Management of Patients with Long QT Syndrome

Identifying genomic variant associated with long QT syndrome type 2 in an ecuadorian mestizo individual: a case report

Introduction

Long QT syndrome (LQTS) is an autosomal dominant inherited cardiac condition characterized by a QT interval prolongation and risk of sudden death. There are 17 subtypes of this syndrome associated with genetic variants in 11 genes. The second most common is type 2, caused by a mutation in the KCNH2 gene, which is part of the potassium channel and influences the final repolarization of the ventricular action potential. This case report presents an Ecuadorian teen with congenital Long QT Syndrome type 2 (OMIM ID: 613688), from a family without cardiac diseases or sudden cardiac death backgrounds.

Case presentation

A 14-year-old girl with syncope, normal echocardiogram, and an irregular electrocardiogram was diagnosed with LQTS. Moreover, by performing Next-Generation Sequencing, a pathogenic variant in the KCNH2 gene p.(Ala614Val) (ClinVar ID: VCV000029777.14) associated with LQTS type 2, and two variants of uncertain significance in the AKAP9 p.(Arg1654GlyfsTer23) (rs779447911), and TTN p. (Arg34653Cys) (ClinVar ID: VCV001475968.4) genes were identified. Furthermore, ancestry analysis showed a mainly Native American proportion.

Conclusion

Based on the genomic results, the patient was identified to have a high-risk profile, and an implantable cardioverter defibrillator was selected as the best treatment option, highlighting the importance of including both the clinical and genomics aspects for an integral diagnosis.

TANGO2: A Rare but Important Mutation

We report the case of a 7-year-old boy who presented with post-viral myositis, rhabdomyolysis, and hepatitis, who was later readmitted due to a seizure-like activity and ultimately found to have episodes of recalcitrant polymorphic ventricular tachycardia secondary to simultaneous QT prolongation and severe hypothyroidism. Temporary transvenous atrial pacing was successful at controlling the ventricular arrhythmias in the intensive care unit. With levothyroxine therapy and cessation of QT-prolonging medications, the corrected QT (QTc) normalized. A comprehensive arrhythmia panel identified a pathogenic mutation in KCNQ1, consistent with long QT syndrome (LQTS) type 1. After the patient experienced progressive neurodegeneration and seizures, he was referred to a genetics clinic to rule out genetic epilepsy. On the epilepsy panel of genetic testing, he was found to have two pathogenic variants in TANGO2. TANGO2 deficiency explains the initial presentation of myositis, rhabdomyolysis, hypothyroidism, and life-threatening arrhythmias surrounding a viral illness more so than the initial diagnosis of mere LQTS. However, the TANGO2 gene is not included in most comprehensive arrhythmia and cardiomyopathy panels. TANGO2 deficiency is a rare condition that often presents with arrhythmias but may be unfamiliar to many cardiologists and electrophysiologists. This case describes management strategies and caveats, which could aid in the successful diagnosis and treatment of TANGO2 deficiency at the time of presentation.

Mechanistic understanding of KCNQ1 activating polyunsaturated fatty acid analogs

The KCNQ1 channel is important for the repolarization phase of the cardiac action potential. Loss of function mutations in KCNQ1 can cause long QT syndrome (LQTS), which can lead to cardiac arrythmia and even sudden cardiac death. We have previously shown that polyunsaturated fatty acids (PUFAs) and PUFA analogs can activate the cardiac KCNQ1 channel, making them potential therapeutics for the treatment of LQTS. PUFAs bind to KCNQ1 at two different binding sites: one at the voltage sensor (Site I) and one at the pore (Site II). PUFA interaction at Site I shifts the voltage dependence of the channel to the left, while interaction at Site II increases maximal conductance. The PUFA analogs, linoleic-glycine and linoleic-tyrosine, are more effective than linoleic acid at Site I, but less effective at Site II. Using both simulations and experiments, we find that the larger head groups of linoleic-glycine and linoleic-tyrosine interact with more residues than the smaller linoleic acid at Site I. We propose that this will stabilize the negatively charged PUFA head group in a position to better interact electrostatically with the positively charges in the voltage sensor. In contrast, the larger head groups of linoleic-glycine and linoleic-tyrosine compared with linoleic acid prevent a close fit of these PUFA analogs in Site II, which is more confined. In addition, we identify several KCNQ1 residues as critical PUFA-analog binding residues, thereby providing molecular models of specific interactions between PUFA analogs and KCNQ1. These interactions will aid in future drug development based on PUFA-KCNQ1 channel interactions.

