QT dispersion: time for an obituary?

Predicting Long-Term Ventricular Arrhythmia Risk in Children with Acute Lymphoblastic Leukemia Using Normal Values of Ventricular Repolarization Markers Established from Japanese Cohort Study

BACKGROUND

Cardiac complications due to anthracycline treatment may become evident several years after chemotherapy and are recognized as a serious cause of morbidity and mortality in cancer patients or childhood cancer survivors.

OBJECTIVES

We analyzed ventricular repolarization parameters in electrocardiography for pediatric acute lymphoblastic leukemia patients during chemotherapy and in long-term follow-up. To establish the reference values of ventricular repolarization parameters in children, we retrospectively summarized the Tpe interval, QT interval, QTc interval, and Tpe/QT ratio in healthy Japanese children.

METHODS

Electrocardiography data recorded from students in 1st and 7th grades were randomly selected from a database maintained by the school-based screening system in the Oita city cohort, Japan. Subsequently, chronological data of the Tpe/QT ratio in 17 pediatric patients with acute lymphoblastic leukemia were analyzed over time.

RESULTS

The mean ± standard deviation of the Tpe interval in 1st and 7th graders was 70 ± 7 and 78 ± 17 ms, respectively, while the mean ± standard deviation of the Tpe/QT ratio was 0.21 ± 0.02 and 0.22 ± 0.02 ms, respectively. During the intensive phase of treatment, the Tpe/QT ratios of 3 high-risk patients among the 17 patients with acute lymphoblastic leukemia exceeded the upper limit.

CONCLUSION

The Tpe/QT ratio has a potential clinical application in predicting the risk of long-term ventricular arrhythmia of cancer patients or childhood cancer survivors from childhood to adulthood.

The impact of electroconvulsive therapy on the spatial QRS-T angle and cardiac troponin T concentration in psychiatric patients

Background

Electroconvulsive therapy (ECT) is an effective treatment method used in psychiatry; however, its cardiac safety has not been clearly demonstrated. The aim of the study was evaluation of the ECT effects on the myocardium based on troponin T concentrations and the following ECG parameters: the spatial QRS-T angle (QRS-TA), QRS duration (QRSd) and the corrected QT interval (QTc).

Methods

In the study 44 patients (12 female and 32 male) were enrolled diagnosed with schizophrenia (n = 21) and major depressive disorders (n = 23), according to the DSM-IVR criteria. All cases were undergoing ECT procedures. The mean age of the patients was 36.9±16 years (range: 18–74). Resting ECG was recorded before performing ECG and 1 hour after. The spatial QRS-TA was reconstructed from 12-lead ECG using the inverse Dower method. Troponin T concentration was assessed before the procedure and 6 hours after ECT.

Results

No significant changes to troponin T concentrations were observed during the ECT series. The pre-ECT value of the spatial QRS-TA was 41.1±18.9°. The follow-up examinations did not reveal any significant increase of this parameter (p = 0.09) in any of the consecutive measurements. There were no significant changes in the QTc interval duration or the QRS complex duration demonstrated before the third, fifth and last procedure in the cycle (p>0.05). No significant changes to troponin T concentrations were observed during the ECT series.

Conclusions

Our findings indicate a lack of negative ECT effects on the risk of adverse cardiovascular events measured by the spatial QRS-T angle and cardiac troponin T concentration.

Effect of obstructive sleep apnea on QT dispersion: a potential mechanism of sudden cardiac death

OBJECTIVES

QT dispersion (QT(d)) measures the variability of the ventricular recovery time. QT(d) may identify patients at risk for ventricular arrhythmias and sudden cardiac death (SCD). The purpose of our study was to determine the effect of obstructive sleep apnea (OSA) on QT(d).

METHODS

There were 199 patients studied: 101 patients (28 women, 73 men) with OSA diagnosed in our sleep center and 98 patients (49 women, 49 men) without OSA from the outpatient clinic, representing the control group. QT intervals (milliseconds) were measured in each of the 12 leads of a standard surface electrocardiogram during wakefulness and QT(d) calculated (QT(max) - QT(min)). QT(c)(d), which corrects for heart rate, was also calculated.

