Heart rate variability after radiofrequency ablation of epicardial ganglionated plexuses on the ovine left atrium.

BACKGROUND: Ganglionated plexuses (GP) are terminal parts of cardiac autonomous nervous system (ANS). Radiofrequency ablation (RFA) for atrial fibrillation (AF) possibly affects GP. Changes in heart rate variability (HRV) after RFA can reflect ANS modulation. METHODS: Epicardial RFA of GP on the left atrium (LA) was performed under the general anesthesia in 15 mature Romanov sheep. HRV was used to assess the alterations in autonomic regulation of the heart. A 24 - hour ECG monitoring was performed before the ablation, 2 days after it and at each of the 12 following months. Ablation sites were evaluated histologically. RESULTS: There was an instant change in HRV parameters after the ablation. A standard deviation of all intervals between normal QRS (SDNN), a square root of the mean of the squared differences between successive normal QRS intervals (RMSSD) along with HRV triangular index (TI), low frequency (LF) power and high frequency (HF) power decreased, while LF/HF ratio increased. Both the SDNN, LF power and the HF power changes persisted throughout the 12 - month follow - up. Significant decrease in RMSSD persisted only for 3 months, HRV TI for 6 months and increase in LF/HF ratio for 7 months of the follow - up. Afterwards these three parameters were not different from the preprocedural values. CONCLUSIONS: Epicardial RFA of GP's on the ovine left atrium has lasting effect on the main HRV parameters (SDNN, HF power and LF power). The normalization of RMSSD, HRV TI and LF/HF suggests that HRV after epicardial RFA of GPs on the left atrium might restore over time.

Radiofrequency catheter ablation of pulmonary vein roots results in axonal degeneration of distal epicardial nerves.

BACKGROUND: In treatment of atrial fibrillations (AF), radiofrequency ablation (RFA) at the pulmonary vein (PV) roots isolates AF triggers in the myocardial sleeves, but also can destroy PV ganglia and branches of the intrinsic cardiac nerve plexus. AIM: To determine the long-term impact of RFA at the PV roots on the structure of epicardial nerves located distally from the RFA site. METHODS: Five black-faced sheep underwent epicardial RFA of the left and middle PV roots. Two to 3 months after RFA, we obtained samples of epicardial nerves from remote locations of the left dorsal (LD) neural subplexus that extends along the roots of the superior PVs toward the coronary sinus (CS) and dorsal left ventricle (LV). Right atrial epicardial nerves from the right ventral (RV) neural subplexus of the ablated animals and epicardial nerves from LD neural subplexus of five additional intact sheep were used as control. Nerve morphology was examined using histochemical, immunohistochemical and transmission electron microscopy. RESULTS: Histochemical acetylcholinesterase staining did not reveal any epicardial nerve alterations. However, tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) staining showed clearly the reduced numbers of TH and ChAT immunoreactive (IR) nerve fibers within epicardial nerves derived from the remote LD subplexus; control samples from all examined animals were full of evenly distributed TH-IR and ChAT-IR nerve fibers. In sharp contrast to control nerves, numerous swollen or disintegrated axons and Schwann cells with pyknotic nuclei inside unmyelinated and myelinated nerve fibers were identified by electron microscopy of ultrathin sections of epicardial nerves from the CS and LV regions in all ablated animals. CONCLUSIONS: Degeneration of remote atrial and ventricular epicardial nerves is evident 2-3 months after epicardial RFA at the PV roots. Such nerves are likely to be non-functional. Therefore, long-term autonomic dysfunction is a potential risk of PV isolation by RFA.

Immunohistochemical characterization of the intrinsic cardiac neural plexus in whole-mount mouse heart preparations.

BACKGROUND: The intrinsic neural plexus of the mouse heart has not been adequately investigated despite the extensive use of this species in experimental cardiology. OBJECTIVE: The purpose of this study was to determine the distribution of cholinergic, adrenergic, and sensory neural components in whole-mount mouse heart preparations using double immunohistochemical labeling. METHODS/RESULTS: Intrinsic neurons were concentrated within 19 ± 3 ganglia (n = 20 mice) of varying size, scattered on the medial side of the inferior caval (caudal) vein on the right atrium and close to the pulmonary veins on the left atrium. Of a total of 1,082 ± 160 neurons, most somata (83%) were choline acetyltransferase (ChAT) immunoreactive, whereas 4% were tyrosine hydroxylase (TH) immunoreactive; 14% of ganglionic cells were biphenotypic for ChAT and TH. The most intense ChAT staining was observed in axonal varicosities. ChAT was evident in nerve fibers interconnecting intrinsic ganglia. Both ChAT and TH immunoreactivity were abundant within the nerves accessing the heart. However, epicardial TH-immunoreactive nerve fibers were predominant on the dorsal and ventral left atrium, whereas most ChAT-positive axons proceeded on the heart base toward the large intrinsic ganglia and on the epicardium of the root of the right cranial vein. Substance P-positive and calcitonin gene-related peptide-immunoreactive nerve fibers were abundant on the epicardium and within ganglia adjacent to the heart hilum. Small intensely fluorescent cells were grouped into clusters of 3 to 8 and were dispersed within large ganglia or separately on the atrial and ventricular walls. CONCLUSION: Although some nerves and neuronal bundles of the mouse epicardial plexus are mixed, most express either adrenergic or cholinergic markers. Therefore, selective stimulation and/or ablation of the functionally distinct intrinsic neural pathways should allow the study of specific effects on cardiac function.

