Sex differences in ventricular repolarization: from cardiac electrophysiology to Torsades de Pointes

Gender differences in electrophysiological gene expression in failing and non-failing human hearts

The increasing availability of human cardiac tissues for study are critically important in increasing our understanding of the impact of gender, age, and other parameters, such as medications and cardiac disease, on arrhythmia susceptibility. In this study, we aimed to compare the mRNA expression of 89 ion channel subunits, calcium handling proteins, and transcription factors important in cardiac conduction and arrhythmogenesis in the left atria (LA) and ventricles (LV) of failing and nonfailing human hearts of both genders. Total RNA samples, prepared from failing male (n = 9) and female (n = 7), and from nonfailing male (n = 9) and female (n = 9) hearts, were probed using custom-designed Taqman gene arrays. Analyses were performed to explore the relationships between gender, failure state, and chamber expression. Hierarchical cluster analysis revealed chamber specific expression patterns, but failed to identify disease- or gender-dependent clustering. Gender-specific analysis showed lower expression levels in transcripts encoding for K_v4.3, KChIP2, K_v1.5, and K_ir3.1 in the failing female as compared with the male LA. Analysis of LV transcripts, however, did not reveal significant differences based on gender. Overall, our data highlight the differential expression and transcriptional remodeling of ion channel subunits in the human heart as a function of gender and cardiac disease. Furthermore, the availability of such data sets will allow for the development of disease-, gender-, and, most importantly, patient-specific cardiac models, with the ability to utilize such information as mRNA expression to predict cardiac phenotype.

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.

Computational approaches to understand cardiac electrophysiology and arrhythmias

Cardiac rhythms arise from electrical activity generated by precisely timed opening and closing of ion channels in individual cardiac myocytes. These impulses spread throughout the cardiac muscle to manifest as electrical waves in the whole heart. Regularity of electrical waves is critically important since they signal the heart muscle to contract, driving the primary function of the heart to act as a pump and deliver blood to the brain and vital organs. When electrical activity goes awry during a cardiac arrhythmia, the pump does not function, the brain does not receive oxygenated blood, and death ensues. For more than 50 years, mathematically based models of cardiac electrical activity have been used to improve understanding of basic mechanisms of normal and abnormal cardiac electrical function. Computer-based modeling approaches to understand cardiac activity are uniquely helpful because they allow for distillation of complex emergent behaviors into the key contributing components underlying them. Here we review the latest advances and novel concepts in the field as they relate to understanding the complex interplay between electrical, mechanical, structural, and genetic mechanisms during arrhythmia development at the level of ion channels, cells, and tissues. We also discuss the latest computational approaches to guiding arrhythmia therapy.

Postoperative QT interval prolongation in patients undergoing noncardiac surgery under general anesthesia

BACKGROUND

Abnormal cardiac repolarization, indicated by a prolongation of the QT interval, increases the risk for torsades de pointes, a potentially life-threatening arrhythmia. Many perioperatively administered drugs and conditions prolong the QT interval. Despite several reports of perioperative torsades de pointes, systematic evidence regarding perioperative QT interval prolongation is limited.

METHODS

Serial postoperative 12-lead electrocardiograms were obtained from 469 adult patients undergoing major noncardiac surgery under general anesthesia. Heart rate corrected QT-interval duration (Fridericia formula) was the primary outcome. All perioperatively administered drugs were recorded. Emphasis was placed on absolute QTc prolongation greater than 500 ms and relative increases of 30 and 60 ms.

RESULTS

At the end of surgery, 80% of the patients (345 of 429) experienced a significant QTc interval prolongation (ΔQTc 23 ± 26 ms (mean and SD), 95% CI 20-25 ms, P less than 0.001). Approximately 51% (219 of 429) had a QTc greater than 440 ms, and 4% (16 of 429) a QTc greater than 500 ms. In 39% (166 of 429), the ΔQTc was greater than 30 ms, in 8% (34 of 429) >60 ms, and in greater than 0.5% (2 of 429) >100 ms. No changes in ΔQTc occurred at subsequent time points. One patient developed torsades de pointes with a ΔQTc: 29 ms (0.4% incidence rate). Several drugs had a large effect on ΔQTc: isoflurane, methadone, ketorolac, cefoxitin, zosyn, unasyn, epinephrine, ephedrine, and calcium. Postoperative body temperature had a weak negative correlation with ΔQTc (r = -0.15, P = 0.02); serum magnesium, potassium, and calcium concentrations were not correlated.

CONCLUSION

Postoperative QT-interval prolongation is common. Several perioperatively administered drugs are associated with a substantial QT-interval prolongation. The exact cause and its clinical relevance are, however, unclear. Nevertheless, an association between postoperative QT prolongation and risk for torsades de pointes is likely.

High prevalence of prolonged QT interval in obese hypogonadal males

Obese subjects show several electrocardiographic alterations, including prolonged QT interval, a marker for fatal cardiac arrhythmias. Prolonged QT interval has recently been linked to low testosterone levels, a frequent occurrence in male obese patients but no study has yet assessed whether hypoandrogenism contributes to QT interval prolongation in this population. Aim of this study was to evaluate whether prolonged QT interval is linked to hypogonadism in male obese subjects. QT interval corrected for heart rate (QTc) was measured from standard electrocardiogram recordings in 136 obese men (BMI 30 >kg/m(2), range 30.1-75.4 kg/m(2)). Obese men were classified as eugonadal or hypogonadal according to serum total testosterone levels (i.e., greater or less than 9.9 nmol/l). Our study showed that QTc measurements corrected by either Bazett (419 ± 3.2 vs. 408 ± 3.4 ms, P < 0.05), Fridericia (406.3 ± 3.39 vs. 396.4 ± 3.03 ms, P < 0.05) or Hodges (407.0 ± 3.12 vs. 397.3 ± 2.84 ms, P < 0.05) were longer in hypogonadal compared with eugonadal obese men; further, prolonged QTc interval (i.e., >440 ms) was more frequent among hypogonadal compared with eugonadal obese men (23% vs. 10%, P < 0.05). The degree of weight excess, diabetes, sleep apnoea and potassium levels were not associated with prolonged QTc. In conclusion, obese hypogonadal men show a greater prevalence of prolonged QT interval compared with their eugonadal counterparts. It appears therefore that low levels of testosterone in obese men may contribute to the arrhythmogenic profile of these patients, a heretofore unknown link which warrants further clinical attention.

