Induced QTc Prolongation Research Articles

Diverse Phenotypic Manifestations in a Family with a Novel RYR2 E4107A Variant.

Cardiac ryanodine receptor (RyR2) gain-of-function mutations cause catecholaminergic polymorphic ventricular tachycardia (CPVT). Conversely, RyR2 loss-of-function mutations cause a new disease entity, termed calcium release deficiency syndrome (CRDS), which may include RYR2-related long QT syndrome (LQTS). Importantly, unlike CPVT, patients with CRDS do not always exhibit exercise- or epinephrine-induced ventricular arrhythmias, which precludes a diagnosis of CRDS. Here we report a boy and his father, who both experienced exercise-induced cardiac events and harbor the same RYR2 E4107A variant. In the boy, an exercise stress test (EST) and epinephrine provocation test (EPT) did not induce any ventricular arrhythmias. QTc was slightly prolonged (QTc: 474 ms), and an EPT induced QTc prolongation (QTc-baseline: 466 ms, peak: 532 ms, steady-state: 527 ms). In contrast, in his father, QTc was not prolonged (QTc: 417 ms), and neither an EST nor EPT induced QTc prolongation. However, an EST induced multifocal premature ventricular contraction (PVC) bigeminy and bidirectional PVC couplets. Thus, they exhibited distinct clinical phenotypes: the boy exhibited LQTS (or CRDS) phenotype, whereas his father exhibited CPVT phenotype. These findings suggest that, in addition to the altered RyR2 function, other unidentified factors, such as other genetic, epigenetic, and environmental factors, and aging, may be involved in the diverse phenotypic manifestations. Considering that a single RYR2 variant can cause both CPVT and LQTS (or CRDS) phenotypes, in cascade screening of patients with CPVT and CRDS, an EST and EPT are not sufficient and genetic analysis is required to identify individuals who are at increased risk for life-threatening arrhythmias.

Roles of aldosterone on ventricular arrhythmias, and associated gap junction and ion channel remodeling in hypertrophic heart

Abstract Background Ventricular arrhythmias are critical causes of death in patients with chronic heart failure (CHF). Aldosterone (Ald) is an exacerbating factor of CHF and mineral corticoid receptor antagonist (MRA) is usual drug for the management of CHF. MRA also suppressed sudden cardiac death, however, mechanisms of these effects remain unknown. We investigated the effects of MRA on ventricular arrhythmias and arrhythmogenic factors using Dahl Salt sensitive (DS) rats. Methods (in vivo) DS rats were divided into three groups; low salt group (LS), high salt group (HS), and eplerenone-, an MRA, treated high salt group (HS+EPL). Low salt (0.3% NaCl) or high salt (8% NaCl) were administrated for 8 weeks and EPL was administrated in the last 4 weeks. Cardiac geometry and function were assessed by echocardiography. Susceptibility of ventricular arrhythmias were assessed using programmed stimulation. Myocyte hypertrophy and cardiac fibrosis were examined by Masson’s trichrome staining. Expression and distribution of connexin43 (Cx43) were examined by immunostaining and western blotting. mRNA expression of Ca transient-related factors, such as phospholamban, SERCA2a, and ryanosin 2, and potassium ion channel-related factors, such as KCNE1 and KCNQ1, was examined by RT-PCR. (in vitro) Ald (1-100 nM) was administrated to cultured rat neonatal cardiomyocytes. Expression of Cx43, Ca transient-related, and potassium ion channel-related factors are also examined as mentioned above. Effects of Src tyrosin kinase inhibitor, PP2, and ERK inhibitor, PD98059, on Ald-induced Cx43 reduction were examined by RT-PCR and immunostaining. Results Systolic blood pressure and Ald concentrations in cardiac tissue were higher in HS group than LS group, and EPL did not affect them. In HS group left ventricular hypertrophy, dilatation and systolic dysfunction were observed in association with myocyte hypertrophy and interstitial fibrosis. EPL significantly recovered cardiac function and histological impairments. In addition, elongation of QTc in ECG and susceptibility of ventricular tachycardia were remarkable in HS group rather than LS and EPL attenuated them. Distribution of Cx43 was scattered in HS group, and EPL attenuated these changes. Decrease in SERCA2a and increase in KCNE1/KCNQ1 mRNA expression were found in HS group, and these changes were attenuated by EPL. In cultured myocytes, Ald decreased Cx43 mRNA and protein expression in a dose dependent fashion. Ald-induced Cx43 reduction was inhibited by PP2 and PD98059. In addition, Ald (100 nM) also decreased SERCA2a and increased KCNE1/KCNQ1 mRNA expression. Conclusion These results indicate that Ald reduced and dispersed the Cx43 expression reduction and dispersion through Src tyrosin kinase and ERK signaling pathways, and also mediated SRECA2A and KCNE1/KCNQ1 expression, which induced QTc prolongation and susceptibility of lethal ventricular arrhythmias in hypertensive cardiac hypertrophy.

