Myocardial dysfunction associated with low-dose endotoxin administration in adult horses

Horses with endotoxemia have variable myocardial function, but little is known about the severity or persistence of myocardial dysfunction (MD).

Horses with experimentally induced endotoxemia have systolic and diastolic MD.

Twelve systemically healthy horses.

Horses were given Escherichia coli lipopolysaccharide 30 ng/kg over 60 min. Echocardiography and cardiac troponin I (cTnI) measurements were performed at baseline, 1, 3, and 5 h post-endotoxin. Fluid therapy (10 L), polymyxin B (6000 IU/kg), and flunixin meglumine (1.1 mg/kg) were administered intravenously, and then echocardiogram and cTnI measurements were performed (post-treatment). Results were compared using linear mixed models and adjusted for multiple comparisons. Significance was set at P < .05.

All horses showed signs of MD. A significant increase in heart rate from baseline was noted at all timepoints (P < .001). No significant increase in cTnI occurred at any timepoint. Ejection fraction decreased from baseline at 3 and 5 h (mean, 72%, 62%, and 65%, respectively; P < .001 at both timepoints). Using tissue Doppler imaging (TDI), the index of myocardial performance increased at 1, 3, and 5 h (mean, 0.40, 0.55, 0.66, 0.55; P < .01 at all timepoints). Using two-dimensional speckle tracking (2DST), the magnitude of global longitudinal strain was decreased from baseline at 3, 5 h, and post-treatment (mean, -21%, -16%, -17%, and -19%; P < .0001, .0001, and .04, respectively).

Systolic and diastolic MD are evident in the absence of increased cTnI. Advanced echocardiographic modalities such as TDI and 2DST improve diagnostic capability for identifying regional abnormalities.