[Impact of late sodium current inhibition on cardiac electrophysiology parameters and ventricular arrhythmias in isolated Langendorff perfused rabbit hearts with short QT interval].

Objective: To determine the electrophysiological effects and related mechanisms of late sodium current inhibitors on hearts with short QT intervals. Methods: The electrophysiological study was performed on isolated Langendorff perfused rabbit hearts. A total of 80 New Zealand White rabbits were used and 34 hearts without drug treatment were defined as control group A, these hearts were then treated with IKATP opener pinacidil, defined as pinacidil group A. Then, 27 hearts from pinacidil group A were selected to receive combined perfusion with sodium channel inhibitors or quinidine, a traditional drug used to treat short QT syndrome, including ranolazine combined group (n=9), mexiletine combined group (n=9), and quinidine combined group (n=9). Nineteen out of the remaining 46 New Zealand rabbits were selected as control group B (no drug treatments, n=19), and then treated with pinacidil, defined as pinacidil group B (n=19). The remaining 27 rabbits were treated with sodium inhibitors or quinidine alone, including ranolazine alone group (n=9), mexiletine alone group (n=9), and quinidine alone group (n=9). Electrocardiogram (ECG) physiological parameters of control group A and pinacidil group A were collected. In control group B and pinacidil group B, programmed electrical stimulation was used to induce ventricular arrhythmias and ECG was collected. ECG physiological parameters and ventricular arrhythmia status of various groups were analyzed. The concentrations of pinacidil, ranolazine, mexiletine and quinidine used in this study were 30, 10, 30 and 1 µmol/L, respectively. Results: Compared with control group A, the QT interval, 90% of the repolarization in epicardial and endocardial monophasic action potential duration (MAPD90-Epi, MAPD90-Endo) was shortened, the transmural dispersion of repolarization (TDR) was increased, and the effective refractor period (ERP) and post-repolarization refractoriness (PRR) were reduced in pinacidil group A (all P<0.05). Compared with the pinacidil group A, MAPD90-Epi, MAPD90-Endo, QT interval changes were reversed in quinidine combined group and mexiletine combined group (all P<0.05), but not in ranolazine combined group. All these three drugs reversed the pinacidil-induced increases of TDR and the decreases of ERP and PRR. The induced ventricular arrhythmia rate was 0 in control group B, and increased to 10/19 (χ2=13.6, P<0.05) in pinacidil group B during programmed electrical stimulation. Compared with the pinacidil group B, incidences of ventricular arrhythmia decreased to 11% (1/9), 11% (1/9) and 0 (0/9) (χ2=4.5, 4.5, 7.4, P<0.05) respectively in ranolazine group, mexiletine group and quinidine group. Conclusions: Inhibition of late sodium current does not increase but even decreases the risk of malignant arrhythmia in hearts with a shortened QT interval. The antiarrhythmic mechanism might be associated with the reversal of the increase of TDR and the decrease of refractoriness (including both ERP and PRR) of hearts with shortened QT interval.

Review of primary and secondary erythromelalgia.

Erythromelalgia is a condition characterized by episodic pain, erythema and temperature of the extremities, which is relieved by cooling and aggravated by warming. It is useful to review this topic in light of recent discoveries of the genetic mutations that now define primary erythromelalgia, as opposed to secondary erythromelalgia, which is often associated with underlying medical disorders.

Complex interactions in a novel SCN5A compound mutation associated with long QT and Brugada syndrome: Implications for Na+ channel blocking pharmacotherapy for de novo conduction disease.

