Drug-induced QT dispersion: does it predict the risk of torsade de pointes?

Effect of reperfusion strategy on QT dispersion in patients with acute myocardial infarction: Impact on in-hospital arrhythmia

BACKGROUND

Myocardial ischemia and ST-elevation myocardial infarction (STEMI) increase QT dispersion (QTD) and corrected QT dispersion (QTcD), and are also associated with ventricular arrhythmia.

AIM

To evaluate the effects of reperfusion strategy [primary percutaneous coronary intervention (PPCI) or fibrinolytic therapy] on QTD and QTcD in STEMI patients and assess the impact of the chosen strategy on the occurrence of in-hospital arrhythmia.

METHODS

This prospective, observational, multicenter study included 240 patients admitted with STEMI who were treated with either PPCI (group I) or fibrinolytic therapy (group II). QTD and QTcD were measured on admission and 24 hr after reperfusion, and patients were observed to detect in-hospital arrhythmia.

RESULTS

There were significant reductions in QTD and QTcD from admission to 24 hr in both group I and group II patients. QTD and QTcD were found to be shorter in group I patients at 24 hr than those in group II (53 ± 19 msec vs 60 ± 18 msec, P = 0.005 and 60 ± 21 msec vs 69+22 msec, P = 0.003, respectively). The occurrence of in-hospital arrhythmia was significantly more frequent in group II than in group I (25 patients, 20.8% vs 8 patients, 6.7%, P = 0.001). Furthermore, QTD and QTcD were higher in patients with in-hospital arrhythmia than those without (P = 0.001 and P = 0.02, respectively).

CONCLUSION

In STEMI patients, PPCI and fibrinolytic therapy effectively reduced QTD and QTcD, with a higher observed reduction using PPCI. PPCI was associated with a lower incidence of in-hospital arrhythmia than fibrinolytic therapy. In addition, QTD and QTcD were shorter in patients not experiencing in-hospital arrhythmia than those with arrhythmia.

Effects of azithromycin on ventricular repolarization in children with COVID-19

Introduction

Azithromycin is used to treat pediatric COVID-19 patients. It can also prolong the QT interval in adults. This study assessed the effects of azithromycin on ventricular repolarization in children with COVID-19.

Method

The study prospectively enrolled children with COVID-19 who received azithromycin between July and August 2020. An electrocardiogram was performed before, one, three, and five days post-treatment. Using ImageJ®, the following parameters were measured: QT max, QT min, Tp-e max, and Tp-e min. The parameters QTc max, QTc min, Tp-ec max, Tp-ec min, QTcd, Tp-ecd, and the QTc/Tp-ec ratio were calculated using Bazett's formula.

Results

The study included 105 pediatric patients (mean age 9.8±5.3 years). The pretreatment heart rate was higher than after treatment (before 92 [79–108]/min vs. Day 1 82 [69–108)]/min vs. Day 3 80 [68–92.2]/min vs. Day 5 81 [70–92]/min; p=0.05).

Conclusion

Azithromycin does not affect the ventricular repolarization parameters on ECG in pediatric COVID-19 cases.

QT Dispersion and Drug-Induced Torsade de Pointes

Background

Amiodarone causes less drug-induced torsade de pointes (TdP) compared to other class III antiarrhythmics. Two theories proposed for this finding include that amiodarone has less repolarization heterogeneity, and/or decreases early after depolarization (EADs). Corrected QT (QTc) dispersion as measured on a surface electrocardiogram (ECG) represents spatial heterogeneity of ventricular repolarization.

Objective

The purpose of this study was to analyze the difference in QT dispersion between amiodarone and other class III antiarrhythmics and to determine the etiology of TdP.

Methods

This was a retrospective, observational study at Montefiore Medical Center between January 2005 and January 2015. Inclusion criteria were adults >18 years on amiodarone, dofetilide, or sotalol with prolonged QT interval on 12-lead ECG. ECGs were reviewed by three blinded observers. QTc was calculated using the Bazett and Framingham formulas. QTc dispersion was calculated by subtracting the shortest from the longest QTc. Analysis of variance (ANOVA) was applied for comparison between antiarrhythmic groups with Bonferroni correction for multiple comparisons.

Results

A total of 447 ECGs were reviewed and 77 ECGs met inclusion criteria. The average QT dispersion for amiodarone, dofetilide, and sotalol was 0.050, 0.037, and 0.034, respectively (p=0.006) and the average QTc dispersion by Bazett was 0.053, 0.038, and 0.037 (p=0.008) and by Framingham was 0.049, 0.036, and 0.035 (p=0.009), respectively.

Conclusion

Our results show that given the increase in QT dispersion seen with amiodarone, heterogeneous ventricular repolarization as measured by QTc dispersion likely does not account for the lower incidence of drug-induced TdP seen with amiodarone. The ability of amiodarone to decrease EADs via sodium-channel blockade is more likely the explanation for its lower incidence of drug-induced TdP.

Twenty-Four-Hour Measures of Heart Rate-Corrected QT Interval, Peak-to-End of the T-Wave, and Peak-to-End of the T-Wave/Corrected QT Interval Ratio During Antipsychotic Treatment

PURPOSE/BACKGROUND

Prolonged ventricular repolarization, measured by heart rate-corrected QT interval (QTc) prolongation, might be a biomarker for risk of torsade de pointes (TdP) and sudden cardiac death. However, the predictive value of QTc has been challenged, and a component of QTc, peak-to-end of the T-wave (Tpe), and a high Tpe/QT ratio might be superior biomarkers because they better reflect increased transmural dispersion of ventricular myocyte repolarization, which can lead to TDP. The purpose of this pilot study was to provide the first measurements of heart rate, QTc, Tpe, Tpe/QTc, and their variability over 24 hours in medication-free patients with schizophrenia, during treatment with ziprasidone or other antipsychotic drugs, and healthy controls.

METHODS

Subjects included 12 patients treated with ziprasidone, 30 treated with other antipsychotic drugs, 3 unmedicated patients, and 15 normal controls. Subjects underwent 24-hour analog Holter recording, and the recordings were digitized. A cardiologist blind to treatment selected multiple 10-cycle segments throughout each recording and measured the electrocardiogram metrics.

RESULTS

Variability in QTc, Tpe, and Tpe/QTc over the 24 hours was present in all groups; 91.1% of patients and 100% of controls had 1 or more QTc values of 450 milliseconds or greater. Mean QTc length was significantly greater in the ziprasidone-treated than the non-ziprasidone-treated patients (P = 0.02). Mean Tpe was not elevated in the ziprasidone patients, whereas mean Tpe/QTc was lower (P < 0.01).