RESULTS

Mean age and heart rate were similar in men and women with or without OSA. Control patients exhibited a significant difference (p < 0.001) in QT(d) between men (48 ± 19) and women (31 ± 13). Men and women with OSA had similar QT(d) (56 ± 35 vs. 54 ± 21) but higher QT(d) compared to the control group. QT(c)(d) results were similar to QT(d).

CONCLUSIONS

Patients with OSA and no structural heart disease have a higher QT(d)/QT(c)(d) compared to an overtly healthy patient population, possibly serving as a marker for an increased risk of SCD.

The prevalence and diagnostic/prognostic utility of sinus arrhythmia in the evaluation of congenital long QT syndrome

BACKGROUND

Congenital long QT syndrome (LQTS) affects 1 in 2,500 people and can cause syncope and sudden death. Sinus arrhythmia (SA) is nonpathologic baseline respiratory variation of the RR interval.

OBJECTIVE

This study sought to determine the frequency of SA and its clinical significance among patients with LQTS.

METHODS

We performed an institutional review board-approved retrospective review of all patients (N = 571) evaluated in our LQTS clinic from 7/2000 to 3/2008 diagnosed with LQTS (N = 281) or dismissed as otherwise normal (N = 290). Blinded to diagnosis, the first available electrocardiogram for each patient was examined to quantitate RR interval variability.

RESULTS

Overall, 151 of 281 patients (54%) with LQTS (159 female patients, average age 21.8 ± 16.5 years, average QTc 466 ± 43 ms) had SA with an average RR variability of 13% ± 8% compared with 201 of 290 (69%) patients dismissed as normal (178 female patients, average age 21.7 ± 16 years, average QTc 424 ± 30 ms) who demonstrated SA with RR variability of 16% ± 10% (P < .0001). These differences remained significant when patients on concurrent beta-blocker therapy were excluded (P < .001). SA was least common in LQT3 (23%) compared with LQT1 (61%, P < .005) and LQT2 (51%, P = .055). Patients presenting with torsades de pointes or aborted cardiac arrest had lower RR variability (10% ± 7%, P < .03).

CONCLUSION

SA frequency and magnitude of RR variability was lower among patients with LQTS compared with those patients dismissed as otherwise normal. This attenuation in RR interval variability remained when patients on beta-blocker therapy were excluded. Although the presence/absence of sinus arrhythmia is of little diagnostic value due to cohort overlap, LQTS patients with negligible RR interval variation may be at higher risk.

Changes in the QT intervals, QT dispersion, and amplitude of T waves after hemodialysis

BACKGROUND

Increased QT dispersion (QTd) has been associated with an increased risk for ventricular arrhythmias and sudden death in the general population and in various clinical states.

METHODS

We investigated the impact of hemodialysis (HD) on QT, QTd, and T-wave amplitude in subjects with end-stage renal failure. Data on 49 patients on chronic HD were studied. The QT, QTd, and the sum of amplitude of T waves (SigmaT) in millimetre in the 12 ECG leads, along with a host of other ECG parameters, body weight, blood pressure, heart rate, electrolytes, and hemoglobin/hematocrit were measured before and immediately after HD.

RESULTS

QT decreased (380.9 +/- 38.4-363.5 +/- 36.8 ms, P = 0.001), the QTc did not change (406.2 +/- 30.8-405.4 +/- 32.2 ms, P = 0.8), the QTd increased (31.3 +/- 14.6-43.9 +/- 18.6 ms, P = 0.003), and the SigmaT decreased (32.3 +/- 15.7-25.9 +/- 12.6 mm, P = 0.0001) after HD. There was no correlation between the change in QTd and the changes in serum cations, heart rate, the subjects' weight, T-wave duration, and SigmaT. However, the change in QTc correlated inversely with the change in serum Ca(++) (r =-0.339, P = 0.021).

CONCLUSION

QTd increased, the SigmaT decreased, and the QTc and T-wave duration remained stable, after HD. The QTd increase, although may be real, could also reflect measurement errors stemming from the decrease in the amplitude of T waves (as shown recently), imparted by HD; this requires clarification, to use QTd in patient on HD.