QTc interval prolongation in patients with systemic lupus erythematosus treated with hydroxychloroquine

Objectives The primary objective is to reveal the effect of hydroxychloroquine (HCQ) treatment on corrected QT (QTc) interval in patients with systemic lupus erythematosus (SLE). The secondary objective is to investigate factors that affect QTc prolongation. Methods SLE patients who had electrocardiograms between 2015 and 2020 were recruited and assigned to two groups based on whether they were treated with HCQ (HCQ group) or not (control group). Change of QTc before and after HCQ administration in the HCQ group was measured and compared with the control group. Patients treated with HCQ were further divided into two groups based on presence or absence of QTc prolongation and the characteristics were compared. Results In total, 126 patients were recruited, of whom 42 were treated with HCQ. In the HCQ group, the mean QTc significantly increased (p < .001), while there was no significant difference of mean QTc in the control group. Moreover, those in the HCQ group with QTc prolongation showed a significantly higher proportion of hypertension and longer SLE duration compared to those without QTc prolongation. However, the multiple logistic regression analysis showed that there were no significant differences among them. Conclusion HCQ could induce QTc prolongation in SLE patients. It might be better that the possibility of QTc prolongation was taken into consideration when HCQ was administered in the patients with longer disease duration of SLE and coincidence of hypertension.

Clinical Efficacy of Intracoronary Papaverine After Nicorandil Administration for Safe and Optimal Fractional Flow Reserve Measurement.

Fractional flow reserve (FFR) is considered the standard for assessment of the physiological significance of coronary artery stenosis. Intracoronary papaverine (PAP) is the most potent vasodilator used for the achievement of maximal hyperemia. However, its use can provoke ventricular tachycardia (VT) due to excessive QT prolongation. We evaluated the clinical efficacy and safety of the administration of PAP after nicorandil (NIC), a potassium channel opener that prevents VT, for optimal FFR measurement.A total of 127 patients with 178 stenoses were enrolled. The FFR values were measured using NIC (NIC-FFR) and PAP (PAP-FFR). We administered PAP following NIC (NIC-PAP). Changes in the FFR and electrogram parameters (baseline versus NIC versus PAP) were assessed and the incidence of arrhythmias after PAP was evaluated. In addition, we analyzed another 41 patients with 51 stenoses by assessing the FFR using PAP before NIC (PAP-NIC). After propensity score matching, the electrogram parameters between 2 groups were compared.The mean PAP-FFR was significantly lower than the mean NIC-FFR (0.82 ± 0.11 versus 0.81 ± 0.11, P < 0.05). The mean baseline-QTc, NIC-QTc, and PAP-QTc values were 425 ± 37 ms1/2, 424 ± 41 ms1/2, and 483 ± 54 ms1/2, respectively. VT occurred in only 1 patient (0.6%). Although PAP induced QTc prolongation (P < 0.05), the PAP-QTc duration was significantly shorter in NIC-PAP compared to PAP-NIC (P < 0.05).The administration of PAP with NIC may induce sufficient hyperemia and prevent fatal arrhythmia through reductions in the PAP-induced QTc prolongation during FFR measurement.

Therapeutic Drug Monitoring-Based Efficacy and Safety of Bedaquiline in Chinese Multidrug-Resistant Tuberculosis

Background: Bedaquiline was approved by the US Food and Drug Administration (FDA) for the treatment of drug-resistant tuberculosis in 2012, and significantly improved multidrug-resistant tuberculosis (MDR-TB) patients treatment outcomes. However, data of the efficacy, safety of bedaquiline for the Chinese tuberculosis patients were still lacked, and the plasma concentration of bedaquiline during the treatment and its elimination after treatment discontinuation also had not yet be elucidated. In this study, we demonstrated the efficacy and safety of bedaquiline for the treatment of MDR-TB or XDR-TB patients based on the therapeutic drug monitoring. Methods: 35 patients who started on bedaquiline for drug-resistant tuberculosis were identified. We extracted the patient's medical record information based on their informed consent, and established a standardized monitoring system to track outcomes of patients started on bedaquiline for MDR-TB. The plasma concentration of bedaquiline were determined by ultra-performance liquid chromatography combined with tandem mass spectrometry. Findings: After the 24 weeks bedaquiline treatment, 80% of these patients’ sputum culture conversed negative, and the median time to culture conversion was 75.5 (IQR 52-126) days. 21 (21/26, 80.8%) patients were eventually cured, 2 (2/26, 7.7%) patients failed. The most frequently adverse events during the treatment included QTc prolongation (16/35, 45.7%), peripheral neuropathy (9/35, 25.7%), and gastrointestinal disturbances (8/35, 22.9%). During treatment, the median plasma bedaquiline were fluctuated around 0.6 µg/ml, and gradually decreased after bedaquiline discontinued, about 0.2 µg/ml of bedaquiline was still undegraded after bedaquiline withdrawal 13 months. Moreover, combination with clofazimine increased the possibility of QTc prolongation during the treatment of MDR-TB with bedaquiline, and the decreased serum potassium concentration was also a reason for the prolonged QTc induction with bedaquiline. Interpretation: This study highlighted the efficacy and safety of bedaquiline based on the plasma concentration monitoring, analyzed the reasons of bedaquiline induced QTc prolongation, which had not yet be elucidated before. Funding: This work was supported by the Hospital Pharmacy Special Project of Zhejiang Pharmaceutical Society (2018ZYY31, 2019ZYY27, 2020ZYY08), Zhejiang Medical and Health Science and Technology Plan (2015PYA008, 2020KY741) and Zhejiang Provincial Natural Science Foundation of China under Grant (LYY18H300001), Medical promising youngster of Hangzhou. Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: This study was approved by the Ethic Committee of Affiliated Hangzhou Chest Hospital, Zhejiang University School of Medicine.