Invited commentary: sex-steroid hormones and QT-interval duration

In this issue of the Journal, Zhang et al. (Am J Epidemiol. 2011;174(4):403-411) make a substantial contribution to research in the area of hormonal influences on cardiac repolarization by demonstrating an inverse association between testosterone levels and the Bazett's adjusted QT interval (QTc) and RR-adjusted QT interval in men but not in postmenopausal women. They suggest that testosterone levels might explain the difference in QTc-interval duration between men and women and could contribute to population variability in QTc-interval duration among men. In this commentary, the gender difference and the role of testosterone in human cardiac repolarization are addressed. In addition, the gender differences in the congenital long-QT syndrome, drug-induced ventricular arrhythmias, and sudden cardiac death are discussed.

Regional genomic regulation of cardiac sodium-calcium exchanger by oestrogen

Female rabbit hearts are more susceptible to torsade de pointes (TdP) in acquired long QT type 2 than males, in-part due to higher L-type Ca2+ current (ICa,L) at the base of the heart. In principle, higher Ca2+ influx via ICa,L should be balanced by higher efflux, perhaps mediated by parallel sex differences of sodium-calcium exchange (NCX) current (INCX). We now show that NCX1, like Cav1.2α, is greater at the base of female than male left ventricular epicardium and greater at the base than at the apex in both sexes. In voltage-clamp studies, inward (0, +20 mV, P < 0.04) and outward (-80, -60, -40, -20 mV, P < 0.01) INCX densities were significantly higher (1.5-2 fold) in female base compared to apex and male (base and apex) myocytes. Myocytes were incubated ±17β-oestradiol (E2 = 1 nm) and INCX was measured on days 0, 1, 2 and 3. Inward and outward INCX decreased over 2 days in female base myocytes becoming similar to INCX at the apex. E2 incubation (24 h) increased NCX1 (50%) and INCX (∼3-fold at 60 mV) in female base but not endocardium, apex or in male base myocytes. INCX upregulation by E2 was blunted by an oestrogen receptor (ER) antagonist (fulvestrant, 1 μm), and inhibition of transcription (actinomycin D, 5 μg ml-1) or translation (cycloheximide, 20 μg ml-1). Dofetilide (an IKr blocker) induced early afterdepolarizations (EADs) in female base myocytes cultured for 1 day if incubated with E2, but not without E2 or with E2+KB-R4973 (an INCX inhibitor), E2+fulvestrant or E2 with apex myocytes. Thus, E2 upregulates NCX1 by a genomic mechanism mediated by ERs, and de novo mRNA and protein biosynthesis, in a sex- and region-dependent manner which contributes to the enhanced propensity to EADs and TdP in female hearts.

Anti-Ro/SSA antibodies and cardiac arrhythmias in the adult: facts and hypotheses

It is well established that the passive trans-placental passage of anti-Ro/SSA antibodies from mother to foetus is associated with the risk to develop an uncommon syndrome named neonatal lupus (NLE), where the congenital heart block represents the most severe clinical feature. Recent evidence demonstrated that also adult heart, classically considered invulnerable to the anti-Ro/SSA antibodies, may represent a target of the arrhythmogenicity of these autoantibodies. In particular, the prolongation of the QTc interval appears the most frequent abnormality observed in adults with circulating anti-Ro/SSA antibodies, with some data suggesting an association with an increased risk of ventricular arrhythmias, also life threatening. Moreover, even though the association between anti-Ro/SSA antibodies and conduction disturbances is undoubtedly less evident in adults than in infants, from the accurate dissection of the literature data the possibility arises that sometimes also the adult cardiac conduction tissue may be affected by such antibodies. The exact arrhythmogenic mechanisms involved in foetus/newborns and adults, respectively, have not been completely clarified as yet. However, increasing evidence suggests that anti-Ro/SSA antibodies may trigger rhythm disturbances through an inhibiting cross-reaction with several cardiac ionic channels, particularly the calcium channels (L-type and T-type), but also the potassium channel hERG, whose different expression and involvement in the cardiac electrophysiology during lifespan might account for the occurrence of age-related differences.

An introduction to QT interval prolongation and non-clinical approaches to assessing and reducing risk

Owing to its association with Torsades de Pointes, drug-induced QT interval prolongation has been and remains a significant hurdle to the development of safe, effective medicines. Genetic and pharmacological evidence highlighting the pivotal role the human ether-a-go-go-related gene (hERG) channel was a critical step in understanding how to start addressing this issue. It led to the development of hERG assays with the rapid throughput needed for the short timescales required in early drug discovery. The resulting volume of hERG data has fostered in silico models to help chemists design compounds with reduced hERG potency. In early drug discovery, a pragmatic approach based on exceeding a given potency value has been required to decide when a compound is likely to carry a low QT risk, to support its progression to late-stage discovery. At this point, the in vivo efficacy and metabolism characteristics of the potential drug are generally defined, as well its safety profile, which includes usually a dog study to assess QT interval prolongation risk. The hERG and in vivo QT data, combined with the likely indication and the estimated free drug level for efficacy, are put together to assess the risk that the potential drug will prolong QT in man. Further data may be required to refine the risk assessment before making the major investment decisions for full development. The non-clinical data are essential to inform decisions about compound progression and to optimize the design of clinical QT studies.

Acute effects of sex steroid hormones on susceptibility to cardiac arrhythmias: a simulation study

Acute effects of sex steroid hormones likely contribute to the observation that post-pubescent males have shorter QT intervals than females. However, the specific role for hormones in modulating cardiac electrophysiological parameters and arrhythmia vulnerability is unclear. Here we use a computational modeling approach to incorporate experimentally measured effects of physiological concentrations of testosterone, estrogen and progesterone on cardiac ion channel targets. We then study the hormone effects on ventricular cell and tissue dynamics comprised of Faber-Rudy computational models. The “female” model predicts changes in action potential duration (APD) at different stages of the menstrual cycle that are consistent with clinically observed QT interval fluctuations. The “male” model predicts shortening of APD and QT interval at physiological testosterone concentrations. The model suggests increased susceptibility to drug-induced arrhythmia when estradiol levels are high, while testosterone and progesterone are apparently protective. Simulations predict the effects of sex steroid hormones on clinically observed QT intervals and reveal mechanisms of estrogen-mediated susceptibility to prolongation of QT interval. The simulations also indicate that acute effects of estrogen are not alone sufficient to cause arrhythmia triggers and explain the increased risk of females to Torsades de Pointes. Our results suggest that acute effects of sex steroid hormones on cardiac ion channels are sufficient to account for some aspects of gender specific susceptibility to long-QT linked arrhythmias.

