The Effect of Antiemetics and Antihistamines on the QTc Interval in Emergent Dialysis Patients With Baseline QTc Prolongation

BACKGROUND

Unfunded patients with end-stage renal disease (ESRD) who do not have routinely scheduled hemodialysis often receive medications known to prolong the QTc interval for their uremic symptoms even though they may have pre-existing QTc prolongation.

OBJECTIVES

The purpose of this study was to determine the effects of these medications on the QTc interval in these patients.

METHODS

Unfunded patients with ESRD presenting to the emergency department (ED) for emergent hemodialysis (HD) with QTc prolongation on their initial electrocardiogram (ECG) were recruited. Approximately 2 hours after receiving an antihistamine or antiemetic, a second ECG was ordered and the QTc was measured. The patients were followed-up 1 week later.

RESULTS

Twenty-nine percent (44/152) of the unfunded patients with ESRD presenting for HD at a county hospital had QT prolongation and were included with 107 total ED visits during the 4-week study period. The mean QTc was 483.7 msec on presentation to the ED, and the mean QTc measured 2 hours after receiving an antihistamine or antiemetic was 483.8 msec. None of the patients were admitted for life-threatening dysrhythmias. Thirty-six percent (16/44) of the recruited patients had QTc intervals >500 msec with a combined total of 31 patient visits, of which only 25.8% (8/31) had an increase in the QTc interval after an antihistamine or antiemetic medication was given. None of these patients had adverse outcomes, such a dysrhythmia or death, at 1-week follow-up.

CONCLUSION

This study shows that medications known to cause QTc prolongation are safe to use in therapeutic doses in patients with ESRD who have pre-existing QT prolongation. Few patients in this cohort had significantly prolonged QTc intervals at baseline.

Efavirenz Inhibits the Human Ether-A-Go-Go Related Current (hERG) and Induces QT Interval Prolongation in CYP2B6*6*6 Allele Carriers

BACKGROUND

Efavirenz (EFV) has been associated with torsade de pointes despite marginal QT interval lengthening. Since EFV is metabolized by the cytochrome P450 (CYP) 2B6 enzyme, we hypothesized that EFV would lengthen the rate-corrected QT (QTcF) interval in carriers of the CYP2B6*6 decreased functional allele.

OBJECTIVE

The primary objective of this study was to evaluate EFV-associated QT interval changes with regard to CYP2B6 genotype and to explore mechanisms of QT interval lengthening.

METHODS

EFV was administered to healthy volunteers (n = 57) as a single 600 mg dose followed by multiple doses to steady-state. Subjects were genotyped for known CYP2B6 alleles and ECGs and EFV plasma concentrations were obtained serially. Whole-cell, voltage-clamp experiments were performed on cells stably expressing hERG and exposed to EFV in the presence and absence of CYP2B6 expression.

RESULTS

EFV demonstrated a gene-dose effect and exceeded the FDA criteria for QTcF interval prolongation in CYP2B6*6/*6 carriers. The largest mean time-matched differences ∆∆QTcF were observed at 6 hours (14 milliseconds; 95% CI [1; 27]), 12 hours (18 milliseconds; 95% CI [-4; 40]), and 18 hours (6 milliseconds; 95% CI [-1; 14]) in the CYP2B6*6/*6 genotype. EFV concentrations exceeding 0.4 μg/mL significantly inhibited outward hERG tail currents (P < 0.05).

CONCLUSIONS

This study demonstrates that homozygous carriers of CYP2B6*6 allele may be at increased risk for EFV-induced QTcF interval prolongation via inhibition of hERG.

Influence of steroid hormones on ventricular repolarization

QT interval prolongation, corrected for heart rate (QTc), either spontaneous or drug-induced, is associated with an increased risk of torsades de pointes and sudden death. Women have longer QTc than men and are at higher risk of torsades de pointes, particularly during post-partum and the follicular phase. Men with peripheral hypogonadism have longer QTc than healthy controls. The role of the main sex steroid hormones has been extensively studied with inconsistent findings. Overall, estradiol is considered to promote QTc lengthening while progesterone and testosterone shorten QTc. New findings suggest more complex regulation of QTc by sex steroid hormones involving gonadotropins (i.e. follicle-stimulating hormone), the relative concentrations of sex steroid hormones (which depends on gender, i.e., progesterone/estradiol ratio in women). Aldosterone, another structurally related steroid hormone, can also prolong ventricular repolarization in both sex. Better understanding of pathophysiological hormonal processes which may lead to increased susceptibility of women (and possibly hypogonadic men) to drug-induced arrhythmia may foster preventive treatments (e.g. progesterone in women). Exogenous hormonal intake might offer new therapeutic opportunities or, alternatively, increase the risk of torsades de pointes. Some exogenous sex steroids may also have paradoxical effects on ventricular repolarization. Lastly, variations of QTc in women linked to the menstrual cycle and sex hormone fluctuations are generally ignored in regulatory thorough QT studies. Investigators and regulatory agencies promoting inclusion of women in thorough QT studies should be aware of this source of variability especially when studying drugs over several days of administration.

Histone Deacetylase Inhibitors Prolong Cardiac Repolarization through Transcriptional Mechanisms

Histone deacetylase (HDAC) inhibitors are an emerging class of anticancer agents that modify gene expression by altering the acetylation status of lysine residues of histone proteins, thereby inducing transcription, cell cycle arrest, differentiation, and cell death or apoptosis of cancer cells. In the clinical setting, treatment with HDAC inhibitors has been associated with delayed cardiac repolarization and in rare instances a lethal ventricular tachyarrhythmia known as torsades de pointes. The mechanism(s) of HDAC inhibitor-induced effects on cardiac repolarization is unknown. We demonstrate that administration of structurally diverse HDAC inhibitors to dogs causes delayed but persistent increases in the heart rate corrected QT interval (QTc), an in vivo measure of cardiac repolarization, at timepoints far removed from the Tmax for parent drug and metabolites. Transcriptional profiling of ventricular myocardium from dogs treated with various HDAC inhibitors demonstrated effects on genes involved in protein trafficking, scaffolding and insertion of various ion channels into the cell membrane as well as genes for specific ion channel subunits involved in cardiac repolarization. Extensive in vitro ion channel profiling of various structural classes of HDAC inhibitors (and their major metabolites) by binding and acute patch clamp assays failed to show any consistent correlations with direct ion channel blockade. Drug-induced rescue of an intracellular trafficking-deficient mutant potassium ion channel, hERG (G601S), and decreased maturation (glycosylation) of wild-type hERG expressed by CHO cells in vitro correlated with prolongation of QTc intervals observed in vivo The results suggest that HDAC inhibitor-induced prolongation of cardiac repolarization may be mediated in part by transcriptional changes of genes required for ion channel trafficking and localization to the sarcolemma. These data have broad implications for the development of these drug classes and suggest that the optimal time to assess potentially transcriptionally mediated physiologic effects will be delayed relative to an epigenetic drug's Tmax/Cmax.

Effect of obesity and weight loss on ventricular repolarization: a systematic review and meta-analysis

We performed a systematic review and meta-analysis of the effects of obesity ± overweight and weight loss on the corrected QT interval (QTc) and QT or QTc dispersion (indices of ventricular repolarization). Mean difference for both QTc and QT or QTc dispersion with 95% confidence intervals (CIs) was calculated comparing obese ± overweight subjects and normal weight controls and QTc and QT or QTc dispersion before and after weight loss from diet ± exercise or bariatric surgery. A total of 22 studies fulfilled the selection criteria. Compared with normal weight controls, there was a significantly longer QTc in obese ± overweight subjects (mean difference of 21.74 msec, 95% CI: 18.76 to 22.32) and significantly longer QT or QTc dispersion (mean difference of 15.17 msec, 95% CI: 13.59 to 16.74). Weight loss was associated with a significant decrease in QTc (mean difference -25.77 msec, 95% CI: -28.33-23.21) and QT or QTc dispersion (mean difference of -13.46 msec, 95% CI: -15.60 to -11.32 in obese ± overweight subjects. Thus, obesity ± overweight is associated with significant prolongation of QTc and QT or QTC dispersion. Weight loss in obese ± overweight subjects produces significant decreases in these variables. © 2016 World Obesity.

Stability of the Effect of a Standardized Meal on QTc

BACKGROUND

The assessment of QTc changes after the intake of a standardized meal has been proposed as an alternative approach to prove assay sensitivity when the proarrhythimic potential of a drug is to be excluded in either TQT or intensive Phase I QT studies.

METHODS

In this article, an analysis of the food effect at baseline across periods in two different studies is presented to support the robustness of the method.

RESULTS

The results show that the time-effect attributed to food is stable over different study periods demonstrating consistency of the physiological response triggered by food.

CONCLUSIONS

Stability and reproducibility of the effect is comparable with moxifloxacin.

A Thorough QTc Study Confirms Early Pharmacokinetics/QTc Modeling: A Supratherapeutic Dose of Omarigliptin, a Once-Weekly DPP-4 Inhibitor, Does Not Prolong the QTc Interval

Omarigliptin is a dipeptidyl peptidase-4 inhibitor being developed as a once-weekly treatment for type 2 diabetes. This double-blind, double-dummy, randomized, 3-period balanced crossover study definitively evaluated the effects of a supratherapeutic omarigliptin dose on QTc interval. Population-specific correction of QT interval (QTcP) was used for the primary analysis. Healthy subjects (n = 60) were enrolled and received treatments separated by a ≥4-week washout: (1) single-dose 25 mg omarigliptin (day 1), single-dose 175 mg omarigliptin (day 2); (2) placebo (day 1) followed by single-dose 400 mg moxifloxacin (day 2); (3) placebo (days 1 and 2). Day 2 QTcP intervals were analyzed. The primary hypothesis was supported if the 90%CIs for the least-squares mean differences between omarigliptin 175 mg and placebo in QTcP interval change from baseline were all < 10 milliseconds at every postdose point on day 2. The upper bounds of the 90%CIs for the differences (omarigliptin-placebo) in QTcP change from baseline for omarigliptin 175 mg were < 10 milliseconds at all postdose times on day 2. In conclusion, a supratherapeutic dose of omarigliptin does not prolong the QTcP interval to a clinically meaningful degree relative to placebo, confirming the results of the earlier concentration-QTc analysis.

