How to correct the QT interval for the effects of heart rate in clinical studies

Antipsychotics and the QTc Interval During Delirium in the Intensive Care Unit: A Secondary Analysis of a Randomized Clinical Trial

Importance

Antipsychotic medications, often prescribed for delirium in intensive care units (ICUs), may contribute to QTc interval prolongation.

Objective

To determine whether antipsychotics increase the QTc interval in patients with delirium in the ICU.

Design, Setting, and Participants

An a priori analysis of a randomized clinical trial in medical/surgical ICUs within 16 centers across the US was conducted. Participants included adults with delirium in the ICU with baseline QTc interval less than 550 ms. The study was conducted from December 2011 to August 2017. Data analysis was performed from April 25 to August 18, 2021.

Interventions

Patients were randomized 1:1:1 to intravenous haloperidol, ziprasidone, or saline placebo administered twice daily until resolution of delirium, ICU discharge, or 14 days.

Main Outcomes and Measures

Twelve-lead electrocardiograms were used to measure baseline QTc before study drug initiation and telemetry was used to measure QTc before each subsequent dose of study drug. Unadjusted day-to-day changes in QTc were calculated and multivariable proportional odds regression was used to estimate the effects of antipsychotics vs placebo on next-day maximum QTc interval, adjusting for prespecified baseline covariates and potential interactions with sex. Safety end points, including the occurrence of torsade de pointes, were evaluated. All analyses were conducted based on the intention to treat principle.

Results

A total of 566 patients were randomized to haloperidol (n = 192), ziprasidone (n = 190), or placebo (n = 184). Median age was 60.1 (IQR, 51.4-68.7) years; 323 were men (57%). Baseline median QTc intervals across the groups were similar: haloperidol, 458.0 (IQR, 432.0-479.0) ms; ziprasidone, 451.0 (IQR, 424.0-472.0) ms; and placebo, 452.0 (IQR, 432.0-472.0) ms. From day 1 to day 2, median QTc changed minimally: haloperidol, -1.0 (IQR, -28.0 to 15.0) ms; ziprasidone, 0 (IQR, -23.0 to 20.0) ms; and placebo, -3.5 (IQR, -24.8 to 17.0) ms. Compared with placebo, neither haloperidol (odds ratio [OR], 0.95; 95% CI, 0.66-1.37; P = .78) nor ziprasidone (OR, 1.09; 95% CI, 0.75-1.57; P = .78) was associated with next-day QTc intervals. Effects were not significantly modified by sex (P = .41 for interaction). There were 2 occurrences of nonfatal torsade de pointes, both in the haloperidol group. Neither was associated with study drug administration.

Conclusions and Relevance

The findings of this trial suggest that daily QTc interval monitoring during antipsychotic use may have limited value in patients in the ICU with normal baseline QTc and few risk factors for QTc prolongation.

Trial Registration

ClinicalTrials.gov Identifier: NCT01211522.

A Longer Tpeak-Tend Interval Is Associated with a Higher Risk of Death: A Meta-Analysis

A noninvasive tool for cardiovascular risk stratification has not yet been established in the clinical routine analysis. Previous studies suggest a prolonged Tpeak-Tend interval (the interval from the peak to the end of the T-wave) to be predictive of death. This meta-analysis was designed to systematically evaluate the association of the Tpeak-Tend interval with mortality outcomes. Medline (via PubMed), Embase and the Cochrane Library were searched from 1 January 2008 to 21 July 2020 for articles reporting the ascertainment of the Tpeak-Tend interval and observation of all-cause-mortality. The search yielded 1920 citations, of which 133 full-texts were retrieved and 29 observational studies involving 23,114 patients met the final criteria. All-cause deaths had longer Tpeak-Tend intervals compared to survivors by a standardized mean difference of 0.41 (95% CI 0.23-0.58) and patients with a long Tpeak-Tend interval had a higher risk of all-cause death compared to patients with a short Tpeak-Tend interval by an overall odds ratio of 2.33 (95% CI 1.57-3.45). Heart rate correction, electrocardiographic (ECG) measurement methods and the selection of ECG leads were major sources of heterogeneity. Subgroup analyses revealed that heart rate correction did not affect the association of the Tpeak-Tend interval with mortality outcomes, whereas this finding was not evident in all measurement methods. The Tpeak-Tend interval was found to be significantly associated with all-cause mortality. Further studies are warranted to confirm the prognostic value of the Tpeak-Tend interval.

Performance of Automated Telemetry in Diagnosing QT Prolongation in Critically Ill Patients

BACKGROUND

QT prolongation increases the risk of ventricular arrhythmia and is common among critically ill patients. The gold standard for QT measurement is electrocardiography. Automated measurement of corrected QT (QTc) by cardiac telemetry has been developed, but this method has not been compared with electrocardiography in critically ill patients.

OBJECTIVE

To compare the diagnostic performance of QTc values obtained with cardiac telemetry versus electrocardiography.

METHODS

This prospective observational study included patients admitted to intensive care who had an electrocardiogram ordered simultaneously with cardiac telemetry. Demographic data and QTc determined by electrocardiography and telemetry were recorded. Bland-Altman analysis was done, and correlation coefficient and receiver operating characteristic (ROC) coefficient were calculated.

RESULTS

Fifty-one data points were obtained from 43 patients (65% men). Bland-Altman analysis revealed poor agreement between telemetry and electrocardiography and evidence of fixed and proportional bias. Area under the ROC curve for QTc determined by telemetry was 0.9 (P < .001) for a definition of prolonged QT as QTc ≥ 450 milliseconds in electrocardiography (sensitivity, 88.89%; specificity, 83.33%; cutoff of 464 milliseconds used). Correlation between the 2 methods was only moderate (r = 0.6, P < .001).

CONCLUSIONS

QTc determination by telemetry has poor agreement and moderate correlation with electrocardiography. However, telemetry has an acceptable area under the curve in ROC analysis with tolerable sensitivity and specificity depending on the cutoff used to define prolonged QT. Cardiac telemetry should be used with caution in critically ill patients.

The negative effects of obesity on heart, especially the electrophysiology of the heart

Obesity is associated with ventricular arrhythmia and sudden cardiac death. Numerous studies have shown that obesity may have effects on the heart by affecting the ventricular re-polarisation (VR). As an effective detection method for VR the measurement of the QT interval has been extensively studied in obese patients (OP). This review aims to investigate the relationship between obesity and obesity-related diseases; including diabetes, hypertension and cardiovascular diseases (CVD). This review compares the advantages and disadvantages of different QT interval measurement methods, as well as explores the possible mechanisms of obesity leading to heart disease. Finally, it also reviews the feasibility of various weight loss methods to reverse the risk of obesity leading to heart disease is discussed.

Top 20 drug - drug interactions, polypharmacy and analysis of the nature of risk factors due to QT interval prolonging drug use in elderly psychiatry outpatients

INTRODUCTION AND OBJECTIVES

Psychotropic medications extend the corrected QT (QTc) period in the ECG. Psychiatric patients exposed to ≥ 1 psychotropic medication (s) represent a group with a marked probability of drug-activated QTc-prolongation. Prolonged QTc interval in elderly patients (age > 60 years) is connected to a greater risk of all-cause and coronary heart disease deaths. We investigated the pattern of utilization of QTc-interval prolonging medications, QT-extending interactions between drugs, and prevalence of QTc-interval prolonging risk factors in elderly patients.