It is well known that female gender is an independent risk factor for some types of cardiac arrhythmias. However, it has been difficult to determine how much of a role physiological concentrations of circulating sex steroid hormones play in gender linked arrhythmia susceptibility because the cardiac system is so extraordinarily complex. Here we employ a computational strategy, based on experimental measurements, to tease out the individual contributions of estrogen, progesterone and testosterone on cardiac electrical behavior and then make predictions about their effects in combination and in the presence of drugs. The computational models convincingly reproduce observed fluctuations of QT intervals (as recorded on the ECG (electrocardiogram), the QT interval reflects the time period between ventricular excitation and relaxation) through the menstrual cycle in females and effects of testosterone on ECG parameters. Our simulations also predict that testosterone and progesterone are protective against drug-induced arrhythmias, while estrogen likely exacerbates the breakdown of normal cardiac electrical activity in the presence of QT-prolonging drugs.

The association of serum testosterone levels and ventricular repolarization

It is assumed that testosterone is an important regulator of gender-related differences in ventricular repolarization. Therefore, our aim was to study whether serum levels of testosterone are associated with QTc, QT and RR interval variation. Setting: two independent population-based cohort studies. Participants: 445 male participants (≥55 years) from the Rotterdam study cohort and 1,428 male participants from the study of health in Pomerania (SHIP) with an electrocardiogram who were randomly sampled for assessment of serum testosterone at baseline, after exclusion of participants with testosterone altering drugs, QTc prolonging drugs or dig(it)oxin, left ventricular hypertrophy and left and right bundle branch block. Endpoints: length of the QTc, QT and RR intervals. Analysis: linear regression model, adjusted for the two individual studies and a pooled analysis of both studies. The pooled analysis of the Rotterdam study and SHIP showed that the QTc interval gradually decreased among the tertiles (P value for trend 0.024). The third tertile of serum testosterone was associated with a lower QTc interval compared to the first tertile [−3.4 ms (−6.5; −0.3)]. However, the third tertile of serum testosterone was not associated with a lower QT interval compared to the first tertile [−0.7 ms (−3.1; 1.8)]. The RR interval gradually increased among the tertiles (P value for trend 0.002) and the third tertile of serum testosterone showed an increased RR interval compared to the first tertile [33.5 ms (12.2; 54.8)]. In the pooled analysis of two population-based studies, serum testosterone levels were not associated with the QT interval, which could be due to a lack of power. Lower QTc intervals in men with higher serum testosterone levels could be due to the association of serum testosterone with prolongation of the RR interval.

Increased prevalence of prolonged QT interval in males with primary or secondary hypogonadism: a pilot study

Symptoms and signs of male hypogonadism span all organ systems, including the cardiovascular apparatus. The electrocardiographic QT interval reflects cardiac ventricular repolarization and, if prolonged, increases the risk of malignant arrhythmias. QT interval duration is similar in boys and girls during childhood, but shortens in males after puberty and experimental studies suggest that testosterone is a major contributor to shortening of QT interval in men. The aim of the present pilot study was to assess the duration of ventricular repolarization in adult males with primary or secondary hypogonadism. Standard ECG recordings were performed in 26 men (mean age 39.2 +/- 2.17 years) with pituitary or testicular hypogonadism and repeated in 15 patients during testosterone replacement. Twenty-six age-matched control men were also analysed. Measured QT intervals were corrected for heart rate according to Bazzett's formula (QTc = QT/radical RR interval). The prevalence of prolonged QTc was considerably higher in hypogonadal patients (four of 26 men) than in control men (none, p < 0.05) and in the general, healthy population (<2.5%). QTc interval normalized on hormone replacement therapy in the four patients presenting prolonged QTc in the hypogonadal state. Heart rate and left ventricular mass did not differ among the two groups and no known QT-prolonging factor was apparent in patients with abnormal QTc interval. In conclusion, a high number prolonged QT interval measurements was observed in hypogonadal men who may therefore be at increased risk for cardiac arrhythmias. This observation reveals an additional feature of male hypogonadism, which may benefit from testosterone replacement therapy.

Secondary effects of antipsychotics: women at greater risk than men

CONTEXT

The health burden of antipsychotic medication is well known, but the disproportionate effect on women as compared with men is underappreciated.

OBJECTIVE

The goal of this article is preventive--to better inform clinicians so that the risks to women and to their offspring can be diminished.

METHOD

All PubMed sources in which the search term gender (or sex) was linked to a side effect of antipsychotic medication were reviewed.

RESULT

There is general agreement in the literature on women's increased susceptibility to weight gain, diabetes, and specific cardiovascular risks of antipsychotics, with less consensus on malignancy risks and risks to the fetus. Cardiovascular death, to which men are more susceptible than women, is disproportionately increased in women by the use of antipsychotics. Sedating antipsychotics raise the risk of embolic phenomena during pregnancy, and postpartum. Prolactin-elevating drugs suppress gonadal hormone secretion and may enhance autoimmune proclivity.

CONCLUSIONS

Clinicians need to be aware of the differential harm that women (and their offspring) can incur from the side effects of antipsychotics.