Nerve supply of the human pulmonary veins: an anatomical study.

BACKGROUND: Atrial ectopic discharges originating in the pulmonary veins (PVs) are known to initiate atrial fibrillation (AF), which may be terminated by catheter-based PV isolation. Because a functional relationship exists between cardiac autonomic effects and PVs in arrhythmogenesis, it has been suggested that discharges of the nerves that proceed to the PVs and interconnect with intrinsic ganglionated nerve plexuses are potential triggers of AF in man. OBJECTIVE: This study sought to determine the characteristics and distribution of neural routes by which autonomic nerves supply the human PVs. METHODS: We examined the intrinsic neural structures of 35 intact (nonsectioned) left atrial (LA)-PV complexes stained transmurally for acetylcholinesterase using a stereomicroscope. RESULTS: The epicardial ganglionated nerves pass onto the extrapulmonary segments of the human PVs from the middle, left dorsal, and dorsal right atrial subplexuses. The left and right inferior PVs involved a lesser number of ganglia than the left and right superior PVs. Abundant extensions of epicardial nerves penetrate transmurally the PV walls and form a patchy neural network beneath the endothelium of PVs. The subendothelial neural meshwork with numerous free nerve endings, which appeared to be typical sensory compact nerve endings, was mostly situated at the roots of the 4 PVs. No ganglia were identified beneath the endothelium of the human PVs. CONCLUSION: The richest areas containing epicardial ganglia, from which intrinsic nerves extend to the human PVs, are concentrated at the inferior surface of both the inferior and left superior PVs. Therefore, these locations might be considered as potential targets for focal pulmonary vein ablation in catheter-based therapy of AF.

Innervation of pulmonary veins: morphologic pattern and pathways of nerves in the human fetus.

The aim of the study was to determine the anatomy of intrinsic nerves supplying human pulmonary veins (PVs). Twenty-two hearts of human fetuses with full sets of PVs were examined using a histochemical method for acetylcholinesterase in order to stain transmurally intrinsic neural structures on non-sectioned PVs for subsequent stereomicroscopic examination. Findings of the study demonstrate that epicardiac nerve extensions from both the dorsal right atrial and the middle dorsal subplexuses reached the right superior as well as the right inferior PVs, whereas the left superior PV was supplied by nerve extensions from the left dorsal subplexus. The left and middle dorsal subplexuses contributed nerves to the left inferior PV. The ganglia related topographically to PVs were patchy in distribution. On the left and right superior PVs, 38+/-6 and 31+/-3 ganglia were found, respectively, whereas 46+/-7 and 38+/-7 ganglia were identified on the left and right inferior PVs. The size of ganglia was similar for all four veins, ranging in area from 0.004+/-0.0003 to 0.007+/-0.0004 mm(2). The total area of ganglia distributed on a given PV was similar, ranging from 0.15+/-0.0003 to 0.25+/-0.0004 mm(2). The present findings demonstrate that the richest ganglion sites supplying intrinsic nerves to the human PVs are located on the posterior sides of both inferior and the left superior PVs and, therefore, these sites may be considered primary targets for focal pulmonary vein ablation in catheter-based therapy of atrial fibrillation.

Morphometric analysis of pulpal myelinated nerve fibers in human teeth with chronic periodontitis and root sensitivity.

BACKGROUND: The reasons why root sensitivity occurs in some periodontally diseased teeth are still unknown. It is possible that root sensitivity may be related to changes of intradental myelinated nerve fibers, which are responsible for dentine sensitivity. OBJECTIVE: The aim of this study was to define the pattern of myelinated nerve fiber changes in the pulps of teeth with and without root sensitivity in the presence of chronic periodontitis. MATERIALS AND METHODS: A total of 33 cross-sectioned human dental pulp specimens were collected from noncarious, intact, permanent teeth sensitive to electric and thermal (cold) stimulus (10 hypersensitive teeth with chronic periodontitis (HTPP group), 15 nonsensitive teeth with chronic periodontitis (NTPP group), and 8 nonsensitive teeth with healthy periodontium (control group)). The morphometric parameters were estimated using light microscopy and image-analyzing computer program Image-Pro Plus. RESULTS: The means of myelinated nerve fiber density, fiber and axon diameter, area, perimeter, length, width, g ratio, index of circularity, and myelin sheath thickness in NTPP group significantly differed from HTPP group and the control group teeth (p<0.001). The great reduction in the density of myelinated nerve fibers in NTPP group was accompanied by unequal decrease in the number of very large-diameter myelinated nerve fibers. The mean values of morphometric parameters of all myelinated nerve fibers in HTPP group were almost the same as those in the control teeth, and no significant difference was observed. CONCLUSION: The findings of the present study suggest that the reason for enhanced root sensitivity has likely nothing to do with changes of the innervation of myelinated nerves in the dental pulp. While, decreased sensitivity of periodontally diseased teeth may be related to the degeneration of myelinated nerve fibers in the pulp.