CONCLUSIONS

The large variability in QTc, Tpe, and Tpe/QTc observed supports the need for 24-hour electrocardiogram recordings to provide an accurate assessment of risk of TdP. Heart rate-corrected QT interval alone does not capture the risk of TdP.

Change and dispersion of QT interval during treatment with quetiapine extended release versus aripiprazole in children and adolescents with first-episode psychosis: results from the TEA trial

OBJECTIVE

The aim of this study was to compare the effect of quetiapine extended release (ER) versus aripiprazole on corrected QT interval (QTc) and QT dispersion (QTd) in youths with first-episode psychosis.

METHODS

Youths 12-17 years were randomized to quetiapine ER (daily dose range = 50 to 800 mg) or aripiprazole (daily dose range = 2.5 to 30 mg) in a 12-week double-blinded trial and examined at weeks 0, 4, and 12. Primary outcome was QTc change using Hodges formula (QTcH); secondary outcomes included QTcH > 450 ms, QTcH > 500 ms, QTcH change > 60 ms, QTd, and heart rate (HR).

RESULTS

Among 113 randomized youths, follow-up ECG was available for 93 patients (82.3%) (age = 15.8 ± 1.3 years, males = 34.4%, schizophrenia = 67.7%). Quetiapine ER treatment (n = 47) was associated with a significant increase in QTcH of + 6.8 ± 20.2 ms (p = 0.025), while the change from baseline in patients receiving aripiprazole (n = 46) was non-significant (- 3.4 ± 18.9 ms, p = 0.225). One patient in the quetiapine ER group had a QTcH change of + 62.3 ms. Age, sex, smoking, body mass index, and concomitant medication were not significantly associated with QTcH change, but higher baseline potassium was correlated to higher QTcH change in the quetiapine ER group. The HR increased significantly with quetiapine ER (+ 11.0 ± 14.2 bpm, p < 0.001) but not with aripiprazole (- 0.8 ± 12.0 bpm, p = 0.643). QTd did not significantly change with quetiapine ER or aripiprazole.

CONCLUSION

QTcH and HR increased significantly with quetiapine ER, although changes were small and likely not clinically significant in otherwise healthy patients. QTcH and HR were unchanged with aripiprazole. No significant change in QTd was seen. ClinicalTrials.gov: NCT01119014, EudraCT: 2009-016715-38.

Meet the relatives: a reintroduction to the clinical pharmacology of ‘typical’ antipsychotics (Part 2)

This second of two articles on the ‘typical’ (‘first-generation’) antipsychotics covers non-phenothiazines: thioxanthenes (flupentixol and zuclopenthixol), butyrophenones/diphenylbutylpiperidines (including one-time world market-leader haloperidol, and pimozide) and sulpiride, for many years the only substituted benzamide available in the UK. Several tolerability issues ascribed specifically or more frequently to older antipsychotics are also discussed.

Electrocardiographic Markers of Appropriate Implantable Cardioverter-Defibrillator Therapy in Young People with Congenital Heart Diseases

Implantable cardioverter-defibrillators (ICDs) are increasingly utilized in patients with congenital heart disease (CHD). Prediction of the occurrence of shocks is important if improved patient selection is desired. The electrocardiogram (ECG) has been the first-line tool predicting the risk of sudden death, but data in CHD patients are lacking. We aim to evaluate the predictive value of electrocardiographic markers of appropriate therapy of ICD in young people with CHD. We conducted a prospective, longitudinal study, in twenty-six CHD patients (mean age 24.7 ± 5.3 years) who underwent first ICD implantation. Forty-two age- and diagnosis-matched controls were recruited. Twelve-lead ECG and 24 h Holter analysis were performed during a mean follow-up of 38.9 months. Data included heart rate, heart rate variability, QRS duration (QRSd), QTc interval and its dispersion, Tpeak-Tend (Tp-Te) interval and its dispersion, presence of fragmented QRS (fQRS), T wave alternans, atrial arrhythmias, and non-sustained ventricular tachycardia. Implant indication was primary prevention in ten cases (38.5%) and secondary prevention in 16 (61.5%). Overall, 17 subjects (65.3%) received at least one appropriate and effective ICD discharge. fQRS was present in 64.7% of cases with ICD therapy compared with patients without events or controls (p < 0.0001). Tp-e and Tp-e dispersion were significantly prolonged in patients with recurrences (113.5 and 37.2 ms) versus patients without ICD discharge (89.6 and 24.1 ms) or controls (72.4 and 19.3 ms) (p < 0.0001 and p < 0.0001, respectively). On univariate Cox regression analysis QRSd (hazard ratio: 1.19 per ms, p = 0.003), QTc dispersion (hazard ratio: 1.57 per ms, p = 0.002), fQRS (hazard ratio: 3.58 p < 0.0001), Tp-e (hazard ratio: 2.27 per ms, p < 0.0001), and Tp-e dispersion (hazard ratio: 4.15 per ms, p < 0.0001), emerged as strong predictors of outcome. On multivariate Cox analysis fQRS, Tp-e and Tp-e dispersion remained in the model. The presence of fQRS, and both Tp-e and Tp-e dispersion are useful ECG tools in daily clinical practice to identify CHD patients at risk for appropriate ICD therapy.

Prevalence and Risk Factors of Prolonged Corrected QT Interval Among Children and Adolescents Treated With Antipsychotic Medications: A Long-Term Follow-Up in a Real-World Population

PURPOSE

This study aimed to describe the prevalence of corrected QT (QTc) interval disorders and the possible predisposing factors in children and adolescents treated with antipsychotic (AP) medications in a real-world population with a long-term follow-up.

METHODS

Data were obtained from the SafEty of NeurolepTics in Infancy and Adolescence (SENTIA) registry (https://sentia.es). The SENTIA includes patients younger than 18 years who are currently taking or initiating treatment with AP medications and have agreed to participate in the registry. The SENTIA's follow-up includes an electrocardiogram (ECG) assessment before starting treatment and at 1, 3, and 6 months after treatment initiation or after any changes in the patient's AP medication treatment. Thereafter, all participants undergo an ECG every 6 months. A QTc interval more than 450 milliseconds, increases in QTc interval of 60 milliseconds or more, or QTc dispersion more than 100 milliseconds were considered abnormal.

RESULTS

Since January 1, 2011, 101 patients have been enrolled in SENTIA and have had at least 1 ECG assessment. The mean age at inclusion was 11.5 years; 75% of the patients were men. The mean follow-up time was 20.0 ± 15.1 months. The most frequently prescribed AP medications were risperidone (52.2%) and aripiprazole (45.5%). Seven patients (6.9%) had abnormal changes in QTc. No patient had a QTc interval more than 500 milliseconds. All patients were asymptomatic. The QTc changes were observed at different times of exposure, with a range of 1 to 39 months after beginning AP treatment. Concomitant use of attention deficit and hyperactivity disorder drugs seemed a possible factor associated with QTc disorders.

