Using skin sympathetic nerve activity to estimate stellate ganglion nerve activity in dogs

Sympathetic toggled paroxysmal atrial fibrillation and recurrent premature atrial contractions in ambulatory patients

BACKGROUND

Autonomic nerve activity is important in the mechanisms of paroxysmal atrial fibrillation (PAF).

OBJECTIVE

The purpose of this study was to test the hypothesis that a single burst of skin sympathetic nerve activity (SKNA) can toggle on and off PAF or premature atrial contraction (PAC) clusters.

METHODS

Simultaneous recording of SKNA and electrocardiogram (neuECG) recording was performed over 7 days in patients with PAF.

RESULTS

In study 1, 8 patients (7 men and 1 woman; age 62 ± 8 years) had 124 episodes of PAF. An SKNA burst toggled both on and off PAF in 8 episodes (6.5%) (type 1), toggled on but not off in 12 episodes (9.7%) (type 2), and toggled on a PAC cluster followed by PAF in 4 episodes (3.2%) (type 3). The duration of these PAF episodes was <10 minutes. The remaining 100 episodes (80.6%) were associated with active SKNA bursts throughout PAF (type 4) and lasted longer than type 1 (P = .0185) and type 2 (P = .0027) PAF. There were 47 PAC clusters. Among them, 24 (51.1%) were toggled on and off, and 23 (48.9%) were toggled on but not off by an SKNA burst. In study 2, 17 patients (9 men and 8 women; age 58 ± 12 years) had <10 minutes of PAF (4, 8, 0, and 31 of types 1, 2, 3, and 4, respectively). There were significant circadian variations of all types of PAF.

CONCLUSION

A single SKNA burst can toggle short-duration PAF and PAC cluster episodes on and off. The absence of continued SKNA after the onset might have affected the maintenance of these arrhythmias.

Biomarker Periodic Repolarization Dynamics Indicates Enhanced Risk for Arrhythmias and Sudden Cardiac Death in Myocardial Infarction in Pigs

BACKGROUND

Periodic repolarization dynamics (PRD) is an electrocardiographic biomarker that captures repolarization instability in the low frequency spectrum and is believed to estimate the sympathetic effect on the ventricular myocardium. High PRD indicates an increased risk for postischemic sudden cardiac death (SCD). However, a direct link between PRD and proarrhythmogenic autonomic remodeling has not yet been shown.

METHODS AND RESULTS

We investigated autonomic remodeling in pigs with myocardial infarction (MI)-related ischemic heart failure induced by balloon occlusion of the left anterior descending artery (n=17) compared with pigs without MI (n=11). Thirty days after MI, pigs demonstrated enhanced sympathetic innervation in the infarct area, border zone, and remote left ventricle paralleled by altered expression of autonomic marker genes/proteins. PRD was enhanced 30 days after MI compared with baseline (pre-MI versus post-MI: 1.75±0.30 deg2 versus 3.29±0.79 deg2, P<0.05) reflecting pronounced autonomic alterations on the level of the ventricular myocardium. Pigs with MI-related ventricular fibrillation and SCD had significantly higher pre-MI PRD than pigs without tachyarrhythmias, suggesting a potential role for PRD as a predictive biomarker for ischemia-related arrhythmias (no ventricular fibrillation versus ventricular fibrillation: 1.50±0.39 deg2 versus 3.18±0.53 deg2 [P<0.05]; no SCD versus SCD: 1.67±0.32 deg2 versus 3.91±0.63 deg2 [P<0.01]).

CONCLUSIONS

We demonstrate that ischemic heart failure leads to significant proarrhythmogenic autonomic remodeling. The concomitant elevation of PRD levels in pigs with ischemic heart failure and pigs with MI-related ventricular fibrillation/SCD suggests PRD as a biomarker for autonomic remodeling and as a potential predictive biomarker for ventricular arrhythmias/survival in the context of MI.

Skin sympathetic nerve activity in different ablation settings for atrial fibrillation

BACKGROUND

Modifying the autonomic system after catheter ablation may prevent the recurrence of atrial fibrillation (AF). Evaluation of skin sympathetic nerve activity (SKNA) is a noninvasive method for the assessment of sympathetic activity. However, there are few studies on the effects of different energy settings on SKNA.

OBJECTIVE

To investigate the changes in SKNA in different energy settings and their relationship to AF ablation outcomes.

METHODS

Seventy-two patients with paroxysmal and persistent AF were enrolled. Forty-three patients received AF ablation with the conventional (ConV) energy setting (low power for long duration), and 29 patients using a high-power, short-duration (HPSD) strategy. The SKNA was acquired from the right arm 1 day before and after the radiofrequency ablation. We analyzed the SKNA and ablation outcomes in the different energy settings.

RESULTS

Both groups had a similar baseline average SKNA (aSKNA). We found that the median aSKNA increased significantly from 446.82 μV to 805.93 μV (p = 0.003) in the ConV group but not in the HPSD group. In the ConV group, patients without AF recurrence had higher aSKNA values. However, the 1-year AF recurrence rate remained similar between both groups (35 % vs. 28 %, p = 0.52).

CONCLUSION

The post-ablation aSKNA levels increased significantly in the ConV group but did not change significantly in the HPSD group, which may reflect different neuromodulatory effects. However, the one-year AF recurrence rates were similar for both groups. These results demonstrate that the HPSD strategy has durable lesion creation but less lesion depth, which may reduce collateral damage.

Autonomic Modulation of Atrial Fibrillation

The autonomic nervous system plays a vital role in cardiac arrhythmias, including atrial fibrillation (AF). Therefore, reducing the sympathetic tone via neuromodulation methods may be helpful in AF control. Myocardial ischemia is associated with increased sympathetic tone and incidence of AF. It is an excellent disease model to understand the neural mechanisms of AF and the effects of neuromodulation. This review summarizes the relationship between autonomic nervous system and AF and reviews methods and mechanisms of neuromodulation. This review proposes that noninvasive or minimally invasive neuromodulation methods will be most useful in the future management of AF.

Skin sympathetic nerve activity and nocturnal blood pressure nondipping in patients with postural orthostatic tachycardia syndrome

OBJECTIVE

Postural orthostatic tachycardia syndrome (POTS) is associated with abnormal blood pressure (BP) regulation and increased prevalence of nocturnal nondipping. We hypothesized that nocturnal nondipping of BP is associated with elevated skin sympathetic nerve activity (SKNA) in POTS.

METHOD

We used an ambulatory monitor to record SKNA and electrocardiogram from 79 participants with POTS (36 ± 11 years, 72 women), including 67 with simultaneous 24-h ambulatory BP monitoring.

RESULTS

Nocturnal nondipping of BP was present in 19 of 67 (28%) participants. The nondipping group had a higher average SKNA (aSKNA) from midnight of day 1 to 0100 h on day 2 than the dipping group ( P  = 0.016, P  = 0.030, respectively). The differences (Δ) of aSKNA and mean BP between daytime and night-time were more significant in the dipping group compared with the nondipping group (ΔaSKNA 0.160 ± 0.103 vs. 0.095 ± 0.099 μV, P  = 0.021, and Δmean BP 15.0 ± 5.2 vs. 4.9 ± 4.2 mmHg, P  < 0.001, respectively). There were positive correlations between ΔaSKNA and standing norepinephrine (NE) (r = 0.421, P  = 0.013) and the differences between standing and supine NE levels ( r  = 0.411, P  = 0.016). There were 53 (79%) patients with SBP less than 90 mmHg and 61 patients (91%) with DBP less than 60 mmHg. These hypotensive episodes were associated with aSKNA of 0.936 ± 0.081 and 0.936 ± 0.080 μV, respectively, which were both significantly lower than the nonhypotensive aSKNA (1.034 ± 0.087 μV, P  < 0.001 for both) in the same patient.

CONCLUSION

POTS patients with nocturnal nondipping have elevated nocturnal sympathetic tone and blunted reduction of SKNA between day and night. Hypotensive episodes were associated with reduced aSKNA.

Evaluation of autonomic nervous system activity in intradialytic hypotension using entropy and skin sympathetic nerve activity

Introduction

The function of the autonomic nervous system (ANS) is crucial in the development of intradialytic hypotension (IDH). This study introduced the entropy of heart rate variability (HRV) and skin sympathetic nerve activity (SKNA) to provide a complementary nonlinear and dynamic perspective for evaluating ANS function concerning IDH.

Methods

93 patients undergoing hemodialysis (HD) were enrolled, and the baseline data, electrocardiogram (ECG), and SKNA were collected. The patients were separated into the IDH and nonIDH groups based on the thresholds, which were characterized as reductions in systolic blood pressure (SBP) of at least 20 mm Hg or mean arterial pressure (MAP) of at least 10 mm Hg. We developed a logistic regression model for IDH after analyzing the changes in the time domain, frequency domain, the entropy of HRV, and SKNA indices during HD.

Results

After 4-h HD, the detected results for heart rate, the ratio of low frequency and high frequency (LF/HF), and average SKNA (aSKNA) all increased in both groups. Nine out of the ten HRV indices and aSKNA in the nonIDH group were higher than those in the IDH group at most moments. aSKNA was positively correlated with heart rate (p = 0.0001) and LF/HF (p = 0.0005) in the nonIDH group, while the correlation disappeared in the IDH group, which indicated a worse ANS response in IDH patients. The logistic regression model exhibited the results of initial SBP [odds ratio (OR) 1.076; p = 0.001], and the difference between the last and first segments (DLF) of heart rate [OR 1.101; p =0.012] and LF/HF [OR 0.209; p =0.034], as well as the extreme value of the difference between other segments and the first segments (EOF) of aSKNA [OR 2.908; p =0.017], which were independent indicators for IDH.

