Long QT syndrome. Why does sex matter?

Evaluation of the Tp-Te interval, Tp-Te/QTc ratio, and QT dispersion in patients with Turner syndrome

Objective:

To evaluate ventricular repolarization parameters using the interval from the peak to the end of the T wave (Tp–Te), together with QT and corrected QT (QTc) intervals, QT dispersion (QTd), and Tp-Te/QTc ratio in patients with Turner syndrome (pwTS) and to compare the results with those from healthy controls.

Methods:

In total, 38 patients previously diagnosed with Turner syndrome (TS) and 35 healthy girls (controls) were included in our cross-sectional study. Twelve-lead electrocardiography (ECG) and echocardiography after a 30-min rest were performed. The QT, QTc, QTd, Tp-Te interval, and Tp-Te/QTc ratio were determined.

Results:

No differences in age or sex were observed between the groups. QT intervals were similar in both groups [pwTS: 354.76±25.33 ms, controls (C): 353.29±17.51 ms, p=0.775]. pwTS had significantly longer QTc and QTd than controls (411.87±22.66 ms vs. 392.06±13.21 ms, p<0.001 and 40.31±2.02 ms vs. 37.54±1.83 ms, p<0.001, respectively). Similarly, the Tp-Te interval and Tp-Te/QTc ratio were significantly longer in pwTS than in controls (71.89±3.39 ms vs. 65.34±2.88 ms, p<0.001 and 0.17±0.01 vs. 0.16±0.01, p=0.01).

Conclusion:

As pwTS have longer QTc, QTd, Tp–Te interval, and Tp-Te/QTc ratio, an annual follow-up with ECG can provide awareness and even prevent sudden death in them. Also avoiding the use of drugs that makes repolarization anomaly and having knowledge about the side effects of these drugs are essential in pwTS.

A molecular pathway analysis informs the genetic risk for arrhythmias during antipsychotic treatment

Arrhythmias are a frequent and potentially fatal side effect of antipsychotic treatment. Strict ECG monitoring and clinical interviews are the standards used to prevent arrhythmias. A biologic predictive tool is missing. The identification of a genetic makeup at risk of antipsychotic-induced arrhythmias is the aim of the present investigation. The aim of this study was to identify a molecular pathway enriched in single nucleotide polymorphisms associated with antipsychotic-induced QTc modifications. In total, 661 schizophrenic individuals from the CATIE study, M=486 (73.52%), mean age=40.92±11.02, were included. QTc variation was measured as a phase-specific change-created variable. A nested mixed regression for a repeated-measures model served in R for the analysis of the clinical and treatment-related covariates and molecular pathway analysis. Plink was used for the genetic genome-wide analysis. Quality checking was the standard (genotype call rate>0.95; minor allele frequency>0.01; Hardy-Weinberg equilibrium<0.0001) and the inflation factor was controlled by λ values. Quetiapine and perphenazine were associated with QTc variation during phase 1. No other significant association was detected. No significant inflation was detected. A number of molecular pathways were associated with QT variation at a conservative (adjusted) P value less than 0.05, including pathways related to neuronal wiring and collagen biosynthesis, along with pathways related to K+ currents and cardiac contraction. Pathways related to neuronal wiring, collagen biosynthesis, and ion currents were identified as possibly involved in QTc modifications during antispsychotic treatment in SKZ patients.

Cardiac Sodium Channel Mutations: Why so Many Phenotypes?