[Sex differences in cardiovascular drug targeting]

Women and men differ in drug needs and drug metabolism. Usually women are smaller and lighter and have a higher body fat percentage and lower kidney function. Primary drug-metabolizing enzymes in the intestinal wall and liver, which are part of the cytochrome P450 family, have different activities in men and women. Their substrates (beta-blockers, blockers of calcium channels such as nifedipine and verapamil, cyclosporine, and many others) are metabolized differently. Sex differences were observed after administration of digitalis, which is often overdosed in women. Furthermore, beta-blockers are found at higher plasma levels in women and ACE inhibitors cause more side effects in women than in men. In women, acetylsalicylic acid provides effective primary prophylaxis against stroke but not myocardial infarction. In men, these drugs have opposite effects. Anticoagulants and thrombolytics often lead to bleeding complications in women, QT prolonging drugs produce more frequently arrhythmia. It is therefore very important to control drugs following approval and to look out for these differences between men and women.

[Drug induced QT prolongation]

Prolongation of the ventricular repolarisation manifests itself as a prolongation of the QT intervall on the surface ECG and represents a major risk for a special form of ventricular tachycardia called "torsades de pointes". Torsades de pointes are often self limited and are associated with palpitations, dizziness or syncope. Degeneration into ventricular fibrillation and sudden cardiac death can occur. In addition to the various forms of the congenital long QT syndrome many drugs, such as antiarrhythmic drugs class IA and III, antibiotics, antihistamines, antidepressants, and methadone are known to prolong the QT interval. Most of these drugs block a specific potassium channel substantially involved in the ventricular repolarisation. In addition, drug interaction or disturbances of drug metabolism may play a major role in the acquired form of the long QT syndrome. The individual risk and the potential of a pharmacologic substance to prolong the QT interval are not predictable. Certain risk factors identify patients at higher risk for drug-induced prolongation of the QT interval. Correctable factors include electrolyte disorders (e.g. hypokalemia) and concomitant administration of different QT prolonging drugs. External defibrillation is the therapy of choice in the hemodynamic unstable patient presenting torsades de pointes. In hemodynamic more stable patients application of intravenous magnesium can terminate torsades de pointes (membrane stabilizing properties). Temporary external or transvenous pacing at high heart rate might terminate incessant torsades de pointes by decreasing QT interval. Repeated ECG controls during therapy with QT prolonging drugs are mandatory, especially when drug doses are changed, additional drugs are prescribed, or in case of vomiting and diarrhea. QT prolongation in individual medical therapy is not always predictable. Therefore, updated lists of drugs with the potential of QT prolongation are available on the Internet (e.g. www.qtdrugs.org ).

Acute effects of oestrogen on the guinea pig and human IKr channels and drug-induced prolongation of cardiac repolarization

Female gender is a risk factor for drug-induced arrhythmias associated with QT prolongation, which results mostly from blockade of the human ether-a-go-go-related gene (hERG) channel. Some clinical evidence suggests that oestrogen is a determinant of the gender-differences in drug-induced QT prolongation and baseline QT(C) intervals. Although the chronic effects of oestrogen have been studied, it remains unclear whether the gender differences are due entirely to transcriptional regulations through oestrogen receptors. We therefore investigated acute effects of the most bioactive oestrogen, 17beta-oestradiol (E2) at its physiological concentrations on cardiac repolarization and drug-sensitivity of the hERG (I(Kr)) channel in Langendorff-perfused guinea pig hearts, patch-clamped guinea pig cardiomyocytes and culture cells over-expressing hERG. We found that physiological concentrations of E2 partially suppressed I(Kr) in a receptor-independent manner. E2-induced modification of voltage-dependence causes partial suppression of hERG currents. Mutagenesis studies showed that a common drug-binding residue at the inner pore cavity was critical for the effects of E2 on the hERG channel. Furthermore, E2 enhanced both hERG suppression and QT(C) prolongation by its blocker, E4031. The lack of effects of testosterone at its physiological concentrations on both of hERG currents and E4031-sensitivity of the hERG channel implicates the critical role of aromatic centroid present in E2 but not in testosterone. Our data indicate that E2 acutely affects the hERG channel gating and the E4031-induced QT(C) prolongation, and may provide a novel mechanism for the higher susceptibility to drug-induced arrhythmia in women.

Molecular aspects of the congenital and acquired Long QT Syndrome: clinical implications

The Long QT Syndrome (LQTS) is a complex and multi-factorial disorder that predisposes to life-threatening ventricular arrhythmias. Both hereditary and acquired subforms have been identified over the years. Recently, it has become clear that the interaction of multiple acquired and genetic aetiologic factors (e.g. disease modifiers) play an important role in differentiating genotype into a continuous spectrum of clinical or subclinical phenotypes. The genotype-phenotype correlation thereby remains very unpredictable in asymptomatic patients, raising important concerns for clinical practice and also for drug development. Therefore, this review aims at providing a comprehensive overview on LQTS highlighting the molecular mechanisms of arrhythmogenesis involved in both the hereditary and the acquired subtypes of the disorder. From this perspective this manuscript then focuses on how the genotype translates into phenotype. A logical overview is provided with the multitude of hereditary and acquired factors that are involved and of the complexity of the interactions that ultimately result in the heterogeneous expressivity and the unpredictability of the phenotype. Based on recent basic and clinical data this review further aims at providing an update on the clinical properties and management of LQT patients including diagnostic work-up and therapy.

A gender-independent proarrhythmic action of 17β-estradiol in anaesthetized rabbits

Women are at increased risk of having drug-induced arrhythmias such as torsade de pointes but less susceptible to arrhythmias associated with myocardial ischaemia. We have shown previously that 17beta-estradiol had greater antiarrhythmic activity in female rats than in male rats subject to myocardial ischaemia. The aim of this work was to investigate the effects of acute administration of 17beta-estradiol in both sexes in an established in vivo model of drug-induced arrhythmias. In alpha(1)-adrenoceptor-stimulated, pentobarbital-anaesthetized rabbits, 17beta-estradiol (100, 300 or 1000 ng/kg bolus followed by 10, 30 or 100 ng/kg/min infusion) tended to increase the incidence of torsade de pointes, induced by clofilium, in both sexes: from 50% in controls to 80%, 70% and 80% in females; from 40% in controls to 60%, 70% and 80% in males with increasing doses of 17beta-estradiol (n=10 per group). The total duration of all episodes of torsade de pointes was increased significantly by the highest dose of 17beta-estradiol compared to vehicle in both female and male rabbits: from 9+/-4 s to 93+/-26 s in females; from 26+/-14 s to 96+/-20 s in males. There were no baseline differences between the sexes in heart rate, QTc interval or epicardial monophasic action potential duration. The proarrhythmic effect of acute administration of 17beta-estradiol in the alpha(1)-adrenoceptor-stimulated anaesthetized rabbit model was independent of gender. This indicates that the underlying mechanism differs from that involved in the gender-selective reduction of ischaemia-induced arrhythmias by 17beta-estradiol.