Discussion

The new nonlinear and dynamic assessment perspectives provided by the entropy of HRV and SKNA help to distinguish differences in ANS patterns between IDH patients and nonIDH patients and have the potential to be used in clinical monitoring for HD patients.

Skin sympathetic nerve activity as a potential biomarker for overactive bladder

PURPOSE

Abnormalities in autonomic function are associated with an overactive bladder (OAB). Heart rate variability is generally used as the sole assessment of autonomic activity; however, we utilized neuECG, a novel method of recording skin electrical signals, to assess autonomic nervous function in healthy controls and patients with OAB before and after treatment.

METHODS

The prospective sample included 52 participants: 23 patients newly diagnosed with OAB and 29 controls. Autonomic function was assessed in all participants in the morning using neuECG, which analyzed the average skin sympathetic nerve activity (aSKNA) and electrocardiogram simultaneously. All patients with OAB were administered antimuscarinics; urodynamic parameters were assessed before treatments; autonomic and bladder functions using validated questionnaires for OAB symptoms were evaluated before and after OAB treatment.

RESULTS

Patients with OAB had significantly higher baseline aSKNA (p = 0.003), lower standard deviation of the normal-to-normal beat intervals, lower root mean square of the successive differences, lower high-frequency, and higher low-frequency than did controls. Baseline aSKNA had the highest value in predicting OAB (AUROC = 0.783, p < 0.001). The aSKNA was negatively correlated with first desire and normal desire in urodynamic studies (both p = 0.025) and was significantly decreased after treatment at rest, stress, and recovery phases, as compared to those before treatment (p = 0.046, 0.017, and 0.017, respectively).

CONCLUSION

Sympathetic activity increased significantly in patients with OAB compared to that in healthy controls, and decreased significantly post-treatment. Higher aSKNA is associated with decreased bladder volume at which voiding is desired. SKNA may be a potential biomarker for diagnosing OAB.

Wireless Self-Powered Optogenetic System for Long-Term Cardiac Neuromodulation to Improve Post-MI Cardiac Remodeling and Malignant Arrhythmia

Autonomic imbalance is an important characteristic of patients after myocardial infarction (MI) and adversely contributes to post-MI cardiac remodeling and ventricular arrhythmias (VAs). A previous study proved that optogenetic modulation could precisely inhibit cardiac sympathetic hyperactivity and prevent acute ischemia-induced VAs. Here, a wireless self-powered optogenetic modulation system is introduced, which achieves long-term precise cardiac neuromodulation in ambulatory canines. The wireless self-powered optical system based on a triboelectric nanogenerator is powered by energy harvested from body motion and realized the effective optical illumination that is required for optogenetic neuromodulation (ON). It is further demonstrated that long-term ON significantly mitigates MI-induced sympathetic remodeling and hyperactivity, and improves a variety of clinically relevant outcomes such as improves ventricular dysfunction, reduces infarct size, increases electrophysiological stability, and reduces susceptibility to VAs. These novel insights suggest that wireless ON holds translational potential for the clinical treatment of arrhythmia and other cardiovascular diseases related to sympathetic hyperactivity. Moreover, this innovative self-powered optical system may provide an opportunity to develop implantable/wearable and self-controllable devices for long-term optogenetic therapy.

Alterations of sympathetic dynamics after atrial fibrillation ablation by analysis sympathetic nerve activity provide prognostic value for recurrence and mechanistic insights into ablation

Background

Pulmonary vein isolation (PVI) is the cornerstone of atrial fibrillation (AF) ablation. Success is associated with autonomic function modulation; however, the relationship between the changes after ablation is not fully understood. We aimed to investigate the effect of ablation on autonomic modulation by skin sympathetic nerve activity (SKNA) using conventional electrocardiogram (ECG) electrodes and to predict the treatment success.

Methods

We enrolled 79 patients. We recorded neuECG for 10 min at 10 kHz before and after ablation. The NeuECG was bandpass-filtered (500–1,000 Hz) and integrated at intervals of 100 ms (iSKNA). iSKNA was averaged over different time windows (1-, 5-,10-s; aSKNAs), and burst analyses were derived from aSKNAs to quantify the dynamics of sympathetic activities. AF recurrence after 3 months was defined as the study endpoint.

Results

Sixteen patients experienced AF recurrence after the ablation. For burst analysis of 1-s aSKNA, the recurrence group had a higher bursting frequency than the non-recurrence group (0.074 ± 0.055 vs. 0.109 ± 0.067; p &lt; 0.05) before ablation. The differences between pre- and post-ablation of firing duration longer than 2 s were more in the non-recurrence group (2.75 ± 6.41 vs. −1.41 ± 5.14; p &lt; 0.05), while no significant changes were observed in the percentage of duration longer than 10 s using 5-s aSKNA. In addition, decreases in differences in firing frequency and percentage of both overall firing duration and longer firing duration (&gt; 2 s) between pre- and post-ablation were independently associated with AF recurrence and more area under receiver operating characteristics (ROC) curve in combination with CHADS2 score (0.833).

Conclusion

We demonstrated the applicability of neuECG for determining sympathetic modulation during AF ablation. Decreasing sympathetic activity is the key to successful ablation.

Higher pre-treatment skin sympathetic nerve activity and elevated resting heart rate after chemoradiotherapy predict worse esophageal cancer outcomes

Background

Chemoradiotherapy (CRT), which might affect the autonomic system, is the mainstay therapy for advanced esophageal squamous cell carcinoma (ESCC). Autonomic dysfunction has been found to possibly lead to cancer mortality in those with elevated resting heart rates (RHR). Skin sympathetic nerve activity (SKNA) is a new method of stimulating electrical signals in skin to evaluate autonomic function from sympathetic tone. In this study, we investigated the association between changes in RHR and autonomic function and ESCC mortality.

Methods

Thirty-nine stage II-IV ESCC patients receiving CRT between March 2019 and November 2020 were prospectively enrolled and carefully selected, followed up and received the same meticulous supportive care. Serial RHR was recorded every two weeks from before CRT to eight weeks after CRT and average SKNA were recorded before and four weeks after CRT. All-cause mortality was defined as primary outcome.

Results

We found the RHR of ESCC patients to be significantly elevated and peaking at four weeks after CRT (p < 0.001) and then to gradually decrease. Those with an elevated RHR above the cutoff level (18 beat-per-minute) at eight weeks after CRT had worse overall survival. In addition, those with higher baseline sympathetic tone (average SKNA ≥ 0.86 μV) also had poor outcome.

Conclusions

Increased pre-treatment sympathetic tone and elevated RHR after CRT are alarm signs of poor ESCC outcome. Further exploration of the mechanisms underlying these associations could potentially lead to intervention strategies for reducing mortality.

Trial registration

This study is registered with ClinicalTrials.gov, identifier: NCT03243448.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-10180-8.

Feature Selection Techniques for a Machine Learning Model to Detect Autonomic Dysreflexia

Feature selection plays a crucial role in the development of machine learning algorithms. Understanding the impact of the features on a model, and their physiological relevance can improve the performance. This is particularly helpful in the healthcare domain wherein disease states need to be identified with relatively small quantities of data. Autonomic Dysreflexia (AD) is one such example, wherein mismanagement of this neurological condition could lead to severe consequences for individuals with spinal cord injuries. We explore different methods of feature selection needed to improve the performance of a machine learning model in the detection of the onset of AD. We present different techniques used as well as the ideal metrics using a dataset of thirty-six features extracted from electrocardiograms, skin nerve activity, blood pressure and temperature. The best performing algorithm was a 5-layer neural network with five relevant features, which resulted in 93.4% accuracy in the detection of AD. The techniques in this paper can be applied to a myriad of healthcare datasets allowing forays into deeper exploration and improved machine learning model development. Through critical feature selection, it is possible to design better machine learning algorithms for detection of niche disease states using smaller datasets.

Alteration of Skin Sympathetic Nerve Activity after Pulmonary Vein Isolation in Patients with Paroxysmal Atrial Fibrillation

Autonomic system plays a pivotal role in the pathogenesis of paroxysmal atrial fibrillation (AF). Skin sympathetic nerve activity (SKNA) is a noninvasive tool for assessing sympathetic tone. However, data on changes in SKNA after ablation are limited. Here, we retrospectively enrolled 37 patients with symptomatic drug-refractory paroxysmal AF who underwent pulmonary vein isolation (PVI) with radiofrequency ablation (RFA) or cryoablation (CBA). SKNA was measured from the chest and right arm 1 day prior to ablation, as well as 1 day and 3 months after ablation. One day after ablation, the SKNA-Arm increased from 517.1 µV (first and third quartiles, 396.0 and 728.0, respectively) to 1226.2 µV (first and third quartiles, 555.2 and 2281.0), with an increase of 179.8% (125% and 376.0%) (p < 0.001); the SKNA-Chest increased from 538.2 µV (first and third quartiles, 432.9 and 663.9) to 640.0 µV (first and third quartiles, 474.2 and 925.6), with an increase of 108.3% (95.6% and 167.9%) (p = 0.004), respectively. In those without recurrence, there was a significant increase in SKNA 1 day after ablation as compared with those before ablation. Twelve patients received SKNA measurement 3 months after ablation; both SKNA-Arm (p = 0.31) and SKNA-Chest (p = 0.27) were similar to those before ablation, respectively. Among patients with symptomatic drug-refractory paroxysmal AF receiving PVI, increased SKNA was observed 1 day after ablation and returned to the baseline 3 months after ablation. Elevation of SKNA was associated with lower early and late recurrences following ablation.

