Effects of aging and gender on QT dispersion in an overtly healthy population

Antiarrhythmic Drugs for Atrial Fibrillation: Selected Features of Ventricular Repolarization That Facilitate Proarrhythmic Torsades de Pointes and Favor Inpatient Initiation

The management approaches to patients with atrial fibrillation (AF) include rhythm-control strategies for those patients who are symptomatic despite rate control and for selected others in whom sinus rhythm is necessary for reasons beyond current symptoms (including commercial pilots, those who are felt likely to develop symptoms as comorbidities progress, and more). First-line therapies among the rhythm-control options are antiarrhythmic drugs (AADs). For many AADs, their initiation in-hospital is either a requirement or strongly advised- especially when the patient is in AF. This article explores some of the rationale behind this requirement to give clinicians a better understanding of the reasons for this undesired inconvenience.

Effect of nicorandil on QT dispersion in patients with stable angina pectoris undergoing elective angioplasty: A triple-blind, randomized, placebo-controlled study

Background

Nicorandil leads to the relaxation of fine vascular smooth muscle, and thus causes vasodilatation of major epicardial. Also, it has anti-arrhythmic and cardio-protective effects by improving reperfusion, and ultimately leads to a reduction in microvascular damage caused by percutaneous coronary intervention (PCI).

Objective

The aim of this study was to determine the effect of nicorandil on QT interval dispersion (QTd) in patients with stable angina pectoris during elective angioplasty.

Methods

This triple-blind and randomized clinical trial was performed on patients with stable angina pectoris, candidates for elective angiography referred to Imam Reza and Ghaem hospitals in Mashhad, Iran, between January and October 2016. The patients were randomly assigned to one of two groups receiving nicorandil (60 mg as 20 mg before and 40 mg after PCI) and placebo. All the patients underwent electrocardiography 12 hours before and 12 hours after PCI. The values of maximal corrected QT interval (QTc max) and QTd in these intervals, and the levels of changes in the QTd (QTd difference before angiography and after PCI) were compared between the two groups. Data were analyzed statistically using SPSS version 18 software via Chi-square and Independent-samples t-test.

Results

This study was performed on 90 patients (55 males and 35 females) with a mean age of 58.6±10.8 years, on two groups of 45 people. The two groups were matched for age, body mass index, cardiovascular risk factors and baseline testing. The QTd before angiography had no statistically significant difference between the patients of both groups (control: 77.7±17.1 vs. nicorandil: 80.7±14.2 ms; p=0.371). The QTd after PCI in the nicorandil group was lower than the control group (48.1±14.2 vs. 59.2±15.6 ms; p=0.000). The decrease rate in QTd had a statistically significant difference between the two groups (control: 18.9±11.0 vs. nicorandil: 33.5±9.5 ms; p=0.000).

Conclusions

The results of this study showed that oral administration of nicorandil around the PCI could further reduce QTd following PCI, compared to the control group.

Trial registration

The trial was registered at the Iranian Registry of Clinical Trials (http://www.irct.ir) with the Irct ID: IRCT2016120631159N1

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Daytime cardiac repolarization in patients with obstructive sleep apnea

PURPOSE

Obstructive sleep apnea (OSA) has been implicated in complications of cardiovascular disease, including arrhythmias and sudden cardiac death (SCD). Prolonged QT interval is associated with arrhythmias and SCD in patients with cardiovascular disease and apparently healthy humans. Apneic episodes during sleep in OSA patients are associated with QT prolongation due to increased vagal activity, but it is not understood whether chronic QT prolongation persists during normoxic daytime wakefulness.

METHODS

To determine whether daytime QT intervals in OSA patients are prolonged compared to control subjects, we recruited 97 (76 male, 21 female) newly diagnosed patients with OSA [apnea-hypopnea index (AHI) ≥5 events/h] and 168 (100 male, 68 female) healthy volunteers (AHI <5 events/h) and measured daytime resting QT and RR intervals from the electrocardiograms to determine QT prolongation corrected for heart rate (QTc).