Ascending Single-Dose, Double-Blind, Placebo-Controlled Safety Study of Noribogaine in Opioid-Dependent Patients

Ibogaine is a psychoactive substance that may reduce opioid withdrawal symptoms. This was the first clinical trial of noribogaine, ibogaine's active metabolite, in patients established on methadone opioid substitution therapy (OST). In this randomized, double-blind, placebo-controlled single ascending-dose study, we evaluated the safety, tolerability, and pharmacokinetics of noribogaine in 27 patients seeking to discontinue methadone OST who had been switched to morphine during the previous week. Noribogaine doses were 60, 120, or 180 mg (n = 6/dose level) or matching placebo (n = 3/dose level). Noribogaine was well tolerated. The most frequent treatment-emergent adverse events were noneuphoric changes in light perception ∼1 hour postdose, headache, and nausea. Noribogaine had dose-linear increases for AUC and C_max and was slowly eliminated (mean t_1/2 range, 24-30 hours). There was a concentration-dependent increase in QTcI (0.17 ms/ng/mL), with the largest observed mean effect of ∼16, 28, and 42 milliseconds in the 60-, 120-, and 180-mg groups, respectively. Noribogaine showed a nonstatistically significant trend toward decreased total score in opioid withdrawal ratings, most notably at the 120-mg dose; however, the study design may have confounded evaluations of time to resumption of OST. Future exposure-controlled multiple-dose noribogaine studies are planned that will address these safety and design issues.

Assessment of QT and JT Intervals in Patients With Left Bundle Branch Block

Background

Prolongation of the QT interval is considered a risk factor for cardiac adverse events and mortality. Left bundle branch block (LBBB) lengthens the QT interval. The corrected QT interval (QTc) is most likely overestimated because its prolongation is caused by increases in depolarization duration and not in repolarization.

Objectives

In this study, we aimed to apply corrected JT interval (JTc) as an appropriate measure of ventricular repolarization for predicting QTc in a formula.

Patients and Methods

The study population consisted of 101 patients with sinus rhythm (SR) and narrow QRS complexes (< 120 milliseconds). All patients underwent electrophysiology studies or ablation. A diagnostic catheter was positioned in the right ventricular apex (RVA) to induce LBBB at two different cycle lengths (CLs; 600 and 700 mv). The intrinsic QRS complex, QT time, and JT time were measured during SR and subsequent RVA pacing. The JTc was derived simply by subtracting the QRS duration from the QTc.

Results

Stimulation from the RVA increased the QTc from 456.20 ± 38.63 ms to 530.67 ± 47.73 ms at a CL of 600 (P < 0.0001) and to 502.32 ± 47.26 ms at 700 CL (P < 0.0001). JTc showed no significant changes with stimulation from the RVA (102.97 ± 11.35 ms vs. 103.59 ± 10.67 ms, P = 0.24). There was no significant correlation between JTc and QRS complex duration. A significant correlation was seen between QRS and QTc at both CLs. The ROC curve indicated that sensitivity of 80% and specificity of 67% were obtained with JTc duration of 92.6 ms.

Conclusions

Right ventricular pacing increases the QT interval without increasing the JT interval. Our results confirm that JTc, as an index of repolarization, is independent of ventricular depolarization. Therefore, it can be applied for predicting QTc in patients with LBBB.

Evaluation of the potential for QTc prolongation in patients with solid tumors receiving nivolumab

PURPOSE

The fully human monoclonal antibody nivolumab binds to the programmed death-1 (PD-1) receptor, blocking interactions between PD-1 and its ligands on tumor cells and preventing T cell exhaustion in patients with cancer. The potential for corrected QT interval (QTc) prolongation was assessed in a subset of patients enrolled in a phase 2 dose-ranging study of nivolumab.

METHODS

Triplicate 12-lead electrocardiograms (ECGs) obtained predose and post-dose were assessed by an independent ECG core laboratory. QTc derived from Fridericia's formula (QTcF) was evaluated by central tendency, categorical, and concentration-response analyses.

RESULTS

No patients had QTcF intervals or changes from baseline in QTcF (ΔQTcF) exceeding prespecified thresholds indicating borderline or prolonged QTcF (>480 ms) or ΔQTcF (>60 ms). Among 146 patients randomized to nivolumab 0.3, 2.0, or 10.0 mg/kg every 3 weeks, the maximum increases in mean (± SD) ∆QTcF at any time point were 4.9 (± 13.4), 1.2 (± 10.1), and 2.0 (± 8.9) ms, respectively. There was no relationship between ∆QTcF and nivolumab serum concentration and no association between predicted maximum ∆QTcF and mean maximum nivolumab concentration in any dosage group.

CONCLUSION

Results of these intensive ECG analyses indicate that nivolumab has no clinically meaningful effect on QTc interval when administered at doses up to 10.0 mg/kg.

The Effect of a Combination Treatment Using Palonosetron, Promethazine, and Dexamethasone on the Prophylaxis of Postoperative Nausea and Vomiting and QTc Interval Duration in Patients Undergoing Craniotomy under General Anesthesia: A Pilot Study

Introduction

Postoperative nausea and vomiting (PONV) is a displeasing experience that distresses surgical patients during the first 24 h after a surgical procedure. The incidence of postoperative nausea occurs in about 50%, the incidence of postoperative vomiting is about 30%, and in high-risk patients, the PONV rate could be as high as 80%. Therefore, the study design of this single arm, non-randomized, pilot study assessed the efficacy and safety profile of a triple therapy combination with palonosetron, dexamethasone, and promethazine to prevent PONV in patients undergoing craniotomies under general anesthesia.

Methods

The research protocol was approved by the institutional review board and 40 subjects were provided written informed consent. At induction of anesthesia, a triple therapy of palonosetron 0.075 mg IV, dexamethasone 10 mg IV, and promethazine 25 mg IV was given as PONV prophylaxis. After surgery, subjects were transferred to the surgical intensive care unit or post anesthesia care unit as clinically indicated. Ondansetron 4 mg IV was administered as primary rescue medication to subjects with PONV symptoms. PONV was assessed and collected every 24 h for 5 days via direct interview and/or medical charts review.

Results

The overall incidence of PONV during the first 24 h after surgery was 30% (n = 12). The incidence of nausea and emesis 24 h after surgery was 30% (n = 12) and 7.5% (n = 3), respectively. The mean time to first emetic episode, first rescue, and first significant nausea was 31.3 (±33.6), 15.1 (±25.8), and 21.1 (±25.4) hours, respectively. The overall incidence of nausea and vomiting after 24–120 h period after surgery was 30% (n = 12). The percentage of subjects without emesis episodes over 24–120 h postoperatively was 70% (n = 28). No subjects presented a prolonged QTc interval ≥500 ms before and/or after surgery.

Conclusion

Our data demonstrated that this triple therapy regimen may be an adequate alternative regimen for the treatment of PONV in patients undergoing neurological surgery under general anesthesia. More studies with a control group should be performed to demonstrate the efficacy of this regimen and that palonosetron is a low risk for QTc prolongation.

ClinicalTrials.gov Identifier

NCT02635828 (https://clinicaltrials.gov/show/NCT02635828).

Exercise-induced ventricular re-polarisation changes in moderate congenital aortic valve stenosis

Introduction Pressure overload increases in patients with moderate aortic valvular stenosis during exercise. In the absence of symptoms, it remains difficult, however, to discriminate patients for surgery based only on pressure overload. Other parameters, such as the dispersion of ventricular re-polarisation (d-QT), which reportedly increases with the transvalvular pressure gradient, have not been fully studied in this condition.

OBJECTIVE

To determine the pattern of QT and d-QT response to exercise testing in children with moderate aortic valve stenosis in order to evaluate the impact of pressure overload from an electrophysiological perspective. Materials and methods In all, 15 patients were compared with 15 controls paired for age (14.8±2.5 versus 14.2±1.5 years old) and gender (66.7% male). All the patients underwent exercise stress testing with 12-lead electrocardiograph recording. QT was measured from the onset of QRS to the apex (QTa) at rest, at peak exercise, and at 1 and 3 minutes upon recovery. QT was corrected using the Fridericia equation, and d-QT was calculated.

RESULTS

Resting QTc was similar among the study groups, but increased significantly in study patients compared with the control group at maximal effort (p=0.004) and after 1 (p<0.001) and 3 (p<0.001) minutes of recovery. A significant association was identified between groups for d-QT (p=0.034), and post-hoc tests revealed a significant difference only at rest (p=0.001).

CONCLUSIONS

Ventricular re-polarisation abnormalities can be unmasked and highlighted by the assessment of electrical re-polarisation during exercise challenge in patients with asymptomatic moderate aortic valve stenosis. Using QT response to exercise could be beneficial for better optimisation of risk stratification in these patients.

