A new model for infective endocarditis of the mitral valve in rabbits.

To produce an experimental model of infective endocarditis without inserting catheters into the heart, we injected a bacterial suspension into rabbits in which mitral complex lesions had been induced by electrical stimulation of the cervical vagus. Typical infective vegetations grew on the surface of the mitral valves 1 week later. The formation of vegetations was related to the timing of the inoculation. Streptococcus viridans injected just after vagal stimulation produced vegetations in 10 of 17 animals (58.8%), but the same bacteria injected 14 days after vagal stimulation did so in only 2 of 11 animals (18.2%). The incidence of infective endocarditis was significantly higher after early inoculation compared with delayed inoculation (p < 0.01). The susceptibility to infection depended on the species of bacteria injected. Both S. viridans and Pseudomonas pseudoalkaligenes injected just after vagal stimulation produced vegetations in 10 of 17 (58.8%) and 6 of 13 (46.2%) animals, respectively, but Staphylococcus epidermidis injected just after vagal stimulation did not produce vegetations in any of the 10 animals. S. viridans injected into nine normal animals never produced vegetations. These findings indicate that infective endocarditis develops after intravenous injection of bacterial suspensions alone in rabbits with mitral complex lesions.