Metabolic and cardiovascular changes in women with polycystic ovary syndrome

OBJECTIVE

To analyze the relationship between QTc interval and cardiovascular risk factors in women with polycystic ovary syndrome (PCOS).

METHODS

Study group included 119 PCOS women (age: 32.2+/-5.2 years) and the control group 64 age-matched healthy women; they all underwent QT interval measurement, and plasma levels of high-sensitivity CRP (hsCRP), endothelin-1 (ET1), insulin, and testosterone determinations.

RESULTS

In PCOS women hsCRP (2.35+/-2.14 mg/L vs. 1.01+/-1.28 mg/L; P=0.04), ET1 (23.6+/-10.3 ng/L vs. 7.7+/-15.9 ng/L; P=0.01), and insulin (16.5+/-7.8 mIU/L vs. 11.8+/-10.7 mIU/L; P=0.03) levels were significantly higher, and QTc interval significantly shorter than in controls (401+/-61 ms vs. 467+/-61 ms; P=0.007). In 67 (56%) PCOS patients with a short QTc interval (<400 ms), plasma testosterone levels were significantly higher than in PCOS women with normal QTc interval (2.3+/-2.1 nmol/L vs. 1.4+/-1.7 nmol/L; P=0.02).

CONCLUSIONS

In patients with polycystic ovary syndrome increased testosterone levels may attenuate the effects of coronary risk factors.

Risk factors and predictors of Torsade de pointes ventricular tachycardia in patients with left ventricular systolic dysfunction receiving Dofetilide

The purpose of this study was to identify risk factors of Torsade de pointes (TdP) ventricular tachycardia in patients medicated with a class III antiarrhythmic drug (dofetilide) and left ventricular systolic dysfunction with heart failure (HF) or recent myocardial infarction (MI). The 2 Danish Investigations of Arrhythmia and Mortality on Dofetilide (DIAMOND) studies enrolled patients with HF (DIAMOND-HF) or MI (DIAMOND-MI) and left ventricular systolic dysfunction. The present analysis includes only patients treated solely with dofetilide. The incidence of TdP was 2.1% (32 of 1,511). Twenty-five of the incidences occurred in the DIAMOND-HF study and 7 cases in the DIAMOND-MI study (p = 0.0015). TdP was more frequent in women than in men (47% vs 28%, p = 0.02). Risk factors for developing TdP were female gender (odds ratio 2.2, 95% confidence interval [CI] 1.0 to 5.0), MI within 8 weeks (odds ratio 0.3, 95% CI 0.1 to 0.7), being in New York Heart Association class III or IV (odds ratio 3.2, 95% CI 1.2 to 8.6), and baseline QTc duration (odds ratio 1.14, 95% CI 1.00 to 1.30) per 10 ms. Women with chronic HF, QTc duration >400 ms. and New York Heart Association class III or IV had a risk of TdP of 10%, whereas no TdP episodes were observed in patients with QTc duration <400 ms. In conclusion, severity of HF, female gender, and QTc duration make it possible to identify patients with a high risk of early TdP when treated with dofetilide. Patients with recent MI less often had TdP compared with patients with chronic HF.

Lack of electrocardiographic changes in women with polycystic ovary syndrome

OBJECTIVE

The aim of the present study was to investigate the potential alterations in electrocardiographic (ECG) pattern in patients with polycystic ovary syndrome (PCOS).

PATIENTS

Fifty PCOS patients and 50 age- and body mass index-matched healthy women were studied.

METHODS

We assessed hormonal and metabolic pattern, and performed ECG analysis for evaluating PQ interval, QRS duration, minimum and maximum QT interval corrected for heart rate (QT(c)min and QT(c)max, respectively), corrected QT dispersion (QT(c)d), corrected J point/T-wave interval (JTend(c)), corrected JTmax interval (JTmax(c)), and corrected Tmax-end interval (Tmax-end(c)).

RESULTS

QT(c)min (399 +/- 21 vs. 396 +/- 25 ms, P = 0.51); QT(c) max (445 +/- 25 vs. 443 +/- 27 ms, P = 0.70); and QT(c)d (46 +/- 13 vs. 47 +/- 15 ms, P = 0.72); JTend(c) (337 +/- 14 vs. 336 +/- 16 ms(1/2), P = 0.74); and JTmax(c) (256 +/- 22 vs. 258 +/- 21 ms(1/2), P = 0.64); Tmax-end(c) (81 +/- 18 vs. 78 +/- 19 ms(1/2), P = 0.42) were not significantly different between PCOS and healthy women.

CONCLUSION

Despite profound differences in hormonal and metabolic pattern, our data demonstrate no significant difference in ECG pattern in PCOS compared to healthy controls.

Differential role of PI3K/Akt pathway in the infarct size limitation and antiarrhythmic protection in the rat heart

