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. Author manuscript; available in PMC: 2013 Oct 1.
Published in final edited form as: Circ Arrhythm Electrophysiol. 2012 Aug 23;5(5):1010–1116. doi: 10.1161/CIRCEP.112.972836

Extra-Cardiac Neural Remodeling in Humans with Cardiomyopathy

Olujimi A Ajijola 1,2, Jonathan J Wisco 3,4, H Wayne Lambert 5, Aman Mahajan 1,2,6, Elena Stark 3,4, Michael C Fishbein 3, Kalyanam Shivkumar 1,2
PMCID: PMC3529182  NIHMSID: NIHMS410072  PMID: 22923270

Abstract

Background

Intra-myocardial nerve sprouting after myocardial infarction is associated with ventricular arrhythmias (VAs). Whether human stellate ganglia remodel in association with cardiac pathology is unknown. The purpose of this study was to determine whether cardiac pathology is associated with remodeling of the stellate ganglia in humans.

Methods and Results

Left stellate ganglia (LSG) were collected from patients undergoing sympathetic denervation for intractable ventricular arrhythmias, and from cadavers, along with intact hearts. Clinical data on patients and cadaveric subjects were reviewed. We classified ganglia from normal; scarred; and non-ischemic cardiomyopathic hearts without scar as NL (n=3); SCAR (n=24); and NICM (n=7), respectively. Within LSG, neuronal size, density, fibrosis, synaptic density and nerve sprouting were determined. Nerve density and sprouting were also quantified in cadaveric hearts. Mean neuronal size in NL, SCAR, and NICM groups were; 320±4μm2, 372±10μm2,and 435±10μm2 (p=0.002). No significant differences in neuronal density and fibrosis were present between the groups. Synaptic density in SCAR and NICMganglia were 57.8±11.2um2/ mm2 (p=0.039) and 44.5±7.9um2/ mm2 (p=0.084) respectively, compared to the NL, 17.8±7um2/ mm2 (overall p=0.162). There were no significant differences in LSG nerve sprouting or myocardial nerve density between the groups.

Conclusions

Neuronal hypertrophy withinLSGis associated with chronic cardiomyopathy in humans. Ganglionic and myocardial nerve sprouting and nerve density were not significantly different. These changes may be related to increased cardiac sympathetic signaling and VAs. Further studies are needed to determine the electrophysiologic consequences of extra-cardiac neuronal remodeling in humans.

Keywords: cardiomyopathy, nervous system, autonomic, nervous system, sympathetic, ventricular arrhythmia

Introduction

The sympathetic nervous system (SNS) exerts profound influence on cardiac function and electrophysiology. The SNS is associated with sudden cardiac death(1-3), increased dispersion of repolarization(4, 5), and ventricular arrhythmias in ischemic and non-ischemic myocardial substrates(6-8). Pharmacologic and non-pharmacologic modulation of adrenergic signaling remains a focal point in managing myocardial ischemia and ventricular arrhythmias(9-12).

Intra-myocardial neural remodeling (nerve sprouting) occurring at border zones of myocardial scar and normal tissue has been associated with ventricular arrhythmias and sudden cardiac death in animal models and in humans(12, 13). Data regarding physiologic function and pathological evidence of extra-cardiac neural remodeling after myocardial injury has been reported in animal models. There are minimal data on extra-cardiac neural remodeling in humans. Of the available studies, evidence for extra-cardiac neural remodeling includes trans-differentiation of sympathetic nerves to cholinergic within stellate ganglia of rats with heart failure (14), and stellate ganglion neuronal hypertrophy in chronically exercise-trained rats (15). Recently, in a rabbit model of ischemia-reperfusion injury, nerve sprouting and hyper-innervation within bilateral stellate ganglia was observed up to a month after myocardial injury (16).

Patients with cardiopulmonary disease have been reported to have greater fibrosis and neuron density within their stellate ganglia than those without such conditions, although the differences were marginal (17, 18). Whether extra-cardiac neurons undergo physical remodeling due to cardiac pathology remains unknown in man.