CONCLUSIONS

Patients should undergo a baseline ECG assessment before starting AP medication treatment, particularly patients with concomitant use of attention deficit and hyperactivity disorder drugs or a family/personal history of heart disease.

Effects of epinephrine over P wave duration and ventricular repolarization in subjects without structural heart disease

BACKGROUND

Little is known about the effects of epinephrine over atrial electrical function, AV conduction and ventricular repolarization in normal subjects. We intended to study the effects of intravenous epinephrine on the duration of P wave, inter-atrial conduction time, PR, QRS, QT, corrected QT (QTc), QTc dispersion (QTc max-min), the peak-to-end interval of T wave (Tp-e), the Tp-e/QT index, and the middle portion of ventricular repolarization length (QT-(QRS+Tp-e)) in healthy subjects.

METHODS

Forty-three, 37.20 ± 17.05 year-old, 25 (58%) female patients without structural heart disease took part in the study. They underwent an electrophysiological study. An epinephrine infusion (50 to 100 ng/kg/min) was administered for 5 min until an increase of at least 10% of the initial heart rate (HR) was achieved.

RESULTS

No complication arose from epinephrine infusion, and the drug facilitated arrhythmia induction. A significant increase in heart rate, systolic blood pressure, QRS, QTc, Tp-e, Tp-e/QT index, and QTc max-min interval duration was documented. No significant effect on diastolic blood pressure, P wave duration, inter-atrial conduction time, and PR, QT and QT-(Tp-e+QRS interval) was observed.

CONCLUSIONS

In this group of patients without structural heart disease, epinephrine infusion did not produce any complication and it facilitated arrhythmia induction. It did not modify P wave duration, PR interval or inter-atrial conduction time. Moreover, it significantly increased the duration of depolarization, the final portion of repolarization, transmural dispersion of repolarization, and regional dispersion of repolarization without inducing significant changes in the middle portion of repolarization.

Effects of balanced propofol sedation on QT, corrected QT, and P-wave dispersion on upper endoscopy

Objective:

Combined sedation with propofol and benzodiazepines, known as balanced propofol sedation (BPS), was developed to increase patient comfort during endoscopy. However, the effects of BPS on P-wave dispersion (Pwd), QT interval, and corrected QT (QTc) interval after endoscopy have not been investigated.

Methods:

The study population consisted of 40 patients with BPS and 42 without sedation who were scheduled to undergo upper endoscopy in this cross-sectional prospective study. Patients with hypertension, diabetes mellitus, renal failure, chronic obstructive pulmonary disease, coronary artery disease, or valvular heart disease and those on medications that interfere with cardiac conduction times were excluded. Electrocardiograms (ECGs) was recorded in all patients pre-endoscopy and 10 min post-endoscopy. QT, QT dispersion (QTd), and Pwd were defined from 12-lead ECG. The QTc interval was calculated using Bazett’s formula. All analyses were performed using SPSS 15.0.

Results:

Post-endoscopy P max duration and Pwd were prolonged compared with baseline values (86±13 ms vs. 92±10 ms and 29±12 ms vs. 33±12 ms, respectively; p<0.05). Post-endoscopy QTc and QTd were decreased compared with baseline values, but these decreases were not statistically significant (431±25 ms vs. 416±30 ms and 62±28 ms vs. 43±22 ms, respectively; p>0.05).

Conclusion:

The present study showed that P-wave duration and Pwd values increased after endoscopy with a combination of midazolam and propofol sedation. Physicians should be made aware of the potential effects of BPS in terms on P-wave duration and Pwd values.

Sustained release oral morphine as an alternative to methadone for the treatment of opioid-use disorder post Torsades de Pointes cardiac arrest

In most settings, approved medications for the treatment of opioid-use disorder include methadone and buprenorphine/naloxone, and in some settings, naltrexone. We present a case in which methadone administration was associated with an in-hospital episode of Torsades de Pointes in a patient who was subsequently maintained on sustained release oral morphine (SROM) for treatment of his opioid-use disorder. This transition was made in the context of long-term compliance to methadone maintenance, and with a previous adverse reaction to buprenorphine/naloxone precluding its use. The change to SROM, supported by emerging evidence, resulted in a reduction in the patient's measured QTc interval, prevention of further arrhythmias and continued abstinence from illicit opioid-use. In this context, we believe careful consideration should be given to the use of SROM.

Electrocardiographic P-Wave Duration, QT Interval, T Peak to End Interval and Tp-e/QT Ratio in Pregnancy with Respect to Trimesters

BACKGROUND

P-wave duration helps to determine the risk of atrial arrhythmia, especially atrial fibrillation. QT interval, T peak to end interval (Tp-e), and Tp-e/QT ratio are electrocardiographic indices related to ventricular repolarization which are used to determine the risk of ventricular arrhythmias. We search for any alterations in electrocardiographic indices of arrhythmia in the pregnancy period with respect to trimesters.

METHODS

We enrolled 154 pregnant and 62 nonpregnant, healthy women into this cross-sectional study. Maximum and minimum P-wave durations (Pmax, Pmin), and QT intervals (QTmax, QTmin) were measured from 12 leads. QT measurements were corrected using Fridericia (QTc-Fr) and Bazett's (QTc-Bz) correction. Tp-e interval was obtained from the difference between QT interval, and QT peak interval (QTp) measured from the beginning of the QRS until the peak of the T wave. Tp-e/QT ratio was calculated using these measurements.

RESULTS

Pmax were 93.0 ± 9.1, 93.9 ± 8.9, 97.9 ± 5.6, 99.0 ± 6.1 in nonpregnant women, first, second, third trimesters of pregnancy, respectively (P = 0.001); whereas Pmin values were not significantly different. QTc-Fr max were 407.4 ± 14.2, 408.5 ± 16.1, 410.1 ± 13.1, 415.1 ± 10.1 (P = 0.007); Tp-e were 72.7 ± 6.2, 73.2 ± 6.5, 77.2 ± 8.9, 87.2 ± 9.6 (P < 0.001); and Tp-e/QT were 0.17 (0.14-0.20), 0.17 (0.14-0.20), 0.18 (0.15-0.23), 0.20 (0.16-0.25) in nonpregnant women, first, second, and third trimesters of pregnancy respectively (P < 0.001). None of the participants experienced any arrhythmic event.

