Peripheral regional anaesthesia and outcomes: a narrative review of the literature from 2013 to 2023

The use of peripheral regional anaesthesia continues to increase, yet the evidence supporting its use and impact on relevant outcomes often lacks scientific rigour, especially when considering the use of specific blocks for a particular surgical indication. In this narrative review, we consider the relevant literature in a 10-yr period from 2013. We performed a literature search (MEDLINE and EMBASE) for articles reporting randomised controlled trials and other comparative trials of peripheral regional anaesthetic blocks vs systemic analgesia in adult patients undergoing surgery. We evaluated measures of effective treatment and complications. A total of 128 studies met our inclusion criteria. There remains variability in the technical conduct of blocks and the outcomes used to evaluate them. There is a considerable body of evidence to support the use of interscalene blocks for shoulder surgery. Saphenous nerve (motor-sparing) blocks provide satisfactory analgesia after knee surgery and are preferred to femoral nerve blocks which are associated with falls when patients are mobilised early as part of enhanced recovery programmes. There are additional surgical indications where the efficacy of cervical plexus, intercostal nerve, and ilioinguinal/iliohypogastric nerve blocks have been demonstrated. In the past 10 yr, there has been a consolidation of the evidence indicating benefit of peripheral nerve blocks for specific indications. There remains great scope for rigorous, multicentre, randomised controlled trials of many peripheral nerve blocks. These would benefit from an agreed set of patient-centred outcomes.

Conduction slowing, conduction block and temporal dispersion in demyelinating, dysmyelinating and axonal neuropathies: Electrophysiology meets pathology

Nerve conduction studies are usually the first diagnostic step in peripheral nerve disorders and their results are the basis for planning further investigations. However, there are some commonplaces in the interpretation of electrodiagnostic findings in peripheral neuropathies that, although useful in the everyday practice, may be misleading: (1) conduction block and abnormal temporal dispersion are distinctive features of acquired demyelinating disorders; (2) hereditary neuropathies are characterized by uniform slowing of conduction velocity; (3) axonal neuropathies are simply diagnosed by reduced amplitude of motor and sensory nerve action potentials with normal or slightly slow conduction velocity. In this review, we reappraise the occurrence of uniform and non-uniform conduction velocity slowing, conduction block and temporal dispersion in demyelinating, dysmyelinating and axonal neuropathies attempting, with a translational approach, a correlation between electrophysiological and pathological features as derived from sensory nerve biopsy in patients and animal models. Additionally, we provide some hints to navigate in this complex field.

Granuloma, vasculitis, and demyelination in sarcoid neuropathy

BACKGROUND

Despite the suggestion that direct compression by granuloma and ischemia resulting from vasculitis can cause nerve fiber damage, the mechanisms underlying sarcoid neuropathy have not yet been fully clarified.

METHODS

We examined the clinicopathological features of sarcoid neuropathy by focusing on electrophysiological and histopathological findings of sural nerve biopsy specimens. We included 18 patients with sarcoid neuropathy who had non-caseating epithelioid cell granuloma in their sural nerve biopsy specimens.

RESULTS

Although electrophysiological findings suggestive of axonal neuropathy were observed, particularly in the lower limbs, all but three patients showed ≥1 abnormalities in nerve conduction velocity or distal motor latency. Additionally, a conduction block was observed in 11 of the 16 patients for whom waveforms were assessed; five of them fulfilled motor nerve conduction criteria strongly supportive of demyelination as defined in the European Academy of Neurology/Peripheral Nerve Society (EAN/PNS) guideline for chronic inflammatory demyelinating polyneuropathy (CIDP). In most patients, sural nerve biopsy specimens revealed a mild to moderate degree of myelinated fiber loss. Fibrinoid necrosis was observed in one patient, and electron microscopy analysis revealed demyelinated axons close to granulomas in six patients.

CONCLUSIONS

Patients with sarcoid neuropathy may meet the EAN/PNS electrophysiological criteria for CIDP due to the frequent presence of conduction blocks. Based on our results, in addition to the ischemic damage resulting from granulomatous inflammation, demyelination may play an important role in the mechanism underlying sarcoid neuropathy.

[Calcification distributional density of the aortic-valvular complex is an independent risk factor for conduction block following self-expanding transcatheter aortic valve replacement]

OBJECTIVE

To evaluate the effect of calcification distributional density in different regions of aortic-valvular complex (AVC) on postoperative new-onset conduction block (CB) following transcatheter aortic valve replacement (TAVR) using self-expandable valves (SEV) made in China.

METHODS

From January, 2016 to December, 2022, 73 patients with severe aortic valve stenosis received Venus-A prosthetic valve replacement using SEV made in China, and postoperative new-onset CB occurred in 18 (24.7%) of the patients. The baseline data, imaging and intervention- related data were compared were between the patients with CB and those without CB. Univariate and multivariate logistic regression analysis was used for investigating the independent risk factors for new- onset CB after TAVR, and the predictive performance of these risk factors was evaluated using receiver operating characteristic (ROC) curve and DeLong test.

RESULTS

Compared with those with CB, the patients experiencing postoperative new-onset CB had a greater implantation depth (6.77±2.45 mm vs 5.11±3.28 mm, P=0.027), a smaller difference between the membranous septum length and the implantation depth (MSID) (0.68±3.49 mm vs 2.82±3.88 mm, P= 0.036), and a higher calcification distributional density of the left coronary sinus (LCS) in the device landing zone (DLZ) (P= 0.026). Multivariate logistic analysis revealed that DLZ-LCS calcification distributional density and MSID were independent risk (protective) factors for new-onset CB following TAVR. ROC curve analysis showed that the AUC of MSID and DLZ-LCS calcification distributional density was 0.775 and 0.716, respectively, and their combination had had a significantly higher AUC of 0.890 (P=0.041 and 0.027, respectively).

CONCLUSION

The DLZ-LCS calcification distributional density is an independent risk factor for new-onset CB following TAVR using SEV. The conduction complications following TAVR can be effectively predicted using this calcification indicator combined with MSID.

Conduction blocks of the median nerve at the wrist in pregnancy and postpartum carpal tunnel syndromes

INTRODUCTION/AIMS

The aim in this study is to describe the clinical and electrophysiological patterns of pregnancy-related carpal tunnel syndrome (PRCTS) occurring during pregnancy or after delivery.

METHODS

Clinical, epidemiological, and electrodiagnostic (EDx) data were studied in 130 women with PRCTS onset during pregnancy (n = 80) or after delivery (n = 50). Twenty-six women with PRCTS underwent EDx analysis during pregnancy and 104 after delivery (83 within 6 months of delivery and 21 up to 24 months after pregnancy onset). PRCTS was compared with idiopathic CTS in a control group consisting of 57 age-matched women with 98 cases of CTS. Twenty-four women with PRCTS had clinical and electrophysiological follow-up after corticosteroid injection (CSI) at the wrist.

RESULTS

Clinical analysis showed a higher rate of bilateral and diurnal/permanent paraesthesia and more severe symptoms in PRCTS compared with idiopathic CTS. EDx analysis showed more severe abnormalities in classical tests and a higher rate of conduction block (CB) in PRCTS. Statistical analysis showed a strong negative correlation between the incidence and importance of CB and the time interval at which PRCTS women underwent EDx examination, between pregnancy onset and 24 months later. CSI resulted in significant clinical and EDx improvement in 22 of 24 PRCTS women, with disappearance of all motor and most sensory CBs.

