A computational method for identifying an optimal combination of existing drugs to repair the action potentials of SQT1 ventricular myocytes.

Mutations are known to cause perturbations in essential functional features of integral membrane proteins, including ion channels. Even restricted or point mutations can result in substantially changed properties of ion currents. The additive effect of these alterations for a specific ion channel can result in significantly changed properties of the action potential (AP). Both AP shortening and AP prolongation can result from known mutations, and the consequences can be life-threatening. Here, we present a computational method for identifying new drugs utilizing combinations of existing drugs. Based on the knowledge of theoretical effects of existing drugs on individual ion currents, our aim is to compute optimal combinations that can 'repair' the mutant AP waveforms so that the baseline AP-properties are restored. More specifically, we compute optimal, combined, drug concentrations such that the waveforms of the transmembrane potential and the cytosolic calcium concentration of the mutant cardiomyocytes (CMs) becomes as similar as possible to their wild type counterparts after the drug has been applied. In order to demonstrate the utility of this method, we address the question of computing an optimal drug for the short QT syndrome type 1 (SQT1). For the SQT1 mutation N588K, there are available data sets that describe the effect of various drugs on the mutated K+ channel. These published findings are the basis for our computational analysis which can identify optimal compounds in the sense that the AP of the mutant CMs resembles essential biomarkers of the wild type CMs. Using recently developed insights regarding electrophysiological properties among myocytes from different species, we compute optimal drug combinations for hiPSC-CMs, rabbit ventricular CMs and adult human ventricular CMs with the SQT1 mutation. Since the 'composition' of ion channels that form the AP is different for the three types of myocytes under consideration, so is the composition of the optimal drug.

Fibrosis and Conduction Abnormalities as Basis for Overlap of Brugada Syndrome and Early Repolarization Syndrome.

Brugada syndrome and early repolarization syndrome are both classified as J-wave syndromes, with a similar mechanism of arrhythmogenesis and with the same basis for genesis of the characteristic electrocardiographic features. The Brugada syndrome is now considered a conduction disorder based on subtle structural abnormalities in the right ventricular outflow tract. Recent evidence suggests structural substrate in patients with the early repolarization syndrome as well. We propose a unifying mechanism based on these structural abnormalities explaining both arrhythmogenesis and the electrocardiographic changes. In addition, we speculate that, with increasing technical advances in imaging techniques and their spatial resolution, these syndromes will be reclassified as structural heart diseases or cardiomyopathies.

Computational prediction of drug response in short QT syndrome type 1 based on measurements of compound effect in stem cell-derived cardiomyocytes.

Short QT (SQT) syndrome is a genetic cardiac disorder characterized by an abbreviated QT interval of the patient's electrocardiogram. The syndrome is associated with increased risk of arrhythmia and sudden cardiac death and can arise from a number of ion channel mutations. Cardiomyocytes derived from induced pluripotent stem cells generated from SQT patients (SQT hiPSC-CMs) provide promising platforms for testing pharmacological treatments directly in human cardiac cells exhibiting mutations specific for the syndrome. However, a difficulty is posed by the relative immaturity of hiPSC-CMs, with the possibility that drug effects observed in SQT hiPSC-CMs could be very different from the corresponding drug effect in vivo. In this paper, we apply a multistep computational procedure for translating measured drug effects from these cells to human QT response. This process first detects drug effects on individual ion channels based on measurements of SQT hiPSC-CMs and then uses these results to estimate the drug effects on ventricular action potentials and QT intervals of adult SQT patients. We find that the procedure is able to identify IC50 values in line with measured values for the four drugs quinidine, ivabradine, ajmaline and mexiletine. In addition, the predicted effect of quinidine on the adult QT interval is in good agreement with measured effects of quinidine for adult patients. Consequently, the computational procedure appears to be a useful tool for helping predicting adult drug responses from pure in vitro measurements of patient derived cell lines.

Long-term prognosis of short QT interval in Korean patients: a multicenter retrospective cohort study.