The purpose of this study was to perform an in-depth study to determine whether the presence of cardiac pathology and severe ventricular arrhythmias are associated with extra-cardiac neural remodeling in humans.

Methods

Specimen Collection

Cadaveric Specimens

Whole intact hearts, and left stellate ganglia were collected from cadavers (Donated Body Program, University of California-Los Angeles (UCLA), and West Virginia University (WVU). Use of preserved human specimens was in accordance with institutional guidelines. All available clinical information regarding cause of death and medical history of the cadavers was collected. Hearts were grossly dissected by a cardiac pathologist to identify any cardiac pathology, including epicardial coronary artery disease, myocardial infarction, valvular pathology, and other abnormalities. Any surgical interventions performed previously on the hearts were also noted, and correlated with clinical history as available. Postero-medial and antero-lateral papillary muscles at the mid ventricular level were harvested from all specimens for histologic analyses. All regions with or suspected to have myocardial pathology including infarctions was also sampled for histologic analysis.

The ganglia were marked for supero-inferior orientation, and sectioned for histologic analyses.

Clinical Specimens

Left stellate ganglia were collected from patients with ventricular arrhythmias undergoing thoracic sympathetic denervation for arrhythmia control. These were patients with normal or abnormal myocardial function, but with severe ventricular arrhythmias recalcitrant to conventional therapies including invasive catheter ablation. Use of these human pathologic specimens was in accordance with institutional guidelines and was approved by the institutional review board (IRB). Detailed clinical information on the patients was also collected. These included coronary angiography, nuclear myocardial perfusion studies, positive emission tomography (PET), echocardiography, cardiac computed tomography (CT) and/or magnetic resonance imaging (MRI). Electro-anatomic mapping (EAM), and electrophysiologic details of patients’ hearts and arrhythmias were collected. Health records were also reviewed for clinical and anatomic information and retrospective review of this data was approved by the IRB.

Arrhythmias

“Ventricular tachycardia (VT) storm” was defined as 20 episodes of VT or ventricular fibrillation (VF) per day, or4 VT/VF episodes per hour. “Recurrent VT” referred to frequent ventricular arrhythmias not meeting the above criteria. “Recurrent ICD shocks” was used as a designation for patients with ICD shocks not meeting criteria for VT storm.

Classification

Based on cardiac substrate, left stellate ganglia from cadaveric and surgical pathologic sources were segregated into NL (normal), SCAR (presence of myocardial scar), and NICM (absence of scar but presence of a non-ischemic cardiomyopathy). NL samples were obtained from cadavers without any evidence of gross or histologic cardiac pathology. The SCAR group consisted of stellate ganglia from subjects with documented myocardial scars. This included cadaveric specimens with healed infarcts, and patients with ischemic and non-ischemic cardiomyopathy with intra-myocardial scar documented by a combination of the imaging modalities listed above. NICM samples were obtained from patients with no evidence of myocardial scar, but with a nonischemic cardiomyopathy. These patients had severe ventricular arrhythmias that were refractory to medical and ablative strategies.

Histologic and Immuno-histochemical Studies

Stellate ganglia were serially sectioned, and representative histologic sections from the middle of the ganglia were used for analyses. All slides were scanned and digital images were electronically stored for analysis (Scan Scope, Aperio, Vista, CA). Entire ganglia, excluding nerve tracts were analyzed. Histologic and immuno-histochemical quantifications were performed by computerized morphometry (Tissue Studio, DefiniensInc, Parsippany, NJ). Slides were analyzed in a numerically blinded fashion to avoid bias in data analysis. Intensity of staining was measured during the computerized analysis, and standardized across the studied samples.