DISCUSSION

The EDx pattern of PRCTS is an acute/subacute median nerve lesion at the wrist identified by many CBs. This occurs concurrently with hormonal changes, is responsible for more severe clinical symptoms and EDx data, and it explains why CSI is so effective.

Acute Radial Compressive Neuropathy: The Most Common Injury Induced by Japanese Rope Bondage

Japanese rope bondage (RB), or Shibari, is an art form involving the voluntary and aesthetic binding of a person with a rope, which may result in compression injuries to peripheral nerves. To investigate the nature and extent of nerve injuries associated with this practice, we conducted a survey of four experienced RB practitioners (riggers) and participants who were willing to share their experiences of injury. Injuries presented acutely and immediately following full-body suspensions, with a total of 10 individuals (16 injuries) identified with damage to the radial, axillary, or femoral nerves. Notably, the radial nerve was the most commonly affected structure in our patient cohort, with 90.0% of individuals experiencing an injury at this level. We present a rare case of acute repeated compression of the radial nerve during full-body suspension RB. A 29-year-old female was suspended for 25 minutes using a 6-mm jute rope, resulting in wrist and finger drop, as well as reduced sensation in the left hand. Analysis revealed a 77.3% conduction block in the upper arm segment. Improvement was observed after three months, fully achieved after five months. Seventeen months later, re-compression of both radial nerves occurred during a similar suspension lasting 8-10 minutes. Improvement occurred after one week, fully achieved after four weeks. The third compression episode occurred three years later, lasting five minutes, with full recovery within two minutes. This study focuses on the injury of peripheral nerves, including the radial, axillary, and femoral nerves, namely, acute compression neuropathy induced by Japanese RB. Because the radial nerve is the most frequently injured structure, the findings underscore the significance of recognizing the anatomical course of the radial nerve, particularly its position posteriorly at the distal deltoid tuberosity level, as a means of preventing nerve injury in this region. This knowledge is particularly crucial for individuals engaged in the practice of RB, emphasizing the importance of taking precautions to avoid potential nerve damage.

Dual-Chamber Leadless Pacing: Atrioventricular Synchrony in Preclinical Models of Normal or Blocked Atrioventricular Conduction

BACKGROUND

Dual-chamber leadless pacemakers (LP) require robust communication between distinct right atrial (RA) and right ventricular (RV) LPs to achieve atrioventricular (AV) synchrony.

OBJECTIVE

This preclinical study evaluated a novel, continuous implant-to-implant (i2i™) communication methodology for maintaining AV-synchronous, dual-chamber DDD(R) pacing by the 2 LPs.

METHODS

RA and RV LPs were implanted and paired in 7 ovine subjects, 4 of 7 with induced complete heart block. AV synchrony (% AV intervals <300 ms) and i2i communication success (% successful i2i transmissions between LPs) were evaluated acutely and chronically. During acute testing, 12-lead ECG and LP diagnostic data were collected from 5-minute recordings, in 4 postures and 2 rhythms (AP-VP and AS-VP or AP-VS and AS-VS) per subject. Chronic i2i performance was evaluated through 23 weeks post-implant (final i2i evaluation period: week 16-23).

RESULTS

Acute AV synchrony and i2i communication success across multiple postures and rhythms were 100.0% [100.0-100.0] (median [interquartile range]) and 99.9% [99.9-99.9], respectively. AV synchrony and i2i success rates did not differ across postures (P=0.59, P=0.11) or rhythms (P=1.00, P=0.82). During the final i2i evaluation period, the overall i2i success was 98.9% [98.1-99.0].

CONCLUSION

Successful AV-synchronous, dual-chamber DDD(R) leadless pacing using a novel, continuous, wireless communication modality was demonstrated across variations in posture and rhythm in a preclinical model.

Pro-Arrhythmic Effects of Discontinuous Conduction at the Purkinje Fiber-Ventricle Junction Arising From Heart Failure-Induced Ionic Remodeling - Insights From Computational Modelling

Heart failure is associated with electrical remodeling of the electrical properties and kinetics of the ion channels and transporters that are responsible for cardiac action potentials. However, it is still unclear whether heart failure-induced ionic remodeling can affect the conduction of excitation waves at the Purkinje fiber-ventricle junction contributing to pro-arrhythmic effects of heart failure, as the complexity of the heart impedes a detailed experimental analysis. The aim of this study was to employ computational models to investigate the pro-arrhythmic effects of heart failure-induced ionic remodeling on the cardiac action potentials and excitation wave conduction at the Purkinje fiber-ventricle junction. Single cell models of canine Purkinje fiber and ventricular myocytes were developed for control and heart failure. These single cell models were then incorporated into one-dimensional strand and three-dimensional wedge models to investigate the effects of heart failure-induced remodeling on propagation of action potentials in Purkinje fiber and ventricular tissue and at the Purkinje fiber-ventricle junction. This revealed that heart failure-induced ionic remodeling of Purkinje fiber and ventricular tissue reduced conduction safety and increased tissue vulnerability to the genesis of the unidirectional conduction block. This was marked at the Purkinje fiber-ventricle junction, forming a potential substrate for the genesis of conduction failure that led to re-entry. This study provides new insights into proarrhythmic consequences of heart failure-induced ionic remodeling.

Motor Nerve Conduction Block Estimation in Demyelinating Neuropathies by Deconvolution

A deconvolution method is proposed for conduction block (CB) estimation based on two compound muscle action potentials (CMAPs) elicited by stimulating a nerve proximal and distal to the region in which the block is suspected. It estimates the time delay distributions by CMAPs deconvolution, from which CB is computed. The slow afterwave (SAW) is included to describe the motor unit potential, as it gives an important contribution in case of the large temporal dispersion (TD) often found in patients. The method is tested on experimental signals obtained from both healthy subjects and pathological patients, with either Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) or Multifocal Motor Neuropathy (MMN). The new technique outperforms the clinical methods (based on amplitude and area of CMAPs) and a previous state-of-the-art deconvolution approach. It compensates phase cancellations, allowing to discriminate among CB and TD: estimated by the methods of amplitude, area and deconvolution, CB showed a correlation with TD equal to 39.3%, 29.5% and 8.2%, respectively. Moreover, a significant decrease of percentage reconstruction errors of the CMAPs with respect to the previous deconvolution approach is obtained (from a mean/median of 19.1%/16.7% to 11.7%/11.2%). Therefore, the new method is able to discriminate between CB and TD (overcoming the important limitation of clinical approaches) and can approximate patients’ CMAPs better than the previous deconvolution algorithm. Then, it appears to be promising for the diagnosis of demyelinating polyneuropathies, to be further tested in the future in a prospective clinical trial.

Atrioventricular Nodal Reentrant Tachycardia Ablation Using Mini-Electrode Recordings

Catheter ablation of the slow pathway in patients with atrioventricular nodal reentrant tachycardia (AVNRT) is mainly performed using anatomical landmarks. We sought to see whether a new ablation catheter equipped with mini-electrodes may facilitate the mapping of slow pathway potentials for AVNRT ablation. We prospectively included patients referred for AVNRT in our center. Mapping and ablation were performed using an irrigated catheter equipped with 3 insulated mini-electrodes on the distal tip. Thirteen consecutive patients were included (85% female, median age 46 years). Slow pathway potentials could be identified in 77% of cases on mini-electrode bipolar tracings, versus 15% on conventional bipolar tracings (p = 0.0009). At the end of the procedure, double potentials on the ablation line were identified in all patients, only on mini-electrode bipolar tracings. Following ablation, an interval separating double potentials in sinus rhythm ≥15% of baseline tachycardia cycle length was associated with non-inducibility in all patients (p < 0.0001). No recurrence occurred during 1 year of follow-up. The use of mini-electrodes may help target slow pathway potentials during AVNRT ablation. Identification of sufficiently split double potentials on the ablation line might represent an electrophysiological endpoint in these patients.