BACKGROUND: Short QT syndrome is a rare, inherited channelopathy associated with sudden cardiac arrest (SCA) but the characteristics and prognosis of short QT interval (SQTI) in Korean patients remain unclear. This study aimed to determine the clinical characteristics and outcomes of SQTI in a Korean population. METHODS: Consecutive patients with SQTI from January 1999 to March 2019 in three university hospitals in South Korea were recruited. SQTI was defined as a Bazett's formula-corrected QT interval (QTc) ≤ 340 ms in serial electrocardiograms. Age- and sex-matched patients with a normal QTc and without overt cardiovascular disease were included in a 1:4 ratio. Clinical and ECG features and outcomes were compared between patients with and without SQTI. RESULTS: 34 patients with SQTI [age, 23.5 (21-30.5) years; 31 male] were followed up for 4.8 (2.0-7.8) years. Early repolarization, tall T wave, and U wave were significantly more frequent in patients with SQTI than in those without SQTI. QT dispersion [44.0 (28.0-73.0) vs. 20.0 (12.0-35.0) ms, P < 0.001] was significantly wider and heart rate [52.0 (47.0-58.0) vs. 70.0 (62.3-84.0)/min, P < 0.001] was significantly slower in patients with SQTI than in those without. Atrial fibrillation (AF, 11.8% vs. 2.2%, P = 0.030) and ventricular arrhythmia (VA)/SCA (8.7% vs. 0%, P = 0.007) were significantly more frequent in patients with SQTI than in those without. SQTI was significantly associated with AF [odds ratio, 5.911; 95% confidence interval, 1.257-27.808; P = 0.025] and VA/SCA. CONCLUSIONS: In this subset of Korean population, SQTI was associated with AF and VA/SCA.

Accessory Cardiac Conduction Pathway with an Unusual Presentation.

Pre-excitation syndrome (PES) is a congenital abnormality in which there is conduction through accessory pathway in addition to atrioventricular (AV) node between the atria and the ventricles. Conduction through accessory pathway is without any delay and; hence, results in early excitation of ventricles. This dual connection provides substrate for atrioventricular reciprocating tachycardia (AVRT), a type of supra-ventricular tachycardia. Wolf-Parkinson-White (WPW) syndrome is the commonest form of PES. PES with third degree AV block or complete heart block (CHB) is a rare association. We report here a case of 37-year male with surface ECG findings consistent with PES who presented with syncope. The combination of pre-excitation on ECG with syncope usually draws attention towards tachy-arrhythmias. However, ECG monitoring revealed CHB with intermittent conduction through accessory pathway. It highlights the critical evaluation of PES patients with syncope because therapeutic strategy is entirely different. This case was managed with dual chamber pacemaker implantation instead of accessory pathway ablation.

Drug Testing in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes From a Patient With Short QT Syndrome Type 1.

Short QT syndrome (SQTS) predisposes afflicted patients to sudden cardiac death. Until now, only one drug-quinidine-has been shown to be effective in patients with SQTS type 1(SQTS1). The objective of this study was to use human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from a patient with SQTS1 to search for potentially effective drugs for the treatment of SQTS1 patients. Patch clamp and single-cell contraction measurements were employed to assess drug effects. Ivabradine, mexiletine, and ajmaline but not flecainide, ranolazine, or amiodarone prolonged the action potential duration (APD) in hiPSC-CMs from an SQTS1 patient. Ivabradine, ajmaline, and mexiletine inhibited KCNH2 channel currents significantly, which may underlie their APD-prolonging effects. Under proarrhythmic epinephrine stimulation in spontaneously beating SQTS1 hiPSC-CMs, ivabradine, mexiletine, and ajmaline but not flecainide reduced the epinephrine-induced arrhythmic events. The results demonstrate that ivabradine, ajmaline, and mexiletine may be candidate drugs for preventing tachyarrhythmias in SQTS1 patients.

Genetic and non-genetic determinants of clinical phenotypes in cardiomyopathy.

Cardiomyopathy, a leading cause of death worldwide, is etiologically and phenotypically heterogeneous and is caused by a combination of genetic and non-genetic factors. Major genomic determinants of dilated cardiomyopathy (DCM) are titin truncating mutations and lamin A/C mutations. Patients with these two genotypes show critically different phenotypes, including penetrance, coexistence with a conduction system abnormality, cardiac prognosis, and treatment response. The transcriptomic and epigenomic characteristics of DCM include activation of the DNA damage response, metabolic reprogramming, and dedifferentiation. The proteomic and metabolomic signatures of the DCM heart include a rigorous dependency for free fatty acids, activation of the stress response, and metabolic reprogramming. Proteomic and metabolomic analyses of blood show a distinct immune response and an unexpected link with pathology-specific microbiota in DCM. The direct integration of multi-omics data will not only elucidate inter-omics associations but also enable omics-based patient stratification, which will lead to a deeper understanding of cardiomyopathy and the development of precision medicine in cardiology.

Transgenic short-QT syndrome 1 rabbits mimic the human disease phenotype with QT/action potential duration shortening in the atria and ventricles and increased ventricular tachycardia/ventricular fibrillation inducibility.