The cardiac Na(+) channel (Nav1.5) conducts a depolarizing inward Na(+) current that is responsible for the generation of the upstroke Phase 0 of the action potential. In heart tissue, changes in Na(+) currents can affect conduction velocity and impulse propagation. The cardiac Nav1.5 is also involved in determination of the action potential duration, since some channels may reopen during the plateau phase, generating a persistent or late inward current. Mutations of cardiac Nav1.5 can induce gain or loss of channel function because of an increased late current or a decrease of peak current, respectively. Gain-of-function mutations cause Long QT syndrome type 3 and possibly atrial fibrillation, while loss-of-function channel mutations are associated with a wider variety of phenotypes, such as Brugada syndrome, cardiac conduction disease, dilated cardiomyopathy, and sick sinus node syndrome. The penetrance and phenotypes resulting from Nav1.5 mutations also vary with age, gender, body temperature, circadian rhythm, and between regions of the heart. This phenotypic variability makes it difficult to correlate genotype-phenotype. We propose that mutations are only one contributor to the phenotype and additional modifications on Nav1.5 lead to the phenotypic variability. Possible modifiers include other genetic variations and alterations in the life cycle of Nav1.5 such as gene transcription, RNA processing, translation, posttranslational modifications, trafficking, complex assembly, and degradation. In this chapter, we summarize potential modifiers of cardiac Nav1.5 that could help explain the clinically observed phenotypic variability. Consideration of these modifiers could help improve genotype-phenotype correlations and lead to new therapeutic strategies.

Cardiac sodium channel mutations: why so many phenotypes?

Mutations of the cardiac sodium channel (Nav1.5) can induce gain or loss of channel function. Gain-of-function mutations can cause long QT syndrome type 3 and possibly atrial fibrillation, whereas loss-of-function mutations are associated with a variety of phenotypes, such as Brugada syndrome, cardiac conduction disease, sick sinus syndrome, and possibly dilated cardiomyopathy. The phenotypes produced by Nav1.5 mutations vary according to the direct effect of the mutation on channel biophysics, but also with age, sex, body temperature, and between regions of the heart. This phenotypic variability makes genotype-phenotype correlations difficult. In this Perspectives article, we propose that phenotypic variability not ascribed to mutation-dependent changes in channel function might be the result of additional modifiers of channel behaviour, such as other genetic variation and alterations in transcription, RNA processing, translation, post-translational modifications, and protein degradation. Consideration of these modifiers might help to improve genotype-phenotype correlations and lead to new therapeutic strategies.

Age-and sex-dependent mRNA expression of KCNQ1 and HERG in patients with long QT syndrome type 1 and 2

INTRODUCTION

The main goal of this study was to examine the patient age and sex dependent expression of KCNQ1 and HERG genes that encode potassium channels responsible for the occurrence of long QT syndrome (LQTS).

MATERIAL AND METHODS

The study enrolled 43 families whose members suffered from LQTS type 1 (LQTS1) or 2 (LQTS2) or were healthy. The study attempted to prove that β-actin is a good endogenous control when determining the expression of the studied genes. Examination of gene expression was achieved with quantitative real-time PCR (QRT-PCR). Expression of the investigated genes was inferred from the analysis of the number of mRNA copies per 1 μg total RNA isolated from whole blood.

RESULTS

Significantly lower KCNQ1 and KCNH2 mRNA levels in healthy females than healthy males were observed (p = 0.032; p = 0.02). In male patients both transcripts were expressed at a lower level (p = 0.0084; p = 0.035). The comparison of transcriptional activity of KCNQ1 and KCNH2 in healthy adults and children revealed higher KCNQ1 and lower KCNH2 mRNA levels in healthy adults (p = 0.033; p = 0.04), higher KCNQ1 and lower KCNH2 mRNA levels in adult patients below 55 years old than in adults over 55 years old (p=0.036; p = 0.044), and significantly higher KCNQ1 and lower KCNH2 mRNA levels in adult patients (over 55 years) than in paediatric patients (below 15 years) (p=0.047; p = 0.08).

CONCLUSIONS

The results support the hypothesis that KCNQ1 and HERG gene expression is influenced by age and gender in human patients with long QT syndrome and in healthy subjects.

Probable quetiapine-mediated prolongation of the QT interval

PURPOSE

QT prolongation can occur with both first- (FGA) and second-generation antipsychotics (SGA). QT prolongation was identified in an adult patient who presented to the emergency room with schizophrenia, fluid and electrolyte imbalances, and pneumonia. Quetiapine, an SGA, was a component of the pharmacotherapy regimen. Based on the Naranjo adverse drug reaction probability scale rating criteria, a probable causal association was made.

