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

Sex Differences in Mouse Cardiac Electrophysiology Revealed by Simultaneous Imaging of Excitation-Contraction Coupling

Males and females differ in the basic anatomy and physiology of the heart. Sex differences are evident in cardiac repolarization in humans; women have longer corrected QT and JT intervals. However, the molecular mechanisms that lead to these differences are incompletely understood. Here, we present that, like in humans, sex differences in QT and JT intervals exist in mouse models; female mice had longer corrected QT and JT intervals compared with age-matched males. To further understand the molecular underpinning of these sex differences, we developed a novel technology using fluorescent confocal microscopy that allows the simultaneous visualization of action potential, Ca2+ transients, and contractions in isolated cardiomyocytes at a high temporal resolution. From this approach, we uncovered that females at baseline have increased action potential duration, decreased Ca2+ release and reuptake rates, and decreased contraction and relaxation velocities compared with males. Additionally, males had a shorter overall time from action potential onset to peak contraction. In aggregate, our studies uncovered male and female differences in excitation-contraction coupling that account for differences observed in the EKG. Overall, a better understanding of sex differences in electrophysiology is essential for equitably treating cardiac disease.

Acute exposure to low-dose bisphenol A delays cardiac repolarization in female canine heart - Implication for proarrhythmic toxicity in large animals

Bisphenol A (BPA) is a common environmental chemical with a range of potential adverse health effects. The impact of environmentally-relevant low dose of BPA on the electrical properties of the hearts of large animals (e.g., dog, human) is poorly defined. Perturbation of cardiac electrical properties is a key arrhythmogenic mechanism. In particular, delay of ventricular repolarization and prolongation of the QT interval of the electrocardiogram is a marker for the risk of malignant arrhythmias. We examined the acute effect of 10-9 M BPA on the electrical properties of female canine ventricular myocytes and tissues. BPA rapidly delayed action potential repolarization and prolonged action potential duration (APD). The dose response curve of BPA on APD was nonmonotonic. BPA rapidly inhibited the IKr K+ current and ICaL Ca2+ current. Computational modeling indicated that the effect of BPA on APD can be accounted for by its suppression of IKr. At the tissue level, BPA acutely prolonged the QT interval in 4 left ventricular wedges. ERβ signaling contributed to the acute effects of BPA on ventricular repolarization. Our results demonstrate that BPA has QT prolongation liability in female canine hearts. These findings have implication for the potential proarrhythmic cardiac toxicity of BPA in large animals.

The effect of sex and age on ex vivo cardiac electrophysiology: insight from a guinea pig model

Highlighting the importance of sex as a biological variable, we recently reported sex differences in guinea pig in vivo electrocardiogram (ECG) measurements. However, substantial inconsistencies exist in this animal model, with conflicting reports of sex-specific differences in cardiac electrophysiology observed in vivo and in vitro. Herein, we evaluated whether sexual dimorphism persists in ex vivo preparations, using an isolated intact heart preparation. Pseudo-ECG recordings were collected in conjunction with dual optical mapping of transmembrane voltage and intracellular calcium from Langendorff-perfused hearts. In contrast to our in vivo results, we did not observe sex-specific differences in ECG parameters collected from isolated hearts. Furthermore, we observed significant age-specific differences in action potential duration (APD) and Ca2+ transient duration (CaD) during both normal sinus rhythm (NSR) and in response to dynamic pacing but only a modest sex-specific difference in CaD30. Similarly, the alternans fluctuation coefficient, conduction velocity during sinus rhythm or in response to pacing, and electrophysiology parameters (atrioventricular nodal effective refractory period, Wenckebach cycle length) were comparable between males and females. Results of our study suggest that the observed sex-specific differences in in vivo ECG parameters from guinea pigs are diminished in ex vivo isolated heart preparations, although age-specific patterns are prevalent. To assess sex as a biological variable in cardiac electrophysiology, a comprehensive approach may be necessary using both in vitro measurements from cardiomyocyte or intact heart preparations with secondary follow-up in vivo studies.NEW & NOTEWORTHY We evaluated whether the guinea pig heart has intrinsic sex-specific differences in cardiac electrophysiology. Although we observed sex-specific differences in in vivo ECGs, these differences did not persist ex vivo. Using a whole heart model, we observed similar APD, CaD, conduction velocity, and alternans susceptibility in males and females. We conclude that sex-specific differences in guinea pig cardiac electrophysiology are likely influenced by the in vivo environment and less dependent on the intrinsic electrical properties of the heart.