AIMS: Short-QT syndrome 1 (SQT1) is an inherited channelopathy with accelerated repolarization due to gain-of-function in HERG/IKr. Patients develop atrial fibrillation, ventricular tachycardia (VT), and sudden cardiac death with pronounced inter-individual variability in phenotype. We generated and characterized transgenic SQT1 rabbits and investigated electrical remodelling. METHODS AND RESULTS: Transgenic rabbits were generated by oocyte-microinjection of ß-myosin-heavy-chain-promoter-KCNH2/HERG-N588K constructs. Short-QT syndrome 1 and wild type (WT) littermates were subjected to in vivo ECG, electrophysiological studies, magnetic resonance imaging, and ex vivo action potential (AP) measurements. Electrical remodelling was assessed using patch clamp, real-time PCR, and western blot. We generated three SQT1 founders. QT interval was shorter and QT/RR slope was shallower in SQT1 than in WT (QT, 147.8 ± 2 ms vs. 166.4 ± 3, P < 0.0001). Atrial and ventricular refractoriness and AP duration were shortened in SQT1 (vAPD90, 118.6 ± 5 ms vs. 154.4 ± 2, P < 0.0001). Ventricular tachycardia/fibrillation (VT/VF) inducibility was increased in SQT1. Systolic function was unaltered but diastolic relaxation was enhanced in SQT1. IKr-steady was increased with impaired inactivation in SQT1, while IKr-tail was reduced. Quinidine prolonged/normalized QT and action potential duration (APD) in SQT1 rabbits by reducing IKr. Diverse electrical remodelling was observed: in SQT1, IK1 was decreased-partially reversing the phenotype-while a small increase in IKs may partly contribute to an accentuation of the phenotype. CONCLUSION: Short-QT syndrome 1 rabbits mimic the human disease phenotype on all levels with shortened QT/APD and increased VT/VF-inducibility and show similar beneficial responses to quinidine, indicating their value for elucidation of arrhythmogenic mechanisms and identification of novel anti-arrhythmic strategies.

Thoracoscopic Cardiac Sympathetic Denervation: Adjunct Therapy for Secondary Prevention of Life-Threatening Ventricular Arrhythmias in Children.

BACKGROUND: Cardiac sympathetic denervation (CSD) is a surgical option for patients with life-threatening ventricular arrhythmias. Previously described cohorts included populations in which CSD was performed for primary and secondary prevention. We report the efficacy of CSD as adjunct therapy in children with medically refractory life-threatening arrhythmias. MATERIALS AND METHODS: Retrospective review of patients undergoing thoracoscopic CSD at one institution between January 2008 and July 2017. Patient demographics, indications, procedural details, complications, length of stay, and effectiveness were evaluated. RESULTS: Ten thoracoscopic CSD procedures were performed in 8 patients. Mean age was 8.2 years (8 days-19 years); mean weight was 32.6 kg (2.7-57 kg); and 50% were female. Four had long QT syndrome, 3 catecholaminergic polymorphic ventricular tachycardia, and 1 short QT syndrome. All patients had at least two (2 to >40) episodes of resuscitated ventricular arrhythmia and were maximized on medical therapy. Six patients had implantable cardioverter-defibrillators (ICD) with a mean of 11.9 appropriate discharges (1-40) before CSD. All patients underwent left CSD; 2 subsequently required right CSD. Four of the 6 ICD patients experienced dramatic improvement (total 48 ICD discharges pre-CSD; 3 post-CSD). Two patients noncompliant with medical therapy had no significant improvement (24 ICD discharges pre-CSD; 23 post-CSD) and also underwent right CSD, again with no improvement (23 discharges pre-right CSD; 28 post-right CSD). CONCLUSIONS: Thoracoscopic CSD can be safely performed in the neonate and pediatric populations. When utilized with medication therapy, CSD is an effective adjunct in reducing ICD discharges and arrhythmias.

Modeling Short QT Syndrome Using Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes.

