison of CMR among sham-operated and infarct groups: The routine parameters of SV,CO,and LVEF in the infarct group were significantly lower than sham-operated group [1.21(1.57,1.05)VS(0.98±0.47)mL,P=0.03;(0.35±0.15)VS(0.21±0.14)L/min,P < 0.001;(34.09±12.51)VS(44.82±9.54)%,P=0.001].The global,basal and mid-ventricular PRS at the short axis level were lower in the infarct group than sham-operated group [(16.28±8.91)VS(22.02±9.05)%,P=0.014;(18.38±10.70)VS(24.67±9.59)%,P=0.020;(18.01±10.69)VS(23.87±10.02)%,P=0.031)].The basal and mid-ventricular PCS at the short axis level were lower in the infarct group than sham-operated group [(-11.90±5.58)VS-15.12(-12.89,-19.14)%,P=0.020;(-11.86±5.56)VS-15.53(-13.10,-16.99)%,P=0.047].(2)Multi-parameter comparison of CMR between different LGE area subgroups: CO and LVEF were lower in the medium-plus infarct size group than small infarct size group [(0.20±0.11)VS(0.23±0.17)L/min,P<0.001;(30.39±12.38)VS(40.34±10.29)%,P=0.001].The global,basal,and mid-ventricular PRS at the short axis level were lower in the medium-plus infarct size group than small infarct size group [(13.82±8.81)VS(20.44±7.66)%,P=0.014;(16.24±9.55)VS(22.21±11.89)%,P=0.020;(15.24±10.47)VS(22.69±9.63)%,P=0.031];and the PCS at the base of the short axis was lower than in the small infarct group[(-10.89±5.35)vs(-13.72±5.71)%,P=0.046].The peak strain in the rest of the directional segments was not statistically different from the control group.(3)Multi-parameter comparison of CMR between infarct time subgroups:There were no statistical differences in myocardial volume,myocardial mass,EDV,ESV and HR between the acute,subacute and chronic stage infarction groups.The differences in global myocardial enhancement volume,global enhancement mass and enhancement volume ratio between the groups were statistically significant(P=0.022,0.023,0.015),and the differences in SV,CO and LVEF between the groups were statistically significant(P<0.001,P=0.028,P<0.001).Except for the PLS in the long-axis apical part of the left ventricular myocardium and the PRS in the long-axis mid-ventricular and apical segments,the absolute values of the peak strain in each direction of the myocardium as a whole and in the segments showed a gradual decrease in the acute,subacute,with statistical difference.(4)Univariate logistic regression predicts medium-plus size myocardial infarction: Larger values of LVEF(P=0.017),short-axis global PRS(P=0.025),short-axis bottom PRS(P=0.087),and short-axis mid-ventricular PRS(P=0.034)were associated with a lower probability of major myocardial infarction.(5)Adipose tissue infiltration can occur after myocardial infarction:Pathological HE and Masson staining were performed in 5 cases of MI group,among which 4 cases found that the proliferation of epicardial adipose tissue(EAT)and perivascular adipose tissue in the infarcted area could progress to infiltrating adipose tissue(INFAT),which got progressively worse with time.Conclusion:1)Left ventricular cardiac function indices,global,basal and mid-ventricular PRS,and short-axis basal and mid-ventricular PCS were reduced after MI in rabbits compared with the sham-operated group;2)With the prolongation of myocardial infarction and the increase of myocardial infarction area,some indexes of left ventricular myocardial strain and cardiac function were further reduced,and myocardial strengthening was aggravated in the subacute compared with the acute phases;3)The greater the values of LVEF,short-axis global,basal and mid-ventricular PRS,the less the possibility of large myocardial infarction;4)Adipose tissue infiltration in infarcted myocardium increased with time. |
