Myocardial mechanics in a rat model with banding and debanding of the ascending aorta

Abstract

Background: Aortic banding and debanding models have provided useful information on the development and regression of left ventricular hypertrophy (LVH). In this animal study, we aimed to evaluate left ventricular (LV) deformation related to the development and regression of LVH.

Methods: Minimally invasive ascending aorta banding was performed in rats (10 Sprague Dawley rats, 7 weeks). Ten rats underwent a sham operation. Thirty-five days later, the band was removed. Echocardiographic and histopathologic analysis was assessed at pre-banding, 35 days of banding and 14 days of debanding.

Results: Banding of the ascending aorta created an expected increase in the aortic velocity and gradient, which normalized with the debanding procedure. Pressure overload resulted in a robust hypertrophic response as assessed by gross and microscopic histology, transthoracic echocardiography [heart weight/tibia length (g/m); 21.0 ± 0.8 vs. 33.2 ± 2.0 vs. 26.6 ± 2.8, p < 0.001]. The circumferential (CS) and radial strains were not different between the groups. However, there were significant differences in the degree of fibrosis according to the banding status (fibrosis; 0.10 ± 0.20% vs. 5.26 ± 3.12% vs. 4.03 ± 3.93%, p = 0.003), and global CS showed a significant correlation with the degree of myocardial fibrosis in this animal model (r = 0.688, p = 0.028).

Conclusion: In this animal study, simulating a severe LV pressure overload state, a significant increase in the LV mass index did not result in a significant reduction in the LV mechanical parameters. The degree of LV fibrosis, which developed with pressure overload, was significantly related to the magnitude of left ventricular mechanics.

Keywords: Aortic banding; Debanding; Left ventricular hypertrophy.

Fig. 1

Photograph of the operation procedure showing the minimally invasive ascending aorta banding procedure via upper hemisternotomy (A and B). The Teflon-felt supported banding technique was helpful for the subsequent debanding operation (C).

Fig. 2

Gross findings of the left ventricles detached from a sham rat (A), a rat that underwent the 5-week aortic banding procedure (B) and a rat that underwent the aortic debanding procedure (C) showing significant hypertrophy of the left ventricle in the aortic banding heart.

Fig. 3

Microscopic histopathology showing the myocardial staining for the sham group (A), 5-week banding group (B), and debanding group (C). Myocyte hypertrophy (PAS stain, × 400) with reactive fibrosis (MT stain, × 200) was obviously documented in the banding heart (B). However, in the debanding heart, myocardial fibrosis was documented (MT stain) without myocyte hypertrophy (PAS stain) (C). PAS stain: Periodic acid-Schiff stain, MT stain: Masson's trichrome stain.

Fig. 4

Velocity vector imaging with electrocardiographic gating for 20-30 frames/beat showed the higher fibrotic myocardium (A) and lower circumferential and radial strain than the lower fibrotic myocardium (B).

Fig. 5

Correlation of myocardial fibrosis with the peak global CS (A) and RS (B) had a significant negative correlation between myocardial fibrosis and the magnitude of peak global systolic CS (A). However, there was no significant correlation with the peak global systolic RS (B). CS: circumferential strain, RS: radial strain.