QT interval and dispersion in very young children treated with antipsychotic drugs: a retrospective chart review

OBJECTIVES AND BACKGROUND

QT dispersion (QTd) is a measure of interlead variations of the surface 12-lead electrocardiogram (ECG). Increased QTd, found in various cardiac diseases, reflects cardiac instability and risk for lethal cardiac arrhythmias. Research suggests a link between psychotropic treatment, ECG abnormalities (QT prolongation), and increased sudden cardiac mortality rates. Reports of sudden death in children treated with psychotropic drugs have raised concerns about cardiovascular monitoring and risk stratification. QTd analysis has not been investigated in very young children treated with antipsychotic drugs. In the present retrospective chart review study, we calculated QT interval, QTd, and their rate-corrected values in very young children treated with antipsychotics.

METHODS

The charts of 12 children (ages 5.8 +/- 0.98 yr; 4 girls, 8 boys) were examined before initiation of antipsychotic treatment [risperidone (n = 7), clotinapine (n = 1), and propericiazine (n = 4)] and during the maintenance period after achieving a positive clinical response. Three children were concomitantly maintained on methylphenidate. QT interval, QTd, and their rate-corrected values were calculated.

RESULTS

QT interval, QTd, and their rate-corrected values were all within normal values both before and after successful drug treatment.

CONCLUSIONS

This preliminary, naturalistic, small-scale study suggests that antipsychotic treatment, with or without methylphenidate, in very young children is not commonly associated with significant alterations of QT interval and dispersion, suggesting the relative safety of these agents in this unique age group.

[Clinical significance of dynamic QT-interval-analyses]

Dynamic parameters of ventricular repolarization as Holter derived parameters expressed as QT-interval adaptation to heart rate changes (QT/RR-slope) and QT-interval-variability are being more and more frequently used to identify patients with increased risk for ventricular arrhythmias. Steep QT-RR-slopes, reflecting inadequate adaptation of ventricular repolarization to heart rate changes, as well as increased QT-interval-variability, reflecting temporal inhomogeneity of ventricular repolarization duration, are frequently observed in patients at risk for sudden cardiac death. Additionally, there is strong evidence for significant alterations in the dynamics of action potential duration restitution in patients with structural heart disease. This review gives an up-to-date overview about the current research in methods of assessment and clinical relevance of dynamic parameters of ventricular repolarization.

Ventricular repolarization: An overview of (patho)physiology, sympathetic effects and genetic aspects

Most textbook knowledge on ventricular repolarization is based on animal data rather than on data from the in vivo human heart. Yet, these data have been extrapolated to the human heart, often without an appropriate caveat. Here, we review multiple aspects of repolarization, from basic membrane currents to cellular aspects including extrinsic factors such as the effects of the sympathetic nervous system. We critically discuss some mechanistic aspects of the genesis of the T-wave of the ECG in the human heart. Obviously, the T-wave results from the summation of repolarization all over the heart. The T-wave in a local electrogram ideally reflects local repolarization. The repolarization moment is composed of the moment of local activation plus local action potential duration (APD) at 90% repolarization (APD90). The duration of the latter largely depends on the balance between L-type Ca2+ current and the delayed rectifier currents. Generally speaking, there is an inverse relationship between local activation time and local APD90, leading to less dispersion in repolarization moments than in activation moments or in APD90. In transmural direction, the time needed for activation from endocardium toward epicardium has been considered to be overcompensated by shorter APD90 at the epicardium, leading to the earliest repolarization at the subepicardium. In addition, mid-myocardial cells would display the latest repolarization moments. The sparse human data available, however, do not show any transmural dispersion in repolarization moment. Also, the effect of adrenergic stimulation on APD90 has been studied mainly in animals. Again, sparse human data suggest that the effect of adrenergic stimulation is different in the human heart compared to many other mammalian hearts. Finally, aspects of the long QT syndrome are discussed, because this intrinsic genetic disease results from repolarization disorders with extrinsic aspects.