RESULTS

All subjects with OSA were older and heavier, with increased heart rate, significantly increased AHI and arousal index, and reduced oxygen saturation (SpO2) during sleep, and spent less time in sleep with >90 % SpO2 compared to respective controls. QTc in patients with OSA (410 ± 3.3 for male and 433 ± 5.6 for female) was significantly increased compared to respective control groups (399 ± 2.9 for male and 417 ± 2.9 for female), after adjustment for age and body mass index.

CONCLUSIONS

Our data show that OSA in either men or women is associated with a significant increase in resting daytime QTc. The propensity for ventricular arrhythmias in patients with OSA may be a result of abnormalities in resting cardiac repolarization.

Sex and gender aspects in antiarrhythmic therapy

Although cardiac arrhythmia had long been considered a predominantly male syndrome, it is now clear that arrhythmia is also a primary cause of mortality in women. Notably, the manifestation of specific arrhythmia syndromes appears to be gender specific. In particular, female sex is an independent risk factor for development of torsade de pointes (TdP) arrhythmias not only in congenital long QT syndromes but also in acquired long QT syndromes which occur as adverse effects of existing drugs. Males, on the other hand, are more likely to develop Brugada syndrome. Recent clinical and experimental studies suggest that these differences may stem from intrinsic sex differences in cardiac tissue. These include fundamental electrical differences resulting from variable ion channel expression and diverse sex hormonal regulation via long-term genomic and acute nongenomic pathways, and sex differences in drug responses and metabolisms. Undoubtedly, determining the effect of gender on cardiac function will be difficult and require sophisticated methodologies. However, gender differences underlying predilection to distinct arrhythmia syndromes must be revealed so that new therapeutic strategies that take gender into account can be applied to at-risk patients.

Cardiologic side effects of psychotropic drugs

Psychotropic drugs can produce cardiovascular side effects associated with a degree of cardiotoxicity. The coexistence of a heart disease complicates the management of mental illness, can contribute to a reduced quality of life and a worse illness course. The co-occurrence of psychiatric disorders in cardiac patients might affect the clinical outcome and morbidity. Moreover, the complex underlying mechanism that links these two conditions remains unclear. This paper discusses the known cardiovascular complications of psychotropic drugs and analyzes the important implications of antidepressive treatment in patients with previous cardiac history.

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.

Prognostic evaluation of QT-dispersion in elderly hypertensive and normotensive patients

BACKGROUND

QT-corrected interval dispersion (QTcD) is an indirect index of increased heterogeneity of ventricular repolarization. However, the prognostic value of (QTcD) in elderly hypertensive and normotensive patients has not been thoroughly investigated yet.

METHODS

The study population consisted of 60 consecutive patients (34 males/26 females; mean age: 63+/-11 years) with mild to moderate essential arterial hypertension and 48 consecutive age-matched healthy subjects (24 males/24 females; 65+/-16 years). QTcD was measured by a 12-lead electrocardiogram (ECG) as the difference between maximum and minimum QT-interval, corrected for heart rate. Ventricular arrhythmias were recorded by a 24-hour Holter ECG and classified by a modified Lown's score (range: 0-6). Left ventricular mass was measured echocardiographically and indexed by body surface area [left ventricular mass index (LVMI)]. Nine patients were lost during the follow-up period. Patients were followed up for 54+/-9 months, and the primary end-point was the major cardiovascular events (including cardiac mortality).

RESULTS

Major cardiovascular events occurred in 22 patients (22%). Patients with QTcD>or=45 ms (n=35) had a higher rate of major cardiovascular events (43% vs 11%; log rank: 14.8; P<0.001), a higher LVMI (146+/-29 vs 104+/-21 g/m2; P<0.001), greater values of systolic and diastolic blood pressure (154+/-16 vs 144+/-18 mmHg; P<0.01 and 92+/-10 vs 88+/-8 mmHg; P<0.05, respectively), a higher number of premature ventricular beats (354+/-870 vs 113+/-301; P<0.05), and a greater Lown's score (3.7+/-1.9 vs 1.4+/-1.8; P<0.05) than patients with QTcD<45 ms. QTcD (>or=or<45 ms) was an independent predictor of major cardiovascular events (odds ratio: 4.9; 95% confidence interval: 2.0-12.1; P=0.001) after adjustment for LVMI, Lown's score (>or=or<3), age (>or=or<65 years), and QTc max (>or=or<437 ms).

