Animal models of endocarditis

Right atrial pressure alterations during echocardiography-guided-catheterization predict tricuspid valvular impairment: a novel method for the creation of a rabbit model of Staphylococcus aureus endocarditis

Background

We previously reported the use of a catheter system to damage the tricuspid valve and create infectious endocarditis (IE) in an animal model. The current study aims to create a faint IE model suitable for antibiotic prophylaxis using a low bacterial inoculum. We also aim to explore a way to quantitatively assess valvular impairment and to predict the success of the IE models during catheterization.

Methods

Ninety rabbits were assigned to two groups according to the density of bacteria inoculated (1 × 10⁵ CFU for Group A and 1 × 10⁴ CFU for Group B). A catheter system consisting of a polyethylene catheter and a guide wire were used to damage the valve. The catheter system was passed through the rabbits’ tricuspid valves under echocardiographic guidance. A pressure transducer was used to assess right atrial pressure (P_RA) before and just after valvular damage to calculate the pressure alterations (ΔP_RA). The animals in group A and B were divided into 3 subgroups according to the ΔP_RA (0–5 mmHg for Groups A₁ and B₁; 5–10 mmHg for Groups A₂ and B₂; 10–15 mmHg for Groups A₃ and B₃). Staphylococcus aureus (ATCC 29213) inoculation was performed 24 hr after cardiac catheterization.

Results

Faint IE was confirmed in 20%, 93.3%, 26.7%, 6.7%, 20%, and 33.3% of the rabbits in Groups A₁, A₂, A₃, B₁, B₂, and B₃, respectively. There was no difference in the LV/RV ratio and V_TR of the No-IE, faint-IE, and severe IE animals. Faint IE rabbits had a larger ΔP_RA than No-IE rabbits (7.81 ± 1.21 vs. 2.48 ± 1.0, P < 0.01, for Group A; 7.60 ± 1.32 vs. 2.98 ± 1.08, P < 0.01, for Group B). The ΔP_RA of severe IE and faint IE rabbits was significantly different (13.11 ± 1.31 vs. 7.81 ± 1.21, P < 0.01, for Group A; 12.73 ± 1.44 vs.7.60 ± 1.32, P < 0.01, for Group B).

Conclusion

ΔP_RA could be used to assess valvular impairment. Controlling the value of ΔP_RA during catheterization and inoculating of an appropriate dose of bacteria was associated with a successful IE model.

A rabbit model of right-sided Staphylococcus aureus endocarditis created with echocardiographic guidance

Background

The most widely used experimental models of infective endocarditis (IE) are the rabbit and rat models, in which cardiac valve lesions are induced by a polyethylene catheter introduced into the left ventricle through the aortic valve. Our study was designed to create a rabbit model of IE right-sided with echocardiographic guidance.

Methods

Thirty rabbits underwent both catheterization and inoculation (group A). These were divided into three subgroups of ten based on the time of catheter removal (immediately, after 24 h, and after death or moribundity for groups, A₁, A₂, and A₃, respectively). Ten inoculated-only and ten catheterized-only rabbits served as controls. A catheter system consisted of a polyethylene catheter and a guide wire inside it. This system was passed through the rabbits’ tricuspid valves under echocardiographic guidance to damage them. The ratio of left ventricle to right ventricle (LV/RV) was measured in a four-chamber view before catheterization and at the time of death or moribundity. The peak velocity of tricuspid regurgitation (V_TR) was measured in a four-chamber view at the time of catheterization and at the time of death or moribundity. Staphylococcus aureus (ATCC 29213) inoculation was performed 24 h after right heart catheterization to produce IE.

Results

IE was confirmed in 28 of 30 rabbits by macroscopic and histologic examination of tricuspid valves, blood cultures, and bacterial count in cardiac vegetations. Cardiac vegetations were confirmed in 25 of 28 IE rabbits by echocardiography. Enlargement of right ventricle dimension with a significantly decreased LV/RV ratio was confirmed in all IE rabbits at the time of death or moribundity than at the initial state (1.11 ± 0.35 vs. 1.95 ± 0.39, P < 0.01; 1.21 ± 0.34 vs. 1.98 ± 0.35, P < 0.01; 1.04 ± 0.31 vs. 2.00 ± 0.41, P < 0.01 for groups A₁, A₂, and A₃, respectively). V_TR was significantly higher in all the IE rabbits at the time of death or moribundity than at the time of catheterization (1.89 ± 0.46 vs 0.76 ± 0.45, P < 0.01; 2.04 ± 0.73 vs 0.68 ± 0.66, P < 0.01; 2.24 ± 0.51 vs 0.87 ± 0.55, P < 0.01 for group A₁, A₂ and A₃, respectively).

Conclusion

The models described herein closely reproduced the pathogenesis and pathophysiology of right heart catheter-induced endocarditis in humans. Echocardiographic guidance is helpful in the process of right heart catheterization. Some echocardiographic parameters, such as V_TR and the LV/RV ratio could be used to assess the success or failure of the IE models.