BACKGROUND: The SCN5A mutation, P1332L, is linked to a malignant form of congenital long QT syndrome, type 3 (LQT3), and affected patients are highly responsive to the Na+ channel blocking drug, mexiletine. In contrast, A647D is an atypical SCN5A mutation causing Brugada syndrome. An asymptomatic male with both P1332L and A647D presented with varying P wave/QRS aberrancy and mild QTc prolongation which did not shorten measurably with mexiletine. OBJECTIVE: We characterized the biophysical properties of P1332L, A647D and wild-type (WT) Na+ channels as well as their combinations in order to understand our proband's phenotype and to guide mexilitine therapy. METHODS: Na+ channel biophysics and mexilitine-binding kinetics were assessed using heterologous expression studies in CHO-K1 cells and human ventricular myocyte modeling. RESULTS: Compared to WT, P1332L channels displayed a hyperpolarizing shift in inactivation, slower inactivation and prominent late Na+ currents (INa). While A647D had no effect on the biophysical properties of INa, it reduced peak and late INa density when co-expressed with either WT or P1332L. Additionally, while P1332L channels had greater sensitivity to block by mexiletine compared to WT, this was reduced in the presence of A647D. Modelling studies revealed that mixing P1332L with A647D channels, action potential durations were shortened compared to P1332L, while peak INa was reduced compared to either A647D coexpressing with WT or WT alone. CONCLUSIONS: While A647D mitigates the lethal LQT3 phenotype seen with P1332L, it also reduces mexilitine sensitivity and decreases INa density. These results explain our proband's mild repolarization abnormality and prominent conduction defect in the atria and ventricles, but also suggest that expression of P1332L with A647D yields a novel disease phenotype for which mexiletine pharmacotherapy is no longer suitable.

Therapeutic Strategies Targeting Inherited Cardiomyopathies.

PURPOSE OF REVIEW: Cardiomyopathies due to genetic mutations are a heterogeneous group of disorders that comprise diseases of contractility, myocardial relaxation, and arrhythmias. Our goal here is to discuss a limited list of genetically inherited cardiomyopathies and the specific therapeutic strategies used to treat them. RECENT FINDINGS: Research into the molecular pathophysiology of the development of these cardiomyopathies is leading to the development of novel treatment approaches. Therapies targeting these specific mutations with gene therapy vectors are on the horizon, while other therapies which indirectly affect the physiologic derangements of the mutations are currently being studied and used clinically. Many of these therapies are older medications being given new roles such as mexiletine for Brugada syndrome and diflunisal for transthyretin amyloid cardiomyopathy. A newer targeted therapy, the inhibitor of myosin ATPase MYK-461, has been shown to suppress the development of ventricular hypertrophy, fibrosis, and myocyte disarray and is being studied as a potential therapy in patients with hypertrophic cardiomyopathy. While this field is too large to be completely contained in a single review, we present a large cross section of recent developments in the field of therapeutics for inherited cardiomyopathies. New therapies are on the horizon, and their development will likely result in improved outcomes for patients inflicted by these conditions.

Late sodium current block for drug-induced long QT syndrome: Results from a prospective clinical trial.

Drug-induced long QT syndrome has resulted in many drugs being withdrawn from the market. At the same time, the current regulatory paradigm for screening new drugs causing long QT syndrome is preventing drugs from reaching the market, sometimes inappropriately. In this study, we report the results of a first-of-a-kind clinical trial studying late sodium (mexiletine and lidocaine) and calcium (diltiazem) current blocking drugs to counteract the effects of hERG potassium channel blocking drugs (dofetilide and moxifloxacin). We demonstrate that both mexiletine and lidocaine substantially reduce heart-rate corrected QT (QTc) prolongation from dofetilide by 20 ms. Furthermore, all QTc shortening occurs in the heart-rate corrected J-Tpeak (J-Tpeak c) interval, the biomarker we identified as a sign of late sodium current block. This clinical trial demonstrates that late sodium blocking drugs can substantially reduce QTc prolongation from hERG potassium channel block and assessment of J-Tpeak c may add value beyond only assessing QTc.

Pulmonary artery stenosis due to embryonal carcinoma with primary mediastinal location.