A case study on escitalopram induced QTc prolongation and adverse drug reaction

Antagonistic medication response (ADR) can be characterized as any toxic change which is suspected to be because of a medication, happens at dosages ordinarily utilized in man, requires treatment or decline in portion or shows alert later on the utilization of similar medication. Escitalopram is a medication which goes under the classification of particular serotonin reuptake inhibitors (SSRIs) (antidepressants). It is the S-enantiomer of the racemic subsidiary of citalopram, which specifically restrains the reuptake of serotonin with practically no impact on norepinephrine or dopamine reuptake. Practically all the antidepressants and antipsychotics have been connected to QT prolongation. In a patient with previously diagnosed congenital QTS, we present a drug-induced QT extension owing to the escitalopram overdose. A 15-year-old Caucasian woman was presented with an escalopram overdose after a suicide attempt. The patient has a lengthy QT period of torsade de point incidents. The patient was received and monitored in the telemetry facility. She proceeded to exhibit the persistently extended QT period after the resolution of torsades de punes. She was diagnosed with a congenital QT condition by the cardiology clinic. In this situation, an escitalopram overdose is seen to trigger an immediate QT extension for a patient who has congenital LQTS and the value of an electrocardiogram before SSRIs are started, particularly for those at high risk of QT prolongation.

Significance of integrated in silico transmural ventricular wedge preparation models of human non-failing and failing hearts for safety evaluation of drug candidates

IntroductionTo evaluate the usefulness of in silico assay in predicting drug-induced QTc prolongation and ventricular proarrhythmia, we describe in this study 2-dimensional transmural ventricular wedge preparation model (2D model) of non-failing (non-FH) and failing hearts (FH) based on O'Hara-Rudy dynamic model of human ventricular myocytes. MethodsUsing the prepared 2D model, we simulated ventricular action potential and recorded electrocardiogram for the non-FH and FH. The FH model was constructed based on differences in mRNA, protein, and/or current levels of ion channels between non-diseased heart and failing heart. To simulate the effects of selected drugs, we incorporated changes in ion channel conductance depending on the IC50 value and Hill coefficient at unbound drug blood concentrations. ResultsDofetilide concentration-dependently induced QTc prolongation at therapeutic concentration in the 2D model of both non-FH and FH. The QTc prolongation in FH was longer than that in non-FH. These findings are consistent with previously reported clinical data. At supratherapeutic concentration 20nM, dofetilide induced Torsade de Pointes-like arrhythmia in the 2D non-FH model. In contrast, the single ventricular myocyte model did not quantitatively reproduce experimental data due to lack of electrotonic interaction. The simulated QTc change induced by six drugs examined in the IQ-CSRC prospective study was almost equivalent to that recorded in drug-treated healthy volunteers. DiscussionOur 2D model with or without heart failure faithfully reproduced drug-induced QT prolongation and ventricular arrhythmias, suggesting that the in silico approach is a powerful tool for predicting cardiac safety of drug candidates at preclinical stage.

Induction of autoimmune response to the extracellular loop of the HERG channel pore induces QTc prolongation in guinea-pigs.

