Non-invasive assessment of cardiac function in a mouse model of renovascular hypertension

Abstract

Hypertension continues to be a significant cause of morbidity and mortality, underscoring the need to better understand its early effects on the myocardium. The aim of this study is to determine the feasibility of in vivo longitudinal assessment of cardiac function, particularly diastolic function, in a mouse model of renovascular hypertension. Renovascular hypertension (RVH) was induced in 129S1/SvImJ male mice (n=9). To assess left ventricular (LV) systolic and diastolic function, M-mode echocardiography, pulsed-wave Doppler echocardiography and tissue Doppler imaging were performed at baseline, 2 and 4 weeks after the induction of renal artery stenosis. Myocardial tissue was collected to assess cellular morphology, fibrosis, extracellular matrix remodeling and inflammation ex vivo. RVH led to a significant increase in systolic blood pressure after 2 and 4 weeks (baseline: 99.26±1.09 mm Hg; 2 weeks: 140.90±7.64 mm Hg; 4 weeks: 147.52±5.91 mm Hg, P<0.05), resulting in a significant decrease in LV end-diastolic volume, associated with a significant elevation in ejection fraction and preserved cardiac output. Furthermore, the animals developed an abnormal diastolic function profile, with a shortening in the E velocity deceleration time as well as increases in the E/e' and the E/A ratio. The ex vivo analysis revealed a significant increase in myocyte size and deposition of extracellular matrix. Non-invasive high-resolution ultrasonography allowed assessment of the diastolic function profile in a small animal model of renovascular hypertension.

Figure 1

Echocardiographic images. Representative echocardiographic acquisitions of parasternal long-axis (a), parasternal short-axis (b) and apical four chamber view (c) at baseline. In c, the sample volume position is shown in order to have the mitral inflow as parallel to the transducer as possible. Ao, aorta; AW, anterior wall; LV, left ventricle; LA, left atrium; MV, mitral valve; PW, posterior wall; PM, papillary muscles; RA, right atrium; RV, right ventricle; VS, ventricular septum. A full color version of this figure is available at the Hypertension Research journal online.

Figure 2

Renovascular hypertension mouse model. Representative surgical image of the occlusion cuff placement around the right renal artery (a), and ultrasound image of the cuff around the renal artery 2 weeks after surgery (b).

Figure 3

Left ventricular muscle mass and systolic function assessment. (a) Representative M-mode echocardiographic acquisitions at baseline and 4 weeks after renal vascular hypertension (RVH) induction. Asterisks indicate the anterior wall of the left ventricle (LV), showing the increased LV muscle thickness in RVH animals; LV muscle mass is quantified in the middle panel. (b) Analysis of systolic function parameters, including LV end-diastolic volume, LV ejection fraction and cardiac output at baseline, 2 and 4 weeks post surgery. Data represent medians with interquartile range. *P < 0.05, **P < 0.01 and ***P < 0.001 vs baseline.

Figure 4

Left ventricular diastolic function assessment. The top panels show representative images of the apical four-chamber mitral valve inflow at baseline and 4 weeks after renal vascular hypertension (RVH) induction, showing E wave shortening and a decrease in the mitral inflow deceleration time. Bottom panels show representative images of the mitral annulus tissue Doppler motion at baseline and 4 weeks after RVH induction with a marked decrease of the mitral annulus e′ wave. Middle panel show the quantification of these signals, using clinically used parameters. E: mitral valve E velocity, A: mitral valve A velocity. *P < 0.05, **P < 0.01 and ***P < 0.001 vs baseline. A full color version of this figure is available at the Hypertension Research journal online.

Figure 5

Left ventricular histological assessment. (a) Analysis of myocyte diameter in control and renal vascular hypertension (RVH) animals 4 weeks after surgery. Data represent mean ± s.e.m. *P < 0.05 vs control. (b–d) Representative images of histological staining of myocardium from control animals (left panel) and RVH animals (right panel): (b) Masson’s Trichrome, (c) collagen 3, (d) F4/80 + macrophages.