METHODS

This was a cross-sectional, prospective study at the Psychiatry OPD at All India Institute of Medical Sciences (AIIMS), Rishikesh, Uttarakhand, India from October 1, 2017 to December 31, 2018 employing the pertinent prescriptions.

RESULTS

A total of 208 elderly patients (age 60 years or more) visiting the Psychiatry OPD during the aforementioned study period were investigated. 105 (50.5%) patients were males whereas 103 (49.5%) were females in our study. 147 out of 208 patients (70.7%) were using interacting agents with the capacity to produce TdP. 288 interacting torsadogenic medication pairs were unraveled. As per AzCERT/CredibleMeds Classification, 254 (48.8%), 181 (34.8%), and 62 (12%) interacting medications were identified with known, possible, and conditional risk of TdP, respectively. The common interacting medications belonged to antidepressant (144), proton pump inhibitor (91), antipsychotic (85), anti-nausea (46), antimicrobial (39), and H2 receptor antagonist (15) therapeutic categories.

CONCLUSIONS

Many geriatric patients were administered drugs and drug combinations with heightened proclivity towards QT-interval prolongation. Therefore, we need to exigently embrace precautionary safety interventions, to be vigilant, and forestall QT-prolongation and TdP in clinical settings. Online evidence-based drug information resources can aid clinicians in choosing drugs for psychiatric patients.

Coprescription of QT interval-prolonging antipsychotics with potentially interacting medications in Thailand

Background

The US FDA has designated pimozide, thioridazine, and ziprasidone as contraindicated for patients at risk of QT interval prolongation, and assigned haloperidol, olanzapine, paliperidone, quetiapine, and risperidone as associated with a significant risk of QT prolongation. This study aimed to examine trends and hospital variations in concomitant prescribing among these eight selected antipsychotics, and coprescription with interacting drugs known to increase QT prolongation risk.

Methods

Data on outpatient antipsychotic prescriptions during 2012-2015 were obtained from 16 general hospitals and 10 university hospitals nationwide. A time-series analysis was used for estimating trends in coprescription that led to drug interactions.

Results

Coprescribing among the eight antipsychotics ranged from 7.5% for quetiapine to 33.1% for thioridazine. The rate of coprescription with contraindicated interacting drugs was 9.7% for thioridazine and 21.9% for pimozide, and increased by 1.1 and 1.4 percentage points (% pt.) yearly for thioridazine in general and university hospitals, respectively. Coprescribing with interacting drugs with precautions was 2.8% for quetiapine, 7.4% for ziprasidone, and 27.9% for risperidone; these percentages increased yearly by 1.7% pt. for ziprasidone and 2.6% pt. for risperidone in general hospitals, as well as by 1.0% pt. for risperidone in university hospitals. The median proportion of patients exposed to a QT-prolonging interaction was 12.3% across hospitals (interquartile range, 9.9-19.5%). Wide interhospital variation was found in percentages of drug interactions among patients receiving thioridazine, ziprasidone, paliperidone, or olanzapine in general hospitals, and among patients receiving paliperidone or pimozide in university hospitals.

Conclusions

Coprescription of antipsychotics with interacting drugs that could increase the risk of QT prolongation was common in Thailand, and thioridazine, ziprasidone, and risperidone showed increasing trends. We urge the incorporation of a unified list of QT-prolonging antipsychotics and interacting drugs into a computerized drug interaction warning system, and existing national rational drug use campaigns should cover this important issue.

Frequency, characteristics and nature of risk factors associated with use of QT interval prolonging medications and related drug-drug interactions in a cohort of psychiatry patients

Quite a number of antipsychotic and antidepressant drugs are known to cause significant QT-prolongation. Psychiatric patients constitute a population at notable risk of drug-induced QT-prolongation. The aims were to explore frequency of use of QTc-interval prolonging agents and QT-prolonging drug-drug interactions, and prevalence of risk factors for QTc-interval prolongation in patients reporting to psychiatry out-patient department (OPD) in a tertiary care hospital in India. This prospective cross-sectional study was carried out in the psychiatry OPD at All India Institute of Medical Sciences (AIIMS), Rishikesh, Uttarakhand, India from October 1, 2017 to September 30, 2018 using the relevant prescriptions (i.e., the OPD case record forms and treatment sheets). For each patient, the entire medication list was analyzed for the possibility of interactions, with particular attention on the high-risk QT prolonging ones. Arizona Center for Education and Research on Therapeutics (AZCERT) QT drug lists were used to classify TdP risks of psychotropic and other medications. One thousand three hundred twenty-six (1326) patients attending the psychiatry OPD during the study period were scrutinized. Seven hundred fifty-one 751 patients (56.6%) were males whereas 575 (43.4%) were females in our study. Of the 1326 patients, 636 patients (47.9%) were identified as receiving interacting medications with the ability to induce torsades de pointe (TdP). Nine hundred seventeen (917) interacting medication pairs with torsadogenic risk were encountered. The most frequently interacting medications were from antipsychotic (794), antidepressant (519), antimicrobial (84), proton pump inhibitor (80), anticonvulsant (66), and anti-nausea (25) therapeutic categories. As per AZCERT classification (CredibleMeds TdP risk-stratification lists), 597 (36.8%), 443 (27.3%) and 432 (26.7%) of the interacting medications were associated with known, possible, and conditional risk of TdP, respectively. Concurrent prescriptions of QT-prolonging drugs is frequent in psychiatry OPD setting. Appropriate precautions should be instituted to obviate undesirable outcomes arising out of these interactions. This highlights the pressing need for clear protocols & strategies for implementation to motivate careproviders with clarity in the context of drug use guidelines for rational and safe prescribing in psychiatry.

Value of the New Spline QTc Formula in Adjusting for Pacing-Induced Changes in Heart Rate

AIMS

To determine whether a new QTc calculation based on a Spline fit model derived and validated from a large population remained stable in the same individual across a range of heart rates (HRs). Second, to determine whether this formula incorporating QRS duration can be of value in QT measurement, compared to direct measurement of the JT interval, during ventricular pacing.

METHODS

Individuals (N=30; 14 males) aged 51.9 ± 14.3 years were paced with decremental atrial followed by decremental ventricular pacing.

RESULTS

The new QTc changed minimally with shorter RR intervals, poorly fit even a linear relationship, and did not fit a second-order polynomial. In contrast, the Bazett formula (QTcBZT) showed a steep and marked increase in QTc with shorter RR intervals. For atrial pacing data, QTcBZT was fit best by a second-order polynomial and demonstrated a dramatic increase in QTc with progressively shorter RR intervals. For ventricular pacing, the new QTc minus QRS duration did not meaningfully change with HR in contrast to the HR dependency of QTcBZT and JT interval.