The Mechanism of Cardiac Sympathetic Activity Assessment Methods: Current Knowledge

This review has summarized the methods currently available for cardiac sympathetic assessment in clinical or under research, with emphasis on the principles behind these methodologies. Heart rate variability (HRV) and other methods based on heart rate pattern analysis can reflect the dominance of sympathetic nerve to sinoatrial node function and indirectly show the average activity level of cardiac sympathetic nerve in a period of time. Sympathetic neurotransmitters play a key role of signal transduction after sympathetic nerve discharges. Plasma or local sympathetic neurotransmitter detection can mediately display sympathetic nerve activity. Given cardiac sympathetic nerve innervation, i.e., the distribution of stellate ganglion and its nerve fibers, stellate ganglion activity can be recorded either directly or subcutaneously, or through the surface of the skin using a neurophysiological approach. Stellate ganglion nerve activity (SGNA), subcutaneous nerve activity (SCNA), and skin sympathetic nerve activity (SKNA) can reflect immediate stellate ganglion discharge activity, i.e., cardiac sympathetic nerve activity. These cardiac sympathetic activity assessment methods are all based on the anatomy and physiology of the heart, especially the sympathetic innervation and the sympathetic regulation of the heart. Technological advances, discipline overlapping, and more understanding of the sympathetic innervation and sympathetic regulation of the heart will promote the development of cardiac sympathetic activity assessment methods.

An Artifact-Resistant Feature SKNAER for Quantifying the Burst of Skin Sympathetic Nerve Activity Signal

Evaluation of sympathetic nerve activity (SNA) using skin sympathetic nerve activity (SKNA) signal has attracted interest in recent studies. However, signal noises may obstruct the accurate location for the burst of SKNA, leading to the quantification error of the signal. In this study, we use the Teager−Kaiser energy (TKE) operator to preprocess the SKNA signal, and then candidates of burst areas were segmented by an envelope-based method. Since the burst of SKNA can also be discriminated by the high-frequency component in QRS complexes of electrocardiogram (ECG), a strategy was designed to reject their influence. Finally, a feature of the SKNA energy ratio (SKNAER) was proposed for quantifying the SKNA. The method was verified by both sympathetic nerve stimulation and hemodialysis experiments compared with traditional heart rate variability (HRV) and a recently developed integral skin sympathetic nerve activity (iSKNA) method. The results showed that SKNAER correlated well with HRV features (r = 0.60 with the standard deviation of NN intervals, 0.67 with low frequency/high frequency, 0.47 with very low frequency) and the average of iSKNA (r = 0.67). SKNAER improved the detection accuracy for the burst of SKNA, with 98.2% for detection rate and 91.9% for precision, inducing increases of 3.7% and 29.1% compared with iSKNA (detection rate: 94.5% (p < 0.01), precision: 62.8% (p < 0.001)). The results from the hemodialysis experiment showed that SKNAER had more significant differences than aSKNA in the long-term SNA evaluation (p < 0.001 vs. p = 0.07 in the fourth period, p < 0.01 vs. p = 0.11 in the sixth period). The newly developed feature may play an important role in continuously monitoring SNA and keeping potential for further clinical tests.

Dynamics of Cardiac Autonomic Responses During Hemodialysis Measured by Heart Rate Variability and Skin Sympathetic Nerve Activity: The Impact of Interdialytic Weight Gain

Background: Autonomic nervous regulation plays a critical role in end-stage kidney disease (ESKD) patients with cardiovascular complications. However, studies on autonomic regulation in ESKD patients are limited to heart rate variability (HRV) analysis. Skin sympathetic nerve activity (SKNA), which noninvasively reflects the sympathetic nerve activity, has not been used in ESKD patients.

Methods: Seventy-six patients on maintenance hemodialysis (MHD) treatment (a 4-h HD session, three times a week) were enrolled. Utilizing a noninvasive, single-lead, high-frequency recording system, we analyzed the dynamic change in HRV parameters and SKNA during HD. The different characteristics between the subgroups divided based on interdialytic weight gain (IDWG, &lt;3 kg or ≥3 kg) were also demonstrated.

Results: After the HD, values for heart rate (75.1 ± 11.3 to 80.3 ± 12.3 bpm, p &lt; 0.001) and LF/HF (1.92 ± 1.67 to 2.18 ± 2.17, p = 0.013) were significantly higher than baseline. In subgroup analysis, average voltage of skin sympathetic nerve activity (aSKNA) in IDWG ≥3 kg group was lower than the IDWG &lt;3 kg group at the end of MHD (1.06 ± 0.30 vs 1.32 ± 0.61 μV, p = 0.046). Moreover, there was a linear correlation between mean heart rate (HR) and aSKNA in low IDWG patients (p &lt; 0.001), which was not found in high IDWG patients. At the 1-year follow-up, high IDWG patients had a higher incidence of cardiovascular hospitalization (p = 0.046).

Conclusions: In MHD patients, a gradual activation of sympathetic nerve activity could be measured by HRV and aSKNA. A lower aSKNA at the end of HD and a loss of HR-aSKNA correlation in overhydrated patients were observed. Extensive volume control is promising to improve the autonomic nervous function and clinical outcomes in this population.

Skin Sympathetic Nerve Activity and the Short-Term QT Interval Variability in Patients With Electrical Storm

Background: Skin sympathetic nerve activity (SKNA) and QT interval variability are known to be associated with ventricular arrhythmias. However, the relationship between the two remains unclear.

Objective: The aim was to test the hypothesis that SKNA bursts are associated with greater short-term variability of the QT interval (STVQT) in patients with electrical storm (ES) or coronary heart disease without arrhythmias (CHD) than in healthy volunteers (HV).

Methods: We simultaneously recorded the ECG and SKNA during sinus rhythm in patients with ES (N = 10) and CHD (N = 8) and during cold-water pressor test in HV (N = 12). The QT and QTc intervals were manually marked and calculated within the ECG. The STVQT was calculated and compared to episodes of SKNA burst and non-bursting activity.

Results: The SKNA burst threshold for ES and HV was 1.06 ± 1.07 and 1.88 ± 1.09 μV, respectively (p = 0.011). During SKNA baseline and burst, the QT/QTc intervals and STVQT for ES and CHD were significantly higher than those of the HV. In all subjects, SKNA bursts were associated with an increased STVQT (from 6.43 ± 2.99 to 9.40 ± 5.12 ms, p = 0.002 for ES; from 9.48 ± 4.40 to 12.8 ± 5.26 ms, p = 0.016 for CHD; and from 3.81 ± 0.73 to 4.49 ± 1.24 ms, p = 0.016 for HV). The magnitude of increased STVQT in ES (3.33 ± 3.06 ms) and CHD (3.34 ± 2.34 ms) was both higher than that of the HV (0.68 ± 0.84 ms, p = 0.047 and p = 0.020).

Conclusion: Compared to non-bursting activity, SKNA bursts were associated with a larger increase in the QTc interval and STVQT in patients with heart disease than in HV.

Temporal Clustering of Skin Sympathetic Nerve Activity Bursts in Acute Myocardial Infarction Patients

Backgrounds: Acute myocardial infarction (AMI) affects the autonomic nervous system (ANS) function. The aim of our study is to detect the particular patterns of ANS regulation in AMI. We hypothesize that altered ANS regulation in AMI patients causes synchronized neural discharge (clustering phenomenon) detected by non-invasive skin sympathetic nerve activity (SKNA).

Methods: Forty subjects, including 20 AMI patients and 20 non-AMI controls, participated in the study. The wide-band bioelectrical signals (neuECG) were continuously recorded on the body surface for 5 min. SKNA was signal processed to depict the envelope of SKNA (eSKNA). By labeling the clusters, the AMI subjects were separated into non-AMI, non-cluster appearing (AMI_NCA), and cluster appearing (AMI_CA) groups.

Results: The average eSKNA was significantly correlated with HRV low-frequency (LF) power (rho = −0.336) and high-frequency power (rho = −0.372). The cross-comparison results demonstrated that eSKNA is a valid surrogate marker to assess ANS in AMI patients. The frequency of cluster occurrence was 0.01–0.03 Hz and the amplitude was about 3 μV. The LF/HF ratio of AMI_CA (median: 1.877; Q1–Q3: 1.483–2.413) revealed significantly lower than AMI_NCA (median: 3.959; Q1–Q3: 1.840–6.562). The results suggest that the SKNA clustering is a unique temporal pattern of ANS synchronized discharge, which could indicate the lower sympathetic status (by HRV) in AMI patients.

Conclusion: This is the first study to identify SKNA clustering phenomenon in AMI patients. Such a synchronized nerve discharge pattern could be detected with non-invasive SKNA signals. SKNA temporal clustering could be a novel biomarker to classify ANS regulation ability in AMI patients.

Clinical and Translational Significance: SKNA is higher in AMI patients than in control and negatively correlates with parasympathetic parameters. SKNA clustering is associated with a lower LF/HF ratio that has been shown to correlate with sudden cardiac death in AMI. The lack of SKNA temporal clustering could indicate poor ANS regulation in AMI patients.