Detection of ECG effects of (2R,4R)-monatin, a sweet flavored isomer of a component first identified in the root bark of the Sclerochitin ilicifolius plant

Enzymatically-synthesized (2R,4R)-monatin has, due to its pure sweet taste, been evaluated for potential use in foods. Non-clinical studies have shown that (2R,4R)-monatin is well tolerated at high dietary concentrations, is not genotoxic/mutagenic, carcinogenic, or overtly toxic. In a pharmacokinetic and metabolism study involving 12 healthy males, consumption of a single oral dose (2 mg/kg) of (2R,4R)-monatin resulted in a small reduction of heart rate and prolongation of the QTcF interval of 20-24 ms, corresponding to the time of peak plasma levels (t(max)). These findings were evaluated in a cross-over thorough QT/QTc study with single doses of 150 mg (2R,4R)-monatin, placebo and positive control (moxifloxacin) in 56 healthy males. Peak (2R,4R)-monatin plasma concentration (1720 ± 538 ng/mL) was reached at 3.1 h (mean tmax). The placebo-corrected, change-from-baseline QTcF (ΔΔQTcF) reached 25 ms three hours after dosing, with ΔΔQTcF of 23 ms at two and four hours. Using exposure response (QTc) analysis, a significant slope of the relationship between (2R,4R)-monatin plasma levels and ΔΔQTcF was demonstrated with a predicted mean QT effect of 0.016 ms per ng/mL. While similarly high plasma levels are unlikely to be achieved by consumption of (2R,4R)-monatin in foods, QTc prolongation at this level is a significant finding.

Benefits of Centralized ECG Reading in Clinical Oncology Studies

BACKGROUND

Many clinical trials of investigational oncologic agents utilize electrocardiogram (ECG) machine measurements of QTc, for inclusion/exclusion and dosing decisions, though their reliability in this setting has not been established.

METHODS

We compared the digital ECG machine QTc measurements with those obtained by a centralized ECG core lab on more than 270,000 consecutive ECGs collected from 299 clinical oncology trials.

RESULTS

The mean difference between the ECG machine measurements and the central measured QTcF was 1.8 ± 15.7 milliseconds. In addition, 29.7% of ECGs with an ECG machine-measured QTcF >450 milliseconds had a centrally measured QTcF <450 milliseconds, 44.6% of ECGs with an ECG machine-measured QTcF >470 milliseconds had a centrally measured QTcF <470 milliseconds, and 77.2% of ECGs with an ECG machine-measured QTcF >500 milliseconds had a centrally measured QTcF <500 milliseconds. The likelihood of a large discrepancy between the ECG machine- and centrally measured value for QTcF increased at both the high and low ends of the range of ECG machine QTcF measurements.

CONCLUSIONS

While on average ECG machine-measured QTcF values were very similar to the central core lab measurements; there were very significant discrepancies which will have important implications for patient recruitment for clinical oncology trials as well as for patient safety during dosing with new oncologic agents. Reliance on ECG machine QTc measurements during clinical oncology trials may lead to unnecessary exclusion of patients as well as unneeded treatment interruptions.

Lessons Learned From Hundreds of Thorough QT Studies

BACKGROUND

The coherence between the relationship of QTc and drug plasma concentration (this relationship is measured through the slope) and ICH E14 findings based on hundreds of QT study reports was studied.

RESULTS

Based on ICH E14 analysis, our findings indicate that if the slope was not positive, in most cases (86%) the corresponding QT studies were also negative. If the slope was positive, 92% of the corresponding QT studies were also positive.

CONCLUSIONS

In exploring whether a thorough QT (TQT) study may be needed, we recommend that the relationship analysis between QTc and drug plasma concentration be performed when proper single ascending dose (SAD) and multiple ascending dose (MAD) studies are available. If the relationship cannot be detected and the 90% upper confidence interval at a fixed concentration level (50th or 75th percentile, or mean peak plasma concentration [C_max]) is below a certain threshold level (eg, 10 milliseconds), then a TQT study might be unnecessary. If the relationship can be established and the 90% lower confidence interval at a fixed concentration level (eg, mean C_max) is greater than 10 milliseconds, further investigation is needed. If the signal is real, one might choose intensive safety monitoring during later drug development instead of a TQT study for a good compound. However, there are still some gray areas in which this analysis alone cannot determine the potential QT liability of the drug, and a TQT type of study might be worth considering.

Validation of continuous QTc measurement in critically ill patients

INTRODUCTION

Prolongation of the corrected QT interval (QTc) can lead to torsades de pointes. This study is designed to determine the validity of the continuous QTc (cQTc) measurement in critically ill patients.

METHODS

In a retrospective cohort study, QTc analysis was performed with manual measurements on a single selected lead from a 12-lead ECG and cQTc measurement obtained at the same time. In addition, automated QTc measurement from the 12-lead ECG was also included in the study. Validation was performed by calculating intraclass correlation coefficient (ICC), Pearson's correlation and Bland-Altman plot.

RESULTS

119 patients with QRS<120 ms were included with a mean cQTc of 468 ms (standard deviation (SD) 37) and mean manually measured QTc of 449 ms (SD 41) (p<0.001). Pearson's correlation was 0.65 (p<0.01), ICC was 0.65 (95% CI: 0.53-0.74). Bland-Altman plot shows a mean difference of 19.5 ms (limits of agreement (LOA) -44.6 to 83.7). For cQTc compared to automated QTc from the 12-lead ECG the intraclass correlation coefficient was 0.77 (95% CI: 0.68-0.83, p<0.001) and the Bland-Altman plot shows a mean difference of 7.8 ms (LOA -40.2 to 55.8).

CONCLUSION

cQTc measurement in critically ill patients with a QRS duration shorter than 120 ms shows an acceptable accuracy to be used in routine care.

The positive frequency-dependent electrophysiological effects of the IKur inhibitor XEN-D0103 are desirable for the treatment of atrial fibrillation

Background

Selective inhibitors of K_v1.5 channels are being developed for the treatment of atrial fibrillation (AF).

Objectives

The purpose of this study was to investigate the effects of the highly selective K_v1.5 inhibitor XEN-D0103 on human atrial action potentials (APs) at high excitation rates and to assess safety.

Methods

Intracellular APs (stimulation rates 1–5 Hz) were measured in right atrial trabeculae from patients in sinus rhythm (SR), chronic AF (cAF; AF of >6 months duration), and paroxysmal AF (pAF). The safety and tolerability of XEN-D0103 were tested in a double-blind, randomized, placebo-controlled phase 1 study.

Results

Depending on its concentration, XEN-D0103 elevated the plateau potential. At 1 Hz, XEN-D0103 (3 µM) shortened action potential duration at 90% repolarization (APD₉₀) and effective refractory period (ERP) in SR preparations, but prolonged these parameters in cAF preparations. In SR and pAF preparations, the shortening effects on APD₉₀ and ERP turned into prolongation at high rates. In cAF trabeculae, XEN-D0103 prolonged APD₉₀ and ERP at 2 and 3 Hz. At high rates, more SR and pAF preparations failed to capture excitation in the presence of the drug than in its absence. XEN-D0103 (10 µM) did not significantly affect human ventricular APs. Even with plasma concentrations reaching 7000 ng/mL, XEN-D0103 did not increase ∆∆QTcF (QT interval corrected by the Fridericia formula) in the analysis of electrocardiograms of healthy volunteers, and no subjects receiving an active treatment had a QT or QTcF interval >450 ms, or increase in QTcF from baseline >30 ms.

Conclusion

APD prolongation and suppression of APs by XEN-D0103 at high stimulation rates in SR and pAF tissue, but not cAF, could be of therapeutic benefit for reducing AF burden. This concept needs to be confirmed in clinical trials.

Evaluation of the QT effect of a combination of piperaquine and a novel anti-malarial drug candidate OZ439, for the treatment of uncomplicated malaria

AIMS

The aim was to investigate the QT effect of a single dose combination regimen of piperaquine phosphate (PQP) and a novel aromatic trioxolane, OZ439, for malaria treatment.

METHODS

Exposure-response (ER) analysis was performed on data from a placebo-controlled, single dose, study with OZ439 and PQP. Fifty-nine healthy subjects aged 18 to 55 years received OZ439 alone or placebo in a first period, followed by OZ439 plus PQP or matching placebos in period 2. OZ439 and PQP doses ranged from 100-800 mg and 160-1440 mg, respectively. Twelve-lead ECG tracings and PK samples were collected serially pre- and post-dosing.

RESULTS

A significant relation between plasma concentrations and placebo-corrected change from baseline QTc F (ΔΔQTc F) was demonstrated for piperaquine, but not for OZ439, with a mean slope of 0.047 ms per ng ml(-1) (90% CI 0.038, 0.057). Using an ER model that accounts for plasma concentrations of both piperaquine and OZ439, a largest mean QTc F effect of 14 ms (90% CI 10, 18 ms) and 18 ms (90% CI 14, 22 ms) was predicted at expected plasma concentrations of a single dose 800 mg OZ439 combined with PQP 960 mg (188 ng ml(-1) ) and 1440 mg (281 ng ml(-1) ), respectively, administered in the fasted state.

CONCLUSIONS

Piperaquine prolongs the QTc interval in a concentration-dependent way. A single dose regimen combining 800 mg OZ439 with 960 mg or 1440 mg PQP is expected to result in lower peak piperaquine plasma concentrations compared with available 3 day PQP-artemisinin combinations and can therefore be predicted to cause less QTc prolongation.

Comparative cardiovascular safety of risperidone and olanzapine, based on electrocardiographic parameters and blood pressure: a prospective open label observational study

Objective:

To assess the cardiovascular safety of two commonly prescribed atypical antipsychotics risperidone (RSP) and olanzapine (OZP) in schizophrenic patients, using electrocardiography (ECG) and Blood Pressure (BP).

Materials and Methods:

This was a 10-week prospective open label, observational study, carried out in a newly diagnosed 64 schizophrenic patients receiving either RSP or OZP. RSP (n = 32) was started with dose of 2 mg/day and increased to 4 mg/day after 2 weeks, whereas OZP (n = 32) was started at a dose of 5 mg/day and was increased to 10 mg/day after 2 weeks. Heart rate (HR), ECG parameters (PR, RR, QRS, QT intervals and QTc and QTd) and BP (systolic and diastolic in supine and standing position) were recorded at baseline (before drug therapy)) and during follow-up visits at 2(I), 6(II) and 10(III) weeks.