METHODS

PubMed and Ovid were searched using the terms antipsychotic, psychotropic, QT interval, corrected QT interval (QTc) prolongation, and quetiapine. References were examined for additional articles related to antipsychotic drugs and the QT interval.

DISCUSSION

In this patient, the use of quetiapine was identified as a contributing factor in QT prolongation. Prior QT prolongation was experienced with ziprasidone, another SGA. The antidepressant and dose remained consistent throughout the inpatient course of treatment. Other risk factors in this patient included hypokalemia, dehydration, pneumonia, age, gender, and concurrent usage of an antidepressant. Dual psychiatric diagnoses, preexisting cardiovascular disease, and electrolyte disturbances may increase this risk potential.

CONCLUSION

Psychiatric patients may be more at risk of cardiovascular complications, such as QT interval prolongation. The pharmacist can help evaluate risk factors and provide input into the care of all patients, particularly those identified as at risk.

Association of increased QTc interval with the cardiometabolic syndrome

Recent studies indicate a high prevalence of increased QTc interval length in patients affected by the metabolic syndrome, but there is no data available to demonstrate the correlation of the QTc interval with severity of the cardiometabolic syndrome (CMS). The objective of this study was to estimate the association between increasing number of cardiometabolic abnormalities and increasing QTc interval length. Electrocardiograms were collected from 1420 participants in a cross-sectional study. The QTc interval lengths were corrected for heart rate using Bazett's formula. CMS was determined according to the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) guidelines. Multiple linear regression models were used examining associations between increasing number of individual components of syndrome with QTc interval length. Participants with CMS had significantly longer QTc interval length, controlling for age, body mass index (BMI), sex, and ethnic group. Increasing number of CMS components was significantly associated with increased QTc interval length, even after adjusting for age, BMI, total cholesterol, fasting C peptide, and history of heart disease. These findings suggest that QTc interval length is increased in the presence of CMS and is linearly related to an increase in number of metabolic abnormalities.

Gender differences in drug toxicity

Clinical data suggest that gender dimorphic profiles are emerging in terms of both drug efficacy and adverse drug reactions (ADRs). With an increasing emphasis on individualised therapies and the need to prevent drug attrition there is a compelling need to understand the molecular basis for gender dimorphic profiles in ADRs and the consequences. Classes of agents exhibiting gender-based variation in pharmaceutical efficacy and toxicity include anaesthetics, HIV-1 therapies and antiarrhythmic drugs. Body weight differences are often cited as a reason for differences in drug pharmacokinetics and subsequent toxicity. However, some studies accounted for these factors and still found significance suggesting that dosage versus body weight does not explain the outcome. Here, we present an overview of current understanding of gender-specific drug toxicity and present rational molecular explanations for these adverse events. There is mounting evidence in support of hormonal effects underpinning the majority of the ADR differences observed between the sexes.

Clinical characteristics of patients with drug-induced QT interval prolongation and torsade de pointes: identification of risk factors

The present study aimed to investigate the causative medications and underlying risk factors that predispose to drug-induced QT interval prolongation. Twenty-one patients with drug-induced long QT (90% females, mean age 64.3 +/- 14.1 years) were included in the study. Transthoracic echocardiography as well as continuous or ambulatory 48-h electrocardiographic monitoring was carried out in all patients during their hospitalization. The mean corrected QT (QTc) interval was 542 +/- 56.8 ms. Known cardiac agents (mainly class III antiarrhythmics) were implicated in 13/21 (62%), antipsychotics in 8/21 (38%), and antibiotics in 5/21 patients (24%). Potential drug-interactions through inhibition of cytochrome P450 isoenzymes were considered responsible in 5/21 cases (24%). The underlying cardiovascular diseases included hypertension (57%) with left ventricular hypertrophy (29%), paroxysmal atrial tachyarrhytmias (48%), heart failure (14%), valvular heart disease (10%), and coronary artery disease (5%). Torsade de pointes (TdP) was recorded in 6/21 of patients, and cardiac arrest necessitating resuscitation occurred in five of them. A significant correlation was observed between administration of cardiac agents and TdP events (P < 0.05). TdP and cardiac arrest events were both associated with a QTc interval >510 ms (P < 0.05). Advanced age (>60 years), female gender, hypertension and paroxysmal atrial tachyarrhytmias were the most common identifiable pre-existing factors for drug-induced long QT in our patient cohort. Marked QTc interval prolongation should be considered of prognostic significance for TdP and cardiac arrest events.

