ABC | Volume 110, Nº6, June 2018

Original Article Zhen et al AAC leads to obvious CH using 0.45 mm needle Arq Bras Cardiol. 2018; 110(6):568-576 Table 5 – Percentage of collagen deposition in the left ventricle based on weight and needle size Weight 0.40 mm 0.45 mm 0.50 mm Sham 18 g 5.8 ± 2.2* 8.9 ± 1.3* 5.1 ± 1.3* 2.6 ± 1.0 22 g 5.2 ± 1.6* 4.9 ± 1.5* 2.5 ± 0.9 26 g 6.1 ± 1.0* 5.3 ± 1.8* 3.1 ± 0.8 Data are presented as the mean ± SD (n = 6). *p < 0.05 represents a significant difference between the abdominal aortic constriction (AAC) and sham groups. Table 6 – Body weight changes with AAC under 0.45 mm needle 18 g/0.45 mm (n = 8) 22 g/0.45 mm (n = 7) 26 g/0.45 mm(n = 4) Change in BW(g) 8.4 ± 0.8* 4.4 ± 0.8 2.4 ± 0.3 BW: body weight; AAC: abdominal aortic constriction. Data are presented as the mean ± SD. *p < 0.05 represents a significant difference between the 18 g/0.45 mm group and the 22 g/0.45 mm and 26 g/0.45 mm groups. Table 7 – Body weight and BW changes in 18-g mice 18 g/0.40 mm (n = 6) 18 g/0.45 mm (n = 8) 18 g/0.50 mm (n = 10) 18 g/Sham (n = 10) BW before surgery (g) 18.1 ± 0.4 18.1 ± 0.3 18.0 ± 0.4 17.9 ± 0.4 BW at week 8 (g) 25.3 ± 0.4* 26.5 ± 0.9 26.6 ± 0.8 26.8 ± 0.9 BW change (g) 7.2 ± 0.6* 8.4 ± 0.8 8.6 ± 0.6 8.8 ± 0.9 BW: body weight. BW changes of 18-g mice before and after surgery for 8 weeks. Data are presented as the mean ± SD. *p < 0.05 represents a significant difference between the 18 g/0.40 mm group and the rest groups after surgery. The diagnosis of CH usually depends on changes in cardiac function and morphology. 11 Echocardiography can be performed in vitro noninvasively during the first assessment of CH, and it is especially used to monitor changes in cardiac function. 12 We performed echocardiographic examinations of mice at the end of week 4 and week 8 post-surgery. Data (week 4 data in Table 2) showed that at the end of week 4, the phenomena of thickened ventricular walls, enlarged ventricular chambers, and decreased cardiac functions were emerging in each AAC group compared with the sham groups, and this diversity was consistent with the characteristic cardiac changes that occur with chronic pressure overload. 13,14 These trends became more pronounced at the end of week 8 (week 8 data in Table 2), when EF and FS, which represent cardiac function, were significantly lower compared with the sham groups. CH also increased HW. In our study, the HW, HW/BW ratio, and HW/TL ratio for the AAC groups were significantly increased (Table 3). Cardiac remodeling is the most typical pathological change of CH, including cardiomyocyte hypertrophy and the extracellular matrix increases. 15 Our histological results showed increased external diameters and ventricular thickness in gross hearts and cross-sections under AAC (Figures 1A and B). HE staining of the AAC groups displayed the hypertrophic pathology of cardiomyocytes and nuclei (Figure 1C). PSR staining of the AAC groups displayed extensive collagen depositions (Figure 1D), particularly in the perivascular space (Figure 1E). Statistical analysis showed that the thickness of the left ventricle (Table 4) and the percentage of collagen deposition (Table 5) were significantly increased in the AAC groups compared to the sham group. Regarding the formation of collagen, Kuwahara et al. 16 indicated that cardiac fibroblasts are activated on day 3 after PO, and that the neoformative fibrous tissues mainly affect the diastolic function rather than the systolic function during the initial 4 weeks. Then, excessive myocardial fibrosis is implicated in systolic dysfunction because of its more intensive traction, and cardiac function begins to deteriorate significantly. Regarding EF and FS values for the AAC groups (Table 2), the downward trends from week 4 to week 8 conform to this theory. Choosing the proper needle is critical for establishing the CH model. Based on these results, we found that all mice with AAC died when a 0.35-mm needle was used for ligation for all 3 weight levels and when a 0.40-mm needle was used for ligation for the 22-g and 26-g groups; therefore, these 5 groups of weight–needle pairings were clearly unsuitable for use. The 18g/0.40mm group had obvious CH compared with the sham group, and its survival rate was acceptable (6 out of 10). However, it should still be excluded because the 18 g/0.45 mm group showed more obvious CH and higher survival rates (8 out of 10) (Table 1, Table 3). The 0.45-mm and 0.50-mm needles are available for all 3 weight levels, but both can result in definite myocardial hypertrophy. However, the values of the HW, HW/BW ratio, and HW/TL ratio for the AAC mice when using the 0.45-mm needle were significantly higher than those when using a 0.50-mm needle for each weight level (Table 3). Therefore, for all 3 weight levels of our study, a CH model can be established using a 0.50-mm needle and the survival rate of the mice will not be threatened. However, a 0.45-mm needle leads to more effective CHmodel, and higher mortality than the 0.50-mm needle. 573