BACKGROUND: Short QT syndrome (SQTS), a disorder associated with characteristic ECG QT-segment abbreviation, predisposes affected patients to sudden cardiac death. Despite some progress in assessing the organ-level pathophysiology and genetic changes of the disorder, the understanding of the human cellular phenotype and discovering of an optimal therapy has lagged because of a lack of appropriate human cellular models of the disorder. The objective of this study was to establish a cellular model of SQTS using human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). METHODS AND RESULTS: This study recruited 1 patient with short QT syndrome type 1 carrying a mutation (N588K) in KCNH2 as well as 2 healthy control subjects. We generated hiPSCs from their skin fibroblasts, and differentiated hiPSCs into cardiomyocytes (hiPSC-CMs) for physiological and pharmacological studies. The hiPSC-CMs from the patient showed increased rapidly activating delayed rectifier potassium channel current (IKr) density and shortened action potential duration compared with healthy control hiPSC-CMs. Furthermore, they demonstrated abnormal calcium transients and rhythmic activities. Carbachol increased the arrhythmic events in SQTS but not in control cells. Gene and protein expression profiling showed increased KCNH2 expression in SQTS cells. Quinidine but not sotalol or metoprolol prolonged the action potential duration and abolished arrhythmic activity induced by carbachol. CONCLUSIONS: Patient-specific hiPSC-CMs are able to recapitulate single-cell phenotype features of SQTS and provide novel opportunities to further elucidate the cellular disease mechanism and test drug effects.

Therapeutic effects of a taurine-magnesium coordination compound on experimental models of type 2 short QT syndrome.

Short QT syndrome (SQTS) is a genetic arrhythmogenic disease that can cause malignant arrhythmia and sudden cardiac death. The current therapies for SQTS have application restrictions. We previously found that Mg· (NH2CH2CH2SO3)2· H2O, a taurine-magnesium coordination compound (TMCC) exerted anti-arrhythmic effects with low toxicity. In this study we established 3 different models to assess the potential anti-arrhythmic effects of TMCC on type 2 short QT syndrome (SQT2). In Langendorff guinea pig-perfused hearts, perfusion of pinacidil (20 µmol/L) significantly shortened the QT interval and QTpeak and increased rTp-Te (P<0.05 vs control). Subsequently, perfusion of TMCC (1-4 mmol/L) dose-dependently increased the QT interval and QTpeak (P<0.01 vs pinacidil). TMCC perfusion also reversed the rTp-Te value to the normal range. In guinea pig ventricular myocytes, perfusion of trapidil (1 mmol/L) significantly shortened the action potential duration at 50% (APD50) and 90% repolarization (APD90), which was significantly reversed by TMCC (0.01-1 mmol/L, P<0.05 vs trapidil). In HEK293 cells that stably expressed the outward delayed rectifier potassium channels (IKs), perfusion of TMCC (0.01-1 mmol/L) dose-dependently inhibited the IKs current with an IC50 value of 201.1 µmol/L. The present study provides evidence that TMCC can extend the repolarization period and inhibit the repolarizing current, IKs, thereby representing a therapeutic candidate for ventricular arrhythmia in SQT2.

Modelling the effects of quinidine, disopyramide, and E-4031 on short QT syndrome variant 3 in the human ventricles.

OBJECTIVE: Short QT syndrome (SQTS) is an inherited cardiac channelopathy, but at present little information is available on its pharmacological treatment. SQT3 variant (linked to the inward rectifier potassium current I K1) of SQTS, results from a gain-of-function mutation (Kir2.1 D172N) in the KCNJ2-encoded channels, which is associated with ventricular fibrillation (VF). Using biophysically-detailed human ventricular computer models, this study investigated the potential effects of quinidine, disopyramide, and E-4031 on SQT3. APPROACH: The ten Tusscher et al model of human ventricular myocyte action potential (AP) was modified to recapitulate the changes in I K1 due to heterozygous and homozygous forms of the D172N mutation. Wild-type (WT) and mutant WT-D172N and D172N formulations were incorporated into one-dimensional (1D) and 2D tissue models with transmural heterogeneities. Effects of drugs on channel-blocking activity were modelled using half-maximal inhibitory concentration (IC50) and Hill coefficient (nH) values. Effects of drugs on AP duration (APD), effective refractory period (ERP) and QT interval of pseudo-ECGs were quantified, and both temporal and spatial vulnerability to re-entry was measured. Re-entry was simulated in the 2D ventricular tissue. MAIN RESULTS: At the single cell level, the drugs quinidine, disopyramide, and E-4031 prolonged APD at 90% repolarization (APD90), and decreased maximal transmural voltage heterogeneity (δV); this caused the decreased transmural dispersion of APD90. Quinidine prolonged the QT interval and decreased the T-wave amplitude. Furthermore, quinidine increased ERP and reduced temporal vulnerability and increased spatial vulnerability, resulting in a reduced susceptibility to arrhythmogenesis in SQT3. In the 2D tissue, quinidine was effective in terminating and preventing re-entry associated with the heterozygous D172N condition. Quinidine exhibited significantly better therapeutic effects on SQT3 than disopyramide and E-4031. SIGNIFICANCE: This study substantiates a causal link between quinidine and QT interval prolongation in SQT3 Kir2.1 mutations and highlights possible pharmacological agent quinidine for treating SQT3 patients.