Docosahexaenoic acid normalizes QT interval in long QT type 2 transgenic rabbit models in a genotype-specific fashion

AIM

Long QT syndrome (LQTS) is a cardiac channelopathy predisposing to ventricular arrhythmias and sudden cardiac death. Since current therapies often fail to prevent arrhythmic events in certain LQTS subtypes, new therapeutic strategies are needed. Docosahexaenoic acid (DHA) is a polyunsaturated fatty acid, which enhances the repolarizing IKs current.

METHODS AND RESULTS

We investigated the effects of DHA in wild type (WT) and transgenic long QT Type 1 (LQT1; loss of IKs), LQT2 (loss of IKr), LQT5 (reduction of IKs), and LQT2-5 (loss of IKr and reduction of IKs) rabbits. In vivo ECGs were recorded at baseline and after 10 µM/kg DHA to assess changes in heart-rate corrected QT (QTc) and short-term variability of QT (STVQT). Ex vivo monophasic action potentials were recorded in Langendorff-perfused rabbit hearts, and action potential duration (APD75) and triangulation were assessed. Docosahexaenoic acid significantly shortened QTc in vivo only in WT and LQT2 rabbits, in which both α- and β-subunits of IKs-conducting channels are functionally intact. In LQT2, this led to a normalization of QTc and of its short-term variability. Docosahexaenoic acid had no effect on QTc in LQT1, LQT5, and LQT2-5. Similarly, ex vivo, DHA shortened APD75 in WT and normalized it in LQT2, and additionally decreased AP triangulation in LQT2.

CONCLUSIONS

Docosahexaenoic acid exerts a genotype-specific beneficial shortening/normalizing effect on QTc and APD75 and reduces pro-arrhythmia markers STVQT and AP triangulation through activation of IKs in LQT2 rabbits but has no effects if either α- or β-subunits to IKs are functionally impaired. Docosahexaenoic acid could represent a new genotype-specific therapy in LQT2.

Celebrities in the heart, strangers in the pancreatic beta cell: Voltage-gated potassium channels Kv 7.1 and Kv 11.1 bridge long QT syndrome with hyperinsulinaemia as well as type 2 diabetes

Voltage‐gated potassium (K_v) channels play an important role in the repolarization of a variety of excitable tissues, including in the cardiomyocyte and the pancreatic beta cell. Recently, individuals carrying loss‐of‐function (LoF) mutations in KCNQ1, encoding K_v7.1, and KCNH2 (hERG), encoding K_v11.1, were found to exhibit post‐prandial hyperinsulinaemia and episodes of hypoglycaemia. These LoF mutations also cause the cardiac disorder long QT syndrome (LQTS), which can be aggravated by hypoglycaemia. Interestingly, patients with LQTS also have a higher burden of diabetes compared to the background population, an apparent paradox in relation to the hyperinsulinaemic phenotype, and KCNQ1 has been identified as a type 2 diabetes risk gene. This review article summarizes the involvement of delayed rectifier K⁺ channels in pancreatic beta cell function, with emphasis on K_v7.1 and K_v11.1, using the cardiomyocyte for context. The functional and clinical consequences of LoF mutations and polymorphisms in these channels on blood glucose homeostasis are explored using evidence from pre‐clinical, clinical and genome‐wide association studies, thereby evaluating the link between LQTS, hyperinsulinaemia and type 2 diabetes.