CONCLUSIONS

P-wave duration is prolonged in the second trimester, and resumes a plateau thereafter. Maximum QTc interval, Tp-e interval and Tp-e/QT ratio are increased in the late pregnancy. Although these indices are altered during the course of pregnancy, they all remain in the normal ranges.

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.

Effect of testosterone replacement therapy on cardiac performance and oxidative stress in orchidectomized rats

AIM

To investigate the effects of testosterone on myocardial contractility, oxidative stress status and expression of sodium channel protein (Nav1.5) and inward rectifying K channels (Kir 2.x) in normal and orchidectomized (ORX) rats.

METHODS

One hundred four rats were randomly assigned into four groups (n = 26, each) as follows: (i) untreated controls, (ii) testosterone treated, (iii) orchidectomized rats and (iv) orchidectomized, testosterone-treated rats. Treatments with the vehicle or testosterone were carried out for 12 weeks, three times per week. At the end of treatment, surface ECG, isolated heart, tissue oxidative stress and lipid peroxidation experiments were carried out on the cardiac tissues. Also, immunohistochemical examination for Nav1.5 and PCR detection of mRNA of Kir2.1, Kir2.2 and Kir2.4 subunits of K channels were carried out.

RESULTS

Orchidectomy impaired cardiac contractile function parameters left ventricular developed pressure (LVDP) and the peaks of the positive and negative pressure derivatives (dP/dtmax and -dP/dtmax respectively), increased heart rate and prolonged QT and QTc intervals, elevated pro-oxidant state in rat's hearts and decreased the expression of Kir 2.1 but not Kir2.2, Kir 2.4 and Nav1.5 channels. Exogenous testosterone administration to orchidectomized rats restored heart contractility and shortened QT and QTc intervals to their normal values, ameliorated the generated pro-oxidant state and improved the expression of Nav1.5 and Kir2.1, but not Kir2.2 or Kir2.4 channels.

CONCLUSION

Testosterone improved cardiac contractility and shortened QT and QTc intervals in ORX rats. An effect that might be dependent of reduction in oxidative stress and enhancement of Kir2.1 channels but independent of Nav1.5 channel protein.

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.

Clarithromycin, QTc interval prolongation and torsades de pointes: the need to study case reports

BACKGROUND

The manufacturers of clarithromycin sought a drug similar in efficacy to erythromycin but with a superior side-effect profile. They generally achieved this outcome, but postmarketing findings identified a series of reports linking clarithromycin to QTc interval prolongation and torsades de pointes (TdP) ultimately leading to a Black Box Warning. We sought to clarify risk factors associated with TdP among case reports of patients receiving clarithromycin linked to QTc interval prolongation and TdP.

METHODS AND RESULTS

In a detailed literature search, we found 15 women, five men, and one boy meeting our search criteria. Among the 17 adults with reported clarithromycin dose and concurrent QTc interval measurement, we found no statistically significant relationship between clarithromycin dose and QTc interval duration. This did not change for the adults who developed TdP. Among adults, major risk factors were female sex (15), old age (11) and heart disease (17). A total of eight adult subjects had all three major risk factors and 14 of the 20 adults had at least two major risk factors. All adult subjects had at least two risk factors besides clarithromycin. A total of four of the 20 adults received cisapride and three received disopyramide. Three adults were considered to suffer from some aspect of the congenital long QT syndrome.

CONCLUSIONS

We believe that the risk factor description for this drug should be refined to emphasize the major risk factors of (1) female sex, (2) old age and (3) heart disease.

Improvement of cardiac efficacy and safety models in drug discovery by the use of stem cell-derived cardiomyocytes

BACKGROUND

The pharmaceutical industry suffers from high attrition rates during late phases of drug development. Improved models for early evaluation of drug efficacy and safety are needed to address this problem. Recent developments have illustrated that human stem cell-derived cardiomyocytes are attractive for using as a model system for different cardiac diseases and as a model for screening, safety pharmacology and toxicology.

OBJECTIVE

In this review, we discuss contemporary drug discovery models and their characteristics for cardiac efficacy testing and safety assessment. Additionally, we evaluate various sources of stem cells and how these cells could potentially improve early screening and safety models.

CONCLUSION

We conclude that human stem cells offer a source of physiologically relevant cells that show great potential as a future tool in cardiac drug discovery. However, some technical challenges related to cell differentiation and production and also to validation of improved platforms remain and must be overcome before successful application can become a reality.

Choice of an alternative lead for QT interval measurement in serial ECGs when Lead II is not suitable for analysis

INTRODUCTION

Conventionally, QT interval is measured in lead II. There are no data to select an alternative lead for QT measurement when it cannot be measured in Lead II for any reason.

METHODS AND RESULTS

We retrospectively analyzed ECGs from 1906 healthy volunteers from 41 phase I studies. QT interval was measured on the median beat in all 12 leads. The mean difference in QT interval between lead aVR and in Lead II was the least, followed by aVF, V5, V6 and V4; lead aVL had maximum difference. The T wave was flat (<0.1 mV) in Lead II in 6.9% of ECGs; it was also flat in 20% of these ECGs (1.4% of all ECGs) in Leads aVR, aVF and V5.

CONCLUSIONS

When QT interval cannot be measured in Lead II, the best alternative leads are aVR, aVF, V5, V6 and V4 in that sequence. It differs maximally from that in Lead II in Lead aVL.

Mechanisms, risk factors, and management of acquired long QT syndrome: a comprehensive review

Long QT syndrome is characterized by prolongation of the corrected QT (QTc) interval on the surface electrocardiogram and is associated with precipitation of torsade de pointes (TdP), a polymorphic ventricular tachycardia that may cause sudden death. Acquired long QT syndrome describes pathologic excessive prolongation of the QT interval, upon exposure to an environmental stressor, with reversion back to normal following removal of the stressor. The most common environmental stressor in acquired long QT syndrome is drug therapy. Acquired long QT syndrome is an important issue for clinicians and a significant public health problem concerning the large number of drugs with this adverse effect with a potentially fatal outcome, the large number of patients exposed to these drugs, and our inability to predict the risk for a given individual. In this paper, we focus on mechanisms underlying QT prolongation, risk factors for torsades de pointes and describe the short- and long-term treatment of acquired long QT syndrome.

Cardiovasular changes after placement of a classic endotracheal tube, double-lumen tube, and Laryngeal Mask Airway

STUDY OBJECTIVE

To compare hemodynamic responses, P wave dispersion (Pd), and QT dispersion (QTd) after placement of a classic endotracheal tube (ETT), double-lumen tube (DLT), or Laryngeal Mask Airway (LMA).

DESIGN

Prospective study.

SETTING

Outpatient surgery center.