Endogenous cardiac protection against prolonged ischemic insult can be achieved by repeated brief episodes of ischemia (hypoxia) or by cardiac adaptation to various stresses such as chronic hypoxia. Activation of phosphatidylinositol 3-kinase (PI3K)/Akt is involved in antiapoptotic effects, however, it is not clear whether it is required for overall heart salvage including protection against myocardial infarction and arrhythmias. We focussed on the potential common role of PI3K/Akt in anti-infarct protection, in the experimental settings of long-term adaptation to chronic intermittent hypobaric hypoxia (IHH; 8 h/day, 25-30 exposures, in vivo rats) and acute ischemic preconditioning (IP; Langendorff-perfused hearts). In addition, we explored the role of PI3K/Akt in susceptibility to ischemic ventricular arrhythmias. In normoxic open-chest rats, PI3K/Akt inhibitor LY294002 (LY; 0.3 mg/kg) given 5 min before test occlusion/reperfusion (I/R) did not affect infarct size (IS) normalized to the size of area at risk (AR). In hypoxic rats, LY partially attenuated IS-limiting effect of IHH (IS/AR 59.7 +/- 4.1% vs. 51.8 +/- 4.4% in the non-treated rats; p > 0.05) and increased IS/AR to its value in normoxic rats (64.9 +/- 5.1%). In the isolated hearts, LY (5 muM) applied 15 min prior to I/R completely abolished anti-infarct protection by IP (IS/AR 55.0 +/- 4.9% vs. 15.2 +/- 1.2% in the non-treated hearts and 42.0 +/- 5.5% in the non-preconditioned controls; p < 0.05). In the non-preconditioned hearts, PI3K/Akt inhibition did not modify IS/AR, on the other hand, it markedly suppressed arrhythmias. In the LY-treated isolated hearts, the total number of ventricular premature beats and the incidence of ventricular tachycardia (VT) was reduced from 518 +/- 71 and 100% in the controls to 155 +/- 15 and 12.5%, respectively (p < 0.05). Moreover, bracketing of IP with LY did not reverse antiarrhythmic effect of IP. These results suggest that activation of PI3K/Akt cascade plays a role in the IS-limiting mechanism in the rat heart, however, it is not involved in the mechanisms of antiarrhythmic protection.

Therapeutic implications of the gender-specific aspects of cardiovascular disease

The manifestations of cardiovascular diseases differ between men and women, as do outcomes after therapeutic interventions. It is important that those involved in drug discovery and development, as well as disease treatment, are aware of these differences because such variations are likely to have an increasing role in therapeutic decisions in the future. Here, I review gender differences in the most frequent cardiovascular diseases and their underlying sex-dependent molecular pathophysiology, and discuss gender-specific effects of current cardiovascular drugs and the implications for novel strategies for drug development.

Long QT and ST-T change associated with organophosphate exposure by aerial spray

The relation between the electrocardiographic manifestation and the subjective symptoms accompanying organophosphate pesticide exposure caused by aerial spray was investigated. The study included 39 patients with a diagnosis of organophosphate poisoning, who visited A-clinic within 24h of exposure to aerial spray of organophosphate pesticide in Gumma Prefecture, from July 2001 to September 2001. Ages ranged from 3 to 82 years. Thirty-five patients were female. Three were diagnosed as severe, 11 moderate, and 25 mild, judged from the score of subjective symptoms. Electrocardiographic abnormalities were bradycardia (<50) 2; prolonged PQ interval 4; prolonged QTc interval (>430ms) 22; nonspecific ST-T change 35; supraventricular arrhythmia 13; and ventricular premature complex with R on T 1. Prolonged QTc interval developed in 2-3 severe cases, 4-11 moderate cases, and 16-25 mild cases. QT prolongation, ST-T change and arrhythmia were detected for some patients exposed to organophosphate by aerial spray.

QT interval duration in apparently healthy men is associated with depression-related personality trait neuroticism

OBJECTIVE

High levels of neuroticism and low self-esteem are markers for vulnerability to depression, a condition associated with a higher risk of arrhythmias. The question as to whether these depression-related personality domains are related to cardiac repolarization (duration of QT interval) in apparently healthy men has been addressed in this study.

METHODS

Participants were 658 clinically healthy males who underwent a health screening programme. QT interval duration was determined in the resting 12-lead electrocardiogram using an automated analysis program. Neuroticism was assessed by the short-scale Eysenck Personality Questionnaire and self-esteem by the Rosenberg self-esteem scale.

RESULTS

Heart-rate corrected QT interval {QTc, formula of Bazett [Bazett HC. An analysis of time relations of electrocardiograms. Heart 1920;7:353-370]} progressively increased across quartiles of neuroticism ratings. By contrast, no differences in QTc were observed across different degrees of self-esteem. A multivariate regression analysis showed that neuroticism was a statistically significant, independent predictor of QTc duration.

CONCLUSION

After adjustment for potential confounders, neuroticism scores independently predicted QT interval duration in apparently healthy men. These findings highlight the possibility that higher arrhythmic risk could be present not only in patients with clinical depression but also in depression-prone, otherwise healthy individuals.

Gender differences in the slow delayed (IKs) but not in inward (IK1) rectifier K+ currents of canine Purkinje fibre cardiac action potential: key roles for IKs, beta-adrenoceptor stimulation, pacing rate and gender

As the beagle dog is a commonly used preclinical species to test the effects of new drugs on cardiac repolarisation and Purkinje fibres have become an established in vitro preparation to assess the effects of these new drugs on action potential duration (APD), the main aim of this study was therefore to evaluate the relative contribution of the inward (I(K1)) and slow delayed (I(Ks)) rectifier cardiac K(+) currents to action potential repolarisation in beagle Purkinje fibres under three different experimental conditions: (i) selective block of I(K1) with BaCl(2), (ii) selective block of I(Ks) with (-) chromanol 293B under basal conditions and (iii) selective block of I(Ks) during beta-adrenoceptor stimulation. Furthermore, the dependence of this contribution on gender and pacing rate was investigated. Microelectrode techniques were employed to measure APD in Purkinje fibres from adult female and male dogs. At stimulation rates of 3.33, 1.0 and 0.2 Hz, the degree of prolongation of APD evoked by BaCl(2) (10 microM) was comparable in fibres from female and male dogs. At the same stimulation rates, 10 microM (-) chromanol 293B did not change the APD in fibres from female and male dogs. During beta-adrenoceptor stimulation with 0.1 microM isoproterenol, an APD prolonging effect of (-) chromanol 293B was detected. In the presence of isoproterenol, action potentials in fibres from male dogs get shorter when changing the stimulation rate from 1.0 to 0.2 Hz, while the opposite is seen in fibres from female dogs. This alteration was completely reversed by (-) chromanol 293B. In conclusion, our findings confirm that beta-adrenoceptor stimulation is one condition where there may be an increased role of I(Ks) in action potential repolarisation. Gender differences in the autonomic modulation of I(Ks) could be a contributing factor to the reported increased susceptibility of female hearts to arrhythmias.

Correction of QT values to allow for increases in heart rate in conscious Beagle dogs in toxicology assessment

INTRODUCTION

Estimation of a direct effect of drugs on the duration of the electrocardiogram (ECG) QT interval can be confused by drug-induced increases in heart rate (HR). The objective of this assessment was to identify a correction formula that adequately corrects QT over a wide range of HRs.