The long QT syndrome family of cardiac ion channelopathies: A HuGE review*

Long QT syndrome (LQTS) refers to a group of "channelopathies"-disorders that affect cardiac ion channels. The "family" concept of syndromes has been applied to the multiple LQTS genotypes, LQT1-8, which exhibit converging mechanisms leading to QT prolongation and slowed ventricular repolarization. The 470+ allelic mutations induce loss-of-function in the passage of mainly K+ ions, and gain-of-function in the passage of Na+ ions through their respective ion channels. Resultant early after depolarizations can lead to a polymorphic form of ventricular tachycardia known as torsade de pointes, resulting in syncope, sudden cardiac death, or near-death (i.e., cardiac arrest aborted either spontaneously or with external defibrillation). LQTS may be either congenital or acquired. The genetic epidemiology of both forms can vary with subpopulation depending on the allele, but as a whole, LQTS appears in every corner of the globe. Many polymorphisms, such as HERG P448R and A915V in Asians, and SCN5A S1102Y in African Americans, show racial-ethnic specificity. At least nine genetic polymorphisms may enhance susceptibility to drug-induced arrhythmia (an "acquired" form of LQTS). Studies have generally demonstrated greater QT prolongation and more severe outcomes among adult females. Gene-gene interactions, e.g., between SCN5A Q1077del mutations and the SCN5A H558B polymorphism, have been shown to seriously reduce ion channel current. While phenotypic ascertainment remains a mainstay in the clinical setting, SSCP and DHPLC-aided DNA sequencing are a standard part of mutational investigation, and direct sequencing on a limited basis is now commercially available for patient diagnosis.

QT dispersion, QT maximum and risk of cardiac death in the Caerphilly Heart Study

BACKGROUND

It has been postulated that increased inter-lead differences in QT interval (QT dispersion) and the maximum QT interval (QTmax), in the standard 12-lead electrocardiogram (ECG), may be associated with an increased risk of cardiac death. The aims of this study were to assess the relationship between QT dispersion and QTmax, corrected and uncorrected for heart rate, and the risk of cardiac death.

DESIGN

Nested case-control study within the Caerphilly prospective cohort study.

METHODS

We studied 2512 men who participated in phase 1 of the Caerphilly study between 1979 and 1983. After a mean follow up of 7.1 years, 218 men had died from coronary heart disease and these men were compared with 218 age-matched controls.

RESULTS

Data are presented on 422 patients with ECG suitable for analysis, 207 cases and 215 controls. Four trained observers measured the QT intervals and the reliability of each observer was estimated using repeat measurements on a randomly chosen sub-sample of ECGs. Median corrected QT dispersion and corrected QTmax were significantly higher in cases than in controls (51.9 versus 47.7 ms [P=0.01] and 430 versus 421 ms [P<0.001] respectively). In univariate analyses by quartiles of corrected QT dispersion and corrected QTmax, increased risk was largely confined to the upper quartile of the distribution with these subjects having twice the risk of those in the lower quartile [odds ratio (OR) 2.14, 95% confidence interval (CI) 1.2-3.7 and 2.56 (95% CI 1.5-4.5) respectively]. In logistic regression analysis, adjusted for age, smoking, body mass index, hypertension, history of myocardial infarction and ECG Minnesota code, we observed an increased risk in the upper quartile of the corrected QT dispersion relative to the other three quartiles combined [adjusted OR=1.74 (P=0.03)]. The magnitude of this association was increased in analyses based on the data from the most reliable observers. The association between corrected QTmax and cardiac death was attenuated in multivariate analysis. The findings in relation to both uncorrected QT dispersion and uncorrected QTmax were similar, i.e., consistent with a significant independent effect of QT dispersion but not QTmax for cardiac death in multivariate analysis.

CONCLUSION

The data suggest that QT dispersion is an independent predictor of cardiac death provided it can be measured with sufficient reliability. The association is non-linear with increased risk largely confined to the upper quartile of the distribution. The QT maximum is not an independent predictor of cardiac death.

QT dispersion in the elderly. The ILSA Study

BACKGROUND AND AIMS

In the last few years there has been active interest in the study of QT interval dispersion (QT-d) calculated from the 12-lead ECG, as a non-invasive method of investigating the homogeneity of ventricular recovery time. The aim of this study was to evaluate QT interval dispersion, analyzing in particular gender and age relationships. Discussion of its electrophysiologic and clinic meaning is still open; moreover, the method must be standardized and normal values should be clearly defined.

METHODS

The two common indices, range and standard deviation of QT, were taken into account. The study sample is part of the population-based Italian Longitudinal Study on Aging (ILSA) with individuals older than 64 years. Three groups were identified by clinical data: 256 healthy subjects, 98 patients with only cardiac diseases, and 472 patients with only hypertension.