Neuronal size was quantified by Thionin (Fisher Scientific, Pittsburgh, PA) and Geske's Modification of Verhoeff's elastic and Masson's trichrome (EVG-Trichrome)(19). Fibrosis within stellate ganglia was quantified by EVG-Trichrome staining. A blinded observer scored the severity of fibrosis within ganglia on a scale of 0-5. A value of 0 indicated no fibrosis present. A value of 1 was assigned for peri-vascular fibrosis only. A value of 5 was given for extensive fibrosis throughout the entire ganglia. Values of 2,3, and 4 were assigned respectively for progressive degrees of fibrosis more severe than perivascular, but not covering the entire stellate ganglion.

Diaminobenzidine (DAB, Life Technologies, Green Island, NY) immuno-staining was used to quantify neuronal growth (GAP-43, 1:2000, Life Technologies), and nerve synaptic density (Synaptophysn, (SYN), 1:200, Life Technologies). Neuronal size is expressed in square microns (μm2). Immunoreactivity is expressed as immuno-stained area in um2 / total tissue area studied in mm2 (um2/ mm2). Positive controls (using neuronal cancer tissue) were performed in parallel with all immune-staining experiments to confirm antibody immune-reactivity.

Myocardial tissue was stained with H+E and Geske's Modification of Verhoeff's elastic and Masson's trichrome (EVG-Trichrome) to histologically distinguish scar from normal myocardium. Nerve fiber density was quantified using S100 immuno-staining. S100 immuno-staining was expressed as noted above. Intra-myocardial nerve sprouting was quantified by GAP-43 Immunoreactivity as described above.

Statistical Analyses

Means for continuous variables were compared using a non-parametric one-way analysis of variance (ANOVA) model (Kruskal-Wallis) where p values were computed using exact permutational methods. The three post hoc pairwise mean comparisons under this ANOVA model were judged significant using the Fisher least significant difference (Fisher LSD) criterion, which controls the overall type I error rate when there are three groups.

The mean percentages of small, medium and large neurons were compared using a one way multivariate analysis of variance model since the percentage of small, medium and large must equal 100% for any subject, making these three variables non-independent.

Means and standard error of the mean (SEM) are reported,or individual data points in each group are displayed in jitter plots with lines connecting means across the three groups. An adjustedp value ≤ 0.05 was considered statistically significant.

Results

Table 1 shows characteristics of the cadaveric and patient subjects included in the study. The mean age of the subjects in the study was 63±14 years. Twenty four percent of the study subjects were female. There were 10 cadaveric subjects, and 24 patients included in the study, and a total of 34 ganglia were obtained. Based on cardiac pathology, cadavers were classified as normal (NL), intra-myocardial scar (SCAR), and cardiomyopathic hearts without scar (NICM). All the cadaveric hearts in the SCAR group contained healed infarcts; no acute infarctions were noted histologically. Shown in Figure 1 are representative gross and histologic images of a heart in the (A) NL group, and (B) SCAR group (black arrows). Figures 1C-F show some of various imaging modalities used to confirm the presence of myocardial scar (white arrows) in study patients (SCAR group).

Table.

Characteristics of Patients and Cadaveric Subjects.