Skin sympathetic nerve activity as a biomarker of fitness

BACKGROUND

Exercise stress testing is frequently used to expose cardiac arrhythmias. Aerobic exercise conditioning has been used as a nonpharmacologic antiarrhythmic intervention.

OBJECTIVE

The purpose of this study was to test the hypothesis that noninvasively recorded skin sympathetic nerve activity (SKNA) is increased during exercise and that SKNA response varies according to fitness levels.

METHODS

Oxygen consumption (VO2) and SKNA were recorded in 39 patients undergoing an incremental exercise test. Patients were grouped by 5 levels of fitness based on age, sex, and VO2max.

RESULTS

With exercise, all patients had a significant increase in average SKNA (aSKNA) (1.58 ± 1.12 μV to 4.50 ± 3.06 μV, P = .000) and heart rate (HR) (87.40 ± 20.42 bpm to 154.13 ± 16.82 bpm, P = .000). A mixed linear model of aSKNA was used with fixed effects of fitness, exercise time, and recovery time, and random effects of subject level intercept and slopes for exercise time and recovery times. The poor fitness group had significantly higher aSKNA than the other groups (P = .0273). For all subjects studied, aSKNA increased by 5% per minute with progression of exercise and decreased by 15% per minute with progression of recovery. The fitness variable encodes information on both comorbidities and body mass index (BMI). Once fitness level is known, comorbidities and BMI are not significantly associated with aSKNA. In all groups, aSKNA positively correlated with HR (R2 = 0.47 ± 0.23) and VO2 (R2 = 0.68 ± 0.25).

CONCLUSION

Fitness level determines the magnitude and time course of SKNA increase during exercise. SKNA may be a useful fitness biomarker in exercise stress testing.

High Skin Sympathetic Nerve Activity in Patients with Recurrent Syncope

(1) Background: The autonomic imbalance plays a role in vasovagal syncope (VVS) diagnosed by head-up tilting test (HUT). neuECG is a new method of recording skin electrical signals to simultaneously analyze skin sympathetic nerve activity (SKNA) and electrocardiogram. We hypothesize that SKNA is higher in subjects with tilt-positive than tilt-negative and the SKNA surges before syncope. (2) Methods: We recorded neuECG in 41 subjects who received HUT (according to the “Italian protocol”), including rest, tilt-up, provocation and recovery phases. Data were analyzed to determine the average SKNA (aSKNA, μV) per digitized sample. Electrocardiogram was used to calculate standard deviation of normal-to-normal beat intervals (SDNN). The “SKNA-SDNN index” was calculated by rest aSKNA multiplied by the ratio of tilt-up to rest SDNN. (3) Results: 16 of 41 (39%) subjects developed syncope. The aSKNA at rest phase is significantly higher in the tilt-positive (1.21 ± 0.27 µV) than tilt-negative subjects (1.02 ± 0.29 µV) (p = 0.034). There are significant surges and withdraw of aSKNA 30 s before and after syncope (both p ≤ 0.006). SKNA-SDNN index is able to predict syncope (p < 0.001). (4) Conclusion: Higher SKNA at rest phase is associated with positive HUT. The SKNA-SDNN index is a novel marker to predict syncope during HUT.

Autonomic Modulation of Cardiac Arrhythmias: Methods to Assess Treatment and Outcomes

The autonomic nervous system plays a central role in the pathogenesis of multiple cardiac arrhythmias, including atrial fibrillation and ventricular tachycardia. As such, autonomic modulation represents an attractive therapeutic approach in these conditions. Notably, autonomic modulation exploits the plasticity of the neural tissue to induce neural remodeling and thus obtain therapeutic benefit. Different forms of autonomic modulation include vagus nerve stimulation, tragus stimulation, renal denervation, baroreceptor activation therapy, and cardiac sympathetic denervation. This review seeks to highlight these autonomic modulation therapeutic modalities, which have shown promise in early preclinical and clinical trials and represent exciting alternatives to standard arrhythmia treatment. We also present an overview of the various methods used to assess autonomic tone, including heart rate variability, skin sympathetic nerve activity, and alternans, which can be used as surrogate markers and predictors of the treatment effect. Although the use of autonomic modulation to treat cardiac arrhythmias is supported by strong preclinical data and preliminary studies in humans, in light of the disappointing results of a number of recent randomized clinical trials of autonomic modulation therapies in heart failure, the need for optimization of the stimulation parameters and rigorous patient selection based on appropriate biomarkers cannot be overemphasized.

Loss of nocturnal dipping pattern of skin sympathetic nerve activity during and following an extended-duration work shift in residents in training

BACKGROUND

Extended-duration work shifts (EDWSs) might affect the health of physician residents, causing autonomic alteration. Skin sympathetic nerve activity (SKNA) recorded by noninvasive neuro-electrocardiography (neuECG) is used to estimate cardiac sympathetic tone. In this study, we aim to evaluate the impact of EDWSs on nocturnal SKNA assessed in resident doctors.

METHODS

Twenty-four residents working EDWSs and 12 PhD students not working nightshift schedules were prospectively recruited. The neuECG was performed between 12 am and 6 am for 5 consecutive nights. SKNA was filtered from neuECG recorded signals. The questionnaires regarding work stress and sleep quality, blood pressure, and salivary alpha-amylase and cortisol levels were administered.

RESULTS

The hours of weekly working and sleep opportunities were similar between residents and students, while residents reported more work stress and worse sleep quality. In residents, SKNA at 6 am (SKNA_6am) was significantly higher than SKNA_2am during the precall night, revealing a dipping pattern. However, the SKNA dipping disappeared during the on-call night and prominently flattened during the first postcall night, the full recovery of which was delayed until the second postcall nights. The morning blood pressure and salivary alpha-amylase and cortisol levels were similar between the precall and postcall days. In contrast, SKNA in students exhibited a constant dipping profile for all recorded nights.

CONCLUSIONS

In healthy young adults, SKNA presents a dip night. The SKNA dip is impaired by working a nightshift, with a delayed recovery. The neuECG might serve as a useful tool to detect subclinical autonomic disturbances in shiftworkers.

Absence of reliable physiological signature of illusory body ownership revealed by fine-grained autonomic measurement during the rubber hand illusion

The neural representation of a 'biological self' is linked theoretically to the control of bodily physiology. In an influential model, selfhood relates to internal agency and higher-order interoceptive representation, inferred from the predicted impact of efferent autonomic nervous activity on afferent viscerosensory feedback. Here we tested if an altered representation of physical self (illusory embodiment of an artificial hand) is accompanied by sustained shifts in autonomic activity. Participants (N = 37) underwent procedures for induction of the rubber hand illusion (synchronous stroking of own unseen hand and observed stroking of artificial hand) and a control condition (asychronous stroking). We recorded electrocardiography, electrodermal activity, and a non-invasive measure of multiunit skin sympathetic nerve activity (SKNA) from the chest. We compared these autonomic indices between task conditions, and between individuals who did and did not experience the illusion. Bayes factors quantified the strength of evidence for and against null hypotheses. Observed proprioceptive drift and subjective reports confirmed the efficacy of the synchronous (vs asynchronous) condition in inducing illusory hand ownership. Stringent discriminant analysis classified 24/37 individuals as experiencing the rubber hand illusion. Surprisingly, heart rate, heart rate variability, electrodermal activity, and SKNA measures revealed no autonomic differences between synchronous vs asynchronous conditions, nor between individuals who did or did not experience the rubber hand illusion. Bayes factors indicated substantial evidence for no physiological differences. In contrast to earlier reports, our autonomic data show the absence of a reliable change in physiological state during the rubber hand illusion. More encompassing perturbations of self-experience, for example in full body illusions, may nevertheless be coupled to, or facilitated by, changes in efferent autonomic activity and afferent viscerosensory feedback. Our findings suggest that such changes in bodily physiology are not sustained as an obligatory component of the rubber hand illusion.

Effects and Mechanisms of Cutting Upper Thoracic Sympathetic Trunk on Ventricular Rate in Ambulatory Canines with Persistent Atrial Fibrillation

Objective

The purpose is to observe the effects and neural mechanism of cutting upper thoracic sympathetic trunk (TST) on the ventricular rate (VR) during persistent atrial fibrillation (AF).

Methods

Twelve beagle dogs were halving to the control group and experimental group, 6 dogs for each group. Both groups were performed with left atrial rapid pacing (600 beats/min) to induce sustained AF. The experimental group underwent cutting upper TST  after a sustained AF model was established, while the control group received thoracotomy without cutting TST. Bilateral stellate ganglion (SG) and left atrial myocardium were harvested for tyrosine-hydroxylase (TH) immunohistochemical staining.

Results

After cutting upper TST for 30 minutes, the average VR was 121.5 ± 8.7 bpm (95% CI, 114.8 to 128.0) in the experimental group, which was significantly slower than that of the control group (144.5 ± 4.2 bpm (95% CI, 141.5 to 148.0)) (P < 0.001). After cutting upper TST for 1 month, the average VR of the experimental group (106.5 ± 4.9 bpm (95% CI, 102.0 to 110.0)) was also significantly slower versus that of the control group (139.2 ± 5.6 bpm (95% CI, 135.0 to 143.8)) (P < 0.001). Compared with the control group, both left stellate ganglion (LSG) and right stellate ganglion (RSG) of the experimental group caused neural remodeling characterized by decreased ganglionic cell density and reduced TH staining. TH-positive component was significantly decreased in the left atrium of the experimental group compared with the control group.