Channelopathies of autoimmune origin are novel and are associated with corrected QT (QTc) prolongation and complex ventricular arrhythmias. We have recently demonstrated that anti-SSA/Ro antibodies from patients with autoimmune diseases and with QTc prolongation on the ECG target the human ether-à-go-go-related gene (HERG) K+ channel by inhibiting the corresponding current, IKr , at the pore region. Immunization of guinea-pigs with a peptide (E-pore peptide) corresponding to the extracellular loop region connecting the S5 and S6 segments of the HERG channel induces high titres of antibodies that inhibit IKr , lengthen the action potential and cause QTc prolongation on the surface ECG. In addition, anti-SSA/Ro-positive sera from patients with connective tissue diseases showed high reactivity to the E-pore peptide. The translational impact is the development of a peptide-based approach for the diagnosis and treatment of autoimmune-associated long QT syndrome. We recently demonstrated that anti-SSA/52kDa Ro antibodies (Abs) from patients with autoimmune diseases and corrected QT (QTc) prolongation directly target and inhibit the human ether-à-go-go-related gene (HERG) K+ channel at the extracellular pore (E-pore) region, where homology with SSA/52kDa Ro antigen was demonstrated. We tested the hypothesis that immunization of guinea-pigs with a peptide corresponding to the E-pore region (E-pore peptide) will generate pathogenic inhibitory Abs and cause QTc prolongation. Guinea-pigs were immunized with a 31-amino-acid peptide corresponding to the E-pore region of HERG. On days 10-62 after immunization, ECGs were recorded and blood was sampled for the detection of E-pore peptide Abs. Serum samples from patients with autoimmune diseases were evaluated for reactivity to E-pore peptide by enzyme-linked immunosorbent assay (ELISA), and histology was performed on hearts using Masson's Trichrome. Inhibition of the HERG channel was assessed by electrophysiology and by computational modelling of the human ventricular action potential. The ELISA results revealed the presence of high titres of E-pore peptide Abs and significant QTc prolongation after immunization. High reactivity to E-pore peptide was found using anti-SSA/Ro Ab-positive sera from patients with QTc prolongation. Histological data showed no evidence of fibrosis in immunized hearts. Simulations of simultaneous inhibition of repolarizing currents by anti-SSA/Ro Ab-positive sera showed the predominance of the HERG channel in controlling action potential duration and the QT interval. These results are the first to demonstrate that inhibitory Abs to the HERG E-pore region induce QTc prolongation in immunized guinea-pigs by targeting the HERG channel independently from fibrosis. The reactivity of anti-SSA/Ro Ab-positive sera from patients with connective tissue diseases with the E-pore peptide opens novel pharmacotherapeutic avenues in the diagnosis and management of autoimmune-associated QTc prolongation.

P037: The impact of fever on corrected QT interval in a general emergency department population

Introduction: Fever is one of the most common reasons for presentation to the emergency department (ED). Interestingly, a number of small studies suggest that fever may function as a modulator of the QT interval in healthy individuals and an arrhythmogenic trigger in patients with occult congenital QT abnormalities. The objective of this study was to explore whether presence of fever adversely affects the QT interval, and whether medications known to prolong this interval affect any association found. Methods: We performed a retrospective, single center study identifying patients (age &gt; 18 years) presenting to the ED with fever (temperature &gt; 38.0 °C) between January 1st, 2012 and December 31st, 2013 via electronic chart review. The subset for analysis were those who had an ECG both at time of fever and while afebrile (within 30 days of initial ECG). Temperature measurement was within 30 minutes of ECG. Actively paced patients were excluded. Univariate and multiple regression analysis were used to determine risk factors for QT derangement in patients with fever. Results: 2018 febrile visits occurred during the reviewed period, 181 of these patients went on to be included in the study. 54.1% of study subjects were female, and the average age was 68.9 years old. The etiology of fever was predominately infectious (69.6%), with community acquired pneumonia being the most frequent cause (24.3%). We found the median corrected QT interval to be significantly shorter in febrile as compared to afebrile patients [QTc = 388.7ms, (371.5-407.5) vs 406.7, (386.7-434.4); p &lt; 0.001]. This difference was observed in both sexes. Males were found to be more likely to experience medication induced QTc prolongation [OR 5.35, 95% CI = 1.46 - 19.68; P &lt; 0.05]. Two instances of Torsades de pointes were identified in our study, both occurring in males on QT prolonging medications. Conclusion: In an ED patient population, fever generally shortens the QT interval independent of sex. Prolongation of the QT interval during fever should thus increase clinical suspicion of congenital or acquired QT disorders. Additionally, males appear to be more susceptible to medication-induced derangements in the QT interval and may require more vigilant monitoring when treated with multiple QT prolonging medications.

Drug-Induced QTc Interval Prolongation: A Multicenter Study to Detect Drugs and Clinical Factors Involved in Every Day Practice.