Adult-onset hypothyroidism causes mechanical hypersensitivity due to peripheral nerve hyperexcitability based on voltage-gated potassium channel downregulation in male mice

Thyroid hormones play an important role in the central and peripheral nervous system functions. Approximately 50% of adult-onset hypothyroid patients have sensory symptoms including pain, possibly caused by peripheral neuropathy. However, the mechanism causing the pain has not been clarified. We generated an adult-onset hypothyroid model animal by administering 50 ppm propylthiouracil (PTU) for 5 weeks to male mice. Female mice were not tested in this study. Mechanical hypersensitivity, determined by the von Frey hair test, was observed during the PTU exposure and recovered after the exposure termination. The sciatic nerve compound action potential was also analyzed. Under single-pulse stimulation, no significant change in the threshold and conduction velocity was observed in the PTU-administered group. On the other hand, under train-pulse stimulation, the latency delay in the Aδ-fiber component was less in the PTU-administered group in Week 4 of PTU exposure, indicating relative hyperexcitability. Fluticasone, which is the anti-inflammatory agent with an ability to activate the voltage-gated potassium channel subfamily A (Kv1), restored the decrease in the latency change ratio by PTU exposure under the train-pulse stimulation supporting our hypothesis that Kv1 may be involved in the conductivity change. Kv1.1 protein level decreased significantly in the sciatic nerve of the PTU-administered group. These results indicate that adult-onset hypothyroidism causes mechanical hypersensitivity owing to hyperexcitability of the peripheral nerve and that reduction of Kv1.1 level may be involved in such alteration.

Large discrepancy in optimal atrioventricular delay between sensed and paced atrial events in a pacemaker patient

A 74-year-old man experienced complete atrioventricular (AV) block 2 days after catheter ablation for right atrial (RA) macroreentrant tachycardia. We performed DDD pacemaker implantation with atrial septal pacing because other sites of pacing threshold were not acceptable. The maximum left ventricular outflow tract velocity time integral was 15.8 cm with sensed AV delay (40 ms) and 15.0 cm with paced AV delay (220 ms); however, this exceeded the pacemaker's maximum difference of 100 ms. We herein report the case of a large discrepancy in optimal AV delay intervals between sensed and paced atrial events, requiring consideration of proper pacemaker settings.

Targeting Two-Pore-Domain Potassium Channels by Mechanical Stretch Instantaneously Modulates Action Potential Transmission in Mouse Sciatic Nerves

Recent reports indicate dominant roles of TRAAK and TREK-1 channels, i.e., mechanosensitive two-pore-domain potassium channels (K2P) at the nodes of Ranvier for action potential repolarization in mammalian peripheral nerves. Functional changes in mammalian peripheral nerve conduction by mechanical stretch studied by recording compound action potentials lack the necessary resolution to detect subtle neuromodulatory effects on conduction velocity. In this study, we developed a novel in vitro approach that enables single-fiber recordings from individual mouse sciatic nerve axons while delivering computer-controlled stepped stretch to the sciatic nerve trunk. Axial stretch instantaneously increased the conduction delay in both myelinated A-fibers and unmyelinated C-fibers. Increases in conduction delay linearly correlated with increases in axial stretch ratio for both A- and C-fibers. The slope of the increase in conduction delay versus stretch ratio was steeper in C-fibers than in A-fibers. Moderate axial stretch (14-19% of in vitro length) reversibly blocked 37.5% of unmyelinated C-fibers but none of the eight myelinated A-fibers tested. Application of arachidonic acid, an agonist to TRAAK and TREK-1 to sciatic nerve trunk, blocks axonal transmission in both A- and C-fibers with delayed onset and prolonged block. Also, the application of an antagonist ruthenium red showed a tendency of suppressing the stretch-evoked increase in conduction delay. These results could draw focused research on pharmacological and mechanical activation of K2P channels as a novel neuromodulatory strategy to achieve peripheral nerve block.

[Neuropathy presenting conduction block in ANCA-negative eosinophilic granulomatosis with polyangiitis]

A 74-year-old woman with a history of asthma and allergic rhinitis rapidly developed multiple mononeuropathy. Although anti-neutrophil cytoplasmic antibodies were negative, the presence of eosinophilia and eosinophilic infiltrations in the sural nerve led to a diagnosis of eosinophilic granulomatosis with polyangiitis. A motor nerve conduction study on admission revealed conduction block, which promptly disappeared after initiating immunotherapy without findings suggestive for remyelination or axonal degeneration. This electrophysiological change distinct from that of Wallerian degeneration. A biopsy of the sural nerve showed many eosinophil infiltrations and degranulation of eosinophilic cationic protein within nerve fascicles, whereas findings of necrotizing vasculitis were absent. These findings suggest that a direct effect of eosinophilic cationic protein, rather than ischemic damage due to vasculitis, was the main mechanism of transient nerve conduction failure in this patient.

Theoretical Investigation of the Mechanism by which A Gain-of-Function Mutation of the TRPM4 Channel Causes Conduction Block

In the heart, TRPM4 is most abundantly distributed in the conduction system. Previously, a single mutation, 'E7K', was identified in its distal N-terminus to cause conduction disorder because of enhanced cell-surface expression. It remains, however, unclear how this expression increase leads to conduction failure rather than abnormally enhanced cardiac excitability. To address this issue theoretically, we mathematically formulated the gating kinetics of the E7K-mutant TRPM4 channel by a combined use of voltage jump analysis and ionomycin-perforated cell-attached recording technique and incorporated the resultant rate constants of opening and closing into a human Purkinje fiber single-cell action potential (AP) model (Trovato model) to perform 1D-cable simulations. The results from TRPM4 expressing HEK293 cells showed that as compared with the wild-type, the open state is much preferred in the E7K mutant with increased voltage-and Ca²⁺-sensitivities. These theoretical predictions were confirmed by power spectrum and single channel analyses of expressed wild-type and E7K-mutant TRPM4 channels. In our modified Trovato model, the facilitated opening of the E7K mutant channel markedly prolonged AP duration with concomitant depolarizing shifts of the resting membrane potential in a manner dependent on the channel density (or maximal activity). This was, however, little evident in the wild-type TRPM4 channel. Moreover, 1D-cable simulations with the modified Trovato model revealed that increasing the density of E7K (but not of wild-type) TRPM4 channels progressively reduced AP conduction velocity eventually culminating in complete conduction block. These results clearly suggest the brady-arrhythmogenicity of the E7K mutant channel which likely results from its pathologically enhanced activity.

Local impedance-guided radiofrequency ablation with standard and high power: Results of a preclinical investigation

BACKGROUND

Local impedance (LI) drop measured with microfidelity electrodes embedded in the tip of an ablation catheter accurately reflects tissue heating during radiofrequency (RF) ablation. Previous studies found 15-30 Ω LI drops created successful lesions, while more than 40 Ω drops were associated with steam pops. The objective of this study was to evaluate the safety and efficacy of LI-guided ablation using standard (30 W) and high-power (50 W) in a preclinical model.