Hydrocinnamic Acid Inhibits the Currents of WT and SQT3 Syndrome-Related Mutants of Kir2.1 Channel.

Gain of function in mutations, D172N and E299V, of Kir2.1 will induce type III short QT syndrome. In our previous work, we had identified that a mixture of traditional Chinese medicine, styrax, is a blocker of Kir2.1. Here, we determined a monomer, hydrocinnamic acid (HA), as the effective component from 18 compounds of styrax. Our data show that HA can inhibit the currents of Kir2.1 channel in both excised inside-out and whole-cell patch with the IC50 of 5.21 ± 1.02 and 10.08 ± 0.46 mM, respectively. The time course of HA blockage and washout are 2.3 ± 0.6 and 10.5 ± 2.6 s in the excised inside-out patch. Moreover, HA can also abolish the currents of D172N and E299V with the IC50 of 6.66 ± 0.57 and 5.81 ± 1.10 mM for D172N and E299V, respectively. Molecular docking results determine that HA binds with Kir2.1 at K182, K185, and K188, which are phosphatidylinositol 4,5-bisphosphate (PIP2) binding residues. Our results indicate that HA competes with PIP2 to bind with Kir2.1 and inhibits the currents.

An Unusual Case of Alternating Ventricular Morphology on the 12-Lead Electrocardiogram.

BACKGROUND: One of the principal tasks of an emergency physician is identifying potentially life-threatening conditions in the undifferentiated patient; cardiac dysrhythmia is an example of such a condition. A systematic approach to a patient with atypical dysrhythmia enables proper identification of such-life threatening conditions. CASE REPORT: We describe a 31-year-old man presenting to the emergency department with an undifferentiated dysrhythmia after naloxone reversal of an opiate overdose. A systematic approach to the electrocardiogram led to the rare diagnosis of Wolff-Parkinson-White (WPW) alternans. We review the differential diagnosis of this dysrhythmia and the initial evaluation of a patient with the WPW pattern present on their electrocardiogram. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Emergency physicians should be prepared to use a systematic approach to an undifferentiated dysrhythmia to identify potentially life-threatening conditions.

Prolonged Ventricular Conduction and Repolarization During Right Ventricular Stimulation Predicts Ventricular Arrhythmias and Death in Patients With Cardiomyopathy.

OBJECTIVES: The goal of this study was to evaluate whether prolonged ventricular conduction (paced QRS) and repolarization (paced QTc) times observed during ventricular stimulation predict ventricular arrhythmic events and death. BACKGROUND: Abnormal ventricular conduction and repolarization can predispose patients to ventricular arrhythmias. METHODS: Consecutive patients with left ventricular dysfunction (ejection fraction <50%) undergoing electrophysiology studies from January 2002 until May 2014 were identified at Mayo Clinic (Rochester, Minnesota). Patients were followed up until December 2014 for occurrence of ventricular arrhythmias and death. RESULTS: Among the 501 patients included (mean age 65 years; mean left ventricular ejection fraction 33.1%), longer paced ventricular conduction was associated with longer baseline QRS duration, longer QT interval, and lower ejection fraction. On multivariable analysis, longer paced QRS duration was associated with higher risk of ventricular arrhythmia (hazard ratio [HR]: 1.11 per 10-ms increase; 95% confidence interval [CI]: 1.07 to 1.16; p < 0.001) and all-cause death or arrhythmia (HR: 1.09; 95% CI: 1.09 to 1.13; p < 0.001). A paced QRS duration >190 ms was associated with a 3.6 times higher risk of ventricular arrhythmia (HR: 3.6; 95% CI: 2.35 to 5.53; p < 0.001) and a 2.1 times higher risk of death or arrhythmia (HR: 2.12; 95% CI: 1.53 to 2.95; p < 0.001), independent of left ventricular function or baseline QRS duration. Longer QTc interval during ventricular pacing was associated with a higher risk of ventricular arrhythmia (HR: 1.03 per 10-ms increase; 95% CI: 1.02 to 1.12; p < 0.001) independent of paced QRS duration. CONCLUSIONS: Longer paced QRS duration and paced QTc interval predict ventricular arrhythmias in patients with cardiomyopathy. Ventricular conduction and repolarization prolongation during right ventricular pacing can determine the risk of ventricular arrhythmias.