Cardiovascular Journal of Africa: Vol 27 No 3 (May/June 2016)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 27, No 3, May/June 2016

AFRICA

141

techniques that require open-chest procedures and intubation

of vessels, offering no opportunity for time-course studies,

since they require time-consuming surgeries, with subsequent

euthanasia.

The Sonos 5500 echocardiographic system,

2-4,7

a universal type

of echocardiography instrument used in clinics, is commonly

equipped with a high-frequency transducer that can be used for

rodent studies. This study is the first report to use a standard

echocardiographic system (IE 33) to assess cardiac structure and

function in rats with myocardial hypertrophy. The IE 33 system

can clearly show parasternal long-axis and short-axis views,

apical four-chamber views of the LV, and the abdominal aorta in

rats without requiring an extra transducer. This reduces the cost

of investigation in small animals.

Concentric myocardial hypertrophy is a hallmark of chronic

pressure overload. Increased ventricular wall thickness induced

by overload pressure is initially beneficial to maintain normal

cardiac function. However, the heart could convert to heart

failure with LV dilatation if the hypertrophic stimulus is

maintained. In our study, significant increases in LVPW and

IVS with only small decreases in LVIDs were indicative of pure

concentric hypertrophy, which is often observed during the early

stages of pure pressure overload. Most previous studies have

shown late-stage chamber dilatation, signifying the end of the

compensatory response and the start of heart failure.

However,

in this study, even at six weeks post surgery, there was little

change in LVIDs, LVIDd, EDV and ESV, indicating chamber

dilatation and dysfunction in ventricular relaxation were not

present at this stage of hypertrophy.

FS and EF are commonly used parameters to evaluate systolic

function, which is determined by measuring LV end-diastolic

and end-systolic diameters with M-mode echocardiography.

Since increased afterload may depress stroke volume (SV) in

AAC rats, FS and EF were lower in the AAC rats compared

to sham rats from three to six weeks. Accordingly, significant

decreases in CO were observed in AAC rats, especially at the

four-week time point, since CO may be affected by HR and EF

(both reduced in the AAC groups).

In this study, we measured PFVA and E waves using

echocardiography to evaluate ventricular relaxation and diastolic

function. Significant decreases in PFVA and E-wave values in the

AAC rats suggested restrictive filling, which may result from the

combined effect of elevated ESV and impaired compliance due

to wall thickening and/or fibrosis.

Although E/A ratio is a marker for ventricular relaxation,

it could not be obtained in this study since the E and A waves

were fused in the rats due to their extremely fast heart rates.

To distinguish E and A waves, Kokubo

et al.

used ketamine

hydrochloride and xylazine anaesthesia in the animals in order

to decrease the HR to 70–80% of normal levels in conscious

animals, however control of HR is difficult.

In rats, the heart generally gains ~ 1 g in weight with each

2-mm increase in LV wall thickness. Progressive increases in

heart weight, HMI and LVMI, and increased cross-sectional

areas of the myocytes (determined using histological analysis)

were observed in the ACC rats. Elliott

et al.

found that

echocardiographic determination of LVm is relatively accurate,

yet highly overestimated in rats. As LVm increases, a greater

degree of LVm overestimation occurs. However, a strong

correlation between LVm determined using echocardiography

and the actual heart weights of sacrificed rats was observed in

the present study, indicating that the parameters measured using

echocardiography were closer to the actual values.

Fibrosis is a common response to pressure overload or

infarction, to overcome elevated ventricular wall stress. Excessive

fibrotic deposits around the small vessels may reduce oxygen

and nutrient exchange rates between the blood supply and the

surrounding myocardium. Additionally, extensive interstitial

fibrosis impedes myocardial relaxation, increasing stiffness in the

ventricular wall and reducing LV compliance.

Weeks

Perivascular fibrosis

(PVF/VA)

Sham AAC

Fig. 9.

Comparison of perivascular fibrosis between the sham

and AAC groups using Masson trichrome staining

(A–E) (

200), (E) (

100). Data are presented as mean

SEM. *

0.05 vs sham control, **

0.01 vs sham

control. A: sham rats at three weeks, B: sham rats at

four weeks, C: sham rats at six weeks, D: AAC rats at

three weeks, E: AAC rats at four weeks, F: AAC rats

at six weeks, G: quantitative analysis of perivascular

fibrosis between the sham and AAC groups. ANOVA

was performed to compare the AAC and sham groups

when the probability value was statistically significant.

An LSD

-test was applied for multiple comparisons.