METHODS

RF lesions were created in explanted swine hearts (n = 6) to assess the feasibility of LI-guided ablation by targeting 10, 20, or 30 Ω (n = 20/group) drops. Subsequently, LI-guided ablation was evaluated in a chronic animal model (n = 8 Canines, 25-29 kg, 30/50 W). During the index procedure point-by-point intercaval line ablation and left inferior pulmonary vein (PV) isolation were performed. RF duration was at the operators' discretion but discontinued early if a 15-30 Ω drop was achieved. Operators attempted to avoid LI drops of more than 40 Ω. At 1-month, durable conduction block was evaluated with electroanatomic mapping followed by necropsy and histopathology.

RESULTS

In explanted tissue, terminating ablation at 10, 20, or 30 Ω LI drops created statistically larger lesions (p < .05; 1.8 [1.6-2.4] mm, 3.3 [3.0-3.7] mm; 4.9 [4.3-5.5] mm). LI-guided high-power ablation in vivo significantly reduced RF duration per application compared to standard-power (p < .05; intercaval: 8.9 ± 5.2 vs. 18.1 ± 11.0 s, PV: 9.6 ± 5.4 vs. 23.2 ± 10.3 s). LI drops of 15-40 Ω were more readily achievable for high-power (90.1%, 318/353) than standard-power (71.7%, 243/339). All intercaval lines and PV isolations were durable (16/16) at 1-month. Necropsy revealed no major collateral injury to the pericardium, phrenic nerve, esophagus, or lungs. There was no pericardial effusion, stroke, tamponade, or PV stenosis. Vagal nerve injury was found in two 30 W animals after using 19.7 ± 13.9 and 19.5 ± 11.8 s RF applications.

CONCLUSION

LI-guided ablation was found to be safe and efficacious in a chronic animal model. High-power ablation more readily achieved more than 15 Ω drops, reduced RF duration compared with standard-power, and had no major RF collateral injury.

Sonographic Nerve Enlargement in a Patient with Sarcoidosis

We herein report a 73-year-old woman case with sarcoid neuropathy showing nerve enlargement assessed by nerve ultrasound both before and after treatment. The site of conduction block in the left tibial nerve corresponded to the site of nerve enlargement with a hypo-echoic pattern. After treatment with prednisolone, nerve ultrasound detected the remission of the nerve enlargement, and the conduction block and clinical symptoms also improved. Nerve enlargement may reflect inflammation of the peripheral nerve. A follow-up study of sonographic nerve enlargement may be of clinical significance for assessing the effectiveness of treatment for sarcoid neuropathy.

Gastric ablation as a novel technique for modulating electrical conduction in the in vivo stomach

Gastric motility is coordinated by underlying bioelectrical "slow wave" activity. Slow wave dysrhythmias are associated with motility disorders, including gastroparesis, offering an underexplored potential therapeutic target. Although ablation is widely used to treat cardiac arrhythmias, this approach has not yet been trialed for gastric electrical abnormalities. We hypothesized that ablation can create localized conduction blocks and modulate slow wave activation. Radiofrequency ablation was performed on the porcine serosa in vivo, encompassing a range of parameters (55-85°C, adjacent points forming a line, 5-10 s/point). High-resolution electrical mapping (16 × 16 electrodes; 6 × 6 cm) was applied to define baseline and acute postablation activation patterns. Tissue damage was evaluated by hematoxylin and eosin and c-Kit stains. Results demonstrated that RF ablation successfully induced complete conduction block and a full thickness lesion in the muscle layer at energy doses of 65-75°C for 5-10 s/point. Gastric ablation may hold therapeutic potential for gastric electrical abnormalities in the future.NEW & NOTEWORTHY This study presents gastric ablation as a new method for modulating slow wave activation and propagation in vivo, by creating localized electrical conduction blocks in the stomach, validated by high-resolution electrical mapping and histological tissue analysis. The results define the effective energy dose range for creating conduction blocks, while maintaining the mucosal and submucosal integrity, and demonstrate the electrophysiological effects of ablation. In future, gastric ablation can now be translated toward disrupting dysrhythmic slow wave activation.

Conduction recovery with Wenckebach periodicity at the mitral isthmus

A Wenckebach periodicity at the mitral isthmus (MI) lesion has rarely been reported. We described a case presenting conduction recovery with Wenckebach periodicity at the posterior MI lesion after achieving the MI block. These findings demonstrate a pseudo MI block with Wenckebach periodicity owing to the pacing rate.

The Inhibitory Thermal Effects of Focused Ultrasound on an Identified, Single Motoneuron

Focused ultrasound (US) is an emerging neuromodulation technology that has gained much attention because of its ability to modulate, noninvasively, neuronal activity in a variety of animals, including humans. However, there has been considerable debate about exactly which types of neurons can be influenced and what underlying mechanisms are in play. Are US-evoked motor changes driven indirectly by activated mechanosensory inputs, or more directly via central interneurons or motoneurons? Although it has been shown that US can mechanically depolarize mechanosensory neurons, there are no studies that have yet tested how identified motoneurons respond directly to US and what the underlying mechanism might be. Here, we examined the effects of US on a single, identified motoneuron within a well-studied and tractable invertebrate preparation, the medicinal leech, Hirudo verbana Our approach aimed to clarify single neuronal responses to US, which may be obscured in other studies whereby US is applied across a diverse population of cells. We found that US has the ability to inhibit tonic spiking activity through a predominately thermal mechanism. US-evoked effects persisted after blocking synaptic inputs, indicating that its actions were direct. Experiments also revealed that US-comparable heating blocked the axonal conduction of spontaneous action potentials. Finally, we found no evidence that US had significant mechanical effects on the neurons tested, a finding counter to prevailing views. We conclude that a non-sensory neuron can be directly inhibited via a thermal mechanism, a finding that holds promise for clinical neuromodulatory applications.

Electrophysiological identification of superior vena cava: Novel insight into slow conduction or conduction block

INTRODUCTION

It has not been clarified how to identify the electrophysiological junction between right atrium (RA) and superior vena cava (SVC). The aim of this study was to identify the electrophysiological RA-SVC junction according to slow conduction or conduction bock and to examine the electrophysiological SVC isolation procedure.

METHODS

Seventy-three consecutive atrial fibrillation patients who underwent SVC mapping using a CARTO 3 system were enrolled in this study. Slow conduction or conduction block between the RA and SVC was identified by adjusting the lower threshold criteria of the early meets late function and was described as a white line. The SVC isolation was performed along the white line and with pacing maneuvers to confirm direct SVC capture.

RESULTS

Activation mapping (1296 ± 631 points) was obtained in 66 patients (90%) in 4.6 ± 1.8 min. Slow conduction or conduction block was observed in all patients. The threshold for detecting slow conduction or conduction block was 24 ± 8 ms. The location of the electrophysiological RA-SVC junction was higher in the anterior portion (anterior-septal, anterior, and anterior-lateral) than in the posterior portion (posterior-septal, posterior, and posterior-lateral) (-2.3 ± 6.2 mm vs. 7.1 ± 6.3 mm, p < .001). The SVC isolation at the electrophysiological RA-SVC junction was successful in all patients without any injury to the sinus node function. Asymptomatic phrenic nerve injury was observed in three patients (4.5%).

CONCLUSION

In all patients, the electrophysiological RA-SVC junction determined by slow conduction or conduction block was identified and the electrophysiological SVC isolation was performed successfully and safely.

Epicardial and Endocardial Validation of Conduction Block After Thoracoscopic Epicardial Ablation of Atrial Fibrillation

Objective

It is unknown whether epicardial and endocardial validation of bidirectional block after thoracoscopic surgical ablation for atrial fibrillation is comparable. Epicardial validation may lead to false-positive results due to epicardial tissue edema, and thus could leave gaps with subsequent arrhythmia recurrence. It is the aim of the present study to answer this question in patients who underwent hybrid atrial fibrillation ablation (combined thoracoscopic epicardial and endocardial catheter ablation).