Subject Age/Gender Ganglia Source Cause of Clinical Presentation or death Arrhythmias History of Coronary Artery Disease Myocardial Substrate Myocardial Scar Left Ventricular Ejection Fraction Clinical Outcome
1 67/F Cadaveric NSCLC None No Normal None n/a –
2 58/F Cadaveric Alzheimer's Disease None No Normal None n/a –
3 88/F Cadaveric Pneumonia, Sepsis None No Normal None n/a –
4 64/M Cadaveric VF Arrest Yes No NICM Diffuse n/a –
5 72/M Cadaveric CHF, Renal Failure None Yes, 3v ICM Ant, Post n/a –
6 81/M Cadaveric Anemia, Hemorrhage None Yes, LAD, RCA ICM Ant n/a –
7 80/M Cadaveric NSCLC None Yes, LAD ICM Ant, Post n/a –
8 81/F Cadaveric Alzheimer's Disease None Yes, LCX, PDA ICM Lat n/a –
9 97/F Cadaveric CHF, Urosepsis None No NICM Ant n/a –
10 69/F Cadaveric Metastatic Breast Cancer Yes No NICM Diffuse n/a –
11 53/M Surgical VT Storm Yes Yes, 3v ICM Ant, Apex, Inf-lat, Inf 16% Alive
13 66/M Surgical Recurrent ICD shocks Yes Yes, 3v ICM Ant, Apex, Sep, Inf 15% Death
14 68/M Surgical VT Storm Yes Yes, RCA ICM Inf, Inf-Sep 25% Alive
15 70/M Surgical Recurrent ICD Shocks Yes Yes, LAD ICM Apex, Sep 35% Death
16 72/M Surgical VT Storm Yes Yes, LAD, LCX ICM Inf-lat, Inf-Sep 24% Transplant
17 46/M Surgical Recurrent VT Yes No NICM Ant-Sep, RV Lat 35% Alive
18 47/M Surgical Recurrent VT Yes No NICM Inf, Inf-Lat 20% Alive
19 47/M Surgical VT Storm Yes No NICM Apex, Ant-Sep, Lat, RV Bas-Lat, 15% Alive
20 63/M Surgical VT Storm Yes No NICM LVOT and RVOT 35% Transplant
21 68/M Surgical Recurrent ICD Shocks Yes No Sarcoid CM Basal- Sep 20% Death
22 65/M Surgical Recurrent ICD Shocks Yes No Apical HCM Apex 59% Alive
23 34/M Surgical Recurrent VT Yes No Apical HCM Apex 30% Alive
24 50/M Surgical VT Storm Yes No NICM Post, Post-Lat base 20% Death
25 49/F Surgical Recurrent ICD shocks Yes No NICM Apex, Basal Inf-Sep 30% Death
26 60/M Surgical VT Storm Yes No NICM Post MV annulus 20% Death
27 70/M Surgical VT Storm Yes No NICM Post 20% LTFU
28 66/F Surgical VF Arrest Yes No NICM Inf-lat, Lat 20% Death
29 46/M Surgical Recurrent ICD shocks Yes No Normal None 50% Alive
30 75/M Surgical Recurrent ICD shocks Yes No NICM None 25% Alive
31 62/M Surgical Recurrent ICD shocks Yes No NICM None 45% Alive
32 49/M Surgical Recurrent ICD shocks Yes No NICM None 20% Alive
33 49/M Surgical Recurrent ICD shocks Yes No NICM None 40% Alive
34 47/M Surgical VT Storm Yes No NICM None 15% Alive
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(3v three-vessel coronary artery disease, Ant anterior; CHF congestive heart failure; HCM hypertrophic cardiomyopathy; ICD implantable cardioverter defibrillator; ICM ischemic cardiomyopathy; Inf inferior; LAD left anterior descending coronary artery; Lat lateral; LCX left circumflex coronary artery; LSG left stellate ganglion; LVOT left ventricular outflow tract; LTFU lost to follow up; MV mitral valve; NICM non-ischemic cardiomyopathy; NSCLC non-small cell lung cancer; PDA posterior descending artery; Post posterior; RCA right coronary artery; RV right ventricle; RVOT right ventricular outflow tract; Sep septal; VF ventricular fibrillation; VT ventricular fibrillation.

Figure 1.

Figure 1

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Characterization of Myocardial Scar. Shown are representative gross and Trichrome Elastic von Giessen (Trichrome) images of a (A) normal and (B) infarcted heart from cadaveric subjects. Fibro-elastic tissue (blue), present in the infarcted heart is highlighted by black arrows. Representative images of multi-modal techniques used to determine the presence of scar in hearts of patients from whom stellate ganglia were collected. These included (C) computed tomography with arrows pointing to a region of apical scar and aneurysm; (D) positive emission tomography with arrows indicating a region decreased to absent radiolabeled glucose uptake corresponding to scar; (E) magnetic resonance imaging with arrows indicating delayed gadolinium enhancement indicating scar, and (F) endocardial electro-anatomic map with gray areas (shown by arrows) indicating regions with voltage <0.5mV corresponding to myocardial scar.