CONCLUSIONS

QTcD is an independent predictor of major cardiovascular events in elderly hypertensive and normotensive patients and might be used in their risk stratification.

Sex-specific differences in side effects of psychotropic drugs: genes or gender?

Sex differences observed in the adverse effects associated with psychotropic drugs have not been reported consistently in the literature. In this review, we discuss the current published data on sex differences observed in the occurrence, symptomatology and reporting of the adverse effects associated with psychotropic drug effects, and discuss their clinical relevance. We reviewed the published data up to April 2009 on sex differences in the side effects of antipsychotics, antidepressant and mood stabilizers, by systematically searching PubMed using combinations of search terms and retrieving relevant references specifically reporting on these issues. The majority of the data was retrieved from clinical studies where the main outcome parameters did not relate specifically to sex differences. In most instances, sex was associated with other factors influencing side effects such as age, disease and body weight. Sex-related differences were reported in the side effects associated with antipsychotic drug-induced weight gain and metabolic syndrome, symptoms of sexual dysfunction caused by antidepressants and antipsychotic drugs and cardiac arrhythmic side effects associated with antipsychotic drugs. Women might differ from men not only in incidence but also in the presentation of clinical symptoms associated with adverse psychotropic drug effects. Clinicians should be made aware of the differences reported in the literature regarding the symptomatology, severity and recognition of the adverse psychotropic drug effects found in men and women.

QT dispersion and left ventricular hypertrophy in elderly hypertensive and normotensive patients

Inhomogeneity of ventricular repolarization as detected by QT dispersion may be a potential leading mechanism of sudden death in hypertensive and normotensive (age related) left ventricular hypertrophy. Aim of this study was to investigate QT dispersion, ventricular arrhythmias, and left ventricular mass index in elderly hypertensive and normotensive patients. Study population consisted of 60 consecutive patients (sex: 34 men/26 women; age: 63 +/- 11 years) with essential arterial hypertension and 48 age and sex-matched control subjects (24 men/24 women; 64 +/- 16 years). Measurements included QTc dispersion, ventricular arrhythmias, and left ventricular hypertrophy. Hypertensive patients had greater left ventricular mass index (P = .006) and higher QTc dispersion (P = .004) than controls. Left ventricular hypertrophy was diagnosed in 57 (31 men/26 women) of all subjects. These patients had higher blood pressure (P < .05), Lown's score (P < .001), and QTc dispersion (P < .001). QTc dispersion and Lown's score were independent predictors of left ventricular mass index (P < .001). Conclusively, QTc dispersion is a strong indicator of left ventricular mass index and might be used in risk stratification of hypertensive and normotensive elderly patients.

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.

Is QT dispersion associated with sudden cardiac death in patients with hypertrophic cardiomyopathy?