A 29-year old man was admitted to the intensive care unit after losing consciousness. On physical examination, a loud systolic murmur over the heart was found. Echocardiography revealed narrowing of pulmonary artery with high pressure gradient. Computed tomography of the chest revealed the presence of large tumour localised in the upper anterior mediastinum. Due to the risk of total closure of the pulmonary artery, interventional mediastinotomy was performed and diagnosis of carcinoma embryonale was established. Subsequent chemotherapy (BEP regimen) has brought regression of tumour and significant improvement in haemodynamic parameters (relief of pressure gradient in pulmonary artery). During the second surgery, the resection of all accessible tumour mass together with marginal resection of the right upper lobe was performed. No signs of cardiac or great vessels infiltration was found. Histopathologic examination revealed the necrotic masses and neoplastic foci diagnosed as teratoma immaturum. In a four-month follow-up the patient's condition remained good. The patient is still under the care of both oncological and cardiological specialists. Thus far he has not required further chemotherapy. Holter ECG monitoring revealed no arrhythmia, but the patient is still treated with mexiletine. The patient is planning to return to work.

New daily persistent headache: an update.

New daily persistent headache is a primary headache disorder marked by a unique temporal profile which is daily from onset. For many sufferers this is their first ever headache. Very little is known about the pathogenesis of this condition. It might be a disorder of abnormal glial activation with persistent central nervous system inflammation and it may be a syndrome that occurs in individuals who have a history of cervical hypermobility. At present there is no known specific treatment and many patients go for years to decades without any improvement in their condition despite aggressive therapy. This article will present an up-to-date overview of new daily persistent headache on the topics of clinical presentation, treatment, diagnostic criteria, and presumed pathogenesis. It will also provide some of the authors own treatment suggestions based on recognized triggering events and some suggestions for future clinical trials.

Pharmacological characterization of standard analgesics on oxaliplatin-induced acute cold hypersensitivity in mice.

Oxaliplatin, a platinum-based chemotherapeutic agent, causes an acute peripheral neuropathy triggered by cold in almost all patients during or within hours after its infusion. We recently reported that a single administration of oxaliplatin induced cold hypersensitivity 2 h after the administration in mice. In this study, we examined whether standard analgesics relieve the oxaliplatin-induced acute cold hypersensitivity. Gabapentin, tramadol, mexiletine, and calcium gluconate significantly inhibited and morphine and milnacipran decreased the acute cold hypersensitivity, while diclofenac and amitriptyline had no effects. These results suggest that gabapentin, tramadol, mexiletine, and calcium gluconate are effective against oxaliplatin-induced acute peripheral neuropathy.

An atypical case of SCN9A mutation presenting with global motor delay and a severe pain disorder.

INTRODUCTION: Erythromelalgia due to heterozygous gain-of-function SCN9A mutations usually presents as a pure sensory-autonomic disorder characterized by recurrent episodes of burning pain and redness of the extremities. METHODS: We describe a patient with an unusual phenotypic presentation of gross motor delay, childhood-onset erythromelalgia, extreme visceral pain episodes, hypesthesia, and self-mutilation. The investigation of the patient's motor delay included various biochemical analyses, a comparative genomic hybridization array (CGH), electromyogram (EMG), and muscle biopsy. Once erythromelalgia was suspected clinically, the SCN9A gene was sequenced. RESULTS: The EMG, CGH, and biochemical tests were negative. The biopsy showed an axonal neuropathy and neurogenic atrophy. Sequencing of SCN9A revealed a heterozygous missense mutation in exon 7; p.I234T. CONCLUSIONS: This is a case of global motor delay and erythromelalgia associated with SCN9A. The motor delay may be attributed to the extreme pain episodes or to a developmental perturbation of proprioceptive inputs.

Pharmacotherapy for the prevention of chronic pain after surgery in adults.