CONCLUSION

The new QT correction formula is minimally impacted by HR acceleration induced by atrial or ventricular pacing. The Spline QTc minus QRS duration is an excellent method to estimate QTc in ventricular paced complexes.

Evaluation of QTc Interval Prolongation in Breast Cancer Patients after Treatment with Epirubicin, Cyclophosphamide, and Docetaxel and the Influence of Interobserver Variation

BACKGROUND

Chemotherapy with anthracyclines is associated with life-threatening electrocardiographic alterations including corrected QT (QTc) interval prolongation.

PATIENTS AND METHODS

In this study we assessed the effect of epirubicin, cyclophosphamide, and docetaxel (EC-Doc) on the QTc interval in 10 patients with early breast cancer. Cardiac toxicity was assessed with symptoms, transthoracic echocardiography, electrocardiography (ECG), and serum cardiac markers at baseline and after 4 cycles of EC and 4 cycles of docetaxel. To evaluate the influence of interobserver variation, the QTc interval was analyzed by a cardiologist, a gynecologist, and with automated ECG interpretation software.

RESULTS

There was a significant QTc prolongation after EC treatment independent of the investigator. In addition, a significant increase in N-terminal prohormone of brain natriuretic peptide (NT-proBNP) levels was noted after EC treatment. QTc prolongation and NT-proBNP levels normalized after docetaxel treatment. Other biochemical markers were within normal ranges. No clinically relevant effect on left ventricular ejection fraction was observed.

CONCLUSION

This prospective study demonstrated that EC treatment increases the QTc interval and NT-proBNP levels in women with early breast cancer. This effect was reversible and independent of docetaxel administration. Moreover, the treating physician can safely perform QTc interval evaluation as part of clinical routine independent of his/her specialty. Due to the small number of patients, further conclusions are limited at this point.

Methadone Therapy in Underserved Urban Community: QTc Prolongation and Life-Threatening Ventricular Arrhythmias

AIMS

Methadone has been associated with QTc prolongation and ventricular arrhythmias but the prevalence of QTc prolongation and association with ventricular arrhythmias remains unclear. We investigated this in our inner city urban community (Bronx, New York) that has a large number of patients on methadone.

METHODS

Telemetry records, nursing documentation and electronic charts of 291 patients spanning856 encounters were evaluated. QT was manually measured from ECG utilizing standardized QT measurement guidelines and was corrected for heart rate using Hodges formula. QTc >470 ms in males and >480 ms in females was considered to be prolonged.

RESULTS

Patients had prolonged QTc, QTc >500 ms and ventricular arrhythmias during 25.6%, 14.1% and 3.4% of encounters, respectively. There was a very weak dose dependent relationship between methadone dose and QTc (Spearman's rho = 0.09).In addition to methadone, patients were on at least one QT prolonging drugs during 39% of the encounters. Patients who were receiving two interacting drugs in addition to methadone had the highest prevalence (29%) of QTc prolongation.

CONCLUSION

Although the prevalence of QTc prolongation among patients on methadone therapy is high, the prevalence of ventricular arrhythmia is relatively low. Hospitalized patients on sustained methadone therapy are frequently on multiple additional QTc prolonging drugs. There is no significant dose dependent relationship between methadone dose and QTc. However, the concurrent use of methadone and interacting drugs lead to an increased prevalence of QTc prolongation.

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.

The Half RR Rule: A Poor Rule of Thumb and Not a Risk Assessment Tool for QT Interval Prolongation

OBJECTIVES

Measuring the QT interval on an electrocardiogram (ECG) is integral to risk assessment of Torsade de Pointes (TdP). This study aimed to investigate the accuracy of the 1/2 RR rule as a risk assessment tool for drug-induced TdP, comparing it to the QT nomogram, Bazett's corrected QT (QTcB), and Fridericia's corrected QT (QTcF).

METHODS

The authors calculated sensitivity and specificity of the 1/2 RR rule using a published data set of 129 cases of drug-induced TdP and 316 controls (noncardiotoxic overdoses), compared to the QT nomogram, QTcB > 500 msec and QTcF > 500 msec. To further determine the value of the 1/2 RR rule, its observed positive, and negative agreement were calculated when compared to the QT nomogram for determining an abnormal QT in eight samples of different drugs in overdose.

RESULTS

The sensitivity and specificity of the 1/2 RR rule were 88% (95% confidence interval [CI] = 80% to 93%) and 53% (95% CI = 47% to 58%), respectively, compared to the QT nomogram (sensitivity = 97%, 95% CI = 92% to 99%; specificity = 99%, 95% CI = 97% to 100%). It was also less sensitive than QTcB > 500 msec and had a lower specificity than QTcB > 500 msec and QTcF > 500 msec. In drug overdose patients, the 1/2 RR rule had poor observed agreement averaging 41%, which was mainly due to poor positive agreement, except for amisulpride where there was good agreement.

CONCLUSIONS

The 1/2 RR rule was not as sensitive as the QT nomogram or QTcB > 500 msec for drug-induced TdP. It had poor positive agreement in almost all overdose patients, resulting in over half of patients receiving unnecessary cardiac monitoring and repeat ECGs.

Effects of energy drink consumption on corrected QT interval and heart rate variability in young obese Saudi male university students

BACKGROUND AND OBJECTIVES

Consumption of energy drinks has adverse effects on the heart that might be potentiated in obese individuals. Since the incidence of obesity and use of energy drinks is high among Saudi youth, we used non-invasive tests to study hemodynamic changes produced by altered autonomic cardiac activ.ity following consumption of energy drinks in obese male students.

DESIGN AND SETTING

This cross-sectional study was carried out at Department of Physiology, College of Medicine, University of Dammam, Saudi Arabia, over a one-year period from December 2013 to December 2014.

SUBJECTS AND METHODS

In Saudi male university students we measured continuous ECG recordings and a one-minute deep breathing maneuver to measure the expiratory-to-inspiratory ratio, the mean heart rate range (MHRR), the mean percentage variability. (M%VHR) and the corrected QT interval (QTc) at 0, 30 and 60 minutes after consumption of energy drink.

RESULTS

We enrolled 31 students (18 overweight/obese and 13 normal weights. QTc was significantly in.creased at 60 min as compared with the resting state in overweight/obese subjects (P=.006). Heart rate variability was significantly less in obese as compared with normal weight subjects at 60 minutes as indicated by E:I ratio, (P=.037), MHRR (P=.012), M%VHR (P=.040) after energy drink consumption. Significant increases in diastolic (P=.020) and mean arterial blood pressure (P=.024) were observed at 30 minutes in the obese group.

CONCLUSION

Hemodynamic changes after intake of energy drinks in obese subjects indicate that obesity and energy drinks could synergistically induce harmful effects. This finding warrants efforts to caution the obese on intake of energy drinks and timely intervention to motivate changes in lifestyle.

A double-blind, placebo-controlled study of edivoxetine as an adjunctive treatment for patients with major depressive disorder who are partial responders to selective serotonin reuptake inhibitor treatment

BACKGROUND

This phase 2 study examined the efficacy and tolerability of edivoxetine, a highly selective norepinephrine reuptake inhibitor, as an adjunctive treatment for patients with major depressive disorder (MDD) who have a partial response to selective serotonin reuptake inhibitor (SSRI) treatment.