Conclusions

Cutting upper TST could reduce fast VR during persistent AF. Cutting upper TST induced bilateral SG neural remodeling and reduced sympathetic nerve density in the left atrium, which could contribute to the underlying mechanism of VR control during AF.

Effects of subcutaneous nerve stimulation with blindly inserted electrodes on ventricular rate control in a canine model of persistent atrial fibrillation

BACKGROUND

Subcutaneous nerve stimulation (ScNS) delivered directly to large subcutaneous nerves can be either antiarrhythmic or proarrhythmic, depending on the stimulus output.

OBJECTIVE

The purpose of this study was to perform a prospective randomized study in a canine model of persistent AF to test the hypothesis that high-output ScNS using blindly inserted subcutaneous electrodes can reduce ventricular rate (VR) during persistent atrial fibrillation (AF) whereas low-output ScNS would have opposite effects.

METHODS

We prospectively randomized 16 male and 15 female dogs with sustained AF (>48 hours) induced by rapid atrial pacing into 3 groups (sham, 0.25 mA, 3.5 mA) for 4 weeks of ScNS (10 Hz, alternating 20-seconds ON and 60-seconds OFF).

RESULTS

ScNS at 3.5 mA, but not 0.25 mA or sham, significantly reduced VR and stellate ganglion nerve activity (SGNA), leading to improvement of left ventricular ejection fraction (LVEF). No differences were found between the 0.25-mA and sham groups. Histologic studies showed a significant reduction of bilateral atrial fibrosis in the 3.5-mA group compared with sham controls. Only 3.5-mA ScNS had significant fibrosis in bilateral stellate ganglions. The growth-associated protein 43 (GAP43) staining of stellate ganglions indicated the suppression of GAP43 protein expression in the 3.5-mA group. There were no significant differences of nerve sprouting among all groups. There was no interaction between sex and ScNS effects on reduction of VR and SGNA, LVEF improvement, or results of histologic studies.

CONCLUSION

We conclude that 3.5-mA ScNS with blindly inserted electrodes can improve VR control, reduce atrial fibrosis, and partially improve LVEF in a canine model of persistent AF.

Complex dynamics of skin sympathetic nerve activities as a prognostic predictor for critically ill patients

BACKGROUND

The skin sympathetic nerve activity (SKNA) is a new method to measure sympathetic nerve activity by using conventional ECG electrodes. We developed a novel approach to analyze the complexity of SKNA time series under different time scales and showed its prognostic significance in patients receiving critical care.

METHODS

This study measured SKNA in patients admitted to an intensive care unit (ICU). Each recording is 10-minute long with 10000Hz sampling rate. Multi-scale fluctuation analysis (MSFA) was developed to quantify the variation within each time scale after removing the linear trend. The prognostic value of SKNA was combined with traditional prognostics scoring system to improve the predictive values.

RESULTS

155 patients were recruited. After 30 and 90 days, 30 and 48 patients expired. MSFA was significantly higher in survival group than mortality group for 30-day (0.487 ± 0.185 vs 0.401 ± 0.045, p = 0.018) and 90-day (0.499 ± 0.196 vs 0.414 ± 0.061, p = 0.001) follow-up. Sequential Organ Failure Assessment (SOFA) score was significantly lower in the survival group compared to the expired group for 30-day and 90-day (4.1 ± 2.9 vs. 5.5 ± 4.1, p = 0.032 and 3.9 ± 3.0 vs. 5.4 ± 3.5, p = 0.012). The Kaplan-Meier survival analysis showed MSFA lower than 0.401 (log-rank test:4.96, p = 0.03) or with SOFA score lower than 5 (log-rank test:5.49, p = 0.019) have a significantly higher mortality rate. A multivariate Cox regression model showed that the MSFA is an independent predictor for 30-day mortality (HR = 2.35, 1.08-5.09, p = 0.031) and 90-day mortality (HR = 1.96, 1.08-3.58, p = 0.027).

CONCLUSION

MSFA was a significant prognostic predictor for critically ill patients. MSFA adding to SOFA score could help improve risk prediction.

Skin sympathetic nerve activity and ventricular rate control during atrial fibrillation

BACKGROUND

The relationship between the ventricular rate (VR) during atrial fibrillation (AF) and skin sympathetic nerve activity (SKNA) remains unclear.

OBJECTIVE

The purpose of this study was to test the hypothesis that SKNA bursts accelerate VR during AF.

METHODS

We simultaneously recorded electrocardiogram and SKNA in 8 patients (median age 66.0 years [interquartile range {IQR} 59.0-77.0 years]; 4 men [50%]) with 30 paroxysmal AF episodes (all >10-minute long) and 12 patients (73.0 years [IQR 60.5-80.0 years]; 6 men [50%]) with persistent AF. The average amplitude of SKNA (aSKNA [μV]) during AF was analyzed in 1-minute windows and binned, showing 2 Gaussian distributions. We used the mean + 3SD of the first Gaussian distribution as the threshold that separates burst from baseline (nonburst) SKNA. All 1-minute aSKNA values above the threshold were detected, and the area between aSKNA and baseline of every 1 minute was calculated and added as burst area.

RESULTS

VR was higher during SKNA bursts than during the nonburst period (103 beats/min [IQR 83-113 beats/min] vs 88 beats/min [IQR 76-101 beats/min], respectively; P = .003). In the highest quartile of the burst area during persistent AF, the scatterplot of maximal aSKNA and VR during each SKNA burst shows higher aSKNA and VR. The overall estimate of the correlation between maximal VR and aSKNA during bursts show a positive correlation in the highest quartile of the burst area (0.64; 95% confidence interval 0.54-0.74; P < .0001).

CONCLUSION

SKNA bursts are associated with VR acceleration. These SKNA bursts may be new therapeutic targets for rate control during AF.

Skin sympathetic nerve activity as a biomarker for syncopal episodes during a tilt table test

BACKGROUND

Autonomic imbalance is the proposed mechanism of syncope during a tilt table test (TTT). We have recently demonstrated that skin sympathetic nerve activity (SKNA) can be noninvasively recorded using electrocardiographic electrodes.

OBJECTIVE

The purpose of this study was to test the hypothesis that increased SKNA activation precedes tilt-induced syncope.

METHODS

We studied 50 patients with a history of neurocardiogenic syncope undergoing a TTT. The recorded signals were band-pass filtered at 500-1000 Hz to analyze nerve activity.

RESULTS

The average SKNA (aSKNA) value at baseline was 1.38 ± 0.38 μV in patients without syncope and 1.42 ± 0.52 μV in patients with syncope (P = .77). On upright tilt, aSKNA was 1.34 ± 0.40 μV in patients who did not have syncope and 1.39 ± 0.43 μV in patients who had syncope (P = .65). In all 14 patients with syncope, there was a surge of SKNA before an initial increase in heart rate followed by bradycardia, hypotension, and syncope. The peak aSKNA immediately (<1 minute) before syncope was significantly higher than baseline aSKNA (2.63 ± 1.22 vs 1.39 ± 0.43 μV; P = .0005). After syncope, patients were immediately placed in the supine position and aSKNA dropped significantly to 1.26 ± 0.43 μV; (P = .0004). The heart rate variability during the TTT shows a significant increase in parasympathetic tone during syncope (low-frequency/high-frequency ratio: 7.15 vs 2.21; P = .04).

CONCLUSION

Patients with syncope do not have elevated sympathetic tone at baseline or during the TTT except immediately before syncope when there is a transient surge of SKNA followed by sympathetic withdrawal along with parasympathetic surge.

Effects of anesthetic and sedative agents on sympathetic nerve activity

BACKGROUND

The effects of sedative and anesthetic agents on sympathetic nerve activity (SNA) are poorly understood.

OBJECTIVE

The purpose of this study was to determine the effects of commonly used sedative and anesthetic agents on SNA in ambulatory dogs and humans.

METHODS

We implanted radiotransmitters in 6 dogs to record stellate ganglion nerve activity (SGNA), subcutaneous nerve activity (ScNA), and blood pressure (BP). After recovery, we injected dexmedetomidine (3 μg/kg), morphine (0.1 mg/kg), hydromorphone (0.05 mg/kg), and midazolam (0.1 mg/kg) on different days. We also studied 12 human patients (10 male; age 68.0 ± 9.1 years old) undergoing cardioversion for atrial fibrillation with propofol (0.77 ± 0.18 mg/kg) or methohexital (0.65 mg/kg) anesthesia. Skin sympathetic nerve activity (SKNA) and electrocardiogram were recorded during the study.

RESULTS

SGNA and ScNA were significantly suppressed immediately after administration of dexmedetomidine (P = .000 and P = .000, respectively), morphine (P = .011 and P = .014, respectively), and hydromorphone (P = .000 and P = .012, respectively), along with decreased BP and heart rate (HR) (P <.001 for each). Midazolam had no significant effect on SGNA and ScNA (P = .248 and P = .149, respectively) but increased HR (P = .015) and decreased BP (P = .004) in ambulatory dogs. In patients undergoing cardioversion, bolus propofol administration significantly suppressed SKNA (from 1.11 ± 0.25 μV to 0.77 ± 0.15 μV; P = .001), and the effects lasted for at least 10 minutes after the final cardioversion shock. Methohexital decreased chest SKNA from 1.59 ± 0.45 μV to 1.22 ± 0.58 μV (P = .000) and arm SKNA from 0.76 ± 0.43 μV to 0.55 ± 0.07 μV (P = .001). The effects lasted for at least 10 minutes after the cardioversion shock.