Results:

In the RSP group, at II and III follow-ups, a significant increase in the HR (P = 0.018, P = 0.011 respectively) as well as in QTc (P = 0.025, P = 0.015, respectively) was observed when compared to the basal values. In the OZP group, diastolic BP was significantly decreased in standing position at II and III follow-ups (P = 0.045 and P = 0.024, respectively) compared to the basal values. When the two groups were compared with each other, no significant differences were observed in the changes of HR, PR, QRS, QT, RR, QT, QTd and SBP (supine and standing position); and DBP (supine position). However, DBP in standing position showed a significant decrease in the OZP group at II and III follow-up (P = 0.036 and P = 0.016, respectively) compared to the RSP group.

Conclusions:

Patients treated with OZP are at higher risk to develop postural hypotension as compared with RSP; hence RSP could be better tolerated by patients taking antihypertensive drugs as compared with OZP whereas OZP would have a safer cardiac profile.

The cardiomyocyte molecular clock regulates the circadian expression of Kcnh2 and contributes to ventricular repolarization

BACKGROUND

Sudden cardiac death (SCD) follows a diurnal variation. Data suggest the timing of SCD is influenced by circadian (~24-hour) changes in neurohumoral and cardiomyocyte-specific regulation of the heart's electrical properties. The basic helix-loop-helix transcription factors brain muscle arnt-like1 (BMAL1) and circadian locomotor output control kaput (CLOCK) coordinate the circadian expression of select genes.

OBJECTIVE

We sought to test whether Bmal1 expression in cardiomyocytes contributes to K(+) channel expression and diurnal changes in ventricular repolarization.

METHODS

We used transgenic mice that allow for the inducible cardiomyocyte-specific deletion of Bmal1 (iCSΔBmal1(-/-)). We used quantitative polymerase chain reaction, voltage clamping, promoter-reporter bioluminescence assays, and electrocardiographic telemetry.

RESULTS

Although several K(+) channel gene transcripts were downregulated in iCSΔBmal1(-/-)mouse hearts, only Kcnh2 exhibited a robust circadian pattern of expression that was disrupted in iCSΔBmal1(-/-) hearts. Kcnh2 underlies the rapidly activating delayed-rectifier K(+) current, and the rapidly activating delayed-rectifier K(+) current recorded from iCSΔBmal1(-/-) ventricular cardiomyocytes was ~50% smaller than control ventricular myocytes. Promoter-reporter assays demonstrated that the human Kcnh2 promoter is transactivated by the coexpression of BMAL1 and CLOCK. Electrocardiographic analysis showed that iCSΔBmal1(-/-) mice developed a prolongation in the heart rate-corrected QT interval during the light (resting) phase. This was secondary to an augmented circadian rhythm in the uncorrected QT interval without a corresponding change in the RR interval.

CONCLUSION

The molecular clock in the heart regulates the circadian expression of Kcnh2, modifies K(+) channel gene expression, and is important for normal ventricular repolarization. Disruption of the cardiomyocyte circadian clock mechanism likely unmasks diurnal changes in ventricular repolarization that could contribute to an increased risk of cardiac arrhythmias/SCD.

Effects of Hemodialysis on Methadone Pharmacokinetics and QTc

PURPOSE

Effects of hemodialysis on pharmacokinetic properties and QTc were studied in 4 patients taking daily methadone dose of 100 mg (range, 60-120 mg).

METHODS

Methadone in serum, dialysate, and urine were measured by LC-MS/MS. QTc was calculated with Bazett's formula.

FINDINGS

The serum Cmin methadone level was 1124 nmol/L (range, 547-1581 nmol/L). Methadone dialysate clearance was 17.1 mL/min (range, 13.7-20.6 mL/min). Total loss in dialysate was 2.30% (range, 1,25-3,70%) of daily methadone intake. QTc increased from 391 msec (range, 369-406 msec) to 445 msec (range, 407-479 msec), independently of serum methadone level, which may be explained by normalization of serum electrolytes.

IMPLICATIONS

Methadone dose adjustment is not needed because of hemodialysis.

Evaluation of opicapone on cardiac repolarization in a thorough QT/QTc study

Opicapone, a novel third-generation catechol-O-methyltransferase inhibitor for use as adjunctive therapy in levodopa-treated Parkinson's disease patients, was investigated on cardiac repolarization in healthy adult volunteers. This was a single-center, randomized, double-blind, placebo-controlled, open-label active-controlled, 4-period crossover study conducted in 64 subjects. In each period, subjects received a single oral dose of 50 mg opicapone, 800 mg opicapone, placebo, or 400 mg moxifloxacin and 24-hour 12-lead Holter monitoring was performed on day -1 (baseline) and after each single dose. After a single oral administrations of 50 and 800 mg opicapone, opicapone was the major entity in the circulation, with a median tmax of 1.5-2.0 hours. Opicapone was rapidly eliminated, with an elimination half-life of 1-2 hours. There was no clinically relevant effect of 50 and 800 mg opicapone versus placebo on cardiac depolarization or repolarization. All upper bounds of the 1-sided 95% confidence interval (CI) were below 10 milliseconds, confirming that opicapone has no QT-prolonging effect. Moxifloxacin caused an increase in the QTcI, with a lower bound of the 2-sided 95% CI always higher than 5 milliseconds, around the tmax of peak concentration, demonstrating assay sensitivity. In conclusion, administration of opicapone at therapeutic (50 mg) and supratherapeutic (800 mg) doses did not induce a clinically significant prolongation of the QTc interval.

Electrocardiographic effects of class 1 selective histone deacetylase inhibitor romidepsin

Romidepsin is a histone deacetylase inhibitor approved by the FDA for the treatment of patients with cutaneous or peripheral T-cell lymphoma who have received prior systemic therapy. The objective of this analysis was to evaluate the potential QTc effects of romidepsin. Patients with advanced malignancy received 4-h infusions of 14 mg/m² romidepsin on days 1, 8, and 15 of a 28-day cycle. In cycle 2, a subset of patients received 1-h infusions of 8–12 mg/m² romidepsin. Patients were administered antiemetics before each romidepsin dose and electrolyte supplementation as needed. Electrocardiogram readings were performed prior to antiemetic administration, prior to romidepsin administration, and at specified time points over the subsequent 24 h. Romidepsin exposure and heart rate were also assessed. In the electrocardiogram-evaluable population, 26 patients received romidepsin at 14 mg/m² over 4 h. The maximum mean increases from the preantiemetic baseline for QTcF and heart rate were 10.1 msec (upper 90% CI, 14.5 msec) and 18.2 beats per minute, respectively. No patient in this study had an absolute QTcF value >450 msec and only one patient had an increase from the preantiemetic baseline of >60 msec. There was a mild reduction in the PR interval and no meaningful changes in the QRS interval. Despite the use of QT-prolonging antiemetics, treatment with romidepsin did not markedly prolong the QTc interval through 24 h. Increases in calculated QTc may have been exaggerated as a consequence of transient increases in heart rate.

Cardiac effects of sertindole and quetiapine: analysis of ECGs from a randomized double-blind study in patients with schizophrenia

The QT interval is the most widely used surrogate marker for predicting TdP; however, several alternative surrogate markers, such as Tpeak-Tend (TpTe) and a quantitative T-wave morphology combination score (MCS) have emerged. This study investigated the cardiac effects of sertindole and quetiapine using the QTc interval and newer surrogate markers. Data were derived from a 12 week randomized double-blind study comparing flexible dosage of sertindole 12-20mg and quetiapine 400-600mg in patients with schizophrenia. ECGs were recorded digitally at baseline and after 3, 6 and 12 weeks. Between group effects were compared by using a mixed effect model, whereas assessment within group was compared by using a paired t-test. Treatment with sertindole was associated with QTcF and QTcB interval prolongation and an increase in MCS, T-wave asymmetry, T-wave flatness and TpTe. The mean increase in QTcF from baseline to last observation was 12.1ms for sertindole (p<0.001) and -0.5ms for quetiapine (p=0.8). Quetiapine caused no increase in MCS, T-wave asymmetry, T-wave flatness or TpTe compared to baseline. In the categorical analysis, there were 11 patients (9.6%) receiving quetiapine who experienced more than 20ms QTcF prolongation compared with 36 patients (33.3%) in the sertindole group. Sertindole (12-20mg) was associated with moderate QTc prolongation and worsening of T-wave morphology in a study population of patients with schizophrenia. Although, quetiapine (400-600mg) did not show worsening of repolarization measures some individual patients did experience significant worsening of repolarization. Clinical Trials NCT00654706.

Effects on repolarization using dynamic QT interval monitoring in long-QT patients following left cardiac sympathetic denervation

BACKGROUND

Videoscopic left cardiac sympathetic denervation (LCSD) is an adjunct therapy for reduction of arrhythmia-induced events in patients with long-QT syndrome (LQTS). LCSD reduces LQTS-triggered breakthrough cardiac events. The temporal effects of QTc changes post-LCSD have not been studied.

METHODS

We utilized continuous QTc monitoring on 72 patients with LQTS. We evaluated acute and long-term QTc changes in comparison to 12-lead ECG-derived QTc values prior to surgery, 24 hours postsurgery, and at follow up ≥3 months.

RESULTS

Seventy-two patients underwent LCSD at our institution (46% male, mean age at LCSD was 14 ± 10 years). The mean baseline, pre-LCSD QTc was 505 ± 56 ms, which had decreased significantly at ≥3 months post-LCSD to 491 ± 40 ms (P = 0.001). QTc monitoring revealed that the majority of the cohort (53/72; 74%) had a transient increase >30 ms in QTc from baseline, with an average maximum increase of 72 ± 30 ms. Resolution within 10 ms of baseline or less occurred in 57% (30/53) at 24 hours post-LCSD.