METHODS

Study design consisted of double-blind, 10-week therapy of adjunctive edivoxetine (6-18 mg once daily) or adjunctive placebo with SSRI. Inclusion/entry criteria included partial response to current SSRI by investigator opinion and a GRID 17-item Hamilton Rating Scale for Depression (HAMD17) total score ≥16. The primary efficacy measure was the Montgomery-Asberg Depression Rating Scale (MADRS). Safety measures included treatment-emergent adverse events (TEAE) and vital signs.

RESULTS

For the primary evaluable population (n=63 for adjunctive edivoxetine and n=68 for adjunctive placebo), the treatment groups did not differ significantly on the primary outcome of change from baseline to week 8 in the MADRS total score; the effect size of edivoxetine treatment was 0.26. Significant treatment differences, favoring adjunctive edivoxetine (p≤.05), were shown for improvements in role functioning and the functional impact of fatigue. For the adjunctive edivoxetine randomized group (N=111), the most frequent TEAEs were hyperhidrosis (7.2%), nausea (7.2%), erectile dysfunction (6.3%) and testicular pain (6.3%). Hemodynamic changes were observed in blood pressure and pulse rate between treatment groups.

LIMITATIONS

Study was underpowered for an alpha 2-sided 0.05 significance level for the primary outcome.

CONCLUSIONS

For patients with MDD who had a partial response to SSRIs, adjunctive edivoxetine treatment was not statistically superior to adjunctive placebo on the primary outcome measure. However, pending further study, improved functioning and remission rate suggest a potential role for edivoxetine for patients with depression.

Determinants of torsades de pointes in older patients with drug-associated long QT syndrome: a case-control study

OBJECTIVE

Many elderly patients are routinely exposed to drugs that may prolong the cardiac QT interval and cause Torsades de pointes (TdP). However, predictors of TdP in patients with drug-associated long QT syndrome (LQTS) are not fully understood, especially in the geriatric population. The objective of this study was to identify risk factors of TdP in elderly patients with drug-associated LQTS.

METHODS

In this retrospective, case-control study, documented reports of drug-associated LQTS plus TdP (n = 125) and LQTS without TdP (n = 81) in patients ≥65 years of age were retrieved from the French Pharmacovigilance Database over a 10-year period. Available clinical, biological, and drug therapy data were compared in the two groups and logistic regression was performed to identify significant predictors of TdP.

RESULTS

The uncorrected QT interval was significantly longer in patients with TdP than in patients without TdP (577 ± 79 vs. 519 ± 68 ms; p = 0.0001). The number of drugs with a known risk of TdP administered to each patient was not a predictor of arrhythmia, nor was female gender. Logistic regression analysis identified the uncorrected QT interval as the only significant predictor of TdP. The receiver operating characteristic curve analysis was characterized by an area under the curve of 0.77 (95 % confidence interval 0.64-0.88) and a QT cutoff of 550 ms.

CONCLUSION

The uncorrected QT interval was significantly associated with the probability of TdP in elderly patients with acquired, drug-associated LQTS.

High dose droperidol and QT prolongation: analysis of continuous 12-lead recordings

AIMS

To investigate the QT interval after high dose droperidol using continuous 12-lead Holter recordings.

METHODS

This was a prospective study of patients given droperidol with a continuous Holter recording. Patients were recruited from the DORM II study which included patients with aggression presenting to the emergency department. Patients initially received 10 mg droperidol as part of a standardized sedation protocol. An additional 10 mg dose was given after 15 min if required and further doses at the clinical toxicologist's discretion. Continuous 12-lead Holter recordings were obtained for 2-24 h utilizing high resolution digital recordings with automated QT interval measurement. Electrocardiograms were extracted hourly from Holter recordings. The QT interval was plotted against heart rate (HR) on the QT nomogram to determine if it was abnormal. QTc F (Fridericia's HR correction) was calculated and >500 ms was defined as abnormal.

RESULTS

Forty-six patients had Holter recordings after 10-40 mg droperidol and 316 QT-HR pairs were included. There were 32 abnormal QT measurements in four patients, three given 10 mg and one 20 mg. In three of the four patients QTc F >500 ms but only in one taking methadone was the timing of QTc F >500 ms consistent with droperidol dosing. Of the three other patients, one took amphetamines, one still had QT prolongation 24 h after droperidol and one took a lamotrigine overdose. No patient given >30 mg had a prolonged QT. There were no arrhythmias.

CONCLUSION

QT prolongation was observed with high dose droperidol. However, there was little evidence supporting droperidol being the cause and QT prolongation was more likely due to pre-existing conditions or other drugs.

Risk assessment of drug-induced QT prolongation

Drugs can cause prolongation of the QT interval, alone or in combination, potentially leading to fatal arrhythmias such as torsades de pointes. When prescribing drugs that prolong the QT interval, the balance of benefit versus harm should always be considered. Readouts from automated ECG machines are unreliable. The QT interval should be measured manually. Changes in heart rate influence the absolute QT interval. Heart rate correction formulae are inaccurate, particularly for fast and slow heart rates. The QT nomogram, a plot of QT interval versus heart rate, can be used as a risk assessment tool to detect an abnormal QT interval.

Heart-rate-corrected QT interval evolution in premature infants during the first week of life

Automated monitoring of the QT interval is increasingly common in a variety of clinical settings. A better understanding of how the heart-rate-corrected QT interval (QTc) evolves in early postnatal life is needed before its clinical utility in neonates can be determined. This study aimed to use real-time bedside monitoring as a tool to describe the QTc evolution of premature neonates during the first week of life. All neonates born at a gestation age (GA) of 31 weeks or later and admitted to the level 2 intensive care nursery of the authors' institution between December 2012 and March 2013 were included in this study. The authors prospectively collected QTc values at 15-min intervals during the first week of life, then used two-way analysis of variance (ANOVA) to compare these data among three GA cohorts: 31 to <34 weeks (cohort A), 34 to <37 weeks (cohort B), and ≥37 weeks (cohort C). All the cohorts demonstrated a statistically significant decline in the 24-h average QTc during the first 3-4 days of life before reaching a stable baseline. No diurnal variation in the QTc was identified in any of the study patients. Marked variability and a progressive decline in the QTc of premature neonates occur during the first 3-4 days of life. Understanding this phenomenon is imperative when screening programs for the early detection of QT prolongation are considered.

Prevalence, management, and clinical consequences of QT interval prolongation during treatment with arsenic trioxide

PURPOSE

Arsenic trioxide (ATO) is a highly effective agent for the treatment of acute promyelocytic leukemia (APL). QT interval prolongation is common with ATO and can pose a barrier to effective administration. The objective of this study was to characterize the prevalence, management, and clinical consequences of QT prolongation in a large cohort of patients treated with ATO.