BACKGROUND: Chronic pain can often occur after surgery, substantially impairing patients' health and quality of life. It is caused by complex mechanisms that are not yet well understood. The predictable nature of most surgical procedures has allowed for the conduct of randomized controlled trials of pharmacological interventions aimed at preventing chronic postsurgical pain. OBJECTIVES: The primary objective was to evaluate the efficacy of systemic drugs for the prevention of chronic pain after surgery by examining the proportion of patients reporting pain three months or more after surgery. The secondary objective was to evaluate the safety of drugs administered for the prevention of chronic pain after surgery. SEARCH METHODS: We identified randomized controlled trials (RCTs) of various systemically administered drugs for the prevention of chronic pain after surgery from CENTRAL, MEDLINE, EMBASE and handsearches of other reviews and trial registries. The most recent search was performed on 17 July 2013.   SELECTION CRITERIA: Included studies were double-blind, placebo-controlled, randomized trials involving adults and evaluating one or more drugs administered systemically before, during or after surgery, or both, which measured pain three months or more after surgery. DATA COLLECTION AND ANALYSIS: Data collected from each study included the study drug name, dose, route, timing and duration of dosing; surgical procedure; proportion of patients reporting any pain three months or more after surgery, reporting at least 4/10 or moderate to severe pain three months or more after surgery; and proportion of participants dropping out of the study due to treatment-emergent adverse effects. MAIN RESULTS: We identified 40 RCTs of various pharmacological interventions including intravenous ketamine (14 RCTs), oral gabapentin (10 RCTs), oral pregabalin (5 RCTs), non-steroidal anti-inflammatories (3 RCTs), intravenous steroids (3 RCTs), oral N-methyl-D-aspartate (NMDA) blockers (3 RCTs), oral mexiletine (2 RCTs), intravenous fentanyl (1 RCT), intravenous lidocaine (1 RCT), oral venlafaxine (1 RCT) and inhaled nitrous oxide (1 RCT). Meta-analysis suggested a modest but statistically significant reduction in the incidence of chronic pain after surgery following treatment with ketamine but not gabapentin or pregabalin. Results with ketamine should be viewed with caution since most of the included trials were small (that is < 100 participants per treatment arm), which could lead to the overestimation of treatment effect. AUTHORS' CONCLUSIONS: Additional evidence from better, well designed, large-scale trials is needed in order to more rigorously evaluate pharmacological interventions for the prevention of chronic pain after surgery. Furthermore, available evidence does not support the efficacy of gabapentin, pregabalin, non-steroidal anti-inflammatories, intravenous steroids, oral NMDA blockers, oral mexiletine, intravenous fentanyl, intravenous lidocaine, oral venlafaxine or inhaled nitrous oxide for the prevention of chronic postoperative pain.

Induced pluripotent stem cells used to reveal drug actions in a long QT syndrome family with complex genetics.

Understanding the basis for differential responses to drug therapies remains a challenge despite advances in genetics and genomics. Induced pluripotent stem cells (iPSCs) offer an unprecedented opportunity to investigate the pharmacology of disease processes in therapeutically and genetically relevant primary cell types in vitro and to interweave clinical and basic molecular data. We report here the derivation of iPSCs from a long QT syndrome patient with complex genetics. The proband was found to have a de novo SCN5A LQT-3 mutation (F1473C) and a polymorphism (K897T) in KCNH2, the gene for LQT-2. Analysis of the biophysics and molecular pharmacology of ion channels expressed in cardiomyocytes (CMs) differentiated from these iPSCs (iPSC-CMs) demonstrates a primary LQT-3 (Na(+) channel) defect responsible for the arrhythmias not influenced by the KCNH2 polymorphism. The F1473C mutation occurs in the channel inactivation gate and enhances late Na(+) channel current (I(NaL)) that is carried by channels that fail to inactivate completely and conduct increased inward current during prolonged depolarization, resulting in delayed repolarization, a prolonged QT interval, and increased risk of fatal arrhythmia. We find a very pronounced rate dependence of I(NaL) such that increasing the pacing rate markedly reduces I(NaL) and, in addition, increases its inhibition by the Na(+) channel blocker mexiletine. These rate-dependent properties and drug interactions, unique to the proband's iPSC-CMs, correlate with improved management of arrhythmias in the patient and provide support for this approach in developing patient-specific clinical regimens.