Neuronal Size and Distribution

Examples of mean neuronal size in stellate ganglia from normal controls (NL, n=3), ganglia from scarred hearts (SCAR, n=24), and cardiomyopathic hearts without scar (NICM, n=7) after Thionin and Trichrome/EVG staining are shown in Figure 2A. Thionin staining showed that neurons in SCAR ganglia were significantly larger than NL (371.9±10.2μm2vs 320.1±4μm2). Surprisingly however, neurons from NICM ganglia were the largest of the three groups (435±10μm2, overall p=0.002, Figure 2B).

Figure 2.

Figure 2

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Stellate Ganglion Neurons in The Presence of Cardiac Pathology. (A) Representative images of stellate ganglia stained with Thionin for NL, SCAR, and NICM. (Magnification 40x, Scale bar: 50μm). (B) Quantifications of mean neuronal size from Thionin staining. Solid purple line connects the means. (C) The Percentage of small (<350μm2), medium (350μm2-500μm2), and large (>500μm2) neurons is shown in for NL, SCAR, and NICM. Solid purple line connects the means

The distribution of small (< 350μm2), medium (350 -500μm2), and large (> 500 μm2) neurons observed within Thionin-stained ganglia is shown in Figure 2C. The majority of neurons in all three groups are under 350 μm2, however, compared to NL, the percentage of small neurons is decreased in SCAR and NICM.The percentage of large neurons is increased in SCAR and NICM vs NL (MANOVA p<0.0182, exact Wilks lambda). There was no significant difference amongst the groups in percentage of medium sized neurons.

Ganglion Fibrosis and Neuronal Density

The degree of fibrosis observed in each stellate ganglion was scored by an observer (MCF), blinded to the group assignment of each ganglion. A grading scale of 0-5 was used for fibrosis as described in the methods section. Mean fibrosis grade in NL, SCAR, and NICM were 2.7±0.7, 1.8±0.2, and 2.0±0.4 respectively; overallp=0.423), Figure 3A.

Figure 3.

Figure 3

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Stellate Ganglion Fibrosis and Neuronal Density. (A) The severity of stellate ganglion fibrosis in NL, SCAR, and NICM. (B) A comparison of the mean density of neurons for the groups is depicted. Solid purple line connects the means.

Neuronal density (cell number/tissue area) was not significantly different among the three groups (0.039±0.01 cells/μm2vs 0.028±0.005 cells/μm2vs 0.024±0.004 cells/μm2 for NL, SCAR, and NICM respectively; overall p=0.454), Figure 3B.

Synaptic Density and Nerve Sprouting

Neuron synaptic density was measured by synaptophysin immuno-staining in stellate ganglia from NL, SCAR, and NICM and is shown in Figure 4A. Synaptic densities were 17.8±7.0 um2/mm2 vs. 57.8±11.2 um2/ mm2 (p=0.084) vs. 44.5±7.9 um2/ mm2 (p=0.039) respectively (overall p=0.162).

Figure 4.

Figure 4

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Synaptic Density and Nerve Sprouting Within Stellate Ganglia. Panel (A) shows representative images of synaptophysin(SYN) and growth-associated protein-43 (GAP43) Immunoreactivity in NL, SCAR, and NICM. Arrows indicate punctate structures staining darkly for synaptophysin. (B) and (C) Quantification of synaptophysin and GAP43 Immunoreactivity, respectively, amongst the groups. (Magnification 20x, Scale bar: 100μm).

Growth-associated protein 43 (GAP43) is incorporated into growing neurons and is a marker of neuronal growth. Figure 4A shows GAP43 staining in stellate ganglia from NL, SCAR, and NICM groups. There was no significant difference in GAP43 Immunoreactivity between the groups (2696.2±1004 um2/ mm2vs3992±614 um2/ mm2(p=0.939) vs2564.7±881 um2/ mm2(p=0.210), respectively, overallp=0.194).