QT dispersion is significantly greater in patients with hypertrophic cardiomyopathy (HCM) than that in healthy subjects. Few data exist regarding the prognostic value of QT dispersion in HCM. In this study, we retrospectively investigated the association between QT dispersion and sudden cardiac death in 46 patients with HCM (mean 33.1 +/- 15.5 years, 32 men). The case group consisted of 23 HCM patients who died suddenly, and the control group consisted of 23 HCM patients who survived uneventfully during follow-up. Study patients were pair-matched for age, gender, and maximum left ventricular wall thickness. QT dispersion (maximum minus minimum QT interval) was manually measured on early 12-lead ECGs using a digitizing board. An in-house program was used for calculating QT interval, QT dispersion, JT interval, and JT dispersion (maximum minus minimum J point to T end interval). Patients in the case group tended to have shorter RR intervals than those in the control group (777 +/- 171 vs 856 +/- 192 ms, P = 0.08). Maximum corrected QT and JT intervals did not discriminate the case group from controls (489 +/- 29 vs 479 +/- 27 ms, P = NS; 375 +/- 36 vs 366 +/- 22 ms, P = NS, respectively). Greater QT dispersion and JT dispersion were found in the case group compared with controls (74 +/- 28 vs 59 +/- 21 ms, P = 0.02 and 76 +/- 32 vs 59 +/- 26 ms, P = 0.03, respectively). The measurements of maximum QT, JT, and T peak to T end intervals, precordial QT and JT dispersion, and T peak and T end dispersion were all comparable between the two groups (P = NS for all). No systematic changes in ECG measurements were found from late ECGs of the case group compared to those from early ECGs (P = NS). No correlation between maximum left ventricular wall thickness and QT dispersion, JT dispersion, maximum QTc or JTc intervals was observed (r < 0.29, P > 0.05 for all). Our results show that increased QT dispersion and JT dispersion is weakly associated with sudden cardiac death in the selected patients with HCM.

Evidences of the gender-related differences in cardiac repolarization and the underlying mechanisms in different animal species and human

Clinical and experimental studies have shown that gender differences exist in cardiac repolarization in various animal species and human, as is evidenced by significantly longer QT, JT intervals and action potential duration in females than in males due to a reduced repolarization reserve in females. The latter is shown by the relatively greater increase in ventricular repolarization and higher incidence of torsades de pointes (TdP) in preparations from females by drugs blocking repolarizing K(+) currents. These results can be modulated by gonadectomy, suggesting that gonadal steroids are important determinants of gender difference in repolarization. In human subjects, QT and JT intervals are longer in women, whereas QT dispersion and Tp-e interval (the interval from the peak to the end of T wave) are longer in men. At slow heart rates greater prolongation in QT and increase in transmural repolarization heterogeneity (i.e. increase in Tp-e) may predispose to TdP tachycardias in women. In healthy postmenopausal women, hormone replacement therapy with estrogen alone usually produced a prolongation of QT interval, while estrogen plus progesterone had no significant effects on QT interval but reduced QT dispersion. Along with these, there are still conflicting data reported. Further work is needed before the elucidation of the basis of gender differences in ventricular repolarization.

Evaluation of a Sex-Based Difference in the Pharmacokinetics of Digoxin

STUDY OBJECTIVE

To determine whether a sex-based difference in digoxin pharmacokinetics exists in patients receiving long-term digoxin therapy for chronic heart failure or atrial fibrillation.

DESIGN

Single-center, retrospective review of medical records.

SETTING

University-based teaching hospital and outpatient clinic.

PATIENTS

Sixty-seven adults (32 men, 35 women) with chronic heart failure or atrial fibrillation who were receiving digoxin therapy.

MEASUREMENTS AND MAIN RESULTS

Serum digoxin concentrations and daily digoxin doses were obtained from patients' medical records. Daily doses were adjusted for patients' actual and ideal body weight and body mass index (BMI). The ratio between the serum digoxin concentration and each of the adjusted daily doses of digoxin was compared between men and women. The mean +/- SD serum digoxin concentration was 0.85 +/- 0.51 ng/ml for men compared with 1.02 +/- 0.51 ng/ml for women. Mean +/- SD unadjusted doses of digoxin were 0.180 +/- 0.063 and 0.164 +/- 0.059 mg/day for men and women, respectively; the difference was not statistically significant. Ratios of serum digoxin concentration to daily digoxin doses did not differ by sex when doses were estimated with actual or ideal weight. Only the ratio of the digoxin concentration to the BMI-adjusted dose was significantly different between men and women (0.14 +/- 0.09 and 0.19 +/- 0.11, respectively, p<0.05).

CONCLUSION

Sex-based differences in digoxin pharmacokinetics were absent when actual or ideal body weight was used. However, the ratio of serum digoxin concentration to daily digoxin dose adjusted for BMI differed by sex. Because digoxin is distributed to lean body mass, use of the BMI could have overadjusted body weight, leading to inaccurate pharmacokinetic assumptions and calculations. The pharmacokinetics of digoxin do not appear to differ by sex.

