A novel and efficient model of coronary artery ligation and myocardial infarction in the mouse

Abstract

Rationale: coronary artery ligation to induce myocardial infarction (MI) in mice is typically performed by an invasive and time-consuming approach that requires ventilation and chest opening (classic method), often resulting in extensive tissue damage and high mortality. We developed a novel and rapid surgical method to induce MI that does not require ventilation.

Objective: the purpose of this study was to develop and comprehensively describe this method and directly compare it to the classic method.

Methods and results: male C57/B6 mice were grouped into 4 groups: new method MI (MI-N) or sham (S-N) and classic method MI (MI-C) or sham (S-C). In the new method, heart was manually exposed without intubation through a small incision and MI was induced. In the classic method, MI was induced through a ventilated thoracotomy. Similar groups were used in an ischemia/reperfusion injury model. This novel MI procedure is rapid, with an average procedure time of 1.22 ± 0.05 minutes, whereas the classic method requires 23.2 ± 0.6 minutes per procedure. Surgical mortality was 3% in MI-N and 15.9% in MI-C. The rate of arrhythmia was significantly lower in MI-N. The postsurgical levels of tumor necrosis factor-α and myeloperoxidase were lower in new method, indicating less inflammation. Overall, 28-day post-MI survival rate was 68% with MI-N and 48% with MI-C. Importantly, there was no difference in infarct size or post-MI cardiac function between the methods.

Conclusions: this new rapid method of MI in mice represents a more efficient and less damaging model of myocardial ischemic injury compared with the classic method.

Figure 1

Photographs of various stages of the novel, rapid MI surgical method. See details in method section describing each panel.

Figure 2

Photographs of various stages of the novel, rapid I/R injury model in mice. Mice were subjected to I/R using the same surgical procedure as MI except that a slip knot was made to occlude LCA (A-C).

Figure 3

New method of MI is more efficient and less invasive than classical method. A) Procedure time (open bar) and recovery time (solid bar) in S-N, n=26, S-C, n=26, MI-N, n=80 and MI-C, n=80, groups, ***p<0.001 vs. both S-C and MI-C groups. ###p<0.001 vs. both S-C and MI-C groups. B) Efficiency of procedure time and post procedure recovery time in new method vs. classic way in sham and MI groups. C) Plasma concentration of TNFα measured at 24 h post-surgery in different procedure groups (n=15-17). #p<0.05 MI-N vs. S-N, ###p<0.001 MI-C vs. S-C, **p<0.01 S-N vs. S-C, and ***p<0.001 MI-N vs. MI-C group. D) Plasma concentration of TNFα measured at 7d post-surgery, n= 5-15. E) and F) Heart tissue level of MPO in different procedure groups at 24h and 7d post-surgery, n=5-15, ###p<0.001 MI-N or MI-C vs. Co, S-N and S-C, ***p<0.001 MI-N vs. MI-C.

Figure 4

Survival curves in MI or I/R models. Mice were subjected to MI or sham with either new or classical method and followed for 6 hrs (A, Peri-surgery survival curve) and 28 days (B, overall post-MI survival curves). *p<0.05 MI-N vs. MI-C group. C) I/R Peri-surgery survival rate in all groups. *p<0.05 I/R-N vs. I/R-C group.

Figure 5

Frequency of arrhythmia among the procedure groups. A) and B) are representative ECG of AVB and PVC. C) and D) are frequency of AVB and PVC during the first 30 min after the procedures. n=5-11, *p<0.05 S-N vs. S-N. E) and F) are frequency of AVB and PVC during 7 days after 30 min post-procedures. n=5-8, *p<0.05 vs. MI-C.

Figure 6

Cardiac function measured by echocardiography at 28 days post-surgery. A) Representative echocardiograph from the various groups. B&C) The LV internal diameters of diastole (LVIDd, B) and systole (LVIDs, C) were measured at the view of short-axis from M-mode. D) LV ejection fraction and E) fractional shortening was calculated using VisualSonic analysis software (n=8-12 animals/groups), ***p<0.001 vs. shams.

Figure 7

Cardiac function determined by hemodynamic measurement using Millar catheterization at 28 days post surgery. A) Representative original LV dP/dt data acquired from sham animal. The data was recorded at baseline (B) and upon isoproterenol treatment (0.1-1.0ng/mouse). B) The maximum of LV (+)dP/dt, C) (-)dP/dt, D) LVEDP and E) HR, *p<0.05 MI-N and MI-C vs. sham groups (n=9-10 animals/groups).

Figure 8

LV infarct sizes in mice subjected to MI or I/R. A) Representative photographs of TTC-stained heart sections obtained from S-N (a), MI-N (b), S-C (c) and MI-C (d) groups at 24 hrs post-surgery. B) Graphic representation of the LV infarct size expressed as percentage of infarct area over total LV area individually in each group (n=6 hearts/sham groups, and n=10 hearts/MI groups). C) Representative photographs of TTC-stained heart sections obtained from MI-N and MI-C groups at 28 day post-surgery. D) Percentage of LV infarct size in each group (n=5 hearts/sham groups, and n=8 hearts/MI groups). The infarct size was expressed as the percentage of infarct length over total LV circumference, ***p<0.001 vs. sham groups. E) Representative photographs of Evans blue and TTC double stained heart sections from the groups, see method section for details of the staining. F) Graphic representation of the LV infarct size expressed as percent of infarct area over total AAR in a) SI/R-N (n=8), b) SI/R-C (n=6), c) I/R-N (n=10) and d) I/R-C (n=10), ***p<0.001 vs. sham groups. G) Percentage of LV AAR procedure groups.