CONCLUSIONS

Although LQTS patients may have a paradoxically increased QTc post-LCSD, the effects are transient in most patients. Importantly, no patients experienced any arrhythmias in the postoperative setting related to this transient rise in QTc.

Comparison of the effects of various airway devices on hemodynamic response and QTc interval in rabbits under general anesthesia

In this study, we aimed to compare the effects of various airway devices on QTc interval in rabbits under general anesthesia. The subjects were randomly separated into four groups: Group ETT, Group LMA, Group PLA, Group V-gel. Baseline values and hearth rate, mean arterial pressure and ECG was obtained at the 1st, 5th and 30th minutes after administration of anesthesia and placement of airway device and, QTc interval was evaluated. Difference was observed between ET group and V-gel group in the 5th minute mean arterial pressure values (p < 0.05). It was observed that QTc intervals at the 1st and 5th minute in the ET group significantly increased when compared with the other groups (p < 0.05). Again, it was observed that QTc interval of ET group at the 15th and 30th minute was longer when compared with PLA and V-gel groups (p < 0.05). It was also observed that QTc interval of LMA Group at the 5th minute after intubation significantly increased when compared with V-gel group (p < 0.05). It was observed that HR values of ETT group at the 1st, 5th and 15th minutes after intubation increased with regards to PLA and V-gel groups (p < 0.05). It was determined that the 30th minute hearth rate of ETT group was higher when compared to V-gel group (p < 0.05).

CONCLUSION

In our study we observed that V-gel Rabbit affected both hemodynamic response and QT interval less than other airway devices.

QT dynamics during treatment with sertindole

OBJECTIVES

Sertindole is a nonsedating atypical antipsychotic drug with low propensity to cause extrapyramidal side effects but it has been associated with a 20 ms QTc prolongation and increased risk of cardiac events. It is uncertain whether this drug-induced increase in cardiac risk might also be revealed by dynamic measures of the QT interval such as the ratio of QT variability to heart rate variability (variability ratio [VR]). The aim of this study was to investigate the effect of sertindole on QT dynamics.

METHODS

QTc and the VR were assessed in an observational study using 24-hour Holter monitoring at baseline and after 3 weeks of treatment with sertindole 16 mg. The VR was calculated by dividing the standard deviation of QT intervals with the standard deviation of heart rates. Outcome measures were compared using paired t-test.

RESULTS

A total of 18 patients participated in the study, two were excluded from further analysis due to low amplitude of the T-wave. When patients were shifted to sertindole, the VR increased from 0.192 (SD 0.045) to 0.223 (SD 0.061), p = 0.02. The QTcF interval increased from 388 (SD 16) to 403 ms (SD 14), p = 0.002. There was no difference in heart rate 78 bpm (SD 8) versus 80 bpm (SD 10), p = 0.3 or heart rate variability (SDNN) 127 (SD 40) versus 115 ms (SD 45), p = 0.4.

CONCLUSION

Sertindole was associated with 19 ms QTc prolongation and an increased ratio of QT variability to heart rate variability. Both measures may contribute to the increased cardiovascular mortality found with sertindole.

Corrected QT changes during antipsychotic treatment of children and adolescents: a systematic review and meta-analysis of clinical trials

OBJECTIVE

To evaluate the effect of antipsychotics on the corrected QT (QTc) interval in youth.

METHOD

We searched PubMed (http://www.ncbi.nlm.nih.gov/pubmed) for randomized or open clinical trials of antipsychotics in youth <18 years with QTc data, meta-analyzing the results. Meta-regression analyses evaluated the effect of age, sex, dose, and study duration on QTc. Incidences of study-defined QTc prolongation (>440-470 milliseconds), QTc >500 milliseconds, and QTc change >60 milliseconds were also evaluated.

RESULTS

A total of 55 studies were meta-analyzed, evaluating 108 treatment arms covering 9 antipsychotics and including 5,423 patients with QTc data (mean age = 12.8 ± 3.6 years, female = 32.1%). Treatments included aripiprazole: studies = 14; n = 814; haloperidol: studies = 1; n = 15; molindone: studies = 3; n = 125; olanzapine: studies = 5; n = 212; paliperidone: studies = 3; n = 177; pimozide: studies = 1; n = 25; quetiapine: studies = 5; n = 336; risperidone: studies = 23; n = 2,234; ziprasidone: studies = 10, n = 523; and placebo: studies = 19, n = 962. Within group, from baseline to endpoint, aripiprazole significantly decreased the QTc interval (-1.44 milliseconds, CI = -2.63 to -0.26, p = .017), whereas risperidone (+1.68, CI = +0.67 to +2.70, p = .001) and especially ziprasidone (+8.74, CI = +5.19 to +12.30, p < .001) significantly increased QTc. Compared to pooled placebo arms, aripiprazole decreased QTc (p = .007), whereas ziprasidone increased QTc (p < .001). Compared to placebo, none of the investigated antipsychotics caused a significant increase in the incidence of the 3 studied QTc prolongation measures, but there was significant reporting bias.

CONCLUSION

Based on these data, the risk of pathological QTc prolongation seems low during treatment with the 9 studied antipsychotics in otherwise healthy youth. Nevertheless, because individual risk factors interact with medication-related QTc effects, both medication and patient factors need to be considered when choosing antipsychotic treatment.

Comparison of ranolazine and trimetazidine on glycemic status in diabetic patients with coronary artery disease - a randomized controlled trial

INTRODUCTION

Cardiovascular diseases have become the leading cause of death around the globe and diabetes mellitus (DM) is considered to be a coronary artery disease (CAD) risk equivalent. Ranolazine, an anti anginal drug has been found to reduce Glycated haemoglobin (HbA1c) in diabetes patients with chronic angina. However the effect of another antianginal drug trimetazidine, on glycemic status is not clear.

AIM

To compare the effect of ranolazine and trimetazidine on glycemic status in diabetic patients with CAD.

SETTINGS AND DESIGN

Patients diagnosed with CAD and diabetes mellitus attending Cardiology Out Patient Department (OPD), Jawaharlal Institute of Postgraduate Medical Education & Research (JIPMER), Puducherry, India were recruited for this randomized open label parallel arm trial.

MATERIALS AND METHODS

The study conducted from January-2012 to April-2013 had 47 eligible patients diagnosed with CAD and diabetes mellitus. They were randomized to receive either ranolazine 500 mg BD or trimetazidine 35 mg BD for 12 weeks. HbA1c levels, fasting blood glucose (FBG), lipid profile, QT and QTc intervals were measured at baseline and after 12 weeks.

STATISTICAL ANALYSIS

Unpaired t-test was used to compare the baseline characteristics of between the groups while comparison within the groups were done using Paired t-test. Wilcoxon and Mann Whitney U-tests were used for non parametric data. Graph pad instat version-3 was used for statistical analysis. Values were expressed as mean ± SD. A p < 0.05 was considered statistically significant.

RESULTS

The study could not find any change in HbA1c levels in both ranolazine and trimetazidine groups. The adverse effects reported from patients on ranolazine include angina, constipation, postural hypotension, headache, dizziness, nausea and weakness while patients on trimetazidine complained of constipation, weakness, palpitations, angina, dizziness, nausea, dyspepsia, headache, gastric discomfort, joint pain, etc.

CONCLUSION

In patients with chronic angina and diabetes mellitus Ranolazine 500mg BD and Trimetazidine 35mg BD did not show any effect on HbA1c and fasting blood glucose lebel.

Comparative Evaluation of Corrected QT and Ionized Calcium in Children

Convulsion is one of the most common problems in children and hypocalcemia is one the most frequent etiological items in children's convulsion. Corrected QT (QTc) in EKG is prolonged in hypocalcemia, so it can be a useful tool for evaluation of serum ionized calcium. In three groups (first seizure, multiple seizures, without seizure or control ) every 25 cases, QTc, serum ionized ca, total ca, ABG, and serum albumin level have been checked in the Department of Pediatrics of Imam Khomeini Hospital and outpatient department of Ahari children's medical center in 2008. Prolonged QTc was observed in 72% of convulsive children (36 cases) but only 19% of non-convulsive children (5 cases) showed this pattern. Ionized calcium was significantly higher in non-convulsive than convulsive groups. There was no correlation between prolonged QTc and total serum calcium; however, this correlation with low ionized calcium was significant. QTc is an easy and rapid method for serum ionized calcium evaluation.

Etiology of cardiovascular disease in patients with schizophrenia: current perspectives

Cardiovascular morbidity and mortality are important problems among patients with schizophrenia. A wide spectrum of reasons, ranging from genes to the environment, are held responsible for causing the cardiovascular risk factors that may lead to shortening the life expectancy of patients with schizophrenia. Here, we have summarized the etiologic issues related with the cardiovascular risk factors in schizophrenia. First, we focused on heritable factors associated with cardiovascular disease and schizophrenia by mentioning studies about genetics-epigenetics, in the first-episode or drug-naïve patients. In this context, the association and candidate gene studies about metabolic disturbances in schizophrenia are reviewed, and the lack of the effects of epigenetic/posttranscriptional factors such as microRNAs is mentioned. Increased rates of type 2 diabetes mellitus and disrupted metabolic parameters in schizophrenia are forcing clinicians to struggle with metabolic syndrome parameters and related issues, which are also the underlying causes for the risk of having cardiometabolic and cardiovascular etiology. Second, we summarized the findings of metabolic syndrome-related entities and discussed the influence of the illness itself, antipsychotic drug treatment, and the possible disadvantageous lifestyle on the occurrence of metabolic syndrome (MetS) or diabetes mellitus. Third, we emphasized on the risk factors of sudden cardiac death in patients with schizophrenia. We reviewed the findings on the arrhythmias such as QT prolongation, which is a risk factor for Torsade de Pointes and sudden cardiac death or P-wave prolongation that is a risk factor for atrial fibrillation. For example, the use of antipsychotics is an important reason for the prolongation of QT and some other cardiac autonomic dysfunctions. Additionally, we discussed relatively rare issues such as myocarditis and cardiomyopathy, which are important for prognosis in schizophrenia that may have originated from the use of antipsychotic medication. In conclusion, we considered that the studies and awareness about physical needs of patients with schizophrenia are increasing. It seems logical to increase cooperation and shared care between the different health care professionals to screen and treat cardiovascular disease (CVD)-risk factors, MetS, and diabetes in patients with psychiatric disorders, because some risk factors of MetS or CVD are avoidable or at least modifiable to decrease high mortality in schizophrenia. We suggested that future research should focus on conducting an integrated system of studies based on a holistic biopsychosocial evaluation.