Clinical implication of T-wave morphology analysis as a new repolarization descriptor

BACKGROUND

T-wave morphology analysis (TMA) quantifies irregularities of ventricular repolarization based on singular value decomposition of the 12-lead electrocardiogram (ECG). Furthermore, TMA is useful for risk stratification of patients with myocardial infarction (MI), although gender differences in TMA and the relationship between TMA and heart diseases are unknown. The aim of this study was to evaluate the significance of TMA in healthy individuals and patients with heart diseases.

METHODS AND RESULTS

Patients with heart disease and either with or without an implanted cardioverter defibrillator (ICD, n = 33, 57+/-16 years; non-ICD, n = 50, 67+/-10 years) were studied. Normal control ECGs (n = 114) were selected from Marquette's database (NC, 33+/-13 years) and the TMA descriptors, including T-wave morphology dispersion (TMD) and percentage of the loop area (PL), were calculated. TMD was significantly lower in group NC males than in the group NC females (11+/-5.9 vs 22+/-16, p < 0.0001). PL was significantly higher in group NC than in the ICD and non-ICD groups (0.63+/-0.12 vs 0.53+/-0.15, p < 0.0001). TMD of group NC was significantly lower than that of the ICD and non-ICD groups (14+/-11 vs 47+/-27, p < 0.0001).

CONCLUSION

There are gender differences in TMD. Abnormal values for TMA could reflect abnormalities of ventricular repolarization.

Recent advances in understanding sex differences in cardiac repolarization

A number of gender differences exist in the human electrocardiogram (ECG): the P-wave and P-R intervals are slightly longer in men than in women, whilst women have higher resting heart rates than do men, but a longer rate-corrected QT (QT(C)) interval. Women with the LQT1 and LQT2 variants of congenital long-QT syndrome (LQTS) are at greater risk of adverse cardiac events. Similarly, many drugs associated with acquired LQTS have a greater risk of inducing torsades de pointes (TdP) arrhythmia in women than in men. There are also male:female differences in Brugada syndrome, early repolarisation syndrome and sudden cardiac death. The differences in the ECG between men and women, and in particular those relating to the QT interval, have been explored experimentally and provide evidence of differences in the processes underlying ventricular repolarization. The data available from rabbit, canine, rat, mouse and guinea pig models are reviewed and highlight involvement of male:female differences in Ca and K currents, although the possible involvement of rapid and persistent Na current and Na-Ca exchange currents cannot yet be excluded. The mechanisms underlying observed differences remain to be elucidated fully, but are likely to involve the influence of gonadal steroids. With respect to the QT interval and risk of TdP, a range of evidence implicates a protective role of testosterone in male hearts, possibly by both genomic and non-genomic pathways. Evidence regarding oestrogen and progesterone is less unequivocal, although the interplay between these two hormones may influence both repolarization and pro-arrhythmic risk.

Intravenous nicorandil can reduce QT dispersion and prevent bradyarrhythmia during percutaneous transluminal coronary angioplasty of the right coronary artery

BACKGROUND

Nicorandil, a potassium channel opener, is used for the treatment of angina pectoris and has a pharmacologic preconditioning effect. This study evaluated whether intravenous nicorandil reduces QT dispersion and prevents bradyarrhythmia during percutaneous transluminal coronary angioplasty (PTCA) of the right coronary artery.

METHODS

A historical cohort study on the effect of nicorandil on QT dispersion and bradyarrhythmia was conducted. Fifty patients who underwent PTCA of the right coronary artery were enrolled. The patients were divided into a nicorandil (n = 25) group and control group (n = 25). Nicorandil was injected at 4 mg/h continuously 1 hour before PTCA in the nicorandil group. QT dispersion was measured at 1 hour before PTCA (baseline), immediately before PTCA, and 1 minute after the initiation of the first balloon inflation.