The actual prevalence of drug induced QTc prolongation in clinical practice is unknown. Our objective was to determine the occurrence and characteristics of drug-induced QT prolongation in several common clinical practices. Additionally, a subgroup of patients treated with dextropropoxyphene of particular interest for the regulatory authority was analysed. Medical history and comorbidities predisposing to QT interval prolongation were registered for 1270 patient requiring medical assistance that involved drug administration. Three ionograms and ECGs were performed: baseline, intra- and after treatment; QT interval was corrected with Bazzet formula. Among patients, 9.9% presented QTc >450/470 ms, 3% QTc > 500 ms, 12.7% ΔQTc >30 ms and 5.2% ΔQTc >60 ms. QTc prolongation associated with congestive heart failure, ischemic cardiopathy, diabetes, renal failure, arrhythmias, hypothyroidism, and bradycardia. At univariate analysis, clarithromycin, haloperidol, tramadol, amiodarone, glyceryl trinitrate, amoxicillin + clavulanic acid, amoxicillin + sulbactam, ampicillin + sulbactam, fentanyl, piperacillin + tazobactam, and diazepam prolonged QTc. Prolongation remained significantly associated with furosemide, clarithromycin, glyceryl trinitrate and betalactamase inhibitors after multivariate analysis. QT interval prolongation in everyday practice is frequent, in association to clinical factors and drugs that can be easily identified for monitoring and prevention strategies.

SKF-96365 blocks human ether-à-go-go-related gene potassium channels stably expressed in HEK 293 cells

SKF-96365 is a TRPC channel antagonist commonly used to characterize the potential functions of TRPC channels in different systems, which was recently reported to induce QTc prolongation on ECG by inhibiting TRPC channels. The present study investigates whether the blockade of cardiac repolarization currents would be involved in the increase of QTc interval. Cardiac repolarization currents were recorded in HEK 293 cells stably expressing human ether-à-go-go-related gene potassium (hERG or hKv11.1) channels, hKCNQ1/hKCNE1 channels (IKs) or hKir2.1 channels and cardiac action potentials were recorded in guinea pig ventricular myocytes using a whole-cell patch technique. The potential effect of SKF-96365 on QT interval was evaluated in ex vivo guinea pig hearts. It was found that SKF-96365 inhibited hERG current in a concentration-dependent manner (IC50, 3.4μM). The hERG mutants S631A in the pore helix and F656V of the S6 region reduced the inhibitory sensitivity with IC50s of 27.4μM and 11.0μM, suggesting a channel pore blocker. In addition, this compound inhibited IKs and hKir2.1currents with IC50s of 10.8 and 8.7μM. SKF-96365 (10μM) significantly prolonged ventricular APD90 in guinea pig ventricular myocytes and QTc interval in ex vivo guinea pig hearts. These results indicate that the TRPC channel antagonist SKF-96365 exerts blocking effects on hERG, IKs, and hKir2.1 channels. Prolongation of ventricular APD and QT interval is related to the inhibition of multiple repolarization potassium currents, especially hERG channels.

Amiodarone Induced QTC Prolongation : A Case Report

Anti-arrhythmic drugs like amiodarone have the potential to prolong QT intervals which can result in Torsades de pointe arrhythmia. Eventhough it has few pro-arrhythmic effects, it has a rare chance (<2%) of causing QT prolongation which is associated with TdP (torsado de pointes). If TdP is rapid or prolonged, it can lead to ventricular fibirillation and sudden cardiac arrest. We report on a case of a 50 year old male who is admitted with Atrial Flutter (2:1 AV block). He was started on oral Amiodarone (400mg/day) and was planned for elective DC version. His serial ECG was monitored and he converted to sinus rhythm (HR-56/min) on the third day. Subsequent ECGs showed progressive prolongation of the QTc interval (calculated with Bazet's formula). Amiodarone dose was reduced (100mg/day) and further monitoring revealed gradual normalisation of the QTc interval. Review of the patients medication did not reveal the presence of any other drug capable of prolonging QTc. It has been well recognized that a prolonged QT interval (congenital or acquired) on the surface ECG is associated with an increased risk of TdP and sudden death. By far, the most common cause of acquired long QT syndrome is drug induced with anti-arrhythmic drugs being the most commonly implicated. Co- administration of multiple drugs especially with other QT prolonging drugs and hepatic cytochrome P450 CYP3A4 iso-enzyme inhibitors must be avoided. Health care providers must be careful about the adverse effect (TdP) which is a potentially fatal condition.

Effects of palonosetron on prolongation of corrected QT intervals may be less than reliable.