Oxytocin does not directly alter cardiac repolarization in rabbit or human cardiac myocytes

Oxytocin, a nine amino acid peptide, is highly conserved in placental mammals, including humans. Oxytocin has a physiological role in parturition and parenteral administration of the synthetic peptide is used to induce labor and control postpartum hemorrhage. Endogenous levels of oxytocin before labor are ∼20 pg/mL, but pharmacological administration of the peptide can achieve levels of 110 pg/mL (0.1 nmol/L) following intravenous administration. Cardiac arrhythmia and premature ventricular contractions have been associated with oxytocin administration in addition to QTc interval prolongation. In the conscious rabbit model, intravenous oxytocin produced QT and QTc prolongation. The mechanism of oxytocin-induced QTc prolongation is uncertain but could be the result of indirect changes in autonomic nervous tone, or a direct effect on the duration of cardiomyocyte repolarization. The purpose of this study was to examine the ability of oxytocin to alter cardiac repolarization directly. Two conventional models were used: QTc interval evaluation in the isolated rabbit heart (IRH) and assessment of action potential duration (APD) in human ventricular myocytes (HVM). Oxytocin did not prolong QTc intervals in IRH or APD in HVM when tested at suprapharmacological concentrations, for example, up to 1 μmol/L. The results indicate that oxytocin has very low risk for eliciting QTc and APD prolongation directly, and infer that the QTc changes observed in vivo may be attributed to an indirect mechanism.

Detection of QTc effects in small studies--implications for replacing the thorough QT study

BACKGROUND

ECG assessment with exposure response analysis applied to data from First-in-Man studies has been proposed to replace the thorough QT study for the detection of small QT effects.

METHODS

Data from five thorough QT studies, three with moxifloxacin, one study with a drug with a large QTc effect (∼25 ms) and one with ketoconazole with a smaller QT effect (∼8 ms) were used. By subsampling, studies with 6-18 subjects on drug and six on placebo were simulated 1000 times per sample size to assess whether small QTc effects using ICH E14 criteria could be excluded and the impact of sample size on the estimate and variability of the slope of the concentration/QTc relation.

RESULTS

With a sample size of nine or more on drug and six on placebo, the fraction of "false negative studies" was at or below 5% with data from the studies with moxifloxacin and from the drug with a large QTc effect. With the same sample size and no underlying QTc effect (placebo), the fraction of studies in which an effect above 10 ms could be excluded was above 85%. A treatment effect in the linear concentration-effect model resulted in a lower proportion of "false negatives." Sample size had little influence on the average slope estimate of the concentration/QTc relationship.

CONCLUSIONS

For drugs with a QTc effect of around 12-14 ms, exposure response analysis applied to First-in-Man studies with careful ECG assessment can be used to replace the through QT study.

Effects of Peginesatide Injection on QTc Interval in Healthy Adults

A single-dose, randomized, double-blind, placebo- and positive-controlled, three-period crossover study was conducted to evaluate the effect of peginesatide injection on QT interval in healthy adults. Subjects received single doses of placebo, peginesatide injection 0.1 mg/kg intravenous, or moxifloxacin 400 mg during three treatment periods, separated by 14-day washout intervals. ECG recordings and blood samples for peginesatide and moxifloxacin plasma concentrations were collected prior to dosing and through 22 hours postdose. QT intervals were measured with a high resolution manual on-screen caliper method. The study endpoint was the mean difference between peginesatide and placebo in baseline-adjusted corrected QT interval (ddQTc). The maximum upper bound of the one-sided 95% CI was 2.2 milliseconds at 0.75 hours for Fridericia-corrected ddQTc (ddQTcF) and 2.2 milliseconds at 0.25 hours for individual corrected ddQTcI. The linear relationship between ddQTcF and peginesatide concentrations was essentially flat and not statistically significant [slope = 0.001, P = 0.126, 90% CI: (<−0.0005, 0.002)]. Using this model, the projected ddQTcF effect at the observed mean peak plasma concentration is estimated to be 0.9 milliseconds, 90% CI: (−2.0, 0.3 milliseconds). There were no peginesatide-related effects on heart rate, PR interval, or QRS interval. Thus, there is no anticipated cardiovascular effect of peginesatide injection 0.1 mg/kg in patients.

Assessment of the effect of ofatumumab on cardiac repolarization

Ofatumumab is a human monoclonal antibody that binds to a unique CD20 epitope on the surface of B lymphocytes, resulting in efficient lysis of CD20-expressing cells via complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity. The potential effect of ofatumumab on cardiac repolarization and the relationship between ofatumumab concentration and change in corrected QT interval (ΔQTcF) were evaluated in data from three clinical trials in 82 patients with chronic lymphocytic leukemia receiving ofatumumab alone (n = 14), ofatumumab with chemotherapy (n = 33), and chemotherapy alone (n = 35). Because of ofatumumab accumulation, baseline QTcF interval was recorded prior to the first infusion for each patient. No patient had a post-baseline QTcF interval >480 milliseconds or a ΔQTcF >60 milliseconds; five patients (four on ofatumumab) had a ΔQTcF between 30 and 60 milliseconds. At cycle 6 (week 21; 308 μg/mL), there was an increase in QTcF in patients on ofatumumab treatment, with an estimated between-treatment difference (90% CI) of 12.5 (4.5, 20.5) milliseconds. However, at the visit with the highest median concentration (week 8; 1386 μg/mL), median ΔQTcF was 4.8 milliseconds. There was no significant relationship between ofatumumab plasma concentration and ΔQTcF. Ofatumumab did not have a clinically significant effect on cardiac repolarization.

Effects of combined netupitant and palonosetron (NEPA), a cancer supportive care antiemetic, on the ECG of healthy subjects: an ICH E14 thorough QT trial

Chemotherapy-induced nausea and vomiting is ranked among the worst side effects of chemotherapy. NEPA is an oral fixed-dose combination antiemetic under development, consisting of netupitant 300 mg, a highly selective NK₁ receptor antagonist (RA), and palonosetron 0.5 mg, a pharmacologically and clinically distinct 5-HT₃ RA. Although palonosetron is not associated with relevant ECG effects, this study evaluated cardiovascular safety of netupitant in combination with palonosetron, as well as its tolerability.

This randomised, placebo- and positively controlled study in 197 subjects included 4 treatment groups: placebo, 200 mg netupitant + 0.5 mg palonosetron (NEPA_200/0.5), 600 mg netupitant + 1.5 mg palonosetron (NEPA_600/1.5, a supratherapeutic dose), and 400 mg moxifloxacin. Assessments included a 24-h baseline ECG recording, followed by a single dose of treatment and ECG measurements for 2 days.

Mean placebo-corrected time-averaged changes from baseline were similar in NEPA_200/0.5 and NEPA_600/1.5 groups primarily for individually heart rate-corrected QT interval (QTcI: +4.7 and +3.6 ms, respectively) and for heart rate (HR: –3.3 bpm and –3.0 bpm), PR interval (–0.4 ms and 0.2 ms), and QRS interval (1 ms and 0.5 ms). The time-matched analysis showed no upper confidence interval >10 ms, with no suggestion of a QTc effect by pharmacokinetic-pharmacodynamic modeling for parent/metabolites. Moxifloxacin showed the expected placebo-corrected change from baseline (+8.4 ms time average) and the expected profile to establish assay sensitivity. No new morphologic changes of clinical relevance were observed. Treatment-related adverse events were comparable among groups.

This study showed that NEPA treatments produced no significant effects on QTcI, HR, PR interval, QRS interval, and cardiac morphology relative to placebo, even at supratherapeutic doses.

Effects of High-Dose Rocuronium on the QTc Interval During Anaesthesia Induction in Patients Undergoing Coronary Artery Bypass Graft Surgery

OBJECTIVE

Existing myocardial damage in coronary artery disease patients causes prolonged QT syndrome. The primary objective of this trial is to explore the effects of different doses of the muscle relaxant agent rocuronium (0.6 mg kg(-1) and 1.2 mg kg(-1)) on QTc following anaesthetic induction. The second objective is to determine the incidence and kinds of arrhythmias.

METHODS

In this prospective and randomized trial, patients undergoing elective coronary artery revascularization surgery were included in one of two groups. Both groups took the same anaesthetic induction agents: midazolam and fentanyl. Rocuronium was administered in Group 1 (n=20) with dose of 0.6 mg kg(-1) and in Group 2 (n=20) with a dose of 1.2 mg kg(-1) for muscle relaxation. Heart rate, average arterial pressure and QTc were recorded before induction (T0), after induction (T1), after muscle relaxant (T2), and 2 minutes (T3) and 5 minutes after intubation (T4).

RESULTS

QTc was significantly longer 2 minutes after intubation (in Group 1 and Group 2, respectively, 447.9±28.3 and 466.1±37.8 ms) than at the beginning (respectively, 426.9±25.7, 432.0±35.5 ms) (p<0.01). In the intergroup comparison, average QTc values were similar in all trial periods (p>0.05). The prevalence of arrhythmias in between Group 1 (35%, n=7) and Group 2 (15%, n=3) was similar (p=0.06). Arrhythmias were recorded 2 minutes after intubation in both groups (n=10, 25%).

