Effect of Loading Changes on the Intraventricular Pressure Measured by Color M-Mode Echocardiography in Rats

Abstract

Evaluation of diastolic function is a pivotal challenge due to limitations of the conventional echocardiography, especially when the heart rate is rapid as in rats. Currently, by using color M-mode echocardiography (CMME), intraventricular pressure difference (IVPD) and intraventricular pressure gradient (IVPG) in early diastole can be generated and are available as echocardiographic indices. These indices are expected to be useful for the early diagnosis of heart failure (HF), especially diastolic dysfunction. There have not been any studies demonstrating changes in IVPD and IVPG in response to changes in loading conditions in rats. Therefore, the present study aims to evaluate CMME-derived IVPD and IVPG changes in rats under various loading conditions. Twenty rats were included, divided into two groups for two different experiments, and underwent jugular vein catheterization under inhalational anesthetics. Conventional echocardiography, CMME, and 2D speckle tracking echocardiography were measured at the baseline (BL), after intravenous infusion of milrinone (MIL, n = 10), and after the infusion of hydroxyethyl starch (HES, n = 10). Left ventricular IVPD and IVPG were calculated from color M-mode images and categorized into total, basal, mid-to-apical, mid, and apical parts, and the percentage of the corresponding part was calculated. In comparison to the BL, the ejection fraction, mid-to-apical IVPG, mid IVPG, and apical IVPD were significantly increased after MIL administration (p < 0.05); meanwhile, the end-diastolic volume, E-wave velocity, total IVPD, and basal IVPD were significantly increased with the administration of HES (p < 0.05). The increase in mid-to-apical IVPD, mid IVPD, and apical IVPD indicated increased relaxation. A significant increase in basal IVPD reflected volume overloading by HES. CMME-derived IVPD and IVPG are useful tools for the evaluation of various loading conditions in rats. The approach used in this study provides a model for continuous data acquisition in chronic cardiac disease models without drug testing.

Keywords: color m-mode echocardiography; diastolic function; heart failure; intraventricular pressure; preload.

Figure 1

Two-dimensional speckle tracking echocardiography (2DSTE) in rats obtained from the left apical 4-chamber view. The entire left ventricular endocardium was traced for evaluation of strain rate (SR, a) and global longitudinal strain (GLS, b).

Figure 2

Effect of various loading conditions on 2DSTE measurements. Plots showing the median (central horizontal line) and range (n = 10, for each experiment). BL, baseline; MIL, milrinone; HES, hydroxyethyl starch; SR, strain rate; GLS, global longitudinal strain. * p < 0.05 compared with BL.

Figure 3

The echocardiography and IVPD (IVPG) in rats. Images in each column were captured from the same rat. In the first experiment, the heart function was evaluated at the baseline (a–d) and after milrinone (MIL, e–g). In the second experiment, measurements were recorded at the baseline (BL, i–l) and after hydroxyethyl starch infusions (HES, m–p). Firstly, the mitral inflow was evaluated in all groups by pulsed-wave Doppler echocardiography from the left apical 4-chamber view (a,e,i,m) that showed significantly increased E-wave after HES infusion. Color m-mode echocardiography (CMME) was switched on and photos were captured (b,f,j,n) for further calculation. The IVPD was calculated by MATLAB software using in-house coding, and the three-dimensional temporal and spatial profiles of the left ventricular IVPD was obtained where the time, IVPD, and distance were determined (c,g,k,o). Subsequently, the IVPD (IVPG) in early diastole was identified (d,h,i,p). The top (blue), middle (red), and bottom (blue) lines represent inertial, total, and convective IVPD, respectively.