Cardiac dysfunction in a rat model of chronic bacteremia

Cardiac function was examined in vivo and in vitro in rats to determine if cardiac dysfunction could be demonstrated in a nonlethal model of infection. Bacteremic rats (n = 6) had a subcutaneous polymicrobial abscess produced via repeated inoculations of an encapsulated foreign body with Escherichia coli, Bacteroides fragilis, and Staphylococcus aureus while control rats (n = 6) had the same subcutaneous, encapsulated foreign body (an inflammatory focus) but were not inoculated with bacteria. Cardiovascular function was assessed indirectly in vivo by measuring the maximal O2 uptake during a progressive exercise test in both groups before and 14 days after the initiation of inoculations. Cardiac function was also assessed in vitro in the same rats by measuring stroke volumes generated at six different preloads with constant heart rate and afterload. Bacteremic rats had a significantly different fever curve and leukocytotic response than control rats over the 14 day period. The majority of rats that received inoculations demonstrated bacteremias, while none of the control animals had positive cultures for the inoculated organisms. Although in vivo assessment of cardiovascular function showed no evidence of dysfunction, in vitro assessment demonstrated a significant rightward shift of the Starling curve in bacteremic rats. These data suggest that LV dysfunction occurs even during nonlethal infections but may be masked in vivo by compensatory mechanisms.