PATIENTS

75 adult, ASA physical status 1 and 2 patients undergoing cystoscopy and thoracoscopic surgery.

INTERVENTIONS

Patients were randomized to undergo placement of an ETT (Group T; n = 25), DLT (Group D; n = 25), or LMA (Group L; n = 25). Anesthesia was induced by etomidate 0.3 mg/kg and fentanyl 1.0 μg/kg, and maintained with nitrous oxide, oxygen, 2% to 3% sevoflurane, and rocuronium 0.5 mg/kg.

MEASUREMENTS

Mean arterial pressure (MAP) and heart rate (HR) were recorded immediately before intubation and after intubation at one, 3, 5, 10,15, 20, 25, and 30 minutes after intubation/airway insertion.

RESULTS

QT dispersion after tube placement was significantly higher than before tube placement in Group D (P = 0.0001) and Group L (P = 0.03). Mean arterial pressure and HR in Group T were significantly higher than in Group L at the first minute after tube placement (P = 0.02). Heart rate and MAP at baseline were significantly higher than the other measurement times in Groups T and D (P < 0.01).

CONCLUSIONS

The LMA caused no change in Pd, HR, or MAP values during or after airway placement, but caused QTd after airway insertion. The ETT caused a sudden increase at the first minute after tube placement, without any Pd or QTd. In addition, DLT caused QTd without any serious change in hemodynamics.

Biological drug treatment of rheumatoid arthritis and spondyloarthritis: effects on QT interval and QT dispersion

OBJECTIVE

Tumor necrosis factor-α (TNF-α) antagonists bring about significant improvement in chronic inflammatory diseases such as rheumatoid arthritis (RA) and spondyloarthritis (SpA). There is some evidence that they can also have negative myocardial effects, but to date this issue has not been clarified. We evaluated changes in electrocardiographic measures [QT interval, corrected, dispersion, and dispersion corrected (QT, QTc, QTd, QTdc, respectively)] in patients with RA or SpA treated with anti-TNF agents (infliximab and etanercept), those treated with other biological agents (rituximab), and with methotrexate.

METHODS

We studied 38 consecutive patients with RA (21 patients) or SpA (19 patients) being treated with TNF-α antagonists, 8 patients with RA being treated with rituximab, and 13 patients (8 with RA and 5 with SpA) taking methotrexate. Electrocardiographs (ECG) were performed on all participants at baseline and 12 months after initiation of treatment, and the QT, QTc, and QTd were calculated with standard procedures.

RESULTS

After 12 months of treatment, significant increases over baseline values were observed in the mean QT (p < 0.009), QTd (p < 0.0001), and QTdc (p < 0.0001) of the anti-TNF group, but no significant changes were observed in those taking rituximab. QT changes in the anti-TNF group were unrelated to the disease (RA vs SpA) or drug (infliximab vs etanercept), and none were associated with clinical manifestations of cardiac disease.

CONCLUSION

In patients with RA and SpA, TNF-α antagonists seem to increase the QT and QTd measures. Although these changes were completely asymptomatic, ECG may be indicated in patients being considered for anti-TNF therapy to identify those at risk for cardiac complications.

QTc prolongation: is clozapine safe? Study of 82 cases before and after clozapine treatment

OBJECTIVE

The most feared cardiological consequence of clozapine is sudden cardiac death. A potential marker of it is QTc interval (QTc) prolongation. This study aimed to determine the prevalence of QTc prolongation in patients before and after 18 weeks of clozapine treatment and to detect predictors of QTc prolongation.

METHODS

Patients undergoing treatment with clozapine who had been given an electrocardiogram prior to the treatment and had their electrocardiogram, serum clozapine and norclozapine levels taken on the 18th week were selected. Exclusion criteria were thioridazine, pimozide, diuretics or beta-blocker treatment, electrolytic alteration, heart diseases and substance misuse diagnosis. Prolonged QTc was defined as >450 ms in men and >470 ms in women.

RESULTS

No significant differences were detected in prevalence of prolonged QTc or mean QTc before and after 18 weeks of clozapine treatment (p = 0.15, p = 0.32, respectively). Age, heart rate at 18th week and QTc prior to clozapine treatment had significant effects on QTc at follow-up. Prolonged QTc during previous treatment and heart rate >95 beats/min at 18 weeks were found to be predictors of QTc prolongation.

CONCLUSION

No significant differences were detected in prevalence of QTc prolongation or mean QTc among patients before and after 18 weeks on clozapine.

QT interval duration and dispersion in children and adolescents treated with ziprasidone

OBJECTIVE

To assess the incidence of symptoms (palpitations, syncope) and electrocardiographic signs (increased QT duration and dispersion) of an increased risk of torsades de pointes in youth treated with ziprasidone.

METHOD

Data for this study were collected as part of a prospective, observational, mixed inpatient and outpatient cohort study of youth who were administered antipsychotic treatment for the first time. For this study, we focus on 29 patients (mean ± SD age 15.3 ± 2.9 years) receiving ziprasidone (112.8 ± 50.6 mg/d; range, 20-240) for 99.3 ± 108.7 days. All patients had normal electrocardiograms (ECGs) and no serious medical illness at baseline. Patients had a mean of 2.7 ± 1.3 (median = 3; range, 1-7; total = 49) follow-up ECGs performed monthly for 3 months and every 3 months thereafter, with concurrent blood ziprasidone level measurements. Heart rate-corrected QT interval (QTc) duration and dispersion were measured manually in ≥ 6 ECG leads. QTc > 450-millisecond or ≥ 60-millisecond increase and QTc dispersion > 100 milliseconds were considered abnormal. The study was conducted from December 2001 to September 2007.

RESULTS

No patient reported syncope or symptomatic arrhythmias. Seven patients (24.1%) developed ECG abnormalities; 5 had peak QTc durations > 450 milliseconds, and 2 had peak QTc dispersion > 100 milliseconds. The baseline-to-peak QTc duration increased by 22.9 ± 21 milliseconds (P < .0001). The baseline-to-peak QTc dispersion increased by 6.1 ± 31.4 milliseconds (P = .30). The peak QTc duration and dispersion occurred after 47.6 ± 46.0 and 60.4 ± 73.2 treatment days, respectively. Baseline-to-peak QTc duration and dispersion changes were not correlated with ziprasidone dose (P = .65) or plasma levels (P = .50).

CONCLUSIONS

Ziprasidone was associated with a dose- and level-independent, significant prolongation of QTc duration in one-quarter of youth. However, prolongation of QTc dispersion was nonsignificant, and no patient experienced concomitant abnormal prolongation of both QTc duration and QTc dispersion. The dissociation between prolonged QTc duration and dispersion suggests low arrhythmogenic potential in youth with normal baseline ECGs.