CONCLUSION

In patients undergoing coronary artery revascularization surgery, rocuronium doses of 0.6 mg kg(-1) and 1.2 mg kg(-1) prolong the QTc interval after intubation. Cardiac arrhythmias related to long QTc arising after intubation should be taken into consideration.

Concentration-effect modeling based on change from baseline to assess the prolonging effect of drugs on QTc together with an estimate of the circadian time course

As ICH E14 was adopted by the US FDA and the EU CPMC in 2005, thorough QT studies have routinely been analyzed by looking at the time-matched difference between (baseline corrected) QTcF or QTcI under the supra-therapeutic dose and placebo. A study is considered negative, if the two-sided 90% confidence interval for this difference is below 10 ms for all investigated time points. ICH E14 suggests including a positive control, such as moxifloxacin, for assay sensitivity. Concentration-response analysis has been considered a more powerful alternative, but its application to parallel group studies was hampered as a double difference of QTcF per subject cannot be calculated. Recently, a new model based on change from baseline with fixed time and concentration effects has been proposed. It allows for a placebo-corrected prediction of the drug effect with an unbiased standard error, and the estimate of a time effect can be used for assay sensitivity. We demonstrate this approach, utilizing 2 studies reported elsewhere with a crossover design. We compare the results from a conventional concentration-response analysis based on the difference to placebo with results from the novel analysis based on the change from average baseline that includes a fixed time effect.

Absence of QTc Prolongation with Domperidone: A Randomized, Double-Blind, Placebo- and Positive-Controlled Thorough QT/QTc Study in Healthy Volunteers

Domperidone effects on QTc duration were assessed in a single-center, double-blind, four-way crossover study of 44 healthy participants randomized to one of four treatment sequences consisting of four treatment periods separated by 4–9 days washout. On Day 1 of each 4-day period, participants began oral domperidone 10 or 20 mg q.i.d., matching placebo q.i.d., or single-dose moxifloxacin 400 mg (positive control)/placebo q.i.d. In each period, triplicate 12-lead electrocardiograms were recorded at baseline (30, 20, and 10 minutes predose), 8 timepoints after dosing on Days 1 and 4, and predose on Day 4. In mixed effects models, the largest difference for domperidone in least squares means for change from baseline QTcP versus placebo was 3.4 milliseconds (20 mg q.i.d., Day 4), 90% CI: 1.0–5.9, and <10 milliseconds at all timepoints for both domperidone dosages. Moxifloxacin response confirmed assay sensitivity. Participants achieved expected domperidone plasma exposures. No significant exposure-response relationship was found for QTc increase per ng/mL domperidone (90% CI of the slope estimate included zero at mean C_max on Day 1 or Day 4). In summary, domperidone at doses up to 80 mg/day did not cause clinically relevant QTc interval prolongation.

Corrected QT-interval prolongation and variability in intensive care patients

PURPOSE

Critically ill patients are at risk for prolongation of the interval between the Q wave and the T wave in the electrocardiogram (corrected QT [QTc]). Corrected QT prolongation is probably a dynamic process. It is unknown how many patients have a QTc prolongation during their intensive care stay and how variable QTc prolongation is.

MATERIALS AND METHODS

In a prospective cohort study, continuous 5-minute QTc measurements of 50 consecutive patients were collected. A prolonged QTc interval was more than 500 milliseconds for at least 15 minutes. The QT variance and variability index was used to evaluate QTc variation.

RESULTS

Fifty-two percent of included patients had a prolonged QTc interval. In a single patient, 0.2% to 91.3% of the QTc intervals over time were prolonged. The use of erythromycin and amiodarone was associated with the mean QTc (P = .02 and P = .006, respectively). The Acute Physiology and Chronic Health Evaluation IV and Sequential Organ Failure Assessment scores were significantly higher in patients with a prolonged QTc interval (30.8 vs 8.6 and 7 vs 5.5, respectively). Eighty-four percent of all patients received at least 1 QTc-prolonging drug. The QT variance and QTc variance were significantly higher in patients with a prolonged QTc (P = .019 and P = .001, respectively).

CONCLUSION

Continuous QTc monitoring showed a prolonged QTc interval in 52% of intensive care patients. Severity of illness and QT and QTc variances are higher in these patients.

Cardiac autonomic dysfunction in sickle cell anaemia and its correlation with QT parameters

Background:

Abnormalities of QT parameters together with cardiac autonomic neuropathy (CAN) confer significant risks of cardiac morbidity and mortality in patients with diabetes mellitus. We questioned whether or not CAN influences occurrence of QT interval prolongation and dispersion in patients with sickle cell anaemia (SCA).

Materials and Methods:

Forty stable adult sickle cell patients with 44 healthy haemoglobin AA controls were studied. Baseline electrocardiograms were obtained and cardiovascular autonomic function tests were performed using standard protocols.

Results:

Mean corrected QT (QTc) in sickle cell patients was significantly higher (P = 0.001) than the mean of controls. Similarly, mean QT dispersion (QTcd) was higher (P = 0.001) in the former than in the latter. Mean QTc in patients with CAN was longer than patients with normal autonomic function (461 ± 26 ms versus 411 ± 23 ms), P = 0.001 (OR of 17.1, CI 3.48–83.71). Similarly, QTcd was higher (P = 0.001) in patients with CAN than those with normal cardiac autonomic function. Positive correlations were found between CAN with QTc and QTcd (r = 0.604, P = 0.001, r = 0.523, P = 0.001, respectively).

Conclusion:

CAN is a risk factor for abnormalities of QT parameters in SCA and both may be harbinger for cardiac death.

Voriconazole associated torsades de pointes in two adult patients with haematological malignancies

Voriconazole can prolong the QT interval contributing to life-threatening cardiac arrhythmia. Torsades de pointes is an uncommon but serious complication of voriconazole use which may be under-recognised. We present torsades de pointes in two patients with underlying haematological malignancy being treated for invasive fungal infection with voriconazole. Patients receiving voriconazole should be screened and monitored for evidence of QT prolongation, and if prolongation detected, consideration given to alternative treatments or more intensive cardiac monitoring.

Randomized, placebo-controlled study to assess the impact on QT/QTc interval of supratherapeutic doses of ceftazidime-avibactam or ceftaroline fosamil-avibactam

Potential effects of supratherapeutic doses of intravenous (IV) ceftazidime-avibactam and ceftaroline fosamil-avibactam on cardiac repolarization were assessed in a thorough QT/QTc study. This was a double-blind, randomized, placebo-controlled, four-period crossover Phase I study (NCT01290900) in healthy males (n = 51). Subjects received, in randomized order and separated by ≥3 days washout: single doses of IV ceftaroline fosamil 1,500 mg with avibactam 2,000 mg; IV ceftazidime 3,000 mg with avibactam 2,000 mg; oral moxifloxacin 400 mg (open-label positive control); and IV placebo (saline). Least square mean and two-sided 90% confidence intervals (CI) for change from baseline in Fridericia-corrected QT interval (ΔQTcF) for active treatments versus placebo were estimated at 10 time points over 24 hours. The upper bound of the two-sided 90% CI for placebo-corrected ΔQTcF did not exceed 10 milliseconds at any time point over 24 hours for ceftaroline fosamil-avibactam or ceftazidime-avibactam. The lower bound of the two-sided 90% CI for the difference between moxifloxacin and placebo in ΔQTcF over 1-4 hours was >5 milliseconds, confirming assay sensitivity. Pharmacokinetics results confirmed achievement of supratherapeutic plasma concentrations. No safety concerns were raised. In conclusion, supratherapeutic doses of ceftaroline fosamil-avibactam or ceftazidime-avibactam were not associated with QT/QTc prolongation in this study population.

Perioperative doses of ondansetron or dolasetron do not lengthen the QT interval

OBJECTIVE

To test the primary hypothesis that ondansetron or dolasetron extends the rate-corrected QT electrocardiographic interval (QTc) greater than 60 milliseconds or increases the fraction of patients with QTc greater than 500 milliseconds in patients having noncardiac surgery, and the secondary hypothesis that QTc prolongation is worse in diabetic patients.

PATIENTS AND METHODS

We extracted data from the Cleveland Clinic's Perioperative Health Documentation System between March 25, 2006, and September 30, 2010, and additional perioperative medications from Cleveland Clinic pharmacy's Epic Cost of Goods Sold (COGS) system. We searched for patients who had a preoperative electrocardiogram within 1 month of surgery and postoperatively within 2 hours. We excluded patients given an antiemetic drug other than ondansetron or dolasetron perioperatively, and those given amiodarone.

RESULTS

A total of 1429 patients given serotonin-3 receptor (5HT3R) antagonists and 1022 controls met the enrollment criteria. Seventeen percent of patients given 5HT3R antagonists (n=242) and 22% of controls (n=220) had postoperative QTc exceeding 500 milliseconds. Mean ± SD presurgical and postsurgical QTc, respectively, were 438±37 milliseconds and 464±41 milliseconds for 5HT3R antagonist patients and 443±40 milliseconds and 469±47 milliseconds for control patients. Univariable mean ± SD perioperative increases in QTc were 26±39 and 26±48 milliseconds in the 2 groups. After adjusting for confounding variables, there were no differences in the mean increase in QTc in patients who were and were not given 5HT3R antagonists: -0.1 milliseconds (97.5% CI, -5.2 to 5.0 milliseconds; multivariable P=.97). The QTc was prolonged, but not significantly, in diabetic patients given 5HT3R antagonists (P=.16).

CONCLUSIONS

The average QTc prolongation from baseline was only 6%. Perioperative use of ondansetron or dolasetron was not associated with extended QT prolongation, and these results did not vary by diabetic status. Perioperative use of 5HT3R antagonists does not produce potentially dangerous perioperative electrocardiographic changes and does not seem to warrant a drug safety warning from the Food and Drug Administration.