PATIENTS AND METHODS

We analyzed 3,011 electrocardiograms from 113 patients with non-APL acute myeloid leukemia and myelodysplastic syndrome who were treated on a previously reported clinical trial. QT intervals were assessed using four different correction formulas, and data were correlated with clinical parameters and treatment with ATO.

RESULTS

There were no clinically significant cardiac events in the study population. Of those receiving ATO therapy, 29 patients (26%) had rate-uncorrected QT values above 470 ms and 13 (12%) had values exceeding 500 ms. With the commonly used Bazett rate correction formula, 102 patients (90%) had QTc greater than 470 ms, including 74 (65%) above 500 ms. By using alternative rate correction formulas, only 24% to 32% of patients had rate-corrected QT intervals above 500 ms.

CONCLUSION

QT interval prolongation is common with ATO treatment, but clinically significant arrhythmias are rare and can be avoided with appropriate precautions. Use of the Bazett correction may result in unnecessary interruptions in ATO therapy, and alternative rate correction formulas should be considered for routine electrocardiographic monitoring.

QTc interval prolongation and torsade de pointes associated with second-generation antipsychotics and antidepressants: a comprehensive review

We comprehensively reviewed published literature to determine whether it supported the link between corrected QT (QTc) interval prolongation and torsade de pointes (TdP) for the 11 second-generation antipsychotics and seven second-generation antidepressants commonly implicated in these complications. Using PubMed and EMBASE, we identified four thorough QT studies (one each for iloperidone, ziprasidone, citalopram, and escitalopram), 40 studies specifically designed to assess QTc interval prolongation or TdP, 58 publications based on data from efficacy and safety trials, 18 toxicology studies, and 102 case reports. Thorough QT studies, QTc prolongation-specific studies, and studies based on efficacy and safety trials did not link drug-associated QTc interval prolongation with TdP. They only showed that the drugs reviewed caused varying degrees of QTc interval prolongation, and even that information was not clear and consistent enough to stratify individual drugs for this risk. The few toxicology studies provided valuable information but their findings are pertinent only to situations of drug overdose. Case reports were most informative about the drug-QTc interval prolongation-TdP link. At least one additional well established risk factor for QTc prolongation was present in 92.2 % of case reports. Of the 28 cases of TdP, six (21.4 %) experienced it with QTc interval <500 ms; 75 % of TdP cases occurred at therapeutic doses. There is little evidence that drug-associated QTc interval prolongation by itself is sufficient to predict TdP. Future research needs to improve its precision and broaden its scope to better understand the factors that facilitate or attenuate progression of drug-associated QTc interval prolongation to TdP.

Frequency of use of QT-interval prolonging drugs in psychiatry in Belgium

INTRODUCTION

Drug-induced QT-prolongation is an established risk factor for Torsade de pointes and sudden cardiac death. The list of QT-prolonging drugs is extensive and includes many drugs commonly used in psychiatry.

AIM

In this study we performed a cross-sectional analysis of medication profiles to assess the prevalence of drug interactions potentially leading to QT-prolongation.

SETTING

6 psychiatric hospitals in Flanders, Belgium.

METHODS

For each patient, the full medication list was screened for the presence of interactions, with special attention to those with an increased risk for QT-prolongation. Current practice on QT monitoring and prevention of drug-induced arrhythmia was assessed.

MAIN OUTCOME MEASURE

Number of drug interactions with risk of QT-prolongation.

RESULTS

592 patients (46 % female; mean age 55.7 ± 17.1 years) were included in the analysis. 113 QT-prolonging interactions were identified in 43 patients (7.3 %). QT-prolonging interactions occurred most frequently with antidepressants (n = 102) and antipsychotics (n = 100). The precautions and follow-up provided by the different institutions when combining QT-prolonging drugs were very diverse.

CONCLUSION

Drug combinations that are associated with QT-prolongation are frequently used in the chronic psychiatric setting. Persistent efforts should be undertaken to provide caregivers with clear guidelines on how to use these drugs in a responsible and safe way.

QT interval in healthy dogs: which method of correcting the QT interval in dogs is appropriate for use in small animal clinics?

The electrocardiography (ECG) QT interval is influenced by fluctuations in heart rate (HR) what may lead to misinterpretation of its length. Considering that alterations in QT interval length reflect abnormalities of the ventricular repolarisation which predispose to occurrence of arrhythmias, this variable must be properly evaluated. The aim of this work is to determine which method of correcting the QT interval is the most appropriate for dogs regarding different ranges of normal HR (different breeds). Healthy adult dogs (n=130; German Shepherd, Boxer, Pit Bull Terrier, and Poodle) were submitted to ECG examination and QT intervals were determined in triplicates from the bipolar limb II lead and corrected for the effects of HR through the application of three published formulae involving quadratic, cubic or linear regression. The mean corrected QT values (QTc) obtained using the diverse formulae were significantly different (ρ<0.05), while those derived according to the equation QTcV = QT + 0.087(1- RR) were the most consistent (linear regression). QTcV values were strongly correlated (r=0.83) with the QT interval and showed a coefficient of variation of 8.37% and a 95% confidence interval of 0.22-0.23 s. Owing to its simplicity and reliability, the QTcV was considered the most appropriate to be used for the correction of QT interval in dogs.

Influence of high ovarian hormones on QT interval duration in young African women

The longer QT interval duration observed in women compared to men is usually attributed to sexual hormones. The aim of our study was to investigate, among black African women, the influence of hormonal variations during the menstrual cycle on the duration of the QT interval. Fourteen young black African women, healthy, sedentary, aged 24 ± 1.7 years, with a regular menstrual cycle (28 ± 1 days) were selected from 59 volunteers. At each phase of their menstrual cycle, menstrual 2.9 ± 0.6 days, follicular 13 ± 1.5 days, and luteal 23.1 ± 1.4 days, an electrocardiogram was performed in supine position after a resting period of 30 min, to measure QT interval duration. QT interval was corrected by Bazett's (QTc_b) and Fridericia's (QTc_f) formulae. Then, blood samples were obtained to measure estradiol, progesterone, and serum electrolytes (K⁺, Ca²⁺, Mg²⁺). There was no significant difference in uncorrected QT intervals between the three phases of the menstrual cycle. It was the same for QTc_b and QTc_f. Moreover, during the menstrual cycle, we did not observe any correlation between each QT, QTc_b, QTc_f, and estradiol levels which raised during the follicular phase (356.61 ± 160.77 pg/mL) and progesterone levels which raised during the luteal phase (16.38 ± 5.88 ng/mL). Finally, the method of Bland and Altman demonstrated that the corrections of QT by Bazett and Fridericia formulae were not interchangeable. The results of this study showed that high levels of estradiol and progesterone in young black African women did not influence the QT, QTc_b and QTc_f intervals duration during the menstrual cycle.

