Abstract
BackgroundStudies have shown regional and functional selectivity of cardiac postganglionic neurones indicating there might exist a similar heterogeneity in spinal segmental preganglionic neurones, which requires further investigation. MethodsRight and left sympathetic chains were electrically stimulated from T6 to T1 in the innervated isolated rabbit heart preparation (n = 18). Sinus rate, left ventricular pressure, retrograde ventriculo-atrial conduction, monophasic action potential duration, effective refractory period, ventricular fibrillation threshold and electrical restitution were measured. ResultsRight sympathetic stimulation had a greater influence on heart rate (T1-T2: right; 59.9 ± 6.0%, left; 41.1 ± 5.6% P < 0.001) and left stimulation had greater effects on left ventricular pressure (T1-T2: right; 20.7 ± 3.2%, left; 40.3 ± 5.4%, P < 0.01) and ventriculo-atrial conduction (T1-T2: right; −6.8 ± 1.1%, left; −15.5 ± 0.2%) at all levels, with greater effects at rostral levels (T1-T3). Left sympathetic stimulation caused shorter monophasic action potentials at the base (T4-T5: right; 119.3 ± 2.7 ms, left; 114.7 ± 2.5 ms. P < 0.05) and apex (T4-T5: right; 118.8 ± 1.2 ms, left; 114.6 ± 2.6 ms. P < 0.05), greater shortening of effective refractory period (T4-T5: right; −3.6 ± 1.3%, left; −7.7 ± 1.8%. P < 0.05), a steeper maximum slope of restitution (T4-T5 base: right; 1.3 ± 0.2, left; 1.8 ± 0.2. P < 0.01. T4-T5 apex: right; 1.0 ± 0.2, left; 1.6 ± 0.3. P < 0.05) and a greater decrease in ventricular fibrillation threshold (T4-T5: right; −22.3 ± 6.8%, left;-39.0 ± 1.7%), with dominant effects at caudal levels (T4-T6). ConclusionsThe preganglionic sympathetic efferent axons show functionally distinct pathways to the heart. The caudal segments (T4-T6) of the left sympathetic chain had a greater potential for arrhythmia generation and hence could pose a target for more focused clinical treatments for impairments in cardiac function.
Highlights
Excitation of small distal branches of cardiac postganglionic nerve bundles, elicits highly localized changes in spatially restricted portions of the heart [1,2,3]
Studies reviewed by Randall [4] support this selectivity and led him to suggest the innervation from the spinal cord preganglionic neurones must be regionally specific
This depends on Abbreviations: APD, action potential duration; CL, cycle length; ERP, effective refractory period; LV, left ventricle; LVP, left ventricular pressure; Monophasic action potential (MAP), monophasic action potential; RT, restitution; VA, ventriculo-atrial; VF threshold (VFT), ventricular fibrillation threshold
Summary
Excitation of small distal branches of cardiac postganglionic nerve bundles, elicits highly localized changes in spatially restricted portions of the heart [1,2,3]. Studies reviewed by Randall [4] support this selectivity and led him to suggest the innervation from the spinal cord preganglionic neurones must be regionally specific This depends on Abbreviations: APD, action potential duration; CL, cycle length; ERP, effective refractory period; LV, left ventricle; LVP, left ventricular pressure; MAP, monophasic action potential; RT, restitution; VA, ventriculo-atrial; VFT, ventricular fibrillation threshold. To elicit an action in a discrete region of the heart by activation within the spinal cord would require projections of spinal axons onto discrete ganglion cells Such an organization is supported by studies of innervation and transmission in sympathetic ganglia, which indicate that the discharge of a single ganglion cell is dominated by a single preganglionic fibre [10,11,12]. The caudal segments (T4-T6) of the left sympathetic chain had a greater potential for arrhythmia generation and could pose a target for more focused clinical treatments for impairments in cardiac function
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