Min et al. [1] investigated the effects of palonosetron, a second-generation 5-hydroxytryptamine-3 receptor antagonist, on corrected QT (QTc) intervals on electrocardiograms of patients undergoing laparotomies under sevoflurane anesthesia. Considering that prolongation of the QTc interval is associated with torsades de pointes, and palonosetron may at least theoretically increase QTc intervals by similar pharmacological mechanisms as ondansetron [2], clinicians will agree that an investigation into the effects of palonosetron on QTc intervals is required. Careful consideration is, however, needed, although Min et al. [1] concluded that palonosetron may induce QTc prolongation during general anesthesia with sevoflurane. In the present study [1], there was a significantly different factor, famotidine, which also can influence the QTc interval. Consequently, it is difficult to exclude its effect on the QTc intervals, in contrast to the authors' description. Additionally, underlying diseases, electrolyte abnormalities, other drugs, adrenergic tone, temperature, and circadian variation, have other effects that may also result in prolongation of QTc intervals [3]. All of these influences may result in QTc prolongation, diminishing the effects of palonosetron alone. Furthermore, a less well-defined target population, risk of selection bias, and confounding factors in retrospective studies may affect the results [4]. Finally, Min et al. [1] concluded that palonosetron could induce QTc prolongation during general anesthesia with sevoflurane, whereas the prospective, randomized, and double-blinded study by Kim et al. [5] showed that preanesthetic administration of palonosetron (0.075 mg) did not affect the QTc interval during the intraoperative period. Thus, to better understand the effects of palonosetron on QTc intervals, it is essential to consider all of the factors related to QTc intervals, the weaknesses of retrospective studies, and related research results. Further well-designed studies on this issue from various perspectives will also be helpful.

Hypokalemia: A potent risk for QTc prolongation in clarithromycin treated rats

Clarithromycin belongs to macrolide group of antibiotics commonly known for their proarrhythmic potency. Besides agents interfering with CYP 3A, electrolyte imbalance might influence repolarization problems of clarithromycin. The proarrhythmic tendency of clarithromycin particularly in association with hypokalemia manifested a change in QT interval in rat electrocardiogram (ECG). Varying degree of hypokalemia was induced by intraperitoneal injection of furosemide (50, 30, and 10mg/kg, for seven days). The serum electrolyte levels confirmed that hypokalemia was established in the groups receiving furosemide. Simultaneously, clarithromycin was orally administered in the doses of 100 and 80mg/kg for seven days. ECG was measured for 5min in anaesthetised rat before and after 2h of treatment. The QT interval was corrected for heart rate and reported as corrected QT (QTc). Distinct QTc interval prolongation was observed in groups receiving furosemide (50 and 30mg/kg) alone and in all the groups receiving clarithromycin alongside furosemide. Neither, clarithromycin (80mg/kg) nor furosemide (10mg/kg) exhibited any significant change in the QTc interval but in combination these drugs led to a significant increase in the QTc interval. Most interestingly, potassium supplementation was found to reduce QTc interval in the group presenting with maximum QTc prolongation. These results suggest that hypokalemic condition potentiates the clarithromycin induced QTc prolongation, thereby indicating the importance of monitoring serum electrolyte during clarithromycin therapy. Although, selection of rat for examination of proarrhythmic liability is controversial, this report may be considered as an evidence of hypokalemia potentiating clarithromycin induced QTc prolongation.

Intravenous palonosetron increases the incidence of QTc prolongation during sevoflurane general anesthesia for laparotomy

BackgroundPalonosetron is a recently introduced 5-hydroxytryptamine-3 (5-HT3) receptor antagonist useful for postoperative nausea and vomiting prophylaxis. However, 5-HT3 receptor antagonists increase the corrected QT (QTc) interval in patients who undergo general anesthesia. This retrospective study was performed to evaluate whether palonosetron would induce a QTc prolongation in patients undergoing general anesthesia with sevoflurane.MethodsWe reviewed a database of 81 patients who underwent general anesthesia with sevoflurane. We divided the records into palonosetron (n = 41) and control (n = 40) groups according to the use of intraoperative palonosetron, and analyzed the electrocardiographic data before anesthesia and 30, 60, 90, and 120 min after skin incision. Changes in the QTc interval from baseline, mean blood pressure, heart rate, body temperature, and sevoflurane concentrations at each time point were compared between the two groups.ResultsThe QTc intervals at skin incision, and 30, 60, 90, and 120 min after the skin incision during general anesthesia were significantly longer than those at baseline in the two groups (P < 0.001). The changes in the QTc intervals were not different between the two groups (P = 0.41). However, six patients in the palonosetron group showed a QTc interval > 500 ms 30 min after skin incision, whereas no patient did in the control group (P = 0.01). No significant differences were observed between the two groups in mean blood pressure, body temperature, heart rate, or sevoflurane concentrations.ConclusionsPalonosetron may induce QTc prolongation during the early general anesthesia period with sevoflurane.