Effect of mexiletine on dynamic allodynia induced by chronic constriction injury of the sciatic nerve in rats.

Static and dynamic allodynia occurred in a rat model of neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve. Static allodynia was detected within 1 day after the CCI surgery, and persisted for 28 days. Dynamic allodynia displayed a slower course of development with a late onset, and statistically significant changes were achieved between 14 and 28 days after the surgery. Mexiletine at 10 and 30 mg/kg, s.c. produced a significant and dose-dependent inhibition of CCI-induced static and dynamic allodynia on day 14 post-surgery. Pregabalin, used as a reference drug, also significantly inhibited both static and dynamic allodynia at 30 and 60 mg/kg, p.o. These findings rationalize the clinical use of mexiletine for treatment of neuropathic pain.

Intravenous lidocaine infusion for the treatment of post-acoustic neuroma resection headache: a case report.

Presentation of a case report of a 47-year-old male with a post-acoustic neuroma resection intractable headache responding to intravenous lidocaine infusion. The patient was then switched to mexiletine, with good response.

Experimental studies of potential analgesics for the treatment of chemotherapy-evoked painful peripheral neuropathies.

OBJECTIVE: We investigated potential analgesics for chemotherapy-evoked neuropathic pain using rats treated with paclitaxel. DESIGN: Drugs were tested in a repeated dosing paradigm (four daily injections). Topiramate was tested with a long-term treatment paradigm (12 days). A literature search was performed to summarize prior data. MEASURES: Mechanical stimulation of the hind paw was used to assay antiallodynic and antihyperalgesic effects acutely and 24 hours after injection. RESULTS: Amitriptyline produced significant analgesia, but this was not apparent until after the second injection. Baclofen produced significant effects, but the response varied erratically. Mexiletine and NMED-126 (a mixed N- and T-type calcium channel blocker) produced consistent, significant analgesia when tested acutely, but the pain relief did not persist at 24 hours postinjection. Oxcarbazepine had no effect at any time. Tramadol produced consistent, near-complete analgesia when tested acutely, but the analgesia did not persist to 24 hours postinjection. Topiramate produced significant effects that were first evident after 6-8 days of dosing. CONCLUSIONS: The present data and data from the literature review suggest that there are several potential treatments for chemotherapy-evoked neuropathic pain. Nonsteroidal anti-inflammatory drugs have little or no efficacy. Opioids have an effect, but probably only with high doses. At least some antidepressants are analgesic in these conditions. Some, but clearly not all, anticonvulsants and sodium channel blockers have efficacy. Tramadol is a particularly promising candidate. Topiramate, acetyl-L-carnitine, carbamazepine, and venlafaxine may have protective or restorative effects. Clinical trials of these candidates are needed to advance the treatment of chemotherapy-evoked pain.

Malignant perinatal variant of long-QT syndrome caused by a profoundly dysfunctional cardiac sodium channel.

BACKGROUND: Inherited cardiac arrhythmia susceptibility contributes to sudden death during infancy and may contribute to perinatal and neonatal mortality, but the molecular basis of this risk and the relationship to genetic disorders presenting later in life is unclear. We studied the functional and pharmacological properties of a novel de novo cardiac sodium channel gene (SCN5A) mutation associated with an extremely severe perinatal presentation of long-QT syndrome in unrelated probands of different ethnicity. METHODS AND RESULTS: Two subjects exhibiting severe fetal and perinatal ventricular arrhythmias were screened for SCN5A mutations, and the functional properties of a novel missense mutation (G1631D) were determined by whole-cell patch clamp recording. In vitro electrophysiological studies revealed a profound defect in sodium channel function characterized by approximately 10-fold slowing of inactivation, increased persistent current, slowing of recovery from inactivation, and depolarized voltage dependence of activation and inactivation. Single-channel recordings demonstrated increased frequency of late openings, prolonged mean open time, and increased latency to first opening for the mutant. Subjects carrying this mutation responded clinically to the combination of mexiletine with propranolol and survived. Pharmacologically, the mutant exhibited 2-fold greater tonic and use-dependent mexiletine block than wild-type channels. The mutant also exhibited enhanced tonic (2.4-fold) and use-dependent block ( approximately 5-fold) by propranolol, and we observed additive effects of the 2 drugs on the mutant. CONCLUSIONS: Our study demonstrates the molecular basis for a malignant perinatal presentation of long-QT syndrome, illustrates novel functional and pharmacological properties of SCN5A-G1631D, which caused the disorder, and reveals therapeutic benefits of propranolol block of mutant sodium channels in this setting.