A KCNQ1 V205M missense mutation causes a high rate of long QT syndrome in a First Nations community of northern British Columbia: a community-based approach to understanding the impact

PURPOSE

Hereditary long QT syndrome is named for a prolonged QT interval reflecting predisposition to ventricular arrhythmias and sudden death. A high rate in a remote, northern Canadian First Nations community was brought to attention.

METHODS

Two severely affected index cases and 122 relatives were ascertained using community-based participatory research principles. Genetic sequencing of five known genes responsible for long QT syndrome was carried out on the index cases, leading to the identification of a novel missense mutation. Functional properties of the identified mutation were studied in transfected mouse ltk- cells using whole cell patch clamp techniques. Corrected QT interval measurements were obtained from participants and subsequent genotyping of relatives was carried out.

RESULTS

In the two index cases, a novel missense mutation (V205M) was identified in the S3 transmembrane helix of KvLQT1, the pore forming domain of the IKs channel complex. In transfected mouse ltk-cells the V205M mutation suppressed IKs by causing a dramatic depolarizing shift in activation voltage coupled with acceleration of channel deactivation. Twenty-two mutation carriers had a significantly higher mean corrected QT interval than noncarriers (465 +/- 28 milliseconds vs. 434 +/- 26 milliseconds, P < 0.0001); however, 30% of carriers had a corrected QT interval below 440 milliseconds.

CONCLUSION

A novel KCNQ1 mutation in this founder population likely confers increased susceptibility to arrhythmias because of decreased IKs current. Even with a common mutation within a relatively homogenous population, clinical expression remains variable, exemplifying the multifactorial nature of long QT syndrome, and supporting the difficulty of definitive diagnosis without genetic testing. A community participatory approach enabled a comprehensive evaluation of the impact.

Drug-induced long QT syndrome in women: review of current evidence and remaining gaps

BACKGROUND

Women are at an increased risk of drug-induced long QT syndrome (LQTS). This major cardiac adverse effect may lead to malignant polymorphic ventricular tachycardias, termed torsades de pointes, which may degenerate into ventricular fibrillation and cause sudden death.

OBJECTIVE

This article reviews current evidence and remaining gaps in knowledge about drug-induced LQTS in women.

METHODS

Using the search terms gender, sex, and sex differences in combination with cardiac electrophysiology, long QT syndrome, HERG, membrane transporters, and cytochromes, we conducted a systematic review of the available literature in the PubMed database. Relevant English- and French-language publications (to October 2007) on sex differences in LQTS were identified.

RESULTS

Clinical and experimental studies have reported that gonadal hormones play a role in sex-related differences of QT interval prolongation. Androgens may diminish drug effects on heart repolarization, and estrogens may facilitate arrhythmias. Furthermore, sex-related differences in the density of ion channels may partially explain this phenomenon. However, the magnitude of hormone-dependent differences observed in these studies remains very small compared with the large differences observed in clinical settings. Therefore, many scientists agree that the mechanisms responsible for sex-related differences in the risk of proarrhythmia from drugs remain largely undefined.

CONCLUSIONS

Other factors, such as sex-related modulation of drug disposition in situ, may fill the gaps in our understanding of the sex differences observed in drug-induced LQTS. We suggest that mechanisms such as the modulation of the pharmacokinetics of IKr (rapid component of the delayed rectifier potassium current) blockers, via modulation of intra- and extracellular concentrations, may be of major importance. Sex-specific changes in drug transport and metabolism will result in different plasma and intracellular levels acting along a dose-response effect on IKr block. Consequently, important hormone-dependent factors such as metabolic enzymes and membrane transporters need to be investigated in new basic research studies.