Thorough QT/QTc study of ritonavir-boosted saquinavir following multiple-dose administration of therapeutic and supratherapeutic doses in healthy participants

The effect of saquinavir-boosted ritonavir at therapeutic (1000/100 mg twice daily [bid]) and supratherapeutic (1500/100 mg bid) doses was evaluated in a double-blind, placebo- and positive-controlled (moxifloxacin 400 mg) 4-way crossover thorough QT/QTc study. Least squares mean estimated study-specific QTc (QTcS) change from dense predose baseline (ddQTcS(dense)) was the primary endpoint. Greatest mean increase in ddQTcS(dense) occurred 12 hours postdose for the 1000/100-mg group (18.9 ms) and 20 hours for the 1500/10-mg group (30.2 ms). The upper 1-sided 95% confidence interval was >20 ms from 2 to 20 hours postdose in both groups. ddQTcB(dense) and ddQTcF(dense) were similar to ddQTcS(dense). No QTcS, QTcF, or QTcB measurements were >500 ms. One participant receiving 1000/100 mg and 3 receiving 1500/100 mg had a maximum ddQTcS(dense) >60 ms. More participants with ≥1 adverse event received saquinavir/ritonavir. PubMed search and Roche postmarketing data did not reveal publications or reports directly presenting the effect of saquinavir on QT/QTc or causing torsade de pointes.

Impact of ABCB1 allelic variants on QTc interval prolongation

PURPOSE

Although the ABCB1 (P-glycoprotein) drug transporter is a constituent of several blood-tissue barriers (i.e., blood-brain and blood-nerve), its participation in a putative blood-heart barrier has been poorly explored. ABCB1 could decrease the intracardiac concentrations of drugs that cause QT prolongation and cardiotoxicity.

EXPERIMENTAL DESIGN

ABCB1-related romidepsin transport kinetics were explored in LLC-PK1 cells transfected with different ABCB1 genetic variants. ABCB1 plasma and intracardiac concentrations were determined in Abcb1a/1b (-/-) mice and wild-type FVB controls. These same mice were used to evaluate romidepsin-induced heart rate-corrected QT interval (QTc) prolongation over time. Finally, a cohort of 83 individuals with available QTcB and ABCB1 genotyping data were used to compare allelic variation in ABCB1 versus QTc-prolongation phenotype.

RESULTS

Here, we show that mice lacking the ABCB1-type P-glycoprotein have higher intracardiac concentrations of a model ABCB1 substrate, romidepsin, that correspond to changes in QT prolongation from baseline (ΔQTc) over time. Consistent with this observation, we also show that patients carrying genetic variants that could raise ABCB1 expression in the cardiac endothelium have lower ΔQTc following a single dose of romidepsin.

CONCLUSIONS

To our knowledge, this is the first evidence that Abcb1-type P-glycoprotein can limit intracardiac exposure to a drug that mediates QT prolongation and suggests that certain commonly inherited polymorphisms in ABCB1 may serve as markers for QT prolongation following the administration of ABCB1-substrate drugs.

The effect of sertindole on QTD and TPTE

OBJECTIVE

Recent research suggests that other surrogate markers than QTc, including QTc dispersion and Tpeak-Tend, may better correlate with cardiac arrhythmia risk. While sertindole significantly prolongs the QTc interval, the effects on other markers of arrhythmia risk, such as QTc dispersion and Tpeak-Tend are unknown.

METHOD

Digital 12-lead ECG was recorded at baseline and at steady-state in 37 patients switched to sertindole. ECG was analysed for Fridericia-corrected QT duration (QTcF), QT dispersion and Tpeak-Tend.

RESULTS

From a baseline QTcF of 407 +/- 22 ms, mean QTcF prolongation during sertindole treatment was 20 +/- 23 ms, P < 0.01. No effect on QTc dispersion was found (-1 +/- 11 ms; P = 0.41). No increased duration of the Tpeak-Tend interval from baseline was found (+7 +/- 21 ms; P = 0.05).

CONCLUSION

These findings might be related to the absence of confirmed Torsade de Pointes (TdP) cases related to sertindole exposure, despite sertindole's QTc prolonging effects.

Drug-Induced QTc-Interval Prolongation in the Intensive Care Unit: Incidence and Predictors

There is a paucity of information regarding QTc prolongation in critically ill patients. A prospective observational study was conducted to assess the incidence and predictors of QTc prolongation associated with medications in intensive care unit (ICU) patients. Consecutive adult patients prescribed prespecified QTc-prolonging medications were assessed for development of the combined incidence of QTc >500 ms at anytime and QTc increase >60 ms above baseline. Over 3 months, 200 consecutive patients (63 ± 18 years; 52% female; 73% Caucasian; baseline QTc 447.3 ± 51.5 ms) were evaluated. The primary end point occurred in 48% of the patients (QTc >500 ms 40%, QTc increase >60 ms 29%). The majority of patients experienced a QTc >470 or 450 ms (60.5%). Mean increase in QTc at 48 hours was 20 ± 35 ms. Upon multivariate analysis, length of stay [odds ratio 1.30, 95% confidence interval (1.15, 1.47)] and baseline QTc [1.01 (1.01, 1.02)] were associated with an increased risk for the primary end point, while beta-blockers [0.41 (0.20, 0.81)] were associated with a risk reduction. In conclusion, increased risk of proarrhythmia, as assessed by QTc prolongation, occurs in the majority of ICU patients when prescribed medications with electrophysiologic properties. Increased vigilance is warranted. The possible protective effect of beta-blockers requires confirmation.

Randomized, double-blind, crossover study to investigate the effect of rivaroxaban on QT-interval prolongation

BACKGROUND

Rivaroxaban (BAY 59-7939) is a novel, oral, direct Factor Xa inhibitor in advanced clinical development for the prevention and treatment of thromboembolic disorders. Unwanted pro-arrhythmic effects are a common reason for drugs failing to gain regulatory approval; these properties can be detected by assessing the effect of the drug on the QT interval.

OBJECTIVE

This study was performed, in accordance with International Conference on Harmonisation (ICH) E14 guidance, to assess whether rivaroxaban prolongs the QT interval.

STUDY DESIGN

This was a prospective, randomized, double-blind, double-dummy, four-way crossover study.

SETTING

The study was conducted at a clinical pharmacology research unit.

SUBJECTS

Healthy male and female subjects (n = 54) aged > or =50 years were enrolled and remained in the study unit for 3 days for each treatment. Of these, 50 patients were eligible for the QT analysis.

INTERVENTION

Subjects received single oral doses of rivaroxaban 45 mg or 15 mg, moxifloxacin 400 mg (positive control), or placebo.