Myocardial Nerve Density

Intra-myocardial nerve density was assayed by S100 immuno-staining. As shown in Figure 5, S100 Immunoreactivity was similar between NL and SCAR hearts (33±12 um2/ mm2vs 28±6 um2/ mm2 respectively, p=0.903) indicating no increase in nerve density in SCAR hearts with healed infarcts compared to normal (NL). Nerve sprouting as assessed by GAP43 Immunoreactivity was not different between NL and SCAR (data not shown).

Figure 5.

Figure 5

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Intra-myocardial Nerve Density. (A) Representative images of S100 nerve staining within myocardium from NL and SCAR. Black arrows depict nerve bundles, tracts, or fibers within the myocardium. Blue arrows show regions of intra-myocardial scarring. (B) Quantification of nerve density in NL and SCAR myocardium expressed as μm2/mm2 of S100 Immunoreactivity. Solid purple line connects the means. (Magnification 20x, Scale bar: 100μm).

Discussion

Major Findings

The major findings of the present study are: 1) left stellate ganglion neurons from patients with abnormal hearts are significantly larger compared to those from normal hearts. Further, neurons from ganglia from patients with non-ischemic cardiomyopathies are larger than those associated with scar-based pathology; and 2) the degree of nerve sprouting and synaptic density in these chronically diseased hearts was not different from normal. This study represents the first evidence of extra-cardiac neural remodeling associated with cardiac pathology in humans.

Neuronal Characteristics and Cardiac Pathology

Hypertrophy of neurons in response to injury is a recognized phenomenon, and has been described in animal models of neural injury(20-23). Neuronal hypertrophy within the stellate ganglia after myocardial infarction has not been previously reported. The myocardium is a highly innervated by sympathetic and parasympathetic nerves, as well as sensory C fibers which convey nociceptive stimuli to dorsal root ganglia. Myocardial injury, such as infarction or scarring, results in axonal injury. Neurotrophic signals including nerve growth factor (NGF)(8, 24), are transmitted to the soma (via retrograde axonal transport and/or circulation) to signal axonal injury(25). Within the tissue, the NGF signaling is important for the hyper-innervation that results after myocardial injury(26). The resulting process of chromatolysis, of which soma hypertrophy is a component, ensues. This process may explain the etiology of neuronal hypertrophy observed in our study.

Neurons may also hypertrophy in response to chronic signaling. Cavalcanti et al. showed in a rat model of exercise training that neuronal size was increased within bilateral stellate ganglia(15). The mechanism of hypertrophy in this model is likely different from that of myocardial and axonal injury, although similar signals may be involved. It is likely that chronic sympathetic signaling occurring with chronic exercise training may contribute to neuronal hypertrophy. This finding may in part explain our finding that stellate ganglion neurons from cardiomyopathic (NICM) hearts showed significantly greater hypertrophy compared to those from scarred hearts. It is consistent with the suggestion that in non-ischemic cardiomyopathies, neuro-hormonal activation involving the stellate ganglia is a major component of the pathophysiologic process resulting in progressive cardiomyopathy(27, 28). Further, that these stellate ganglia were obtained from patients with refractory ventricular arrhythmias, may also suggest the involvement of these hypertrophied ganglia in ventricular arrhythmogenesis. This hypothesis underscores the rationale for a landmark randomized trial comparing placebo to beta-adrenergic receptor blocker therapy and cardiac sympathetic denervation(29). The trial showed a profound decrease in the incidence of ventricular arrhythmias and sudden death, in patients after myocardial infarction. A potential mechanism for this benefit is the removal of remodeled (and possibly hyperactive) stellate ganglia.

Neuronal density was similar between normal, scarred, and NICM hearts in our study. Since neurons in peripheral ganglia do not replicate (unlike glial cells), this suggests no significant neuronal loss under cardiac pathologic conditions compared to normal. Fibrosis within the stellate ganglia was reported to differ in cadavers with cardiopulmonary disease compared to cadavers without (17). Another study from the same group showed greater neuronal density in stellate ganglia from cadavers with fibrosis detected within the inter-ventricular septum (18). The differences in both studies were however marginal. In our study, there was no significant difference in fibrosis or mean neuronal density. This may be due to age of the subjects included in our study, which were younger that subjects in the study by Docimo et al (17).