Polyunsaturated fatty acids produce a range of activators for heterogeneous IKs channel dysfunction

Repolarization and termination of the ventricular cardiac action potential is highly dependent on the activation of the slow delayed-rectifier potassium IKs channel. Disruption of the IKs current leads to the most common form of congenital long QT syndrome (LQTS), a disease that predisposes patients to ventricular arrhythmias and sudden cardiac death. We previously demonstrated that polyunsaturated fatty acid (PUFA) analogues increase outward K+ current in wild type and LQTS-causing mutant IKs channels. Our group has also demonstrated the necessity of a negatively charged PUFA head group for potent activation of the IKs channel through electrostatic interactions with the voltage-sensing and pore domains. Here, we test whether the efficacy of the PUFAs can be tuned by the presence of different functional groups in the PUFA head, thereby altering the electrostatic interactions of the PUFA head group with the voltage sensor or the pore. We show that PUFA analogues with taurine and cysteic head groups produced the most potent activation of IKs channels, largely by shifting the voltage dependence of activation. In comparison, the effect on voltage dependence of PUFA analogues with glycine and aspartate head groups was half that of the taurine and cysteic head groups, whereas the effect on maximal conductance was similar. Increasing the number of potentially negatively charged moieties did not enhance the effects of the PUFA on the IKs channel. Our results show that one can tune the efficacy of PUFAs on IKs channels by altering the pKa of the PUFA head group. Different PUFAs with different efficacy on IKs channels could be developed into more personalized treatments for LQTS patients with a varying degree of IKs channel dysfunction.

Long QT syndrome type 2: mechanism-based therapies

Long QT syndrome type 2 is a life-threatening disorder of cardiac electrophysiology. It can lead to sudden cardiac death as a result of QT prolongation and can remain undetected until it presents clinically in the form of life-threatening cardiac arrythmias. Current treatment relies on symptom management largely through the use of β-adrenergic blockade and presently no mechanism-based therapies exist to treat the dysfunction in the hERG channels responsible for the rapid delayed rectifier K⁺ current which is the pathological source of long QT syndrome type 2. We review the pathophysiology, diagnosis and current management of this life-threatening condition and also analyze some promising potential mechanism-based therapies.

Video-thoracoscopic left cardiac sympathetic denervation for long-QT syndrome

BACKGROUND

Congenital long-QT syndrome represents the most common cardiac channelopathy and manifests as potentially lethal ventricular arrhythmias. Prevention strategies include beta-blockade pharmacotherapy, implantable cardioverter-defibrillators, and left cardiac sympathetic denervation, which can increase the threshold for ventricular fibrillation. Herein, we report our experience with video-assisted thoracoscopic left cardiac sympathetic denervation.

METHODS

We performed a retrospective review of the electronic medical records of all patients with congenital long-QT syndrome who underwent video-assisted thoracoscopic left cardiac sympathetic denervation at our institution.

RESULTS

From September 2009 to May 2016, 6 patients with a mean age of 30.5 years (range 20-47 years) underwent video-assisted thoracoscopic left cardiac sympathetic denervation for medically refractory long-QT syndrome. All patients had an uneventful recovery and were discharged 1-3 days after the operation. At a median follow-up of 14 months (range 12-60 months), 4 patients had no cardiac events while 2 experienced 1 episode of arrhythmic syncope and 1 episode of appropriate implantable cardioverter-defibrillator shock. Following surgery, the mean annual cardiac events in the study cohort decreased from 2.13 to 0.33 (p = 0.004) and the mean corrected QT interval reduced from 560 ms to 491 ms (p = 0.006).

CONCLUSIONS

Video-assisted thoracoscopic left cardiac sympathetic denervation is a safe and effective therapy in patients with congenital long-QT syndrome who continue to suffer from recurrent life-threatening arrhythmias or frequent implantable cardioverter-defibrillator discharges despite maximum tolerated doses of beta blockers.