QTc interval prolongation in children with Ulrich-Turner syndrome

INTRODUCTION

The Ullrich-Turner-Syndrome (UTS) is the most commonly occurring sex chromosome abnormality in females. Cardiac malformations are well known, but no data exist on specific electrocardiogram (ECG) patterns in children and adolescents. A prolongation of the QT interval on the ECG has been correlated to an increased risk for sudden cardiac death, and medical treatment is warranted in patients with long QT syndrome (LQTS). Moreover, several drugs of common use are contraindicated in LQTS because of their effects on myocardial repolarization.

METHODS

The ECG tracings of 86 UTS patients [mean age (+/-SD): 11.0+/-3.6 years; mean height-SD: -2.6+/-1.0] were analyzed and compared to age-matched control groups of 75 boys (mean age: 11.3+/-3.5 years; mean height-SD: -1.9+/-1.0) and 62 girls (mean age: 10.1+/-3.2 years; mean height-SD: -2.5+/-0.9) with short stature.

RESULTS

Eighteen UTS patients (20.9%) had an abnormally prolonged QTc >0.45 s in contrast to only one control subject (0.9%). The QTc interval of UTS patients was significantly prolonged compared to that of the controls (p<0.01) and normal values.

CONCLUSIONS

There is an increased prevalence of a long QT interval among UTS patients. This should be taken into account for the cardiovascular screening of such patients. Patients with UTS have an intrinsically prolonged QT interval and as such may be at higher risk for arrhythmias in the context of a QT-prolonging medication.

Pharmacogenomics: challenges and opportunities

The outcome of drug therapy is often unpredictable, ranging from beneficial effects to lack of efficacy to serious adverse effects. Variations in single genes are 1 well-recognized cause of such unpredictability, defining the field of pharmacogenetics (see Glossary). Such variations may involve genes controlling drug metabolism, drug transport, disease susceptibility, or drug targets. The sequencing of the human genome and the cataloguing of variants across human genomes are the enabling resources for the nascent field of pharmacogenomics (see Glossary), which tests the idea that genomic variability underlies variability in drug responses. However, there are many challenges that must be overcome to apply rapidly accumulating genomic information to understand variable drug responses, including defining candidate genes and pathways; relating disease genes to drug response genes; precisely defining drug response phenotypes; and addressing analytic, ethical, and technological issues involved in generation and management of large drug response data sets. Overcoming these challenges holds the promise of improving new drug development and ultimately individualizing the selection of appropriate drugs and dosages for individual patients.

Cardiac structure and apnea/hypopnea index in patients with arterial hypertension and excessive weight

BACKGROUND/AIMS

Arterial hypertension is frequently associated with sleep apnea, excessive weight, and with changes in the echocardiographic characteristics of the left cardiac chambers. The present investigation was conducted in order to search for a possible relation between left cardiac structure and sleep apnea magnitude in patients with arterial hypertension and excessive weight.

METHODS

A group of 56 patients with arterial hypertension and mean body mass index of 30.6 +/- 3.8 (weight in kilograms/height in meters squared) was studied by echocardiography, sleep study and electrocardiography.

RESULTS

A relatively high mean apnea-hypopnea index (AHI) was found (17.9 +/- 17.2 episodes/h sleep), but this parameter was not found to be correlated with cardiac echocardiographic diameters. Patients with an AHI <5 episodes/h had smaller mean values for left atrial diameter, left ventricular mass index and left ventricular relative wall thickness, when compared to patients with an AHI value of > or =5. The mean corrected QT interval was found to be longer in female patients, whereas left ventricular end-diastolic diameter was smaller than in male patients.

CONCLUSION

In patients with arterial hypertension and excessive weight, significant apnea seems to be very common. In such patients, left ventricle wall thickness, left ventricle mass index and the left atrium diameter may act as surrogate markers for significant sleep apnea. Thus, the hypothesis is raised that hypoxia may lead to changes in heart structure.