CONCLUSION

Propofol, methohexital, dexmedetomidine, morphine, and hydromorphone suppressed, but midazolam had no significant effects on, SNA.

Periodic repolarization dynamics as a risk predictor after myocardial infarction: Prospective validation study

BACKGROUND

Periodic repolarization dynamics (PRD) is a novel electrocardiographic phenomenon that refers to sympathetic activity-associated low-frequency modulations of cardiac repolarization. Retrospective post-myocardial infarction (MI) studies revealed that increased PRD indicates an increased risk of subsequent death.

OBJECTIVE

This is the first prospective study to validate PRD in patients after MI receiving up-to-date treatment.

METHODS

Four hundred fifty-five survivors of MI (age ≤80 years) in sinus rhythm were enrolled. PRD was assessed from 20-minute electrocardiographic recordings (2048 Hz) and prospectively dichotomized at 5.75 deg². Primary and secondary end points were total mortality and cardiovascular mortality, respectively. Multivariable analyses additionally included Global Registry of Acute Coronary Events score (dichotomized at >140), left ventricular ejection fraction (dichotomized at ≤35%), diabetes mellitus, and deceleration capacity of heart rate (dichotomized at ≤2.5 ms). The prognostic power of PRD was evaluated using receiver operating characteristic curve analysis, Cox regression analysis, and the integrated discrimination improvement index.

RESULTS

During a median follow-up period of 27 months, 47 patients died. Twenty-three of these deaths were classified as cardiovascular. Increased PRD was significantly associated with both end points, yielding areas under receiver operating characteristic curves of 69.3% (60.2%-77.8%) and 79.1% (69.7%-86.7%) for total mortality and cardiovascular mortality, respectively (P < .001 for both). In multivariable analysis, increased PRD indicated a 2.2- and 9.5-fold risk of total mortality and cardiovascular mortality (P = .024 and P = .003, respectively). Addition of PRD to the models significantly improved the integrated discrimination improvement index for total (P = .047) and cardiovascular mortality (P = .007).

CONCLUSION

PRD is a strong and independent predictor of total mortality and cardiovascular mortality in patients after MI treated with contemporary therapy.

Skin sympathetic nerve activity and the temporal clustering of cardiac arrhythmias

BACKGROUND

Simultaneous noninvasively recorded skin sympathetic nerve activity (SKNA) and electrocardiogram (neuECG) can be used to estimate cardiac sympathetic tone. We tested the hypothesis that large and prolonged SKNA bursts are associated with temporal clustering arrhythmias.

METHODS

We recorded neuECG in 10 patients (69 ± 10 years old) with atrial fibrillation (AF) episodes and in 6 patients (50 ± 13 years old) with ventricular tachycardia (VT) or fibrillation (VF) episodes. Clustering was defined by an arrhythmic episode followed within 1 minute by spontaneous recurrences of the same arrhythmia. The neuECG signals were bandpass filtered between 500-1000 Hz to display SKNA.

RESULTS

There were 22 AF clusters, including 231 AF episodes from 6 patients, and 9 VT/VF clusters, including 99 VT/VF episodes from 3 patients. A total duration of SKNA bursts associated with AF was longer than that during sinus rhythm (78.9 min/hour [interquartile range (IQR) 17.5-201.3] vs. 16.3 min/hour [IQR 14.5-18.5], P = 0.022). The burst amplitude associated with AF in clustering patients was significantly higher than that in nonclustering patients (1.54 μV [IQR 1.35-1.89], n = 114, vs. 1.20 μV [IQR 1.05-1.42], n = 21, P < 0.001). The SKNA bursts associated with VT/VF clusters lasted 9.3 ± 3.1 minutes, with peaks that averaged 1.13 ± 0.38 μV as compared with 0.79 ± 0.11 μV at baseline (P = 0.041).

CONCLUSION

Large and sustained sympathetic nerve activities are associated with the temporal clustering of AF and VT/VF.

FUNDING

This study was supported in part by NIH grants R42DA043391 (THE), R56 HL71140, TR002208-01, R01 HL139829 (PSC), a Charles Fisch Cardiovascular Research Award endowed by Suzanne B. Knoebel of the Krannert Institute of Cardiology (TK and THE), a Medtronic-Zipes Endowment, and the Indiana University Health-Indiana University School of Medicine Strategic Research Initiative (PSC).

Effects of Renal Denervation via Renal Artery Adventitial Cryoablation on Atrial Fibrillation and Cardiac Neural Remodeling

Introduction

Catheter-based renal denervation (RDN) could reduce cardiac sympathetic nerve activity (SNA) and inhibit atrial fibrillation (AF). However, the reliability is uncertain, because the renal sympathetic nerves are mainly distributed in the adventitial surface of the renal artery.

Objective

The aims of this study were to test the hypothesis that renal artery adventitial ablation (RAAA) definitely had the effects of RDN and to study the effects of RDN via renal artery adventitial cryoablation (RAAC) on AF and cardiac neural remodeling.

Methods

Twenty beagle canines were randomly assigned to two groups: the left RDN group (LRDN, n=10), which underwent left RDN via RAAC; the Sham group (n=10). After 2 months of postoperative recovery, AF vulnerability, AF duration, and histological examination were performed in both groups.

Results

Compared with the Sham group, left stellate ganglion (LSG) tissue fibrosis was increased in the LRDN group. LRDN significantly increased the percentage of TH-negative ganglionic cells and decreased the density of TH-positive nerves in the LSG (P < 0.001). Also, the densities of TH-positive nerves and GAP43 immunoreactivity within the left atrium (LA) were significantly decreased in the LRDN group (P < 0.05). After LA burst pacing, all 10 canines (100%) could be induced AF in the Sham group, but only 4 of 10 canines (40%) could be induced AF in the LRDN group (P=0.011). The percentage of LA burst stimulation with induced AF was 26.7% (8/30) in the LRDN group, which was significantly decreased compared with that of the Sham group (53.3%, 16/30) (P=0.035). In addition, AF duration was also significantly decreased in the LRDN group (13.3 ± 5.1 s) compared with that of the Sham group (20.3 ± 7.3 s, P=0.024).

Conclusions

RDN via RAAC could cause cardiac neural remodeling and effectively inhibit AF inducibility and shorten AF duration. It may be useful in selecting therapeutic approaches for AF patients.

Effects of Vagal Nerve Stimulation on Ganglionated Plexi Nerve Activity and Ventricular Rate in Ambulatory Dogs With Persistent Atrial Fibrillation

OBJECTIVES

This study was designed to test the hypothesis that low-level vagal nerve stimulation (VNS) reduces the ventricular rate (VR) during atrial fibrillation (AF) through the activation of the inferior vena cava (IVC)-inferior atrial ganglionated plexus nerve activity (IAGPNA).

BACKGROUND

Increased IVC-IAGPNA can suppress atrioventricular node conduction and slow VR in canine models of AF.

METHODS

Persistent AF was induced in 6 dogs and the IVC-IAGPNA, right vagal nerve activity, left vagal nerve activity, and an electrocardiogram were recorded. After persistent AF was documented, VNS was programed to 14 s "on" and 1.1 min "off." After 1 week, the VNS was reprogramed to 3 min off and stimulation continued for another week. Neural remodeling of the stellate ganglion (SG) was assessed with tyrosine hydroxylase staining and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling staining.

RESULTS

Average IVC-IAGPNA was increased during both VNS 1.1 min off (8.20 ± 2.25 μV [95% confidence interval (CI): 6.33 to 9.53 μV]; p = 0.002) and 3 min off (7.96 ± 2.03 μV [95% CI: 6.30 to 9.27 μV]; p = 0.001) versus baseline (7.14 ± 2.20 μV [95% CI: 5.35 to 8.52 μV]). VR was reduced during both VNS 1.1 min off (123.29 ± 6.29 beats/min [95% CI: 116.69 to 129.89 beats/min]; p = 0.001) and 3 min off (120.01 ± 4.93 beats/min [95% CI: 114.84 to 125.18 beats/min]; p = 0.001) compared to baseline (142.04 ± 7.93 bpm [95% CI: 133.72 to 150.37]). Abnormal regions were observed in the left SG, but not in the right SG. Terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling-positive neurons were found in 22.2 ± 17.2% [95% CI: 0.9% to 43.5%] of left SG cells and 12.8 ± 8.4% [95% CI: 2.4% to 23.2%] of right SG cells.

CONCLUSIONS

Chronic low-level VNS increases IVC-IAGPNA and damages bilateral stellate ganglia. Both mechanisms could contribute to the underlying mechanism of VR control during AF.

Antiarrhythmic effects of stimulating the left dorsal branch of the thoracic nerve in a canine model of paroxysmal atrial tachyarrhythmias

BACKGROUND

Stellate ganglion nerve activity (SGNA) precedes paroxysmal atrial tachyarrhythmia (PAT) episodes in dogs with intermittent rapid left atrial (LA) pacing. The left dorsal branch of the thoracic nerve (LDTN) contains sympathetic nerves originating from the stellate ganglia.

OBJECTIVE

The purpose of this study was to test the hypothesis that high-frequency electrical stimulation of the LDTN can cause stellate ganglia damage and suppress PATs.

METHODS

We performed long-term LDTN stimulation in 6 dogs with and 2 dogs without intermittent rapid LA pacing while monitoring SGNA.