METHODS

Paired recordings of HR and QT interval measurements were obtained from 177 conscious Beagle dogs from both sexes in 9 toxicology studies. ECGs used for this evaluation were collected in either control vehicle-treated dogs, or from dogs prior to the first dose of a daily dosing regimen. Where more than one recording was available per dog, only one was used in the analyses. The assessments were made based on the lowest and highest pre-dose HR for each dog. Correction factors according to [Bazett, H.C. (1920). An analysis of the time relationships or time-relations of electrocardiograms. Heart 7:353-380], [Sagie, A., Larson, M.G., Goldberg, R.J., Bengtson, J.R., & Levy, D. (1992). An improved method for adjusting the QT interval for heart rate (the Framingham heart study). American Journal of Cardiology 70:797-801], [Fridericia, L.S. (1920). Die sytolendauer in elektrokardiogramm bei normalen menschen und bei herzkranken. Acta Medica Scandinavica 53:469-505.], [Todt, H., Krumpl, G., Krejcy, K. & Raberger, G. (1992). Mode of QT correction for heart rate: implications for the detection of inhomogeneous repolarization after myocardial infarction. American Heart Journal 124(3):602-609.] and [Van de Water, A., Verheyen, J., Xhonneux, R., & Reneman, R.S. (1989). An improved method to correct the QT interval of the electrocardiogram for changes in heart rate. Journal of Pharmacological Methods 22:207-217.] were applied to these QT intervals and plotted against HR. Linear regression statistical analyses using a single or multiple (i.e., baseline, sex and study) parameters model was then applied to trend lines.

RESULTS

Although two correction factors ([Todt, H., Krumpl, G., Krejcy, K. & Raberger, G. (1992). Mode of QT correction for heart rate: implications for the detection of inhomogeneous repolarization after myocardial infarction. American Heart Journal 124(3):602-609.] and [Van de Water, A., Verheyen, J., Xhonneux, R., & Reneman, R.S. (1989). An improved method to correct the QT interval of the electrocardiogram for changes in heart rate. Journal of Pharmacological Methods 22:207-217.]) adequately corrected QT for changes in HR [i.e., slope of QTc versus HR not statistically significantly different from zero (p>0.05)] that of Van de Water showed a statistically superior correction. Although the method of analyses accounted for baseline, sex and study it was independently demonstrated that sex did not influence the outcome of the evaluations. Furthermore, higher HRs (i.e., maximum HRs for each dog) were better corrected than the lower HRs. In addition, statistical power analysis applied to these data showed that group sizes of 4-8 could, with 80% chance, detect a 10-5% change, respectively, in appropriately corrected QT.

DISCUSSION

Overall, the data suggest that an evaluation of the most appropriate correction factor should be applied to each laboratory using their own data collected by their own method in their particular strain of dog.

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.

A new method to calculate the beat-to-beat instability of QT duration in drug-induced long QT in anesthetized dogs

INTRODUCTION

Instability of QT duration is a marker to predict Torsade de Pointes (TdP) associated with both congenital and drug-induced long QT syndrome. We describe a new method for the quantification of instability of repolarization.

METHODS

Female, adult beagle dogs anesthetized with a potent morphinomimetic were treated with either solvent (n=7) or dofetilide (n=7). Poincaré plots with QT(n) versus QT(n+1) were constructed to visualize the beat-to-beat variation in QT intervals from the lead II ECG. Short-term instability (STI), long-term instability (LTI) and total instability (TI) were quantified by calculating the distances of 30 consecutive data-points from the x and y-coordinate to the "centre of gravity" of the data cluster. Dofetilide at 0.0025 to 0.04 mg/kg i.v. (plasma concentrations of 4+/-0.6 to 41+/-2.7 ng/ml), dose-dependently prolonged QT and QTcV (at 0.04 mg/kg i.v.: QT: 280+/-ms versus 236+/-5 ms with solvent; p<0.05 and QTcV: 290+/-9 ms versus 252+/-4 ms with solvent; p<0.05). Concomitantly, the compound induced an increase in the instability parameters in a similar dose-dependent manner (at 0.04 mg/kg i.v.: TI: 6.8+/-0.9 ms versus 1.7+/-0.3 ms; p<0.05, LTI: 3.6+/-0.5 ms versus 1.0+/-0.2 ms; p<0.05 and STI: 4.2+/-0.6 ms versus 1.0+/-0.2 ms; p<0.05). The increases induced by dofetilide were associated with a high incidence of early afterdepolarizations (EADs) in the endocardial monophasic action potential (in 6 out of the 7 compound-treated animals versus 0 out of the 7 solvent animals; p<0.05).

CONCLUSION

Quantification of beat-to-beat QT instability by our method clearly detects changes in short-term, long-term and total instability induced by dofetilide, already at pre-arrhythmic doses. Dofetilide administration to anesthetized dogs prolongs ventricular repolarization, concomitantly increases beat-to-beat QT instability and induces early after depolarizations (EADs). As such, the use of these parameters in this in vivo model shows clear potential for risk identification in cardiovascular safety assessment.

Are hERG channel inhibition and QT interval prolongation all there is in drug-induced torsadogenesis? A review of emerging trends

Contemporary preclinical in vitro and in vivo methods have been imperfect in predicting drug-induced Torsades de Pointes (TdP) in humans. A better understanding of additional relevant factors in the genesis of drug-induced TdP is necessary. New sophisticated in vitro techniques, such as arterially perfused ventricular wedge preparations or isolated perfused hearts, potentially offer a better understanding of torsadogenic mechanisms and a refinement of drug testing. Of particular interest are the dispersion of repolarization and the refractoriness of different cell types across the ventricular wall, triangulation of the action potential, reverse use dependence and instability of the action potential duration. In vivo models are currently refined by establishing parameters such as beat-to-beat variability and T-wave morphology as derived from the in vitro proarrhythmia indices. Animal models of proarrhythmia are to date not recommended for routine evaluation. A pharmacodynamic interaction with combinations of torsadogenic compounds is another area to be considered. Little is known about channel/receptor cross talk, although considerable evidence exists that cardiac G protein-coupled receptors can modulate hERG channel function. More investigations are necessary to further evaluate the role of altered gene expression, mutations, and polymorphisms in drug-induced TdP. A novel mechanism of drug-induced torsadogenesis is the reduced expression of hERG channel protein on the plasma membrane due to a trafficking defect. Pharmacokinetic and metabolism data are crucial for calculating the risk of a torsadogenic potential in man. Consideration of intracardiac accumulation can help in delineating pharmacokinetic-pharmacodyamic relationships. In silico virtual screening procedures with new chemical entities to predict hERG block may develop as a promising tool. The role of in silico modeling of TdP arrhythmia is likely to become increasingly important for organizing and integrating the vast amount of generated data. At present, however, in silico methods cannot replace existing preclinical in vitro and in vivo models.