OUTCOME MEASURES

Multiple ECGs were taken at frequent intervals after drug administration, and the QT interval was measured manually under blinded conditions at a central laboratory. The Fridericia correction formula (QTcF) was used to correct the QT interval for heart rate. The primary outcome was the effect of rivaroxaban or moxifloxacin on the placebo-subtracted QTcF 3 hours after administration. The frequency of outlying QTcF values and the tolerability of the treatments were also assessed.

RESULTS

All treatments were well tolerated and had no effect on heart rate. Moxifloxacin established the required assay sensitivity; placebo-subtracted QTcF 3 hours after moxifloxacin administration was prolonged by 9.77 ms (95% CI 7.39, 12.15). Placebo-subtracted QTcF values 3 hours after rivaroxaban administration were -0.91 ms (95% CI -3.33, 1.52) and -1.83 ms (95% CI -4.19, 0.54) with rivaroxaban 45 mg and 15 mg, respectively. QTcF was not prolonged with rivaroxaban at any time, and the frequency of outlying results with rivaroxaban and placebo was similar.

CONCLUSION

This thorough QT study, which was performed in accordance with ICH E14 guidelines, shows that rivaroxaban does not prolong the QTc interval. Therefore, the potential of rivaroxaban for the prevention and treatment of thromboembolic disorders, including chronic cardiovascular disorders, can be investigated in appropriate clinical studies without the need for intensive monitoring of the QTc interval.

Pharmacist monitoring of QTc interval-prolonging medications in critically ill medical patients: a pilot study

BACKGROUND

No data exist regarding the value of pharmacist monitoring of drugs associated with QTc interval prolongation.

OBJECTIVE

To assess the capability, clinical impact, and economic impact of pharmacists monitoring for drug-induced QTc interval prolongation in critically ill medical adult patients.

METHODS

In a prospective, parallel-group study, 149 consecutive medical intensive care unit (ICU) patients prescribed a QTc interval-prolonging drug at the Los Angeles County + University of Southern California Medical Center were assigned on alternating days to an intervention group (clinical pharmacist on physician team monitored drugs using a standardized algorithm) or a standard care group (team without pharmacist using an algorithm). The monitoring algorithm used daily assessments of electrocardiograms and laboratory data to generate pharmacotherapeutic recommendations. The primary endpoint was the frequency of QTc interval prolongation (>500 msec at any time or an increase > or =60 msec over baseline). Secondary endpoints included QTc interval greater than 470 msec in women or greater than 450 msec in men, mean increase in QTc interval at 48 hours, recommendation acceptance rate, and cost of care.

RESULTS

QTc interval prolongation occurred less frequently in the intervention group compared with the standard care group (19% vs 39%, respectively; p = 0.006). Incidence of QTc interval greater than 500 msec (13% vs 33%, respectively; p = 0.003) was also lower in the intervention group. Incidence of QTc interval increase of 60 msec or more over baseline (12% vs 21%, respectively; p = 0.12) and increase in QTc interval at 48 hours over baseline (mean +/- SD; 6.4 +/- 40.8 vs 18.2 +/- 42.3 msec, respectively; p = 0.097) were not significantly different between the groups. Algorithm-generated recommendations were accepted 70% of the time by the intervention group physician team. Total cost and cost per day were not significantly different between groups.

CONCLUSIONS

In this preliminary study, pharmacist monitoring of QTc interval-prolonging drugs using a simple algorithm was feasible and reduced the risk of QTc interval prolongation. Further studies that monitor other proarrhythmic medications are warranted.

Monotherapy versus Combination Therapy with Class III Antiarrhythmic Agents to Attenuate Transmural Dispersion of Repolarization: A Potential Risk Factor for Torsade de Pointes

Class III antiarrhythmic agents are used for conversion to and maintenance of sinus rhythm from arrhythmias of atrial or ventricular origin. Monotherapy can be limited by adverse events or recurrent arrhythmias. Sotalol, dofetilide, and ibutilide may induce torsade de pointes in 2-8% of patients, whereas amiodarone induces torsade de pointes in less than 1%. We reviewed the literature regarding the possible combination of class III antiarrhythmics and risk for inducing torsade de pointes. Animal studies using amiodarone plus sotalol or d-sotalol suggest that these drug combinations prolong the QTc interval but do not induce torsade de pointes. Similar data extracted from human studies of ibutilide in patients also receiving amiodarone or sotalol showed greater efficacy with combination therapy than with monotherapy, without increased torsade de pointes induction. Reduced transmural dispersion of repolarization with amiodarone and sotalol combination therapy may serve as a mechanism for reducing the risk of torsade de pointes compared with sotalol monotherapy.

Current concepts in the mechanisms and management of drug-induced QT prolongation and torsade de pointes

Drug-induced long QT syndrome is characterized by a prolonged corrected QT interval (QTc) and increased risk of a polymorphic ventricular tachycardia known as torsade de pointes (TdP). We review mechanisms, predispositions, culprit agents, and management of this potentially fatal phenomenon. Virtually all drugs that prolong QTc block the rapid component of the delayed rectifier current (I(kr)). Some drugs prolong QTc in a dose-dependent manner, others do so at any dose. Most patients that develop drug-induced TdP have underlying risk factors. Female sex is the most common. Implicated drugs include class 1A and III antiarrhythmics, macrolide antibiotics, pentamidine, antimalarials, antipsychotics, arsenic trioxide, and methadone. Treatment for TdP includes immediate defibrillation for hemodynamic instability and intravenous magnesium sulfate. Potassium levels should be maintained in the high normal range, and all QT prolonging agents must be promptly discontinued.

Thorough QT Study with Recommended and Supratherapeutic Doses of Tolterodine

The objective of our study was to determine the QTc effects of tolterodine. A crossover-design thorough QT study of recommended (2 mg twice daily) and supratherapeutic (4 mg twice daily) doses of tolterodine, moxifloxacin (400 mg once daily), and placebo was performed. Electrocardiograms (ECGs) and pharmacokinetic samples were obtained on days 1-4; time-matched baseline ECGs were taken on day 0. Mean placebo-subtracted change from baseline Fridericia-corrected QT (QTcF) during peak drug exposure on day 4 was the primary end point. Mean QTcF prolongation of moxifloxacin was 8.9 ms (machine-read) and 19.3 ms (manual-read). At recommended and supratherapeutic tolterodine doses, mean QTcF prolongation was 1.2 and 5.6 ms (machine-read), respectively, and 5.0 and 11.8 ms (manual-read), respectively. The QTc effect of tolterodine was lower than moxifloxacin. No subject receiving tolterodine exceeded the clinically relevant thresholds of 500 ms absolute QTc or 60 ms change from baseline. In conclusion, tolterodine does not have a clinically significant effect on QT interval.