RESULTS

QT dispersion at 1 minute after the initiation of the first balloon inflation in the control group increased significantly (QT dispersion: 37.1 +/- 17.8 msec and 21.7 +/- 12.2 msec, respectively, P < .001 vs baseline in the control group), and this was larger than at 1 minute after the initiation of the first balloon inflation in the nicorandil group (QT dispersion: 37.1 +/- 17.8 msec and 20.8 +/- 9.4 msec, respectively, P < .001). By two-way repeated measures analysis of variance, there were significant interactions between the time factor and the grouping factor in QT dispersion (P < .001). Bradyarrhythmia was observed in 6 patients in the control group, but none was observed in the nicorandil group.

CONCLUSIONS

Intravenous nicorandil reduces QT dispersion and prevents bradyarrhythmia during PTCA of the right coronary artery.

Sex differences in QTc interval and QT dispersion: dynamics during exercise and recovery in healthy subjects

BACKGROUND

Sex differences have been described in resting cardiac repolarization and susceptibility to torsade de pointes in humans. This study compares the QT-interval and QT-dispersion dynamics during exercise and recovery between healthy men and women.

METHODS

Twenty healthy subjects (10 males aged 30 +/- 4 years, 10 females aged 31 +/- 11 years) underwent symptom-limited bicycle ergometry followed by a 10-minute recovery period. Digital 12-lead electrocardiograms (ECG) were recorded every 10 seconds during exercise and recovery. For each lead, the QTp interval (Q onset to T peak) was automatically measured by use of QT Guard (GE Marquette, Milwaukee, Wis). QTp dispersion was defined as the difference between the maximum and minimum QTp for each ECG. To quantify QT dynamics, we fit the QTp in lead V(3) (QTpV(3)) versus cycle length (CL) relationship to a quadratic function during exercise and recovery with nonlinear regression analysis. Similar regression analysis was performed for the QTp dispersion versus CL relationship.

RESULTS

At baseline, QTpcV(3) was longer in women than in men (338 +/- 25 vs 278 +/- 15 ms, P <.0001), but QTp dispersion was similar (35 +/- 18 vs 41 +/- 19 ms). At peak exercise, QT dispersion decreased compared with baseline in both men and women. During exercise and recovery, women had a steeper QTpV(3)-CL relationship. QTpV(3) hysteresis, a measure of the exercise and recovery QTpV(3)-CL curve separation, was greater in women than in men when measured 1 minute into recovery (33 +/- 20 vs 6 +/- 8 ms, P <.001). No sex difference in QTp-dispersion-rate adaptation was observed during exercise or recovery.

CONCLUSIONS

Healthy women exhibit greater QT-interval-rate adaptation during both exercise and recovery than men, resulting in more QT-interval hysteresis. Greater QT prolongation during decelerating heart rates in recovery may play a role in increasing proarrhythmia risk in women.

Serum quinidine concentrations and effect on QT dispersion and interval

OBJECTIVE

To establish a relationship between serum quinidine concentrations (SQCs) and QT interval dispersion, compared with corresponding QT intervals, in order to identify a reason why many reports describe torsade de pointes as occurring at subtherapeutic concentrations.

DESIGN

Retrospective study.

SETTING

University teaching hospital.

PARTICIPANTS

Eleven patients with atrial arrhythmias managed with quinidine therapy.

MAIN OUTCOME MEASURES

Patients with subtherapeutic (<2 microg/mL) and therapeutic (2-5 microg/mL) SQCs with corresponding 12-lead electrocardiograms (ECGs) (25 mm/sec) and baseline ECG were evaluated for QT interval dispersion, calculated as the maximum minus the minimum QT interval on the 12-lead ECG.