RESULTS

LDTN stimulation reduced average SGNA from 4.36 μV (95% confidence interval [CI] 4.10-4.62 μV) at baseline to 3.22 μV (95% CI 3.04-3.40 μV) after 2 weeks (P = .028) and completely suppressed all PAT episodes in all dogs studied. Tyrosine hydroxylase staining showed large damaged regions in both stellate ganglia, with increased percentages of tyrosine hydroxylase-negative cells. The terminal deoxynucleotidyl transferase dUTP nick end labeling assay showed that 23.36% (95% CI 18.74%-27.98%) of ganglion cells in the left stellate ganglia and 11.15% (95% CI 9.34%-12.96%) ganglion cells in the right stellate ganglia were positive, indicating extensive cell death. A reduction of both SGNA and heart rate was also observed in dogs with LDTN stimulation but without rapid LA pacing. Histological studies in the 2 dogs without intermittent rapid LA pacing confirmed the presence of extensive stellate ganglia damage, along with a high percentage of terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells.

CONCLUSION

LDTN stimulation damages both left and right stellate ganglia, reduces left SGNA, and is antiarrhythmic in this canine model of PAT.

Effects of Stellate Ganglion Cryoablation on Subcutaneous Nerve Activity and Atrial Tachyarrhythmias in a Canine Model of Pacing-Induced Heart Failure

OBJECTIVES

This study aimed to test the hypothesis that subcutaneous nerve activity (SCNA) can adequately estimate the cardiac sympathetic tone and the effects of cryoablation of the stellate ganglion in dogs with pacing-induced heart failure (HF).

BACKGROUND

Recording of SCNA is a new method to estimate sympathetic tone in dogs. HF is known to increase sympathetic tone and atrial arrhythmias.

METHODS

Twelve dogs with pacing-induced HF were studied using implanted radiotransmitters to record the stellate ganglia nerve activity (SGNA), vagal nerve activity, and SCNA. Of these, 6 dogs (ablation group) underwent bilateral stellate ganglia cryoablation before the rapid ventricular pacing; the remaining 6 dogs (control group) had rapid ventricular pacing only. In both groups, SCNA was compared with SGNA and the occurrence of arrhythmias.

RESULTS

SCNA invariably increased before the 360 identified atrial tachyarrhythmia episodes in the 6 control dogs before and after HF induction. SCNA and SGNA correlated in all dogs with an average correlation coefficient of 0.64 (95% confidence interval: 0.58 to 0.70). Cryoablation of bilateral stellate ganglia significantly reduced SCNA from 0.34 ± 0.033 μV to 0.25 ± 0.028 μV (p = 0.03) and eliminated all atrial tachyarrhythmias.

CONCLUSIONS

SCNA can be used to estimate cardiac sympathetic tone in dogs with pacing-induced HF. Cryoablation of the stellate ganglia reduced SCNA and arrhythmia vulnerability.

Long-term intermittent high-amplitude subcutaneous nerve stimulation reduces sympathetic tone in ambulatory dogs

BACKGROUND

Reducing sympathetic efferent outflow from the stellate ganglia (SG) may be antiarrhythmic.

OBJECTIVE

The purpose of this study was to test the hypothesis that chronic thoracic subcutaneous nerve stimulation (ScNS) could reduce SG nerve activity (SGNA) and control paroxysmal atrial tachycardia (PAT).

METHODS

Thoracic ScNS was performed in 8 dogs while SGNA, vagal nerve activity (VNA), and subcutaneous nerve activity (ScNA) were monitored. An additional 3 dogs were used for sham stimulation as controls.

RESULTS

Xinshu ScNS and left lateral thoracic nerve ScNS reduced heart rate (HR). Xinshu ScNS at 3.5 mA for 2 weeks reduced mean average SGNA from 5.32 μV (95% confidence interval [CI] 3.89-6.75) at baseline to 3.24 μV (95% CI 2.16-4.31; P = .015) and mean HR from 89 bpm (95% CI 80-98) at baseline to 83 bpm (95% CI 76-90; P = .007). Bilateral SG showed regions of decreased tyrosine hydroxylase staining with increased terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive nuclei in 18.47% (95% CI 9.68-46.62) of all ganglion cells, indicating cell death. Spontaneous PAT episodes were reduced from 9.83 per day (95% CI 5.77-13.89) in controls to 3.00 per day (95% CI 0.11-5.89) after ScNS (P = .027). Left lateral thoracic nerve ScNS also led to significant bilateral SG neuronal death and significantly reduced average SGNA and HR in dogs.

CONCLUSION

ScNS at 2 different sites in the thorax led to SG cell death, reduced SGNA, and suppressed PAT in ambulatory dogs.

Left cervical vagal nerve stimulation reduces skin sympathetic nerve activity in patients with drug resistant epilepsy

BACKGROUND

We recently reported that skin sympathetic nerve activity (SKNA) can be used to estimate sympathetic tone in humans. In animal models, vagal nerve stimulation (VNS) can damage the stellate ganglion, reduce stellate ganglion nerve activity, and suppress cardiac arrhythmia. Whether VNS can suppress sympathetic tone in humans remains unclear.

OBJECTIVE

The purpose of this study was to test the hypothesis that VNS suppresses SKNA in patients with drug-resistant epilepsy.

METHODS

ECG patch electrodes were used to continuously record SKNA in 26 patients with drug-resistant epilepsy who were admitted for video electroencephalographic monitoring. Among them, 6 (2 men, age 40 ± 11 years) were previously treated with VNS and 20 (7 men, age 37 ± 8 years) were not. The signals from ECG leads I and II were filtered to detect SKNA.

RESULTS

VNS had an on-time of 30 seconds and off-time of 158 ± 72 seconds, with output of 1.92 ± 0.42 mA at 24.17 ± 2.01 Hz. Average SKNA during VNS off-time was 1.06 μV (95% confidence interval [CI] 0.93-1.18) in lead I and 1.13 μV (95% CI 0.99-1.27) in lead II, which was significantly lower than 1.38 μV (95% CI 1.01-1.75; P = .036) and 1.38 μV (95% CI 0.98-1.78; P = .035) in the control group, respectively. Heart rate was 65 bpm (95% CI 59-71) in the VNS group, which was significantly lower than 77 bpm (95% CI 71-83) in the control group.

CONCLUSION

Patients with VNS had significantly lower SKNA than those without VNS.

Simultaneous recordings of intrinsic cardiac nerve activity and skin sympathetic nerve activity from human patients during the postoperative period

BACKGROUND

Intrinsic cardiac nerve activity (ICNA) and skin nerve activity (SKNA) are both associated with cardiac arrhythmias in dogs.

OBJECTIVE

The purpose of this study was to test the hypothesis that ICNA and SKNA correlate with postoperative cardiac arrhythmias in humans.

METHODS

Eleven patients (mean age 60 ± 13 years; 4 women) were enrolled in this study. Electrical signals were simultaneously recorded from electrocardiogram (ECG) patch electrodes on the chest wall and from 2 temporary pacing wires placed during open heart surgery on the left atrial epicardial fat pad. The signals were filtered to display SKNA and ICNA. Premature atrial contractions (PACs) and premature ventricular contractions were determined manually. The SKNA and ICNA of the first 300 minutes of each patient were calculated minute by minute to determine baseline average amplitudes of nerve activities and to determine their correlation with arrhythmia burden.

RESULTS

We processed 1365 ± 973 minutes of recording per patient. Low-amplitude SKNA and ICNA were present at all time, while the burst discharges were observed much less frequently. Both SKNA and burst ICNA were significantly associated with the onset of PACs and premature ventricular contractions. Baseline average ICNA (aICNA), but not average SKNA, had a significant association with PAC burden. The correlation coefficient (r) between aICNA and PAC burden was 0.78 (P < .01). A patient with the greatest aICNA developed postoperative atrial fibrillation.

CONCLUSION

ICNA and SKNA can be recorded from human patients in the postoperative period. The baseline magnitude of ICNA correlates with PAC burden and development of postoperative atrial fibrillation.

Autonomic Modulation in Patients with Heart Failure Increases Beat-to-Beat Variability of Ventricular Action Potential Duration

Background: Exaggerated beat-to-beat variability of ventricular action potential duration (APD) is linked to arrhythmogenesis. Sympathetic stimulation has been shown to increase QT interval variability, but its effect on ventricular APD in humans has not been determined.

Methods and Results: Eleven heart failure patients with implanted bi-ventricular pacing devices had activation–recovery intervals (ARI, surrogate for APD) recorded from LV epicardial electrodes under constant RV pacing. Sympathetic activity was increased using a standard autonomic challenge (Valsalva) and baroreceptor indices were applied to determine changes in sympathetic stimulation. Two Valsalvas were performed for each study and were repeated, both off and on bisoprolol. In addition sympathetic nerve activity (SNA) was measured from skin electrodes on the thorax using a novel validated method. Autonomic modulation significantly increased mean short-term variability in ARI; off bisoprolol mean STV increased from 3.73 ± 1.3 to 5.27 ± 1.04 ms (p = 0.01), on bisoprolol mean STV of ARI increased from 4.15 ± 1.14 to 4.62 ± 1 ms (p = 0.14). Adrenergic indices of the Valsalva demonstrated significantly reduced beta-adrenergic function when on bisoprolol (Δ pressure recovery time, p = 0.04; Δ systolic overshoot in Phase IV, p = 0.05). Corresponding increases in SNA from rest both off (1.4 uV, p < 0.01) and on (0.7 uV, p < 0.01) bisoprolol were also seen.