Ventricular ectopy during REM sleep: implications for nocturnal sudden cardiac death.

BACKGROUND: A young adult female presented with syncope and periodic weakness. A 12-lead electrocardiogram showed frequent premature ventricular contractions and prolonged QU interval. Repetitive runs of nonsustained ventricular tachycardia were recorded at night. INVESTIGATIONS: Electromyography, muscle biopsy, MRI, echocardiography, exercise stress testing using Bruce protocol with microvolt T-wave alternans testing, 24 h Holter monitoring, electrophysiological testing and examination of the effects of sleep and sleep stage on the patient's ventricular arrhythmias. DIAGNOSIS: Type 1 Andersen-Tawil syndrome, (also known as type 7 long QT syndrome). Severe ventricular arrhythmia was observed, predominantly during rapid eye movement sleep. We speculate that the autonomic instability present during rapid eye movement sleep precipitates increasing vulnerability to sleep-related ventricular tachycardia. MANAGEMENT: Beta-blocker therapy alone, subsequently combined with mexiletine treatment.

Myotonia congenita--a cause of muscle weakness and stiffness.

BACKGROUND: A 56-year-old woman was referred to a neurogenetic clinic with a history of stiffness and transient weakness. A previous needle electromyogram had confirmed the presence of myotonia, but a muscle biopsy had revealed no evidence of dystrophy. INVESTIGATIONS: Neurological examination, electrophysiological studies and genetic testing. DIAGNOSIS: Recessive myotonia congenita (Becker's disease). MANAGEMENT: Explanation of the nature of the disease and treatment with mexiletine 200 mg twice daily.

[An uncommon cause of recurrent abdominal pain in a 63-year-old obese woman]. / Ungewöhnlicher Grund für rezidivierende Bauchschmerzen bei einer adipösen 63-jährigen Patientin.

HISTORY AND CLINICAL FINDINGS: A 63-year-old woman was admitted because of abdominal pain for 12 months, associated with an increasing abdominal distension. One month before a gastroscopy had revealed mild gastritis. The taking of proton pump inhibitors did not improve her symptoms. There was no relevant neurological or psychiatric past history. INVESTIGATIONS: Ultrasound and laboratory tests demonstrated a fatty liver and increased serum levels of lipoproteins. Magnetic resonance imaging revealed an increase in subcutaneous and intraperitoneal adipose tissue. Endoscopy did not show any additional significant findings. DIAGNOSIS AND TREATMENT: The patient had adiposis dolorosa. Initially she was given daily a combination of mexiletine 400 mg and 75 mg Amitriptyline. After a few days the ailment decreased and had disappeared completely after one week. Three months later the dosage was reduced to 100 mg mexiletine and 25 mg Amitriptyline daily. After another two months all medication was discontinued. At follow-up after 12 months the symptoms had not recurred. CONCLUSION: This case demonstrates that abdominal pain is not always caused by diseases of the visceral hollow organs. It must also be borne in mind that abdominal pain may be associated with adipose tissue, as is the case in adiposis dolorosa. The disease can be successfully treated, as in this case, using a combination of mexiletine and Amitriptyline.