Trends in the use of implantable cardioverter-defibrillators for prevention of sudden cardiac arrest: A South Korean nationwide population-based study

BACKGROUND

The benefits of implantable cardioverter-defibrillators (ICDs) for the prevention of sudden cardiac arrest (SCA) are well established. However, a significant knowledge gap remains regarding current indications and utilization of ICDs in real-world settings in Asia.

METHODS

Patients who underwent ICD implantation in South Korea from 2007 to 2015 were identified using the Health Insurance Review and Assessment Service database. We investigated trends in use of ICD for the prevention of SCA.

RESULTS

A total of 4649 ICDs were implanted during 9 years. ICDs were implanted in 1448 (31.2%) patients for primary prevention and in 3201 (68.8%) for secondary prevention. The proportion of ICDs for primary prevention increased from 6.1% in 2007 to 41.9% in 2015. Primary prevention was more frequent in older (≥40 years) recipients (34.4% vs. 14.6%, P < .0001). The rates of ICD implantation for primary prevention were highest for nonischemic dilated cardiomyopathy (55.1%) and lowest (9.7%) for inherited primary arrhythmia syndrome (IPAS).

CONCLUSION

Our data showed a trend of progressively increasing rates of ICD implantation in Asia, especially for primary prevention of SCA. Primary prevention as an indication for ICD in patients with IPAS remained low.

ω-6 and ω-9 polyunsaturated fatty acids with double bonds near the carboxyl head have the highest affinity and largest effects on the cardiac IK s potassium channel

Aim

The I_Ks channel is important for termination of the cardiac action potential. Hundreds of loss‐of‐function mutations in the I_Ks channel reduce the K⁺ current and, thereby, delay the repolarization of the action potential, causing Long QT Syndrome. Long QT predisposes individuals to Torsades de Pointes which can lead to ventricular fibrillation and sudden death. Polyunsaturated fatty acids (PUFAs) are potential therapeutics for Long QT Syndrome, as they affect I_Ks channels. However, it is unclear which properties of PUFAs are essential for their effects on I_Ks channels.

Methods

To understand how PUFAs influence I_Ks channel activity, we measured effects on I_Ks current by two‐electrode voltage clamp while changing different properties of the hydrocarbon tail.

Results

There was no, or weak, correlation between the tail length or number of double bonds in the tail and the effects on or apparent binding affinity for I_Ks channels. However, we found a strong correlation between the positions of the double bonds relative to the head group and effects on I_Ks channels.

Conclusion

Polyunsaturated fatty acids with double bonds closer to the head group had higher apparent affinity for I_Ks channels and increased I_Ks current more; shifting the bonds further away from the head group reduced apparent binding affinity for and effects on the I_Ks current. Interestingly, we found that ω‐6 and ω‐9 PUFAs, with the first double bond closer to the head group, left‐shifted the voltage dependence of activation the most. These results allow for informed design of new therapeutics targeting I_Ks channels in Long QT Syndrome.

Assessing Candidacy for Primary Preventative Implantable Cardioverter-defibrillators in Pediatric Patients with Ion Channelopathies: Weighing the Risks and Benefits

Inherited ion channelopathies have come to the forefront as a significant cause of sudden cardiac death (SCD) in pediatric patients with structurally normal hearts. Implantable cardioverter-defibrillator (ICD) placement can be a life-saving primary preventative therapy, but because of actors inherent in the pediatric population, careful thought must be given to the specific indications for placement in each patient. The most common inherited ion channelopathies are long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia. All have the potential to cause SCD. However, thanks to current research, more is now known about the range of phenotypes present within each disorder and also the benefits that medical therapy can provide. Risk stratification can allow clinicians to best predict which patients may most benefit from a primary preventative ICD while at the same time avoid placement in the larger group who may remain asymptomatic with the aid of medical therapy or even simply observation.