RESULTS

Mean +/- SD subtherapeutic and therapeutic SQCs were 1.48 +/- 0.39 microg/mL and 3.78 +/- 0.88 microg/mL (p < 0.001). Baseline values for QT/QTc intervals were 376.4 +/- 59.2/429.5 +/- 57.3 msec. At subtherapeutic and therapeutic SQCs, mean QT/QTc intervals were 403.6 +/- 59.9/450.5 +/- 38.5 msec and 439.1 +/- 48.9/472.4 +/- 44.6 msec, respectively. Mean QT dispersion was 47 +/- 16.2 msec at baseline, 98.2 +/- 27.5 msec at subtherapeutic SQC, and 70.9 +/- 33.9 msec at therapeutic SQCs (p = 0.001 for overall analysis; p < 0.001 for baseline vs. subtherapeutic concentrations; p = NS for therapeutic vs. subtherapeutic in post hoc comparison).

CONCLUSIONS

Despite QT interval lengthening with increasing SQCs, QT dispersion was numerically greatest at subtherapeutic SQCs. Further study is required to determine the value of QT dispersion as a tool for identifying proarrhythmic risk with drugs that prolong the QT interval.

Is gender a risk factor for adverse drug reactions? The example of drug-induced long QT syndrome

Drug-induced torsade de pointes is a rare life-threatening adverse drug reaction (ADR) which is strongly influenced by gender. Drugs that prolong cardiac repolarisation include antiarrhythmics, gastrokinetics, antipsychotics, antihistamines and antibacterials. Such drugs share the potential to block cardiac voltage-gated potassium channels, particularly the rapid component (I(Kr)) of the delayed rectifier potassium current (I(K)). By doing so, such drugs usually, but not always, prolong the QT interval. Even if the electrocardiographic signs are subdued, the underlying blockade of I(Kr) current may precipitate the occurrence of arrhythmia. Women are perceived to be more prone to ADRs than men. Such a propensity may result from gender-associated differences in drug exposure, in the number of drugs prescribed (polypharmacy), in drug pharmacology, as well as from possible differences in the way the adverse event is perceived. A prolonged QT interval on the electrocardiogram (time that elapses from the onset of the cardiac ventricular depolarisation to the completion of its repolarisation) is associated with the occurrence of torsade de pointes and related ventricular arrhythmias. The QT interval is influenced by heart rate, autonomic nervous system, electrolyte disturbances and above all, drugs that block potassium channels. Two-thirds of the cases of drug-induced torsade de pointes occur in women. Therefore, this adverse effect represents a perfect example of gender differences impairing women's health. Clinical and experimental studies show that female gender is associated with a longer corrected QT interval at baseline and a greater response to drugs that block I(Kr), both of which facilitate the emergence of arrhythmia. This results most likely from a specific regulation of ionic channel expression (potassium, calcium, etc) by sex steroids, even though nongenomic effects may play a role as well. Estrogens facilitate bradycardia-induced prolongation of the QT interval and the emergence of arrhythmia whereas androgens shorten the QT interval and blunt the QT response to drugs. Hence, underlying genetic defects of potassium channels that may be asymptomatic in normal conditions, may precipitate drug-induced arrhythmia in women more frequently than in men. Even in the presence of a drug that mildly blocks I(Kr) and seldom prolongs the QT interval, women are still more prone to drug-induced torsade de pointes, due to their reduced cardiac 'repolarisation reserve'. This is an important aspect of I(Kr) blockade to be aware of during the development of new drugs.

Importance of QT interval determination and renal function assessment during antiarrhythmic drug therapy

A major concern associated with the use of antiarrhythmic drugs (AAD) is the occurrence of ventricular proarrhythmia, especially torsade de pointes (TdP). The AADs associated with TdP most commonly include quinidine, procainamide, disopyramide, sotalol, and the newer class III agents, such as ibutilide and dofetilide. It is not simply the administration and nature of an AAD but also several additional factors such as heart rate, ventricular hypertrophy, congestive heart failure, gender, age, concomitant drugs, and impaired drug clearance that influence TdP development. Dosing of these agents should be adjusted to take such factors into account to minimize the incidence of proarrhythmia.

Effect of low estrogen states in healthy women on dispersion of ventricular repolarization

Our data show that although estrogen does not seem to affect the QT interval in healthy women, it significantly decreases the QT dispersion. This finding could provide an explanation to the gender differences in susceptibility to ventricular arrhythmias, besides the difference in the incidence of coronary artery disease.