Drug induced QT prolongation: the measurement and assessment of the QT interval in clinical practice

There has been an increasing focus on drug induced QT prolongation including research on drug development and QT prolongation, following the removal of drugs due to torsades de pointes (TdP). Although this has improved our understanding of drug-induced QT prolongation there has been much less research aimed at helping clinicians assess risk in individual patients with drug induced QT prolongation. This review will focus on assessment of drug-induced QT prolongation in clinical practice using a simple risk assessment approach. Accurate measurement of the QT interval is best done manually, and not using the measurement of standard ECG machines. Correction for heart rate (HR) using correction formulae such as Bazett's is often inaccurate. These formulae underestimate and overestimate the duration of cardiac repolarization at low and high heart rates, respectively. Numerous cut-offs have been suggested as an indicator of an abnormal QT, but are problematic in clinical practice. An alternative approach is the QT nomogram which is a plot of QT vs. HR. The nomogram has an 'at risk' line and QT-HR pairs above this line have been shown in a systematic study to be associated with TdP and the line is more sensitive and specific than Bazett's QTc of 440 ms or 500 ms. Plotting the QT-HR pair for patients on drugs suspected or known to cause QT prolongation allows assessment of the QT interval based on normal population QT variability. This risk assessment then allows the safer commencement of drugs therapeutically or management of drug induced effects in overdose.

QTc Prolongation after Ventricular Septal Defect Repair in Infants

Background and Objectives

Prolonging of the corrected QT interval (QTc) has been reported after cardiac surgery in some studies. However, there have not been many studies on infant open cardiac surgery for ventricular septal defect (VSD) repair. This study was performed to define the changes in QTc and to find related post-surgery factors in this patient group.

Subjects and Methods

From 2008 to 2012, 154 infants underwent VSD repair at the Severance Cardiovascular Hospital. This study includes 105 of these cases. QTc was measured in these patients retrospectively. Demographic data and peri-procedural data, such as Aristotle score, cross-clamp time and bypass time, were analyzed. The exclusion criteria included multiple and small VSDs that underwent direct closure.

Results

Mean post-operative QTc was increased compared to the pre-operative measurements (from 413.6±2.3 to 444.9±2.5, p<0.001). In multiple linear regression, the comprehensive Aristotle score was associated with increasing QTc (p=0.047). The incidence of transient arrhythmia, such as atrial tachycardia, junctional ectopic tachycardia, premature atrial contraction, or premature ventricular contraction, was associated with QTc prolongation (p=0.005). Prolonged QTc was also associated with cross-clamp time (p=0.008) and low weight (p=0.042). Total length of stay at the intensive care unit and intubation time after surgery were not associated with QTc prolongation.

Conclusion

Prolonged QTc could be seen after VSD repair in infants. This phenomenon was associated with peri-procedural factors such as the Aristotle score and cross-clamp time. Patients with QTc prolongation after cardiac surgery had an increased tendency towards arrhythmogenicity in the post-operative period.

Corrected QT interval in white young healthy women: should the norms be updated?

The electrocardiographic QT interval duration is a frequently studied ECG parameter. The aim of this study was to compare the quantitative influence of nine QTc formulae and discuss the duration of QT/QTc normal values. The QTc duration was calculated from manually measured QT intervals and heart rate of the Frank XYZ electrocardiograms in 138 white young healthy Slovak women (18-24 years, 690 primary ECG measurements). Dispersion of the QT/QTc interval values was not Gaussian (Shapiro-Wilk test) in most cases. The course of the measured QT regression lines were -1.9186 HR + 511.13 ms or 0.1504RR + 245.72 ms. Median QTc duration in ms was decreasing in this sequence: Bazett 407.04, Fridericia 394.61, Hodges 393.27, Rautaharju and Arrowood 368.79, Framingham-Sagie 368.78, Lecocq 368.70, Sarma 368.66, and Malik 338.70. No QTc value above 440 ms was found after Hodges' correction only. The differences of median QTc values were significant (P < 0.01) in most possible combinations (Kruskal-Wallis test). We recommend using the QTc formula created from observed persons only and updating the QT interval norms. So-called "ideal" QTc models from other not examined persons are methodically incorrect and may produce the misleading results. The frequently used Bazett formula is appropriate for orientation only.

Assessment of intraventricular time differences in healthy children using two-dimensional speckle-tracking echocardiography

BACKGROUND

Parameters describing intraventricular time differences are increasingly assessed in both adults and children. However, to appreciate the implications of these parameters in children, knowledge of the applicability of adult techniques in children is essential. Hence, the aim of this study was to assess the applicability of speckle-tracking strain-derived parameters in children, paying special attention to age and heart rate dependency.

METHODS

One hundred eighty-three healthy subjects (aged 0-19 years) were included. Left ventricular global peak strain, time to global peak strain, and parameters describing intraventricular time differences were assessed using speckle-tracking strain imaging in the apical two-chamber, three-chamber, and four-chamber views (longitudinal strain) and the parasternal short-axis view (radial and circumferential strain). Parameters describing intraventricular time differences included the standard deviation of time to peak strain and differences in time to peak strain between two specified segments. Age and heart rate dependency were evaluated using regression analysis, and intraobserver and interobserver variability were tested.

RESULTS

Acquisition and analysis of longitudinal six-segment time-strain curves was successful in 94.8% of subjects and radial and circumferential time-strain curves in 89.5%. No clinically significant linear relation was observed between age or heart rate and parameters describing intraventricular time differences. The coefficient of variation of time to global peak strain parameters was <10, while it was >10 for parameters describing intraventricular time differences.

CONCLUSIONS

The feasibility of speckle-tracking strain analysis in children is relatively good. Furthermore, no linear relation was observed between age or heart rate and parameters describing intraventricular time differences. However, the limited reproducibility of some parameters describing intraventricular time differences will confine their applicability in clinical practice.

High-dose desvenlafaxine in outpatients with major depressive disorder

OBJECTIVE

This study investigated the safety and efficacy of long-term treatment with high-dose desvenlafaxine (administered as desvenlafaxine succinate) in major depressive disorder (MDD).

METHODS

In this multicenter, open-label study, adult outpatients with MDD aged 18-75 were treated with flexible doses of desvenlafaxine (200-400 mg/d) for ≤ 1 year. Safety assessments included monitoring of treatment-emergent adverse events (TEAEs), patient discontinuations due to adverse events, electrocardiograms, vital signs, and laboratory determinations. The primary efficacy measure was mean change from baseline in the 17-item Hamilton Rating Scale for Depression [HAM-D(17)] total score.

RESULTS

The mean daily desvenlafaxine dose range over the duration of the trial was 267-356 mg (after titration). The most frequent TEAEs in the safety population (n = 104) were nausea (52%) and headache (41%), dizziness (31%), insomnia (29%), and dry mouth (27%). All TEAEs were mild or moderate in severity. Thirty-four (33%) patients discontinued from the study because of TEAEs; nausea (12%) and dizziness (9%) were the most frequently cited reasons. The mean change in HAM-D(17) total score for the intent-to-treat population (n = 99) was -9.9 at the last on-therapy visit in the last-observation-carried-forward analysis and -14.0 at month 12 in the observed cases analysis. Conclusion High-dose desvenlafaxine (200-400 mg/d) was generally safe and effective in the long-term treatment of MDD.

hERG K+ Channels: Structure, Function, and Clinical Significance

The human ether-a-go-go related gene (hERG) encodes the pore-forming subunit of the rapid component of the delayed rectifier K+ channel, Kv11.1, which are expressed in the heart, various brain regions, smooth muscle cells, endocrine cells, and a wide range of tumor cell lines. However, it is the role that Kv11.1 channels play in the heart that has been best characterized, for two main reasons. First, it is the gene product involved in chromosome 7-associated long QT syndrome (LQTS), an inherited disorder associated with a markedly increased risk of ventricular arrhythmias and sudden cardiac death. Second, blockade of Kv11.1, by a wide range of prescription medications, causes drug-induced QT prolongation with an increase in risk of sudden cardiac arrest. In the first part of this review, the properties of Kv11.1 channels, including biogenesis, trafficking, gating, and pharmacology are discussed, while the second part focuses on the pathophysiology of Kv11.1 channels.