Methods

After epicardial ablation of the pulmonary veins (PVs) and connecting inferior and roof lines (box lesion), exit and entrance block were epicardially and endocardially evaluated using an endocardial His Bundle catheter and electrophysiological workstation. If incomplete lesions were found, endocardial touch-up ablation was performed. Validation results were also compared to predictions about conduction block based on tissue conductance measurements of the epicardial ablation device.

Results

Twenty-five patients were included. Epicardial validation results were 100% equal to the endocardial results for the left superior, left inferior, and right inferior PVs and box lesion. For the right superior PV, 85% similarity was found. Based on tissue conductance measurements, 139 lesions were expected to be complete; however, in 5 (3.6%) a gap was present.

Conclusions

Epicardial bidirectional conduction block in the PVs and the box lesion corresponded well with endocardial bidirectional conduction block. Conduction block predictions by changes in tissue conductance failed in few cases compared to block confirmation. This emphasizes that tissue conduction measurements can provide a rough indication of lesion effectiveness but needs endpoint confirmation by either epicardial or endocardial block testing.

Bilateral Martin-Gruber and Marinacci Anastomoses in the Same Patient: A Case Report

Anomalous innervations are commonly encountered on electrodiagnostic testing and may be mistaken for a pathological process, especially if seen in multiple nerves. While crossover of median-to-ulnar fibers in the forearm (Martin-Gruber anastomosis) has been frequently described, the corresponding ulnar-to-median crossover (Marinacci anastomosis) is much less commonly seen. There have been no reported cases of both of these anomalous innervations occurring together. We describe a novel case of bilateral Martin-Gruber and Marinacci anastomoses in the same patient. The importance of the case lies in the fact that the multiple pseudo-conduction blocks that result from these crossovers could potentially be misinterpreted as being pathological in nature, illustrating the need for electromyographers to be familiar with common anomalous innervations in the upper extremity and with techniques to identify them.

Radial motor nerve conduction studies in the upper arm

INTRODUCTION

The main goal of this study was to determine the contribution of the anterior forearm muscles to the compound muscle action potential (CMAP) recorded from the extensor digitorum (ED) after proximal stimulation.

METHODS

Twenty-one healthy volunteers and 114 patients with compressive and traumatic radial neuropathies were examined. Stimulation was carried out at six different points: distal third of the upper arm; Erb's point; axilla; medial upper arm; antecubital fossa; and ulnar groove.

RESULTS

In the control group, Erb's CMAP area was significantly greater than the distal CMAP area. In compressive neuropathy, there was conduction block, but no change in conduction velocity. There were no differences in Erb's CMAP latencies between the control group and the neuropathies group.

DISCUSSION

CMAPs recorded over the ED with stimulation at the brachial plexus represent the sum of the motor unit action potentials of the posterior and anterior forearm muscles.

Defining Left Bundle Branch Block Patterns in Cardiac Resynchronisation Therapy: A Return to His Bundle Recordings

Left bundle branch block (LBBB) is associated with improved outcome after cardiac resynchronisation therapy (CRT). One historical presumption of LBBB has been that the underlying pathophysiology involved diffuse disease throughout the distal conduction system. The ability to normalize wide QRS patterns with His bundle pacing (HBP) has called this notion into question. The determination of LBBB pattern is conventionally made by assessment of surface 12-lead ECGs and can include patients with and without conduction block, as assessed by invasive electrophysiology study (EPS). During a novel extension of the classical EPS to involve left-sided recordings, we found that conduction block associated with the LBBB pattern is most often proximal, usually within the left-sided His fibres, and these patients are the most likely to demonstrate QRS correction with HBP for resynchronisation. Patients with intact Purkinje activation and intraventricular conduction delay are less likely to benefit from HBP. Future EPS are required to determine the impact of newer approaches to conduction system pacing, including intraseptal or left ventricular septal pacing. Left-sided EPS has the potential to refine patient selection in CRT trials and may be used to physiologically phenotype distinct conduction patterns beyond LBBB pattern.

Infected Thrombus on a TAVI Aortic Valve

After a series of tests, an 86-year-old patient was shown to have an infected thrombus on a TAVI valve and was referred to urgent surgery. The valve with the infected thrombus was removed and a biological prosthetic valve was implanted in its place.

Left Bundle Pacing for Left Bundle Branch Block and Intermittent Third-Degree Atrioventricular Block in a MYH7 Mutation-Related Hypertrophic Cardiomyopathy With Restrictive Phenotype in a Child

Hypertrophic cardiomyopathy (HCM) is a group of myocardial diseases defined by cardiac hypertrophy which cannot be explained by secondary causes with a non-dilated left ventricle and preserved or increased ejection fraction. Sometimes it can be combined with restrictive cardiomyopathy. Here we describe a very rare case of a 12-year-old girl with non-obstructive hypertrophic cardiomyopathy accompanied by restrictive phenotype, complete left bundle branch block and intermittent third-degree atrioventricular block, who presented with recurrent syncope. Her father was also found to have hypertrophic cardiomyopathy and treated with implantable cardioverter defibrillator for ventricular tachycardia. Her younger brother is currently asymptomatic but echocardiogram showed hypertrophic cardiomyopathy. Genetic analysis identified a heterozygous missense mutation (c.2155C>T, p.R719W) of MYH7 in the proband girl, her father and her brother. The girl was treated with left bundle pacing and recovered well. The case we present further demonstrates the feasibility of left bundle pacing in children.

Conduction Block and Nerve Cross-Sectional Area in Multifocal Motor Neuropathy

Introduction: Motor nerve conduction block (CB) is the main electrophysiological feature of multifocal motor neuropathy (MMN). Increased cross-sectional area (CSA) can be detected by nerve ultrasound in MMN. In this study, we aim to analyze the correlation between CB and CSA in MMN.

Methods: Twelve patients with MMN were recruited. Ultrasonography tests and motor nerve conduction studies (NCSs) were performed on median and ulnar nerves simultaneously. CSA was measured at 10 consecutive sites on those nerves, meanwhile nerves were traced continuously and recorded thoroughly under ultrasound.

Results: In motor NCSs, 12 definite CB and 12 probable CB areas were detected across standard segments of median and ulnar nerves. With ultrasound studies, increased CSA was detected at 36 sites. There were 9 standard segments with CB and increased CSA, 15 segments with CB but normal CSA, and 27 segments with increased CSA but no CB.

Discussion: In MMN, motor nerve CB was not always consistent with increased CSA.

Ulnar Neuropathy at the Elbow Associated With Focal Demyelination in the Proximal Forearm and Intraoperative Imaging Correlation

Ulnar nerve focal demyelination (FD) in the forearm [defined as conduction block (CB) and or temporal dispersion (TD)] has been described with immune-mediated neuropathy and with compression affecting the forearm segment of the nerve. The association of FD in the forearm with entrapment ulnar neuropathy at the elbow, as well as the intraoperative imaging of the abnormal ulnar nerve at the flexor carpi ulnaris muscle level (FCU), has not been reported before. We report a 33-years-old woman presented with only sensory symptoms of the right hand suggestive of right ulnar neuropathy for the last 10 years. On clinical examination, she had reduced pinprick sensation on the little and ring fingers with no motor deficit. Nerve-conduction study showed slowing of conduction velocity across the elbow on the right when recording at the abductor digiti minimi (ADM) and first dorsal interossei (FDI). There was 63% amplitude drop when stimulating below the elbow compared to distal stimulation at the wrist. Increment inching study localized the block at 5 cm distal to the medial epicondyle. During surgical transposition, the ulnar nerve was swollen, and edematous in the segment where the nerve enters the FCU muscle, which provides a physiological explanation for the electrophysiological findings. After the surgery, the patient reported complete resolution of the symptoms. This case demonstrate that ulnar nerve motor potential FD at the proximal forearm could be recorded and it is still compatible with ulnar-nerve entrapment at the elbow.