RESULTS

Age (< 75 and > 75) and gender subgroups were considered, showing that age and gender influence the QT-d differently in the three groups. QT-d indices were influenced in the healthy group by gender (p < 0.001), in the cardiopathy group by age (p < 0.001), and in the hypertension group by age (p < 0.02) and gender (p < 0.01). Then the two gender groups were considered separately. In the female group, QT-d increased significantly with age only in the healthy group (p < 0.02), whereas in the male group it increased significantly in the cardiopathy and hypertension groups (p < 0.01).

CONCLUSIONS

The two QT-d indices behaved in a very similar way in all the comparisons. In older people, gender and age influenced the three clinical selected groups differently. However, it was shown that is not possible to indicate a clear, definite threshold value classifying with accuracy a single subject in the clinical groups; and a clear-cut, direct clinic application is still doubtful.

Time course of appearance of markers of arrhythmia in patients with tetralogy of Fallot before and after surgery

Sudden death and ventricular tachycardia are known to occur late after correction of tetralogy of Fallot. Abnormal dispersion of the QT interval, ventricular late potentials, and prolongation of the QRS complex, alone or in combination, are useful markers of the risk for such complications. Our present prospective study investigates the time course of appearance of two markers, dispersion of QT and JT, and ventricular late potentials, before and after corrective surgery. Dispersion of QT and JT, and signal averaged electrocardiographic parameters, were determined sequentially in 20 patients before, a mean of 9 +/- 3 days after, and again 35 +/- 11 days post-operatively. Dispersion of QT was already abnormal before surgery in two-fifths of the patients, but increased markedly in the later post-operative period. Ventricular late potentials were absent before surgery and in the immediate post-operative period, but were found in one-fifth of patients 1 month later. We conclude that abnormal dispersion of QT is, to some extent, a fact of the natural history of tetralogy of Fallot, but is significantly amplified by surgery. Ventricular late potentials, on the other hand, are absent before surgery, but appear with some delay after the operation, probably as a result of scarring rather than the surgical incision itself. Long-term follow-up is needed to assess the significance of these findings.

Safety of non-antiarrhythmic drugs that prolong the QT interval or induce torsade de pointes: an overview

The long and growing list of non-antiarrhythmic drugs associated with prolongation of the QT interval of the electrocardiogram has generated concern not only for regulatory interventions leading to drug withdrawal, but also for the unjustified view that QT prolongation is usually an intrinsic effect of a whole therapeutic class [e.g. histamine H(1) receptor antagonists (antihistamines)], whereas, in many cases, it is displayed only by some compounds within a given class of non-antiarrhythmic drugs because of an effect on cardiac repolarisation. We provide an overview of the different classes of non-antiarrhythmic drugs reported to prolong the QT interval (e.g. antihistamines, antipsychotics, antidepressants and macrolides) and discusses the clinical relevance of the QT prolonging effect. Drug-induced torsade de pointes are sometimes considered idiosyncratic, totally unpredictable adverse drug reactions, whereas a number of risk factors for their occurrence is now recognised. Widespread knowledge of these risk factors and implementation of a comprehensive list of QT prolonging drugs becomes an important issue. Risk factors include congenital long QT syndrome, clinically significant bradycardia or heart disease, electrolyte imbalance (especially hypokalaemia, hypomagnesaemia, hypocalcaemia), impaired hepatic/renal function, concomitant treatment with other drugs with known potential for pharmacokinetic/pharmacodynamic interactions (e.g. azole antifungals, macrolide antibacterials and class I or III antiarrhythmic agents). This review provides insight into the strategies that should be followed during a drug development program when a drug is suspected to affect the QT interval. The factors limiting the predictive value of preclinical and clinical studies are also outlined. The sensitivity of preclinical tests (i.e. their ability to label as positive those drugs with a real risk of inducing QT pronglation in humans) is sufficiently good, but their specificity (i.e. their ability to label as negative those drugs carrying no risk) is not well established. Verapamil is a notable example of a false positive: it blocks human ether-a-go-go-related (HERG) K(+) channels, but is reported to have little potential to trigger torsade de pointes. Although inhibition of HERG K(+) channels has been proposed as a primary test for screening purposes, it is important to remember that several ion currents are involved in the generation of the cardiac potential and that metabolites must be specifically tested in this in vitro test. At the present state of knowledge, no preclinical model has an absolute predictive value or can be considered as a gold standard. Therefore, the use of several models facilitates decision making and is recommended by most experts in the field.