Ventricular repolarisation during exercise challenge occurring late after Kawasaki disease

Exercise testing can highlight repolarisation abnormalities in adults with coronary artery disease. Late after Kawasaki disease (KD), increased QT dispersion (QTd) has been reported on resting ECG in children, but there are no reported studies of QTd during exercise. Our objective was to determine the pattern of QTd response to exercise testing in children late after KD. Twenty-five KD patients without coronary complications, 28 with coronary dilation, and 18 with severe complications were compared with 28 controls. KD patients were 11.6 ± 3.0 years old versus 12.8 ± 2.9 for controls [p = not significant (NS)], and these patients were studied 7.5 ± 3.4 years after the onset of the disease. QT was measured from the onset of QRS to the apex (QTa) and the end (QTe) of T wave. Resting QTd was significantly increased in KD subjects (p < 0.05). The proportion of abnormal QTd was evenly distributed across the three KD groups (29-36%; p = NS). QTd response to exercise was significantly altered in KD, irrespective of resting QTd or coronary sequelae. Abnormal resting- and exercise-induced repolarisation are detectible after KD irrespective of the severity of coronary sequelae.

Cardiac changes in horses with atypical myopathy

BACKGROUND

Atypical myopathy (AM) is an acute, fatal rhabdomyolysis in grazing horses that mainly affects skeletal muscles. Postmortem examinations have shown that myocardial damage also occurs. Limited information is available on the effect of AM on cardiac function in affected and surviving horses.

OBJECTIVES

To describe electrocardiographic and echocardiographic changes associated with AM in the acute stage of the disease and after follow-up.

ANIMALS

Horses (n = 12) diagnosed with AM in which cardiac ultrasound examination and ECG recording were available.

METHODS

All horses underwent clinical examinations, serum biochemistry, electrocardiography, and echocardiography. Four surviving horses underwent the same examinations after 2-10 weeks.

RESULTS

All but 1 horse had increased cardiac troponin I concentrations and 10 horses had ventricular premature depolarizations (VPDs). All horses had prolonged corrected QT (QT(cf) ) intervals on the day of admission and abnormal myocardial wall motion on echocardiography. One of the surviving horses still had VPDs and prolonged QT(cf) at follow-up after 10 weeks.

CONCLUSIONS AND CLINICAL IMPORTANCE

The AM results in characteristic electrocardiographic and echocardiographic changes and may be associated with increased cardiac troponin I concentrations and VPDs. In survivors, abnormal cardiac function still may be found at follow-up after 10 weeks. Additional research in a larger group of horses is necessary to identify the long-term effects of AM on cardiac function.

Relationship of heart rate and electrocardiographic time intervals to body mass in horses and ponies

OBJECTIVES

To investigate the relationship of heart rate (HR) and ECG time intervals to body weight (BWT) in healthy horses and ponies. We hypothesized that HR and ECG time intervals are related to BWT.

ANIMALS

250 healthy horses of >30 breeds; 5.5 (1-30) y [median (range)]; 479 (46-1018) kg.

METHODS

Prospective study. Standard base-apex ECGs were recorded while the horses were standing quietly in a box stall. Mean HR over 15 s was calculated and RR interval, PQ interval, QRS duration, and QT interval were measured by a single observer.QT was corrected for differences in heart rate using Fridericia's formula (QT(cf) = QT/(3)√RR). The relationship between ECG variables and BWT, age, sex, and RR interval was assessed using multivariate backward stepwise regression analyses. Goodness of fit of the model was improved when using log(BWT) compared to BWT. Body weight was overall the strongest predictor of HR and ECG time intervals. Therefore, only log(BWT) was included as an independent variable in the final model. The level of significance was p = 0.05.

RESULTS

HR (R(2) = 0.21) showed a significant negative relationship and PQ (R(2) = 0.53), QRS (R(2) = 0.23), QT (R(2) = 0.14), and QT(cf) (R(2) = 0.02) showed significant positive relationships to log(BWT).

CONCLUSIONS

Small equine breeds undergoing routine ECG recordings have slightly faster heart rates and shorter ECG time intervals compared to larger equine breeds. Although the magnitude of absolute differences may be small, body weight needs to be considered among other factors when comparing HR and ECG time intervals to normal ranges in horses.

Thorough QT study of the effects of vildagliptin, a dipeptidyl peptidase IV inhibitor, on cardiac repolarization and conduction in healthy volunteers

OBJECTIVE

This randomized, double-blind study evaluated the effects of vildagliptin, a dipeptidyl peptidase IV inhibitor for treating type 2 diabetes, on cardiac repolarization and conduction.

METHODS

Healthy volunteers (n = 101) were randomized (1:1:1:1 ratio) to vildagliptin 100 or 400 mg, moxifloxacin 400 mg (active control), or placebo once daily for 5 days. Electrocardiograms were recorded at baseline and day 5 for 24 hours post-dose. Placebo-adjusted mean change from baseline in QT interval, heart-rate-corrected QT intervals by Fridericia's (QTcF) or Bazett's (QTcB) formula, and PR and QRS intervals were compared at each time-point (time-matched analysis) and for values averaged across the dosing period (time-averaged analysis).

RESULTS

For time-matched analysis, mean changes in QTcF with vildagliptin were below predefined limits for QTc prolongation (mean increase <5 ms; upper 90% confidence interval [CI] < 10 ms), except for vildagliptin 100 mg at 1 and 8 hours post-dose (upper 90% CI > 10 ms). With moxifloxacin, significant QTcF prolongation occurred at most time-points, demonstrating assay sensitivity. No vildagliptin- or placebo-treated volunteer had QTcF > 450 ms. Incidences of QTcF increases ≥30 ms with vildagliptin (100 and 400 mg) and placebo were similar (4-8%) and were much lower than with moxifloxacin (39%). No QTcF increase ≥60 ms was observed with vildagliptin or placebo (versus one with moxifloxacin). Time-averaged, time-matched, and categorical analyses of QT/QTcF/QTcB showed similar results. Drug exposure analysis showed no correlation between vildagliptin plasma levels and QTc changes. Vildagliptin had no effect on PR or QRS intervals. Although this study, completed before publication of current ICH E14 guidelines, was underpowered for time-matched analysis, the results are consistent with lack of effect of vildagliptin on QTc.