Nerve Sprouting and Synaptic Density in Cardiac Pathology

Nerve sprouting in the myocardium and within stellate ganglia occurs after myocardial injury in animal models, however nerve sprouting has not been documented in human stellate ganglia. In our study of chronic myocardial injury, synaptic density (synaptophysin immunostaining) within stellate ganglia appeared qualitatively greater in subjects with cardiac pathology (NL 17.8±7um2/mm2 vs. SCAR 57.8±11.2um2/ mm2 (p=0.039) vs. NICM 44.5±7.9um2/ mm2 (p=0.084); overall p=0.162); however, no differences were observed in stellate ganglion nerve sprouting (GAP43) between normal and pathologic hearts. This finding in our study is consistent with previous studies on the dynamics of neural remodeling in animal models. In a rabbit (16) and canine (24) model of myocardial infarction, levels of synaptic density and nerve sprouting were measured at 1 week and 1 month after infarction. Synaptic density was greater at 1 month compared to 1 week post-infarct. This is contrasted with nerve sprouting, which was greatest at 1 week, but decreased by 1 month. This pattern suggests that nerve sprouting may be a transient process, while increases in synaptic density is a more permanent adaptive process. Our study included healed infarcts, with levels of synaptic density persistently elevated compared to controls, while levels of nerve sprouting were similar to normal levels. Similarly, nerve density in the myocardium was similar between normal, scarred, and non-scarred cardiomyopathic hearts.

Limitations

Due to the nature of our study, there are a number of limitations to consider. Our study associates cardiomyopathy with neuronal hypertrophy and synaptic density. It is not possible to tease out whether the stellate ganglion changes are reactive, or contribute to the development of a cardiomyopathy or arrhythmias. Further, the timing of cardiac pathology may be different in the SCAR vs. NICM groups. The differences noted in neuronal size between SCAR and NICM may be related to this temporal difference. The age and gender of subjects also differed between the groups (with NICM patients being generally younger, and NL being mostly females). Although animal studies have not shown differences in neuronal size, the possibility of such differences in this dataset is unknown. Further, our results are in line with existing publications in animal models in which these factors have been controlled(16, 30). Another limitation to note is that immunohistochemical assays are not directly quantitative, and differences are not translatable into fold differences. Although the objective values obtained from morphometric analyses for Synaptophysin did not meet statistical significance, there was a trend towards significance, consistent with qualitative observations. Lastly, there are no physiologic data (such as sympathetic nerve signaling) to correlate with the anatomic findings in this study. Obtaining such data in patients is however difficult, as it would involve a very invasive procedure with significant risks in an already compromised patient population.

Conclusions

In summary, this study demonstrates that human cardiac pathology is associated with remodeling of neurons within left stellate ganglia, including increased neuronal size and synaptic density. These persistent anatomic changes within stellate ganglia may suggest the presence of pathologic signals between the heart and the neuraxis. Further studies are warranted to elucidate the physiologic consequences of neural remodeling in response to cardiac pathology.

Acknowledgments

The authors wish to thank Jacob N. Fox BS, Wei Zhou PhD, Shelly Cote RN MSNP, Jean Gima RN MSNP, and Long Sheng Hong for significant contributions to this project. In addition, we wish to acknowledge Clara Magyar PhD, and the UCLA Translational Pathology Core Laboratory. We also thank contributors to the UCLA and WVUDonated Body Programs, whose generosity allowed us to study cadaveric specimens. We also wish to thank Dr. Jeffrey Gornbeinfrom the UCLA BioMathematics Department for statistical assistance.

Funding Sources: This work was made possible by support from the NHLBI (R01HL084261) to KS.

Footnotes

Conflict of Interest Disclosures: None

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