Effects of cisapride on ventricular depolarization-repolarization and arrhythmia markers in infants

To study prospectively the effects of cisapride on ventricular repolarization, depolarization, and arrhythmia markers in neonates, we determined before and three days after starting cisapride (1 mg/kg/day): corrected QT interval (QTc) and QT dispersion (QTd) on standard ECGs, and duration of filtered QRS (fQRS) and of low amplitude (<40 microV) terminal signals (LAS40, ms) and root mean square of the last 40 ms (RMS40, microV) using high-gain signal-averaged ECG (SAECG). Twenty-four term and 11 preterm infants (gestational age 23-35 weeks) were studied at a median chronological age of 32 days. QTc and QTd were not different between term and preterm infants. Cisapride lengthened QTc (mean +/- SD; ms: 396.6 +/- 24.8 before vs. 417.0 +/- 35.2 after, p < 0.001). Three term and two preterm infants (5/35 = 14%; 95% CI: 5-30%) had a QTc >450 ms after cisapride. QTd after cisapride increased significantly in all infants with prolonged QTc. Filtered QRS, LAS40, and RMS40 before and after cisapride were within our normal values. We conclude that cisapride prolongs ventricular repolarization in neonates and infants without altering depolarization. Although no clinical arrhythmias were observed the dose of 0.8 mg/kg/day should not be exceeded.

Risk assessment for antimicrobial agent-induced QTc interval prolongation and torsades de pointes

Over the past several years a multitude of new pharmaceutical agents have been released to the market. Several of them were withdrawn altogether or their use severely restricted to certain indications due to unexpected adverse events, including fatalities. Progress in developing new compounds clearly has surpassed our technology, in some cases, to measure and predict certain toxicities. Prolongation of the QT interval, which may lead to potentially life-threatening ventricular arrhythmias such as torsades de pointes, is one example. Regulatory agencies such as the Food and Drug Administration are increasing standards by which drugs are evaluated for cardiac toxicity related to QT interval prolongation. It is imperative that clinicians be knowledgeable of the risk factors for QT prolongation and avoid the use of culpable agents in patients at risk for QT prolongation.

Drugs that prolong QT interval as an unwanted effect: assessing their likelihood of inducing hazardous cardiac dysrhythmias

Medicinal products that, as an unwanted effect, prolong the QT interval of the electrocardiogram (ECG) can trigger episodes of polymorphic ventricular dysrhythmias, called torsades de pointes, which occasionally culminate in sudden death. The accurate measurement of QT interval requires the adoption of appropriate criteria of recording, measurement and data processing. Traditionally, QT interval is standardised to a reference heart rate of 60 beats/min by using the Bazett algorithm. However, this correction method can bias observed QT intervals in either direction. The ECG reflects cardiac electrical currents generated by ions (Na+, K+ and Ca2+) entering and leaving the cytosol mainly via transmembrane channels. Na+ and Ca2+ carry inward depolarising currents (INa, ICa) whereas K+ carries outward repolarising currents (Ito, IKr, IKS and IK1). Sometimes, a prolonged QT interval is a desired drug effect but, more commonly it is not, and reflects abnormalities in cardiac repolarisation heralding torsades de pointes. Furthermore, the potential torsadogenic activity of drugs is favoured by concurrent cardiac risk factors (old age, female gender, bradycardia, electrolyte imbalances, cardiac diseases etc.) which reduce cardiac repolarisation reserve. The evaluation of the cardiac safety of drug candidates can be started by determining their potency as IKr blockers in cloned Human Ether-a-go-go Related Gene (HERG) channels expressed in mammalian cells. Compounds passing successfully this test (desirable cardiac safety index > 30, calculated as ratio of IC50 against IKr over ED50 determined in an efficacy test) should be further investigated in other relevant human cardiac ion currents, in in vitro animal heart preparations and finally in in vivo pharmacodynamic models. The decision as to whether the potential benefit of a new drug outweighs the cardiac risk inherent in its therapeutic use should be made in the light of the condition that it is expected to treat and with reference to alternative drug therapies. If a drug represents a unique therapeutic advance, non-clinical and clinical signals of unsatisfactory cardiac safety may not constitute sufficient grounds to abandon its development. However, if the drug offers only marginal benefits over existing therapies, decisions concerning its possible development should be taken by corporate policy makers.