Increased IP-10 production by blood-nerve barrier in multifocal acquired demyelinating sensory and motor neuropathy and multifocal motor neuropathy

OBJECTIVE

Dysfunction of the blood-nerve barrier (BNB) plays important roles in chronic inflammatory demyelinating polyneuropathy (CIDP) and multifocal motor neuropathy (MMN). The aim of the present study was to identify the candidate cytokines/chemokines that cause the breakdown of the BNB using sera from patients with CIDP and MMN.

METHODS

We determined the levels of 27 cytokines and chemokines in human peripheral nerve microvascular endothelial cells (PnMECs) after exposure to sera obtained from patients with CIDP variants (typical CIDP and multifocal acquired demyelinating sensory and motor neuropathy [MADSAM]), MMN and amyotrophic lateral sclerosis (ALS), and healthy controls (HC), using a multiplexed fluorescent bead-based immunoassay system.

RESULTS

The induced protein (IP)10 level in the cells in both the MADSAM and MMN groups was markedly increased in comparison with the typical CIDP, ALS and HC groups. The other cytokines, including granulocyte colony-stimulating factor,vascular endothelial growth factor (VEGF) and interleukin-7, were also significantly upregulated in the MADSAM group. The increase of IP-10 produced by PnMECs was correlated with the presence of conduction block in both the MADSAM and MMN groups.

CONCLUSION

The autocrine secretion of IP-10 induced by patient sera in PnMECs was markedly upregulated in both the MADSAM and MMN groups. The overproduction of IP-10 by PnMECs leads to the focal breakdown of the BNB and may help to mediate the transfer of pathogenic T cells across the BNB, thereby resulting in the appearance of conduction block in electrophysiological studies of patients with MADSAM and MMN.

Multiple Sclerosis: Destruction and Regeneration of Astrocytes in Acute Lesions

There are reports that astrocyte perivascular endfeet are damaged in some cases of multiple sclerosis (MS). This study was designed to determine the origin and outcome of astrocyte damage in acute, resolving, and inactive plaques. Ten acute plaques from 10 early MS cases and 14 plaques of differing histological age from 9 subacute and chronic cases were examined immunohistochemically. Also examined were nonnecrotic early lesions in 3 patients with neuromyelitis optica (NMO). Plaques from 3 MS cases were examined electron microscopically. The edge zones in each of the 10 acute MS lesions revealed a complete loss of astrocyte cell bodies and their pericapillary, perineuronal, and perivascular foot processes. Dendrophagocytosis of degenerate astrocytes was observed. Astrocyte precursors, similar to those that replace destroyed astrocytes in nonnecrotic NMO lesions, were present in areas depleted of astrocytes. Resolving plaques were repopulated initially by stellate astrocytes that stained negatively for the water channel molecule aquaporin4 (AQP4). In older lesions, astrocytes were predominantly AQP4-positive. Loss and recovery of astrocytes in new MS lesions may be as important as myelin loss as a cause of conduction block responsible for symptoms in patients with relapsing and remitting and secondary progressive MS.

Electroneurography and Advanced Neuroimaging Profile in Pediatric-onset Metachromatic Leukodystrophy

Context

Metachromatic leukodystrophy (MLD) is a rare autosomal-recessive disorder characterized by demyelination of central and peripheral nervous system. There is scarcity of literature on the electrophysiological aspects of peripheral nerves and the advanced neuroimaging findings in MLD.

Aim

The aim was to study the nerve conduction parameters and advanced neuroimaging findings in patients with MLD.

Materials and Methods

This study is a retrospective analysis conducted, between 2005 and 2016, of 12 patients who had biochemical, histopathological, or genetic confirmation of MLD and disease onset before 18 years of age. The clinical, electroneurography, and the advanced neuroimaging findings were reviewed and analyzed.

Statistical Analysis

The data were presented as percentages or mean ± standard deviation as defined appropriate for qualitative and quantitative variables.

Results

Mean age of onset was 4.84 (±4.60) years and seven patients were males. Eight patients had juvenile MLD and four had late infantile MLD. Clinical presentation of psychomotor regression was more common in infantile MLD (75%), whereas gait difficulty (62.5%) and cognitive impairment (37.5%) were more frequent in juvenile MLD. Nerve conduction study (NCS) revealed diffuse demyelinating sensorimotor peripheral neuropathy in 9 (75%) patients. One patient had a rare presentation with conduction blocks in multiple nerves with contrast enhancement of cauda equina. Diffusion restriction involving periventricular and central white matter was seen in five patients and bilateral globus pallidi blooming was noted in three patients.

Conclusion

This study highlights the utility of NCS and advanced magnetic resonance imaging sequences in the diagnosis of MLD.

Short segment sensory nerve stimulation in suspected ulnar neuropathy at the elbow: A pilot study

INTRODUCTION

Routine ulnar nerve conduction studies may be normal in very mild ulnar neuropathies at the elbow (UNE). Short segment ulnar sensory stimulation across the elbow may detect mild abnormalities in these cases.

METHODS

Short segment ulnar sensory nerve stimulation was performed in 20 controls and 15 patients with clinically suspected mild UNE. Greatest peak latency shift and amplitude drop between 2 adjacent stimulation sites were calculated.

RESULTS

The upper limit of normal for peak latency shift and amplitude reduction between sites was 0.7 ms and 15%, respectively. Abnormal latency shift was detected in 12 of 15 patients and focal sensory conduction block in 6 of 15 patients. In 5 of 7 patients in whom all other studies were normal, sensory inching was abnormal.

DISCUSSION

Ulnar sensory short segment stimulation may provide diagnostic confirmation and localization of the site of nerve compression in mild UNE, and may improve UNE detection when all other studies are normal. Muscle Nerve 59:125-129, 2019.

Restoration of a Conduction Block after the Long-term Treatment of CIDP with Anti-neurofascin 155 Antibodies: Follow-up of a Case over 23 Years

We herein report a woman with chronic inflammatory demyelinating polyneuropathy (CIDP) in whom positivity for anti-neurofascin 155 antibodies was revealed 23 years after the onset of neuropathy. The patient initially reported numbness in the face at 50 years of age and subsequently manifested features compatible to typical CIDP. Steroid administration initiated at 54 years of age ameliorated her neuropathic symptoms. Although the nerve conduction indices at 59 years of age deteriorated, those at 68, 72, and 73 years of age showed a gradual recovery. The deterioration and subsequent restoration of compound muscle action potential amplitudes was the most dramatic, suggesting that a conduction block can be reversed earlier than other electrophysiological indices.