CONCLUSION

Vildagliptin did not prolong QT interval or affect cardiac conduction at the highest daily therapeutic dose or a fourfold higher dose.

A novel method for patient-specific QTc--modeling QT-RR hysteresis

BACKGROUND

Cardiac repolarization adaptation to cycle length change is patient dependent and results in complex QT-RR hysteresis. We hypothesize that accurate patient-specific QT-RR curves and rate corrected QT values (QTc) can be derived through patient-specific modeling of hysteresis.

METHOD AND RESULTS

Model development was supported by QT-RR observations from 1959 treadmill tests, allowing extensive exploration of the influences of autonomic function on QT adaptation to rate changes. The methodology quantifies and then removes patient-specific repolarization adaptation rates. The estimated average 95% QT confidence limit was approximately 1 msec for the studied population. The model was validated by comparing QT-RR curves derived from a submaximal exercise protocol with rapid exercise and recovery phases, characterized by high hysteresis, with QT-RR values derived from an incremental stepped protocol that held heart rate constant for 5 minutes at each stage of exercise and recovery.

CONCLUSIONS

The underlying physiologic changes affecting QT dynamics during the transitions from rest to exercise to recovery are quite complex. Nevertheless, a simple patient-specific model, comprising only three parameters and based solely on the preceding history of RR intervals and trend, is sufficient to accurately model QT hysteresis over an entire exercise test for a diverse population. A brief recording of a resting ECG, combined with a short period of submaximal exercise and recovery, provides sufficient information to derive an accurate patient-specific QT-RR curve, eliminating QTc bias inherent in population-based correction formulas.

Cardiovascular safety of stimulant medications for pediatric attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a common neurobehavioral disorder that is often treated with stimulants such as methylphenidate and mixed amphetamine salts. Despite their efficacy and long history of use, there is concern about their potential for adverse cardiovascular effects in children and adolescents. Data from placebo-controlled and open-label extension trials published after 2000 were reviewed, and cardiovascular adverse event data were compared. Both placebo-controlled and open-label extension trials have repeatedly shown stimulant-induced increases in mean blood pressure, heart rate, and QT interval in children, adolescents, and adults. Although these increases seem relatively minor, their existence raises questions regarding whether stimulants could influence the likelihood of sudden death or other serious cardiovascular consequences, especially in patients with underlying heart problems. Moreover, questions have been raised regarding the necessity of screening patients for occult or unrecognized heart problems that are felt to be adversely affected by stimulant use. Obtaining a baseline electrocardiogram for any patient starting stimulant treatment is reasonable if access to such screening is readily available and not too costly.

Too long or too short? New insights into abnormal cardiac repolarization in people with chronic epilepsy and its potential role in sudden unexpected death

SUMMARY

Sudden unexpected death in epilepsy (SUDEP) is probably caused by periictal cardiorespiratory alterations such as central apnea, bradyarrhythmia, and neurogenic pulmonary edema. These alterations may occur in people with epilepsy and vary in duration and severity. Seizure-related ventricular tachyarrhythmias have also been hypothesized to be involved in SUDEP, but compelling evidence of these, or of predisposition to these, is lacking. Ventricular tachyarrhythmias are facilitated by pathologic cardiac repolarization. Electrocardiography (ECG) indicators of pathologic cardiac repolarization, such as prolongation or shortening of QT intervals as well as increased QT dispersion, are established risk factors for life-threatening tachyarrhythmia and sudden cardiac death (SDC). Abnormalities in cardiac repolarization have recently been described in people with epilepsy. Importantly, periictal ventricular tachycardia and fibrillation have also been reported in the absence of any underlying cardiac disease. Therefore, pathologic cardiac repolarization could promote SCD in people with epilepsy and could be one plausible cause for SUDEP. Herein, we review abnormal cardiac repolarization in people with epilepsy, describe the putative contribution of antiepileptic drugs, and discuss the potential role of pathologic cardiac repolarization in SUDEP. Based on these, measures to reduce the risk of or prevent SUDEP may include antiarrhythmic medication and implantation of cardiac combined pacemaker-defibrillator devices.

Clinical trial: alvimopan for the management of post-operative ileus after abdominal surgery: results of an international randomized, double-blind, multicentre, placebo-controlled clinical study

BACKGROUND

Post-operative ileus (POI) affects most patients undergoing abdominal surgery.

AIM

To evaluate the effect of alvimopan, a peripherally acting mu-opioid receptor antagonist, on POI by negating the impact of opioids on gastrointestinal (GI) motility without affecting analgesia in patients outside North America.

METHODS

Adult subjects undergoing open abdominal surgery (n = 911) randomly received oral alvimopan 6 or 12 mg, or placebo, 2 h before, and twice daily following surgery. Opioids were administered as intravenous patient-controlled analgesia (PCA) or bolus injection. Time to recovery of GI function was assessed principally using composite endpoints in subjects undergoing bowel resection (n = 738).

RESULTS

A nonsignificant reduction in mean time to tolerate solid food and either first flatus or bowel movement (primary endpoint) was observed for both alvimopan 6 and 12 mg; 8.5 h (95% CI: 0.9, 16.0) and 4.8 h (95% CI: -3.2, 12.8), respectively. However, an exploratory post hoc analysis showed that alvimopan was more effective in the PCA (n = 317) group than in the non-PCA (n = 318) group. Alvimopan was well tolerated and did not reverse analgesia.

CONCLUSION

Although the significant clinical effect of alvimopan on reducing POI observed in previous trials was not reproduced, this trial suggests potential benefit in bowel resection patients who received PCA.

ILSI–HESI cardiovascular safety subcommittee dataset: An analysis of the statistical properties of QT interval and rate-corrected QT interval (QTc)

INTRODUCTION

The Health and Environmental Sciences Institute of the International Life Sciences Institute (ILSI/HESI) Cardiovascular Safety Subcommittee outlined a set of in vivo telemetry studies to determine how well this preclinical model identified compounds known to cause torsades de pointes (TdP) and prolong QT interval in humans. In the original analysis of these data, QT, QTcB (Bazett model), QTcF (Fridericia model), and QTcQ (animal-specific model) were evaluated. We further evaluate the statistical properties of these measurements, using a method that can properly account for the sources of variability in the dataset.

METHODS

The ILSI/HESI telemetry studies were conducted as a double Latin square design where eight dogs each received a vehicle control and three dose levels of a compound on four separate dosing days. We statistically analyzed the QT/QTc intervals using a repeated measures analysis of covariance and evaluate the powers for QT, QTcF and QTcQ based on simulations.

RESULTS

The analyses for QTcF and QTcB intervals show that all six compounds which were known to cause TdP in humans were identified as positive and all six compounds known to be free of TdP events in their clinical use had no statistically significant treatment-related effects, while the analyses for QTcQ identified all positive compounds except pimozide. The power analysis shows that the method can detect a 7% increment of QT, a 5% increment of QTcF, and a 4% increment of QTcQ, with greater than 80% of power when n=8.

DISCUSSION

We describe a repeated measures procedure to perform statistical analysis of covariance on Latin square designs and show that it can be used to detect meaningful changes in the analysis of QT/QTc intervals.