BeKm-1, a Peptide Inhibitor of Human ether-a-go-go-Related Gene Potassium Currents, Prolongs QTc Intervals in Isolated Rabbit Heart

Drug-induced cardiac arrhythmia, specifically Torsades de pointes, is associated with QT/QTc interval prolongation, thus prolongation of the QT interval is considered as a biomarker for Torsades de pointes risk (N Engl J Med 350:1013-1022, 2004). Specific inhibition of human ether-a-go-go-related gene (hERG) potassium channels has been recognized as the main mechanism for QT prolongation (Cardiovasc Res 58:32-45, 2003). This mechanism has been demonstrated for a variety of small-molecule agents, which access the inner pore of the hERG channel preferentially from inside the cell. Peptide inhibitors of hERG, such as BeKm-1, interact with the extracellular amino acid residues close to the external pore region of the channel. In this study, the isolated rabbit heart was used to assess whether BeKm-1 could induce QTc prolongation like dofetilide and N-[4-[[1-[2-(6-methyl-2-pyridinyl)ethyl]-4-piperidinyl]carbonyl]phenyl]methanesulfonamide (E-4031). Five hearts were perfused with 10 and 100 nM BeKm-1 sequentially. ECG parameters and left ventricular contractility were measured with spontaneously beating hearts. Both concentrations of BeKm-1 prolonged QTc intervals significantly and concentration-dependently (4.7 and 16.3% at 10 and 100 nM, respectively). When evaluated for their inhibitory effect in a hERG functional assay, BeKm-1, dofetilide, and E-4031 caused QTc prolongation at concentrations that caused significant hERG channel inhibition. Lastly, two polyclonal anti-hERG antibodies were also assessed in the hERG channel assay and found to be devoid of any inhibitory effect. These results indicated that the isolated rabbit heart assay can be used to measure QTc changes caused by specific hERG inhibition by peptides that specifically block the external pore region of the channel.

Cardiac Safety of One Versus Four Hour Romidepsin (Istodax®) Infusion In the Setting of a Phase I/II Trial of Romidepsin, Dexamethasone and Bortezomib for Relapsed or Refractory Multiple Myeloma

AbstractAbstract 5037Various bortezomib (Bz)-based combinations are being examined in the context of relapsed and/ or refractory Multiple Myeloma (MM). Histone Deacetylase Inhibitors (HDACIs) are a novel group of agents that effect a variety of cellular and intracellular processes by enhancing the acetylation of histone and non-histone targets. Romidepsin (Romi), a cyclic tetrapeptide, is a class 1 HDACi. Initial reports suggested that various HDACi induced QTc prolongation as a class effect, although subsequently it has been shown that careful electrolyte management prevent this from being a clinical problem.32 patients (pts) have been enrolled in a Phase I/II Trial of Romi, Bz and dexamethasone (Dex) in relapsed or refractory MM. The maximum tolerated dose (Romi 10mg/m2, Bz 1.3mg/m2 and Dex 20mg) was determined in the first 6 pts with Romi given on day 1, 8 & 15, Bz on D1, 4, 8 and 11 and Dex D1, 2, 4, 5, 8, 9, 11 and 12 of a 28 day cycle (n=25). In an ongoing expanded Phase IIb cohort Romi is only given on day 1 & 8 of a 21 day cycle (n=7/15).Romidepsin was initially given as the standard 4 hour infusion. However animal and clinical safety data support the use of 1hr Romi infusions. In the expansion cohort, the duration of Romi infusions was reduced to 1 hour from cycle 2. To monitor safety (specifically QT interval), ECGs were mandatory pre and post the 4 hour infusions in cycle one and the 1 hour infusions in cycle 2 and reviewed prior to the continuation of the 1 hour infusion from cycle 3. Prolongation of QTc was defined as an increase of 33%, or 60 msec, or QTc 3500 msec. The maintenance of serum potassium > 4.0 mmol/L and magnesium >0.85 mmol/L prior to Romi infusion was mandated. Any patients in the initial cohort remaining on study and still receiving Romi were eligible to move to 1 hour Romi infusions with ECG monitoring during the first cycle.32 patients have received 598 Romi infusions. 525 infusions have been given over 4 hours and 73 over 1 hour. 19 pts only received 4 hour infusions and 13 pts received at least one 1 hour infusion of Romi.The phase I/II cohort (n=25, median lines of therapy 2 (range1-3)) received 4 hour infusions, the overall response (CR+PR+MR) by modified EBMT criteria was 76% in 21 assessable patients. 2pts had CR (10%), 13 PR (62%), 1 MR (4%), 4 pts had SD, and 1PD. The Phase IIb cohort (n=7, median lines of therapy 2 (range 1–4)) received 1 hour infusions and 6 pts are currently assessable for response with 3 PR and 3 MR.In the first 25 pts receiving the 4 hour infusions, 2 patients experienced arrhythmias during their first cycle, grade 2 atrial flutter possibly related to drug and sinus tachycardia definitely not related. 1pt developed severe ischaemic heart disease and 1pt has died, likely from a PE. Since the introduction of 1hr Romi infusions, only one patient has experienced a Grade 1 cardiac event of asymptomatic lateral T wave flattening and mild ST depression on ECG. This occurred in cycle one, with 4 hour infusions. Full cardiac assessment reveled no clinically significant abnormality. This patient went on to receive the 1 hour infusions without incident.The implementation of the 1 hour infusions has successfully reduced the overall treatment time with Romi/ Bz/ Dex without increase in toxicity. Although numbers are small the response rates appear similar to those using the 4 hour infusions. Disclosures:Off Label Use: Romidepsin and Velcade in combination for the treatment of relapsed/refractory myeloma. Prince:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Harrison:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Antineoplastic Chemotherapy Induced QTc Prolongation