Motor Nerve Conduction Block Predicting Outcome of Guillain-Barre Syndrome

Introduction: Motor nerve conduction blocks (CBs) could be detected in both acute inflammatory demyelinating polyradiculoneuropathy (AIDP) and acute motor axonal neuropathy (AMAN). We aimed to identify the correlation between CBs and functional outcome in the two subtypes of GBS. Methods: Motor nerve conduction studies were performed in 17 patients with AIDP and 23 with AMAN. All patients were treated with intravenous immunoglobulin, and their disabilities were evaluated with Hughes functional grading scale before treatment, 1 month and 6 months after onset. Results: AMAN with CBs had higher reduction of Hughes grade (indicating more improved outcomes) at 1 month (1.71 ± 0.83 vs. 1 ± 0.67, p = 0.034) than AIDP with CBs. AMAN with CBs had higher reduction of Hughes grade at 1 month (1.71 ± 0.83 vs. 0.56 ± 0.73, p = 0.002) than AMAN without CBs. The reduction of Hughes grade at 1 month showed no significant difference between AIDP with and without CBs. Discussion: Motor nerve CBs in AMAN indicated better prognosis than in AIDP.

Absence of Rapid Propagation through the Purkinje Network as a Potential Cause of Line Block in the Human Heart with Left Bundle Branch Block

Background: Cardiac resynchronization therapy is an effective device therapy for heart failure patients with conduction block. However, a problem with this invasive technique is the nearly 30% of non-responders. A number of studies have reported a functional line of block of cardiac excitation propagation in responders. However, this can only be detected using non-contact endocardial mapping. Further, although the line of block is considered a sign of responders to therapy, the mechanism remains unclear.

Methods: Herein, we created two patient-specific heart models with conduction block and simulated the propagation of excitation based on a cellmodel of electrophysiology. In one model with a relatively narrow QRS width (176 ms), we modeled the Purkinje network using a thin endocardial layer with rapid conduction. To reproduce a wider QRS complex (200 ms) in the second model, we eliminated the Purkinje network, and we simulated the endocardial mapping by solving the inverse problem according to the actual mapping system.

Results: We successfully observed the line of block using non-contact mapping in the model without the rapid propagation of excitation through the Purkinje network, although the excitation in the wall propagated smoothly. This model of slow conduction also reproduced the characteristic properties of the line of block, including dense isochronal lines and fractionated local electrocardiograms. Further, simulation of ventricular pacing from the lateral wall shifted the location of the line of block. By contrast, in the model with the Purkinje network, propagation of excitation in the endocardial map faithfully followed the actual propagation in the wall, without showing the line of block. Finally, switching the mode of propagation between the two models completely reversed these findings.

Conclusions: Our simulation data suggest that the absence of rapid propagation of excitation through the Purkinje network is the major cause of the functional line of block recorded by non-contact endocardial mapping. The line of block can be used to identify responders as these patients loose rapid propagation through the Purkinje network.

Partial Conduction Block as an Early Nerve Conduction Finding in Neurolymphomatosis

BACKGROUND AND PURPOSE

Neurolymphomatosis is a rare manifestation of hematological malignancy and is characterized by direct infiltration of the peripheral nervous system. The objective of this study was to identify the clinical and electrophysiological features of neurolymphomatosis.

METHODS

We retrospectively analyzed the medical records of 13 patients with neurolymphomatosis. Seven (54%) of the patients were men, and the median age at symptom onset was 60.0 years.

RESULTS

The most common type of underlying malignancy was diffuse large B-cell lymphoma (69%). Twelve patients had painful asymmetric neuropathies. The median survival time after diagnosis was 7 months, and 12 patients died during the study period. Thirty-eight motor nerve conduction studies (NCSs) were performed in the affected nerves. Ten and 28 motor nerves were classified into the conduction-block and simple-axon-degeneration groups, respectively. The median time interval between symptom onset and the NCS was significantly shorter in the conduction-block group than in the simple-axon-degeneration group (p=0.032). However, no significant differences in the motor nerve conduction velocities, terminal latencies, and distal compound muscle action potential amplitudes were identified between the conduction-block and simple-axon-degeneration groups. The conduction-block group showed excessive temporal dispersion in only five of the ten NCSs (50%). Follow-up NCSs revealed that partial conduction blocks had changed into axonal degeneration patterns.

CONCLUSIONS

This is the first study to analyze the electrophysiological features of patients with neurolymphomatosis. Our findings showed that a partial conduction block is not rare and is an early nerve conduction abnormality in neurolymphomatosis.

Modeling the response of small myelinated axons in a compound nerve to kilohertz frequency signals

OBJECTIVE

There is growing interest in electrical neuromodulation of peripheral nerves, particularly autonomic nerves, to treat various diseases. Electrical signals in the kilohertz frequency (KHF) range can produce different responses, including conduction block. For example, EnteroMedics' vBloc® therapy for obesity delivers 5 kHz stimulation to block the abdominal vagus nerves, but the mechanisms of action are unclear.

APPROACH

We developed a two-part computational model, coupling a 3D finite element model of a cuff electrode around the human abdominal vagus nerve with biophysically-realistic electrical circuit equivalent (cable) model axons (1, 2, and 5.7 µm in diameter). We developed an automated algorithm to classify conduction responses as subthreshold (transmission), KHF-evoked activity (excitation), or block. We quantified neural responses across kilohertz frequencies (5-20 kHz), amplitudes (1-8 mA), and electrode designs.

MAIN RESULTS

We found heterogeneous conduction responses across the modeled nerve trunk, both for a given parameter set and across parameter sets, although most suprathreshold responses were excitation, rather than block. The firing patterns were irregular near transmission and block boundaries, but otherwise regular, and mean firing rates varied with electrode-fibre distance. Further, we identified excitation responses at amplitudes above block threshold, termed 're-excitation', arising from action potentials initiated at virtual cathodes. Excitation and block thresholds decreased with smaller electrode-fibre distances, larger fibre diameters, and lower kilohertz frequencies. A point source model predicted a larger fraction of blocked fibres and greater change of threshold with distance as compared to the realistic cuff and nerve model.

SIGNIFICANCE

Our findings of widespread asynchronous KHF-evoked activity suggest that conduction block in the abdominal vagus nerves is unlikely with current clinical parameters. Our results indicate that compound neural or downstream muscle force recordings may be unreliable as quantitative measures of neural activity for in vivo studies or as biomarkers in closed-loop clinical devices.

Posterior interosseous nerve palsy caused by a ganglion: Conservative treatment with ultrasound-guided needle aspiration

Posterior interosseous nerve palsy caused by a ganglion is not common and most previous patients were treated with excisional surgery. We treated a case conservatively with needle aspiration using ultrasonography, after a nerve conduction study. A 77-year-old man presented with impaired active finger extension of the left metacarpophalangeal joints. The nerve conduction study revealed conduction block of the left radial nerve near the elbow. Ultrasonography demonstrated a hypoechoic mass anterior to the radial neck compressing the posterior interosseous nerve. Then, needle aspiration of the mass was conducted under ultrasonography. Two months later, active finger extension recovered to normal. A ganglion can be diagnosed with ultrasonography and needle aspiration can be carried out safely under ultrasonography. A nerve conduction study can assess the degree of nerve damage. The combination of ultrasonography and a nerve conduction study can facilitate conservative treatment of needle aspiration for posterior interosseous nerve palsy caused by a ganglion.

Optical Mapping Approaches on Muscleblind-Like Compound Knockout Mice for Understanding Mechanistic Insights Into Ventricular Arrhythmias in Myotonic Dystrophy

Background

Cardiac arrhythmias are common causes of death in patients with myotonic dystrophy (dystrophia myotonica [DM]). Evidence shows that atrial tachyarrhythmia is an independent risk factor for sudden death; however, the relationship is unclear.