Pattern of QTc prolongation in Methadone Maintenance Therapy (MMT) subjects receiving different methadone dosages: A prospective cohort study

Objectives: This study aimed to compare the QTc interval between low and high dose methadone groups and evaluate the pattern of QTc variation.

Methods: This is a prospective cohort study conducted from December 2010 till August 2011 at Malaysian University of Science’s Hospital. Forty six subjects, grouped in high dose (>80mg) and low dose (<80mg) oral methadone, were followed-up at 4-weekly for QTc measurements. Relevant demographic and biochemical profiles were taken at intervals with concurrent QTc measurements.

Results: No significant QTc differences between methadone dosage groups were found at Week 0 (434ms vs 444ms, p = 0.166) and week 8 (446.5ms vs 459ms, p = 0.076), but not at week 4(435ms vs 450ms, p = 0.029). However, there were significant associations between the groups with QT_c prolongation at week 0 and 4 (OR 4.29(95% CI 1.01, 18.72) p=0.044 and OR 5.18 (95% CI 1.34, 20.06) p =0.013, respectively) but not at week 8 (OR 2.44 (95% CI 0.74, 8.01) p=0.139). On multivariate analysis, dose group was the sole significant factor for QT_c prolongation for week 0 and 4 (p values 0.047 and 0.017, respectively), but not at week 8.

Conclusion: High-dose methadone group is more likely to develop prolonged QTc than low-dose group. However, such effects were inconsistent and occurred even during chronic methadone therapy, mandating judicious QTc and serum methadone monitoring.

The variant hERG/R148W associated with LQTS is a mutation that reduces current density on co-expression with the WT

BACKGROUND

A variant of the ether-à-go-go related channel (hERG), p.Arg148Trp (R148W) was found at heterozygous state in two infants who died from sudden infant death syndrome (SIDS), one with documented prolonged QTc and Torsade de Pointes (TdP), and in an adult woman with QTc >500 ms, atrioventricular block and TdP. This variant was previously reported in cases of severe ventricular arrhythmia but very rarely in control subjects. Its classification as mutation or polymorphism awaited electrophysiological characterization.

METHODS

The properties of this N-terminal, proximal domain, hERG variant were explored in Xenopus oocytes injected with the same amount of RNA encoding for either hERG/WT or hERG/R148W or their equimolar mixture. The human ventricular cell (TNNP) model was used to test the effects of changes in hERG current.

RESULTS

R148W alone produced a current similar to the WT (369 ± 76 nA (mean ± SEM), n=13 versus 342 ± 55 nA in WT, n=13), while the co-expression of 1/2 WT+1/2 R148W lowered the current by 29% versus WT (243 ± 35 nA, n=13, p<0.05). The voltage dependencies of steady-state activation and inactivation were not changed in the variant alone or in co-expression with the WT. The time constants of fast recovery from inactivation and of fast and slow deactivation analyzed between -120 and +20 mV were not changed. The voltage-dependent distribution of the current amplitudes among fast-, slow- and non-deactivating fractions was unaltered. A 6.6% increase in APD90 from 323.5 ms to 345 ms was observed using the human cardiac ventricular myocyte model.

CONCLUSIONS

Such a decrease in hERG current as evidenced here when co-expressing the hERG/R148W variant with the WT may have predisposed to the observed long QT syndrome and associated TdP. Therefore, the heterozygous carriers of hERG/R148W may be at risk of cardiac sudden death.

Prescribing selective serotonin reuptake inhibitors in older age

Apart from commercial reasons, two motivations have led to the introduction of SSRIs to replace the first and second generation antidepressants already available. One was the search for a more rational treatment, based on specific mechanisms, the other the development of effective treatments with fewer side effects, particularly for older patients, who have a greater sensitivity to cardio-vascular and central nervous system effects. The first has been frustrated up to a point, in that SSRIs and other single mechanism drugs do not appear to be more effective than the earliest relatively non-specific antidepressants. The second has been fulfilled, in that SSRIs generally are better tolerated in older patients and in overdose. However, there is a spectrum of other side effects that are particularly relevant in older age and that need attention when treating depression in this particular patient group.

Evolution of clinical diagnosis in patients presenting with unexplained cardiac arrest or syncope due to polymorphic ventricular tachycardia

BACKGROUND

A systematic evaluation of patients with unexplained cardiac arrest (UCA) yields a diagnosis in 50% of the cases. However, evolution of clinical phenotype, identification of new disease-causing mutations, and description of new syndromes may revise the diagnosis.

OBJECTIVE

To assess the evolution in diagnosis among patients with initially UCA.

METHODS

Diagnoses were reviewed for all patients with UCA recruited from the Cardiac Arrest Survivors with Preserved Ejection Fraction Registry with at least 1 year of follow-up.

RESULTS

After comprehensive investigation of 68 patients (age 45.2 ± 14.9 years; 63% men), the initial diagnosis was as follows: idiopathic ventricular fibrillation (n = 34 [50%]), a primary arrhythmic disorder (n = 21 [31%]), and an occult structural cause (n = 13 [19%]). Patients were followed for 30 ± 17 months, during which time the diagnosis changed in 12 (18%) patients. A specific diagnosis emerged for 7 patients (21%) with an initial diagnosis of idiopathic ventricular fibrillation. A structural cardiomyopathy evolved in 2 patients with an initial diagnosis of primary electrical disorder, while the specific structural cardiomyopathy was revised for 1 patient. Two patients with an initial diagnosis of a primary arrhythmic disorder were subsequently considered to have a different primary arrhythmic disorder. A follow-up resting electrocardiogram was the test that most frequently changed the diagnosis (67% of the cases), followed by genetic testing (17%).

CONCLUSIONS

The reevaluation of patients presenting with UCA may lead to a change in diagnosis in up to 20%. This emphasizes the need to actively monitor the phenotype and also has implications for the treatment of these patients and the screening of their relatives.

Prolonged QTc interval predicts all-cause mortality in patients with rheumatoid arthritis: an association driven by high inflammatory burden

OBJECTIVE

RA associates with an increased rate of sudden cardiac death (SCD). A prolonged QTc interval has been associated with arrhythmogenic and SCD in patients with long QT syndrome. Despite the previously reported contemporary association of CRP with SCD, thus far no studies have examined the association of QTc with mortality in RA, a condition characterized by high inflammatory burden. The aim of this study was to examine the role of electrocardiography (QT corrected interval) in predicting all-cause mortality in patients with RA who have an increased rate of SCD and a high inflammatory burden.

METHODS

Three hundred and fifty-seven RA patients with detailed baseline clinical characterization and 12-lead ECGs were followed up for a mean of 73.0 (S.D. 18.3) months. Linear and Cox regression analyses were used to identify variables that associate with QTc and examine its association with all-cause mortality.

RESULTS

The patients' mean age was 60.6 (S.D. 12.0) years, 267 (74.8%) were females and 54 (15.1%) died during the follow-up period. Age (β = 0.231, P < 0.001), gender (β = 0.137, P = 0.008) and CRP (β = 0.144, P = 0.006) associated independently with QTc in RA patients. The crude hazard ratio (HR) for total mortality per 50-ms increase in QTc was 2.17 (95% CI 1.21, 3.90). This association remained significant [HR = 2.18 (95% CI 1.09, 4.35)] after adjustment for identified confounders (cardiovascular and RA specific), but was lost [HR = 1.73 (95% CI 0.83, 3.62)] when CRP was included in the model.

CONCLUSION

A 50-ms increase in QTc interval associates with a doubling of the hazard for all-cause mortality in patients with RA. The observed contemporary association of QTc with CRP levels indicates a potentially hazardous interplay between inflammation and arrhythmogenesis. Future studies are needed to confirm the above findings and explore underlying mechanisms.

Apamin induces early afterdepolarizations and torsades de pointes ventricular arrhythmia from failing rabbit ventricles exhibiting secondary rises in intracellular calcium

BACKGROUND

A secondary rise of intracellular Ca(2+) (Cai) and an upregulation of apamin-sensitive K(+) current (I(KAS)) are characteristic findings of failing ventricular myocytes. We hypothesize that apamin, a specific I(KAS) blocker, may induce torsades de pointes (TdP) ventricular arrhythmia from failing ventricles exhibiting secondary rises of Cai.

OBJECTIVE

To test the hypothesis that small conductance Ca(2+) activated IKAS maintains repolarization reserve and prevents ventricular arrhythmia in a rabbit model of heart failure (HF).

METHODS

We performed Langendorff perfusion and optical mapping studies in 7 hearts with pacing-induced HF and in 5 normal control rabbit hearts. Atrioventricular block was created by cryoablation to allow pacing at slow rates.

RESULTS

The left ventricular ejection fraction reduced from 69.1% [95% confidence interval 62.3%-76.0%] before pacing to 30.4% [26.8%-34.0%] (N = 7; P < .001) after pacing. The corrected QT interval in failing ventricles was 337 [313-360] ms at baseline and 410 [381-439] ms after applying 100 nmol/L of apamin (P = .01). Apamin induced early afterdepolarizations (EADs) in 6 ventricles, premature ventricular beats (PVBs) in 7 ventricles, and polymorphic ventricular tachycardia consistent with TdP in 4 ventricles. The earliest activation site of EADs and PVBs always occurred at the site with long action potential duration and large amplitude of the secondary rises of Ca(i). Apamin induced secondary rises of Ca(i) in 1 nonfailing ventricle, but no EAD or TdP were observed.

CONCLUSIONS

In HF ventricles, apamin induces EADs, PVBs, and TdP from areas with secondary rises of Ca(i). I(KAS) is important in maintaining repolarization reserve and preventing TdP in HF ventricles.