Functional and histopathological evidence of cardiac parasympathetic dysautonomia in equine grass sickness

The parasympathetic terminal cardiac ganglia were examined in three normal horses and in five horses with grass sickness. Histopathological changes, c onsistent with those observed in other ganglia of horses with grass sicknes s, were identified in the terminal cardiac ganglia of the affected horses. A functional analysis of cardiac autonomic control by time domain analysis (TDA) Of heart rate variability was applied to eight horses with grass sick ness, and double-paired to 16 normal horses on the basis of their age, sex and breed, and the time of day at which the electrocardiographs were obtain ed. There were statistically significant differences between the normal and the affected horses in terms of the triangular index (P=0.009), a geometri c method of TDA, the sNN100 index (P=0.009), a statistical method of TDA, a nd the R to R interval (P<0.0005). These results indicate that there is a p athological and functional parasympathetic decentralisation to the heart in equine grass sickness.