Anticancer drugs are sometimes associated with QT prolongation. Classical, new and candidate agents to treat cancer may affect ventricular repolarization through a set of different mechanisms. Interference on human ether-a-go-go-related gene potassium ion channels (HERG K+) seems to be a common mechanism for many of these drugs. Anthracycline chemotherapy is associated with electrocardiographic alterations including prolongation of QT interval, development of ventricular late potentials and various arrhythmias. The effects of the interaction of anthracyclines with the monoclonal antibody against HER2/neu (Erb-2) trastuzumab could potentiate the cardiotoxic effects. Electrocardiographic changes have been also reported with the use of 5-fluorouracil. QTc alterations have also been reported with some platinum compounds. Taxanes (paclitaxel and docetaxel) have also been associated with cardiotoxicity, promoting both bradi- and tachyarrhythmias and other cardiac disturbances. Among the newest compounds, symptomatic or asymptomatic QTc aberrations were reported with multitargeted tyrosine-kinase inhibitors, anti HERG2, anti-VEGF, vascular disruption agents and histone deacetylase inhibitors. Patients with cancer are at increased risk of sudden death due to severe cardiac arrhythmias because of the high prevalence of predisposing risk factors such as electrolytic abnormalities, starvation and concomitant medications. The use of specific anticancer drug that may prolong the QT interval need to be properly evaluated in each case to reduce this risk.

Cardiac repolarization during hypoglycaemia and hypoxaemia in healthy males: impact of renin-angiotensin system activity

Activity in the renin-angiotensin system (RAS) may influence the susceptibility to cardiac arrhythmia. To study the effect of basal RAS activity on cardiac repolarization during myocardial stress induced by hypoglycaemia or hypoxaemia in healthy humans. Ten subjects with high RAS activity and 10 subjects with low RAS activity were studied on three different occasions: (i) hypoglycaemia (nadir P-glucose 2.7 +/- 0.5 mmol/L), (ii) hypoxaemia (nadir pO(2) 5.8 +/- 0.5 kPa), and (iii) normoglycaemic normoxia (control day). QT parameters were registered by Holter monitoring. Hypoglycaemia and hypoxaemia induced QTc prolongation (P < 0.001, both stimuli). The QT/RR slope and the VR increased as a function of hypoglycaemia, but were unaffected by hypoxaemia. Low RAS activity was associated with a steeper QT/RR slope in the recovery phase after both stimuli: hypoglycaemia: P = 0.04; hypoxia: P = 0.03. RAS activity had no impact on QTc [P = 0.48 (hypoglycaemia) and P = 0.40 (hypoxaemia)] or any of the other outcome variables. Basal RAS activity has significant impact on QT dynamics, but not the corrected QT interval, during recovery from hypoglycaemia and hypoxaemia. The impact, however, is modest and more subtle than initially expected. The clinical relevance is unclear.

Assessment of corrected QT interval in sickle cell disease patients who undergo erythroapheresis

Extension of the QT interval is characterized by syncope and cardiac arrest and often occurs in association with medical therapies and procedures. Whether erythroapheresis (EPH) could influence the QT interval duration in patients with sickle cell disease (SCD) is not known. We aimed to investigate the effects of EPH on the heart rate-corrected QT (QTc) interval. The study included 25 patients with SCD who underwent 34 EPH procedures. Two independent observers measured QTc interval duration from electrocardiograms performed continuously for 3 min at three different points during the EPH procedures (prior to EPH, after completion of 50% EPH and 15 min after EPH). Multiple regression analysis was used to determine if the ionized plasma calcium, the level of plasma magnesium, citrate infusion rate and painful crisis significantly contributed to the QTc interval. There was a non-significant trend (P = 0.184) towards increased QTc in sickle cell patients during EPH compared with pre-EPH values. QTc prolongation (>440 ms) occurred in 72% of the procedures. Fifty percent QTc values returned to baseline after the procedure. The independent variables were not significantly associated with QTc interval. Exchange procedures can induce QTc prolongation in patients with SCD.