Methods and Results

Control wild‐type (Mbnl1^+/+; Mbnl2^+/+) and DM mutant (Mbnl1^−/−; Mbnl2^+/−) mice were generated by crossing double heterozygous knockout (Mbnl1^+/−; Mbnl2^+/−) mice. In vivo electrophysiological study and optical mapping technique were performed to investigate mechanisms of ventricular tachyarrhythmias. Transmission electron microscopy scanning was performed for myocardium ultrastructural analysis. DM mutant mice were more vulnerable to anesthesia medications and program electrical pacing: 2 of 12 mice had sudden apnea and cardiac arrest during premedication of general anesthesia; 9 of the remaining 10 had atrial tachycardia and/or atrioventricular block, but none of the wild‐type mice had spontaneous arrhythmias; and 9 of 10 mice had pacing‐induced ventricular tachyarrhythmias, but only 1 of 14 of the wild‐type mice. Optical mapping studies revealed prolonged action potential duration, slower conduction velocity, and steeper conduction velocity restitution curves in the DM mutant mice than in the wild‐type group. Spatially discordant alternans was more easily inducible in DM mutant than wild‐type mice. Transmission electron microscopy showed disarranged myofibrils with enlarged vacuole‐occupying mitochondria in the DM mutant group.

Conclusions

This DM mutant mouse model presented with clinical myofibril ultrastructural abnormality and cardiac arrhythmias, including atrial tachyarrhythmias, atrioventricular block, and ventricular tachyarrhythmias. Optical mapping studies revealed prolonged action potential duration and slow conduction velocity in the DM mice, leading to vulnerability of spatially discordant alternans and ventricular arrhythmia induction to pacing.

Acute temperature effects on function of the chick embryonic heart

AIM

We analysed the effects of acute temperature change on the beating rate, conduction properties and calcium transients in the chick embryonic heart in vitro and in ovo.

METHODS

The effects of temperature change (34, 37 and 40 °C) on calcium dynamics in isolated ED4 chick hearts in vitro were investigated by high-speed calcium optical imaging. For comparison and validation of in vitro measurements, experiments were also performed in ovo using videomicroscopy. Artificial stimulation experiments were performed in vitro and in ovo to uncover conduction limits of heart segments.

RESULTS

Decrease in temperature from 37 to 34 °C in vitro led to a 22% drop in heart rate and unchanged amplitude of Ca(2+) transients, compared to a 25% heart rate decrease in ovo. Increase in temperature from 37 to 40 °C in vitro and in ovo led to 20 and 23% increases in heart rate, respectively, and a significant decrease in amplitude of Ca(2+) transients (atrium -35%, ventricle -38%). We observed a wide spectrum of arrhythmias in vitro, of which the most common was atrioventricular (AV) block (57%). There was variability of AV block locations. Pacing experiments in vitro and in ovo suggested that the AV blocks were likely caused by relative tissue hypoxia and not by the tachycardia itself.

CONCLUSION

The pacemaker and AV canal are the most temperature-sensitive segments of the embryonic heart. We suggest that the critical point for conduction is the connection of the ventricular trabecular network to the AV canal.

Impaired Sarcoplasmic Reticulum Calcium Uptake and Release Promote Electromechanically and Spatially Discordant Alternans: A Computational Study

Cardiac electrical dynamics are governed by cellular-level properties, such as action potential duration (APD) restitution and intracellular calcium (Ca) handling, and tissue-level properties, including conduction velocity restitution and cell-cell coupling. Irregular dynamics at the cellular level can lead to instabilities in cardiac tissue, including alternans, a beat-to-beat alternation in the action potential and/or the intracellular Ca transient. In this study, we incorporate a detailed single cell coupled map model of Ca cycling and bidirectional APD-Ca coupling into a spatially extended tissue model to investigate the influence of sarcoplasmic reticulum (SR) Ca uptake and release properties on alternans and conduction block. We find that an intermediate SR Ca uptake rate and larger SR Ca release resulted in the widest range of stimulus periods that promoted alternans. However, both reduced SR Ca uptake and release promote arrhythmogenic spatially and electromechanically discordant alternans, suggesting a complex interaction between SR Ca handling and alternans characteristics at the cellular and tissue level.

Kilohertz Frequency Deep Brain Stimulation Is Ineffective at Regularizing the Firing of Model Thalamic Neurons

Deep brain stimulation (DBS) is an established therapy for movement disorders, including tremor, dystonia, and Parkinson's disease, but the mechanisms of action are not well understood. Symptom suppression by DBS typically requires stimulation frequencies ≥100 Hz, but when the frequency is increased above ~2 kHz, the effectiveness in tremor suppression declines (Benabid et al., 1991). We sought to test the hypothesis that the decline in efficacy at high frequencies is associated with desynchronization of the activity generated within a population of stimulated neurons. Regularization of neuronal firing is strongly correlated with tremor suppression by DBS, and desynchronization would disrupt the regularization of neuronal activity. We implemented computational models of CNS axons with either deterministic or stochastic membrane dynamics, and quantified the response of populations of model nerve fibers to extracellular stimulation at different frequencies and amplitudes. As stimulation frequency was increased from 2 to 80 Hz the regularity of neuronal firing increased (as assessed with direct estimates of entropy), in accord with the clinical effects on tremor of increasing stimulation frequency (Kuncel et al., 2006). Further, at frequencies between 80 and 500 Hz, increasing the stimulation amplitude (i.e., the proportion of neurons activated by the stimulus) increased the regularity of neuronal activity across the population, in accord with the clinical effects on tremor of stimulation amplitude (Kuncel et al., 2007). However, at stimulation frequencies above 1 kHz the regularity of neuronal firing declined due to irregular patterns of action potential generation and conduction block. The reductions in neuronal regularity that occurred at high frequencies paralleled the previously reported decline in tremor reduction and may be responsible for the loss of efficacy of DBS at very high frequencies. This analysis provides further support for the hypothesis that effective DBS masks the intrinsic patterns of activity in the stimulated neurons and replaces it with regularized firing.

Multifocal Motor Neuropathy Presenting as Pseudodystonia

Multifocal motor neuropathy (MMN) is an immune-mediated neuropathy. Wasting and weakness typically dominate the clinical presentation. We describe four cases presenting with prominent cramping resembling a primary movement disorder. All cases had features of focal motor conduction block on neurophysiological studies. The involuntary movements resolved in all four patients following treatment with intravenous immunoglobulin. The presented cases highlight an unusual presentation of MMN and emphasize that peripheral nerve pathology can present with movement disorders mimicking central nervous system disease. Furthermore, the movement disorder appears particularly sensitive to standard therapy.

Human immune globulin infusion in the management of multifocal motor neuropathy

Multifocal motor neuropathy (MMN) is a debilitating and rare disease causing profound weakness with minimal to no sensory symptoms. Conduction block is frequently seen on electrodiagnostic testing. An immune-mediated pathology is suspected though the exact underlying pathophysiology has yet to be elucidated. The presence of anti-GM1 ganglioside IgM antibodies coupled with favorable response to intravenous and subcutaneous immunoglobulins supports a complement-mediated mechanism which leads to destruction of nerve tissue with probable predilection to the nodes of Ranvier. High-dose immunoglobulin currently is the only treatment with proven efficacy for MMN patients. Unfortunately, many patients experience decreased responsiveness to immunoglobulins over time, requiring higher and more frequent dosing. In this review, we will focus on the pharmacology, efficacy, safety, and tolerability of intravenous and subcutaneous immune globulin infusion for treatment of MMN.