Conclusions: Beat-to-beat variability of ventricular APD increases during brief periods of increased sympathetic activity in patients with heart failure. Bisoprolol reduces, but does not eliminate, these effects. This may be important in the genesis of ventricular arrhythmias in heart failure patients.

Recording sympathetic nerve activity from the skin

Sympathetic tone is important in cardiac arrhythmogenesis; however, methods to estimate sympathetic tone are either invasive or require proper sinus node function that may be abnormal in disease states. Because of the direct and extensive connections among various nerve structures, it is possible for the sympathetic nerves in the various structures to activate simultaneously. Therefore, we hypothesized that nerve activity can be recorded from the skin and it can be used to estimate the cardiac sympathetic tone. Preclinical studies in canines demonstrated that nerve activity is detectable using conventional ECG electrodes and can be used to estimate cardiac sympathetic tone. Subsequent clinical studies further supported this concept. In addition to studying the autonomic mechanisms of cardiac arrhythmia, these new methods may have broad application in studying both cardiac and non-cardiac diseases.

Skin sympathetic nerve activity precedes the onset and termination of paroxysmal atrial tachycardia and fibrillation

BACKGROUND

Skin sympathetic nerve activity (SKNA) is useful for estimating sympathetic tone in humans.

OBJECTIVE

The purpose of this study was to test the hypotheses that (1) increased SKNA is associated with the onset and termination of paroxysmal atrial tachycardia (AT) and atrial fibrillation (AF) and (2) sinoatrial node response to SKNA is reduced in patients with more frequent AT or AF episodes.

METHODS

SKNA and electrocardiogram were recorded in 11 patients (4 men and 7 women; average age 66 ± 10 years), including 3 patients with AT (11 ± 18 episodes per patient) and 8 patients with AF (24 ± 26 episodes per patient).

RESULTS

The average SKNA (aSKNA) 10 seconds before AT onset was 1.07 ± 0.10 μV and 10 seconds after termination was 1.27 ± 0.10 μV; both were significantly (P = .032 and P < .0001) higher than that during sinus rhythm (0.97 ± 0.09 μV). The aSKNA 10 seconds before AF onset was 1.34 ± 0.07 μV and 10 seconds after termination was 1.31 ± 0.07 μV; both were significantly (P < .0001) higher than that during sinus rhythm (1.04 ± 0.07 μV). The aSKNA before onset (P < .0001) and after termination (P = .0011) was higher in AF than in AT. The sinus rate correlated (P < .0001) with aSKNA in each patient (average r = 0.74; 95% confidence interval 0.65-0.84). The r value in each patient negatively correlated with the number of AT and AF episodes (r = -0.6493; 95% confidence interval -0.8990 to -0.08073; P = .0306).

CONCLUSION

Increased SKNA was observed both at the onset and termination of AT and AF. Patients with more frequent AT and AF episodes had a weak correlation between sinus rate and aSKNA, suggesting sinoatrial node remodeling by tachycardia.

Simultaneous noninvasive recording of skin sympathetic nerve activity and electrocardiogram

BACKGROUND

Sympathetic nerve activity is important to cardiac arrhythmogenesis.

OBJECTIVE

The purpose of this study was to develop a method for simultaneous noninvasive recording of skin sympathetic nerve activity (SKNA) and electrocardiogram (ECG) using conventional ECG electrodes. This method (neuECG) can be used to adequately estimate sympathetic tone.

METHODS

We recorded neuECG signals from the skin of 56 human subjects. The signals were low-pass filtered to show the ECG and high-pass filtered to show nerve activity. Protocol 1 included 12 healthy volunteers who underwent cold water pressor test and Valsalva maneuver. Protocol 2 included 19 inpatients with epilepsy but without known heart diseases monitored for 24 hours. Protocol 3 included 22 patients admitted with electrical storm and monitored for 39.0 ± 28.2 hours. Protocol 4 included 3 patients who underwent bilateral stellate ganglion blockade with lidocaine injection.

RESULTS

In patients without heart diseases, spontaneous nerve discharges were frequently observed at baseline and were associated with heart rate acceleration. SKNA recorded from chest leads (V₁-V₆) during cold water pressor test and Valsalva maneuver (protocol 1) was invariably higher than during baseline and recovery periods (P < .001). In protocol 2, the average SKNA correlated with heart rate acceleration (r = 0.73 ± 0.14, P < .05) and shortening of QT interval (P < .001). Among 146 spontaneous ventricular tachycardia episodes recorded in 9 patients of protocol 3, 106 episodes (73%) were preceded by SKNA within 30 seconds of onset. Protocol 4 showed that bilateral stellate ganglia blockade by lidocaine inhibited SKNA.

CONCLUSION

SKNA is detectable using conventional ECG electrodes in humans and may be useful in estimating sympathetic tone.

Ganglionated plexi and ligament of Marshall ablation reduces atrial vulnerability and causes stellate ganglion remodeling in ambulatory dogs

BACKGROUND

Simultaneous activation of the stellate ganglion (SG), the ligament of Marshall (LOM), and the ganglionated plexi often precedes the onset of paroxysmal atrial tachyarrhythmia (PAT).

OBJECTIVE

The purpose of this study was to test the hypothesis that ablation of the LOM and the superior left ganglionated plexi (SLGP) reduces atrial vulnerability and results in remodeling of the SG.

METHODS

Nerve activity was correlated to PAT and ventricular rate (VR) at baseline, after ablation of the LOM and SLGP, and after atrial fibrillation. Neuronal cell death was assessed with tyrosine hydroxylase and terminal deoxynucleotidyl transferase dUTP nick end label (TUNEL) staining.

RESULTS

There were 4 ± 2 PAT episodes per day in controls. None were observed in the ablation group, even though SG nerve activity and VR increased from 2.2 µV (95% confidence interval [CI] 1.2-3.3 µV) and 80 bpm (95% CI 68-92 bpm) at baseline, to 3.0 µV (95% CI 2.6-3.4 µV, P = .046) and 90 bpm (95% CI 75-108 bpm, P = .026) after ablation, and to 3.1 µV (95% CI 1.7-4.5 µV, P = .116) and 95 bpm (95% CI 79-110 bpm, P = .075) after atrial fibrillation. There was an increase in tyrosine hydroxylase-negative cells in the ablation group and 19.7% (95% CI 8.6%-30.8%) TUNEL-positive staining in both the left and right SG. None were observed in the control group.

CONCLUSION

LOM and SLGP ablation caused left SG remodeling and cell death. There was reduced correlation of the VR response and PAT to SG nerve activity. These findings support the importance of SLGP and LOM in atrial arrhythmogenesis.

The need for and the challenges of measuring renal sympathetic nerve activity

Renal denervation (RDN) was primarily developed to treat hypertension and is potentially a new method for treating arrhythmias. Because of the lack of a standardized protocol to measure renal sympathetic nerve activity, RDN is administered in a blind manner. This inability to assess efficacy at the time of treatment delivery may be a large contributor to the ambiguity of RDN outcomes reported in the hypertension literature. The advancement of RDN as a treatment of hypertension or arrhythmias will be hampered by the lack of delivery assessment, a deficiency that the cardiovascular electrophysiology community, with its expertise in recording and mapping, may have a role in addressing and overcoming. The development of endovascular recording of renal nerve action potentials may provide a useful accessory tool for RDN. Innovation in this area will be crucial as we as a community reconsider the therapeutic value of RDN.

Subcutaneous nerve activity and mechanisms of sudden death in a rat model of chronic kidney disease

BACKGROUND

The mechanisms of sudden death in chronic kidney disease (CKD) remain unclear.

OBJECTIVE

The purpose of this study was to test the hypotheses that subcutaneous nerve activity (SCNA) can be used to estimate sympathetic tone in ambulatory rats and that abrupt reduction of SCNA precedes the spontaneous arrhythmic death of Cy/+ rats.

METHODS

Radiotransmitters were implanted in ambulatory normal (N = 6) and Cy/+ (CKD; N = 6) rats to record electrocardiogram and SCNA. Two additional rats were studied before and after chemical sympathectomy with 6-hydroxydopamine.

RESULTS

In normal rats, the baseline heart rate (HR) and SCNA were 351 ± 29 bpm and 5.12 ± 2.97 mV·s, respectively. SCNA abruptly increased HR by 4.31% (95% confidence interval 4.15%-4.47%). In comparison, the CKD rats had reduced baseline HR (336 ± 21 bpm, P < .01) and SCNA (4.27 ± 3.19 mV·s, P < .01). When SCNA was observed, HR increased by only 2.48% (confidence interval 2.29%-2.67%, P < .01). All Cy/+ rats died suddenly, preceded by sinus bradycardia, advanced (second- and third-degree) AV block (N = 6), and/or ventricular tachycardia or fibrillation (N = 3). Sudden death was preceded by a further reduction of SCNA (3.22 ± 2.86 mV·s, P < .01) and sinus bradycardia (243 ± 55 bpm, P < .01). Histologic studies in CKD rats showed myocardial calcification that involved the conduction system. Chemical sympathectomy resulted in progressive reduction of SCNA over 7 days.

CONCLUSION

SCNA can be used to estimate sympathetic tone in ambulatory rats. CKD is associated with reduced HR response to SCNA and conduction system diseases. Abrupt reduction of sympathetic tone precedes AV block, ventricular arrhythmia, and sudden death of CKD rats.