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.

Ibutilide – recent molecular insights and accumulating evidence for use in atrial flutter and fibrillation

Ibutilide is a 'pure' class III antiarrhythmic drug, used intravenously against atrial flutter and fibrillation. At a cellular level it exerts two main actions: induction of a persistent Na+ current sensitive to dihydropyridine Ca2+ channel blockers and potent inhibition of the cardiac rapid delayed rectifier K+ current, by binding within the channel pore cavity upon channel gating. Ibutilide has been shown to terminate atrial flutter and fibrillation in animal studies, with some risk of ventricular pro-arrhythmia. Experimental models of hypertrophy/heart failure show altered sensitivity to ibutilide, with increased dispersion of repolarisation and incidence of pro-arrhythmia. Patient trials show that ibutilide is effective at terminating atrial arrhythmias when given alone, and that it can increase effectiveness and reduce energy requirements of electrical cardioversion. The risk to patients of polymorphic ventricular tachycardia necessitates careful patient selection and monitoring during and after treatment. An ibutilide analogue, trecetilide, requires further investigation but may offer a less readily metabolised and pro-arrhythmic alternative to ibutilide.

QT interval prolongation related to psychoactive drug treatment: a comparison of monotherapy versus polytherapy

BACKGROUND: Several antipsychotic agents are known to prolong the QT interval in a dose dependent manner. Corrected QT interval (QTc) exceeding a threshold value of 450 ms may be associated with an increased risk of life threatening arrhythmias. Antipsychotic agents are often given in combination with other psychotropic drugs, such as antidepressants, that may also contribute to QT prolongation. This observational study compares the effects observed on QT interval between antipsychotic monotherapy and psychoactive polytherapy, which included an additional antidepressant or lithium treatment. METHOD: We examined two groups of hospitalized women with Schizophrenia, Bipolar Disorder and Schizoaffective Disorder in a naturalistic setting. Group 1 was composed of nineteen hospitalized women treated with antipsychotic monotherapy (either haloperidol, olanzapine, risperidone or clozapine) and Group 2 was composed of nineteen hospitalized women treated with an antipsychotic (either haloperidol, olanzapine, risperidone or quetiapine) with an additional antidepressant (citalopram, escitalopram, sertraline, paroxetine, fluvoxamine, mirtazapine, venlafaxine or clomipramine) or lithium. An Electrocardiogram (ECG) was carried out before the beginning of the treatment for both groups and at a second time after four days of therapy at full dosage, when blood was also drawn for determination of serum levels of the antipsychotic.Statistical analysis included repeated measures ANOVA, Fisher Exact Test and Indipendent T Test. RESULTS: Mean QTc intervals significantly increased in Group 2 (24 +/- 21 ms) however this was not the case in Group 1 (-1 +/- 30 ms) (Repeated measures ANOVA p < 0,01). Furthermore we found a significant difference in the number of patients who exceeded the threshold of borderline QTc interval value (450 ms) between the two groups, with seven patients in Group 2 (38%) compared to one patient in Group 1 (7%) (Fisher Exact Text, p < 0,05). CONCLUSIONS: No significant prolongation of the QT interval was found following monotherapy with an antipsychotic agent, while combination of these drugs with antidepressants caused a significant QT prolongation. Careful monitoring of the QT interval is suggested in patients taking a combined treatment of antipsychotic and antidepressant agents.

Drugs, QTc Interval Prolongation and Final ICH E14 Guideline

Regulatory concerns on the ability of an ever-increasing number of non-antiarrhythmic drugs to delay ventricular repolarisation, prolong the corrected QT (QTc) interval and induce potentially fatal ventricular tachyarrhythmias have culminated in the adoption of two, internationally harmonised, regulatory guidelines. On 12 May 2005, the International Conference on Harmonisation (ICH) reached an important milestone when it adopted the final texts for clinical (ICH topic E14) and non-clinical (ICH topic S7B) strategies by which drugs should be investigated for their potential to induce these effects during their development.ICH E14 provides recommendations to sponsors concerning the design, conduct, analysis and interpretation of clinical studies to assess the potential of a drug to delay cardiac repolarisation. Specifically, it calls for a clinical 'thorough QT/QTc study' (typically conducted in healthy volunteers), which is intended to determine whether a drug has a threshold pharmacological effect on cardiac repolarisation, as detected by QT/QTc interval prolongation. The E14 recommendations are generally applicable not only to new drugs that have systemic bioavailability but also to approved drugs when a new dose, route of administration or target population that may result in an increased risk is explored. The guideline provides for exceptions when this study may not be required.Recognising the fractious relationship between ICH E14 and ICH S7B, and the persistence of a number of issues that may require clarity and/or the emergence of other new scientific issues in the future, the ICH Steering Committee has formed an Implementation Working Group that is charged with providing clarity on aspects of the guideline that are ambiguous and responding to issues on which the sponsors are uncertain. This paper provides a commentary on some of the challenges that are likely to be faced by the sponsors of drugs during the next few years of application of these two guidelines. The adoption of these guidelines has left a number of questions unanswered and raised some new ones. When in doubt, the sponsor should seek formal regulatory clarity before making key decisions that may impact further development, assessment and approval of a new chemical entity. Although the goal of developing drugs with much lower torsadogenic potential and without inappropriate restriction in the use (or even rejection) of potentially beneficial drugs is within sight, it is questionable whether the risk of drug-induced pro-arrhythmia will be eliminated completely.