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

Abstract

The parasympathetic terminal cardiac ganglia were examined in three normal horses and in five horses with grass sickness. Histopathological changes, consistent with those observed in other ganglia of horses with grass sickness, 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 sickness, 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 obtained. There were statistically significant differences between the normal and the affected horses in terms of the triangular index (P=0.01), a geometric method of TDA, the sNN100 index (P=0.009), a statistical method of TDA, and the R to R interval (P<0.0005). These results indicate that there is a pathological and functional parasympathetic decentralisation to the heart in equine grass sickness.

The Association between Heart Rate, Heart Rate Variability, Endocrine and Behavioural Pain Measures in Horses Suffering from Laminitis*

“…Heart rate was calculated as mean duration between the R‐R peaks. As indicator of the overall parasympathetic influence on the HRV, the root mean square of successive R‐R intervals (SDRR) was used (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996; Perkins et al., 2000).…”

“…The effect of pain on HRV has been examined in human neonates and infants, where behavioural pain scores correlated with HRV and also blood pressure (van Dijk et al., 2001). In the equine literature there are, to our knowledge, no studies published that investigate the direct influence of pain on HRV (Perkins et al., 2000).…”

Measuring heart rate variability in horses to investigate the autonomic nervous system activity – Pros and cons of different methods

“…Since the parasympathetic system reacts faster than the sympathetic one, high frequency variations represent especially vagal activity (von Borell et al, 2007). However, due to non-additive interplay of SNS and PNS, the determination of mean heart rate and time-domain measures of HRV (Rugh et al, 1992;Perkins et al, 2000;Visser et al, 2002Visser et al, , 2003Kinnunen et al, 2006;Nagel et al, 2010Nagel et al, , 2011aNagel et al, ,b, 2012Schmidt et al, 2010a,b,c,d;König von Borstel et al, 2011a;Becker-Birck et al, 2012;Erber et al, 2012;Munsters et al, 2012Munsters et al, , 2013bvon Lewinski et al, 2013;Wulf et al, 2013;Halmer et al, 2014) should be critically reviewed.…”

Equine grass sickness in a donkey

“…), lack of parasympathetic innervation to the heart resulting from neuronal loss in the vagal nucleus (Barlow ; Gilmour ; Wright and Hodson ) and pathological changes in the terminal parasympathetic cardiac ganglia in EGS cases (Perkins et al . ). More typical clinical signs, however, included bilateral ptosis and muscle fasciculations (Lyle and Pirie ).…”

“…The magnitude of the tachycardia is quite typical of the chronic form of the disease (Lyle and Pirie 2009), a finding which could feasibly be attributed to a combination of various disease-associated pathological processes. These include elevated plasma adrenaline (Hodson et al 1984), increased synthesis of noradrenaline by cardiac sympathetic nerves originating in the thoracic sympathetic chain ganglion (supported by its increased dopamine-βhydroxylase content in EGS) (Griffiths et al 1993;John et al 2001), lack of parasympathetic innervation to the heart resulting from neuronal loss in the vagal nucleus (Barlow 1969;Gilmour 1973;Wright and Hodson 1988) and pathological changes in the terminal parasympathetic cardiac ganglia in EGS cases (Perkins et al 2000). More typical clinical signs, however, included bilateral ptosis and muscle fasciculations (Lyle and Pirie 2009).…”