The QT interval and psychotropic medications in children: recommendations for clinicians

The use of psychotropic medications in children has increased significantly in the last few years. There have been several case reports of sudden death in children taking specific psychotropic medications. Fears that these deaths might have been caused by ventricular arrhythmias have been enhanced by reports of electrocardiographic abnormalities, including prolongation of the QTc interval, in patients taking these medications. Several factors including genetic susceptibility, pre-existing cardiac disease, abnormalities of drug clearance and concomitant use of other medications known to affect the QTc interval can increase the susceptibility of the heart to conduction abnormalities. This article discusses the potential of particular psychotropic drugs to prolong the QTc interval in children, and examines other factors that may contribute to conduction abnormalities. We aim to provide clear clinical recommendations for the prescription of these drugs and the monitoring of children taking them.

Further evidence of inherited long QT syndrome gene mutations in antiarrhythmic drug-associated torsades de pointes

BACKGROUND

Pathophysiologically significant ion-channel mutations have been detected in only a minority of cases of acquired long QT syndrome (LQTS).

OBJECTIVE

The aim of this study was to clarify the putative role of subclinical inherited LQTS in drug-associated torsades de pointes (TdP) and to assess the concomitant proarrhythmic factors.

METHODS

We evaluated 16 consecutive cases with documented, antiarrhythmic drug-induced TdP who were referred to the Laboratory of Molecular Medicine at Helsinki University for LQTS genetic testing between September 2000 and August 2005.

RESULTS

A prolonged QTc interval was observed in 56% of the patients before administration of the drug. TdP was associated with amiodarone in seven, sotalol in six, flecainide in two, and propafenone in one of the cases. Except for the culprit drug, one or more risk factors such as female sex, congestive heart failure, and atrial fibrillation were present in each drug-associated TdP. DNA samples were screened for the four common Finnish founder mutations (KCNQ1 G589D and IVS7-2A-->G, HERG L552S, and R176W), which are known to account for the majority of inherited LQTS in Finland. A total of three (19%) individuals carried one of these four mutations.

CONCLUSIONS

Our data show that previously unsuspected LQTS mutations may be present in patients with antiarrhythmic drug-associated TdPs. A normal QTc interval does not exclude the risk of proarrhythmia.

Thorough QT/QTc not so thorough: removes torsadogenic predictors from the T-wave, incriminates safe drugs, and misses profibrillatory drugs

Drug-induced QT prolongation has such a strong correlation with torsade de pointes (TdP) that it comes to serve as a surrogate for TdP. As a result, drugs that prolong QT by as little as a few ms, even without any evidence of TdP, may get dropped from development or blocked from approval. However, measurement of QT with ms accuracy may be impossible to achieve. Worse, some drugs that lengthen the QT interval are not only not proarrhythmic, they may even be antiarrhythmic; while some that shorten the QT can be strongly proarrhythmic. Indeed, proarrhythmia related to repolarization disturbances is caused by triangulation, reverse use dependence, instability, and dispersion (TRIaD). When TRIaD is present with QT prolongation it commonly yields TdP, but when TRIaD is combined with QT shortening it preferentially leads to VF instead. While TdP is lethal in less than 20% of instances, VF is much more morbid. Worse, available evidence suggests that there is more death from drug-induced fibrillation than TdP. Thus, QT prolongation alone is not very useful. Instead, the T-wave should be used in alternate ways: extraction of TRIaD.

Assessing the proarrhythmic potential of drugs: current status of models and surrogate parameters of torsades de pointes arrhythmias

Torsades de pointes (TdP) is a potentially lethal cardiac arrhythmia that can occur as an unwanted adverse effect of various pharmacological therapies. Before a drug is approved for marketing, its effects on cardiac repolarisation are examined clinically and experimentally. This paper expresses the opinion that effects on repolarisation duration cannot directly be translated to risk of proarrhythmia. Current safety assessments of drugs only involve repolarisation assays, however the proarrhythmic profile can only be determined in the predisposed model. The availability of these proarrhythmic animal models is emphasised in the present paper. It is feasible for the pharmaceutical industry to establish one or more of these proarrhythmic animal models and large benefits are potentially available if pharmaceutical industries and patient-care authorities embraced these models. Furthermore, suggested surrogate parameters possessing predictive power of TdP arrhythmia are reviewed. As these parameters are not developed to finalisation, any meaningful study of the proarrhythmic potential of a new drug will include evaluation in an integrated model of TdP arrhythmia.

Pharmacokinetic-pharmacodynamic modeling in the data analysis and interpretation of drug-induced QT/QTc prolongation

In this review, factors affecting the QT interval and the methods that are currently in use in the analysis of drug effects on the QT interval duration are overviewed with the emphasis on (population) pharmacokinetic-pharmacodynamic (PK-PD) modeling. Among which the heart rate (HR) and the circadian rhythm are most important since they may interfere with the drug effect and need to be taken into account in the data analysis. The HR effect or the RR interval (the distance between 2 consecutive R peaks) effect is commonly eliminated before any further analysis, and many formulae have been suggested to correct QT intervals for changes in RR intervals. The most often used are Bazett and Fridericia formulae introduced in 1920. They are both based on the power function and differ in the exponent parameter. However, both assume the same exponent for different individuals. More recent findings do not confirm this assumption, and individualized correction is necessary to avoid under- or overcorrection that may lead to artificial observations of drug-induced QT interval prolongation. Despite the fact that circadian rhythm in QT and QTc intervals is a well-documented phenomenon, it is usually overlooked when drug effects are evaluated. This may result in a false-positive outcome of the analysis as the QTc peak due to the circadian rhythm may coincide with the peak of the drug plasma concentration. In view of these effects interfering with a potential drug effect on the QTc interval and having in mind low precision of QT interval measurements, a preferable way to evaluate the drug effect is to apply a population PK-PD modeling. In the literature, however, there are only a few publications in which population PK-PD modeling is applied to QT interval prolongation data, and they all refer to antiarrhythmic agents. In this review, after the most important sources of variability are outlined, a comprehensive population PK-PD model is presented that incorporates an individualized QT interval correction, a circadian rhythm in the individually corrected QT intervals, and a drug effect. The model application is illustrated using real data obtained with 2 compounds differing in their QT interval prolongation potential. The usefulness of combining data of several studies is stressed. Finally, the standard approach based on the raw observations and formal statistics, as described in the Preliminary Concept paper of the International Conference on Harmonization, is briefly compared with the method based on population PK-PD modeling, and the advantages of the latter are outlined.