Tpeak-Tend Interval during Pregnancy and Postpartum

BACKGROUND

Pregnancy is a condition in which new cardiac arrhythmias can occur or prior undiagnosed arrhythmias may provide symptoms. The occurrence of severe ventricular arrhythmias and polymorphic ventricular tachycardia that may lead to fainting or sudden cardiac death is promoted by the prolongation of the QTc interval. The post-partum adaptation period is the most arrhythmogenic. TpTe (Tpeak-Tend interval) is a novel marker of arrhythmogenesis by many considered a more sensitive marker than QTc.

OBJECTIVE

The aim of our work was to determine the TpTe interval (Tpeak-Tend) in women in the first, second and third trimester of pregnancy and the post-partum period.

MATERIALS AND METHODS

The study group consisted of 128 women in pregnancy or postpartum and a control group of 32 non-pregnant women. A standard 12-lead ECG (electrocardiograph) recording with evaluation of the duration of TpTe and QTc was performed in all patients.

RESULTS

In comparison to the non-pregnant women, higher values of QTc and TpTe were observed starting in the first trimester with highest values observed in the postpartum period. Mean duration of TpTe interval during pregnancy (81.59 ± 5.92 ms) and in the whole study group (pregnancy + postpartum) (85.46 ± 6.45 ms) was significantly longer (p < 0.001) compared to the TpTe interval in the control group (74.06 ± 6.14 ms). During pregnancy and postpartum, the increase in the TpTe interval in comparison to the increase in the QTc parameter (31.10% vs. 4.18%) was significantly higher (p < 0.001).

CONCLUSIONS

The study showed an increase in the duration of the TpTe interval and QTc parameter during pregnancy and postpartum with the highest values in the postpartum period. TpTe interval increase was significantly higher compared to QTc increase during pregnancy and postpartum. Changes of TpTe interval were not associated with any clinical outcome or measure of arrythmia burden. Further studies are needed in order to see the clinical significance of these ECG findings, in particular for larger groups of patients with automatic measurement in correlation with echocardiography.

Prolongation of QTc interval due to increased parity and great grand multiparity

Women are more prone to cardiac arrhythmias. Increased exposure to sex hormones may alter the ventricular repolarisation of the heart as the parity number increases. In this study, we aim to investigate the effect of parity number to electrocardiographic parameters. A total of 205 adult women were included for the study. Nulliparous (NP), primiparous (PP), multiparous (MP), grand multiparous (GMP) and great grand multiparous (GGMP) women constituted the study population. Increased parity has positive correlation with QTc interval (p=.000, r = 0.303). GGMP has significantly higher QTc compared to NP, PP, MP and GMP (p=.001, p=.000, p=.004 and p=.007, respectively). GGMP and parity have explanatory power on QTc (p=.019 and p=.020, respectively). Parity and GGMP affect cardiac repolarisation and prolong the QTc interval most probably due to repeated exposure to sex hormones. This study showed that GGMP and parity are independent risk factors for QTc interval prolongation.Impact StatementWhat is already known on this subject? Increased exposure to sex hormones may alter the ventricular repolarisation of the heart as the parity number increases. Previous studies showed that increased parity (up to 7) deteriorates ventricular diastolic functions, prolongs QTc interval and these conditions cause cardiovascular diseases.What do the results of this study add? In this study, we added great grand multiparity (10 or more parity) (GGMP) group that have never been studied before. We found that GGMP has much more impact on QTc prolongation than fewer parity groups and this result shows us that GGMP deteriorates ventricular functions more.What are the implications of these findings for clinical practice and/or further research? These results show us that women should be discouraged from having more delivery. Also, women with a pregnancy history of five and more (grand multiparity) should be evaluated with an electrocardiography and a cardiology consultation should be performed before re-conception. In the future, larger prospective studies are needed on this subject. In addition, other electrocardiographic parameters (QRS-T angle and Tpe/QTc in electrocardiography, etc.) that related with diastolic functions should be evaluated for comparison of GGMP and non-GGMP populations in future studies.

Non-Coding RNAs in the Cardiac Action Potential and Their Impact on Arrhythmogenic Cardiac Diseases

Cardiac arrhythmias are prevalent among humans across all age ranges, affecting millions of people worldwide. While cardiac arrhythmias vary widely in their clinical presentation, they possess shared complex electrophysiologic properties at cellular level that have not been fully studied. Over the last decade, our current understanding of the functional roles of non-coding RNAs have progressively increased. microRNAs represent the most studied type of small ncRNAs and it has been demonstrated that miRNAs play essential roles in multiple biological contexts, including normal development and diseases. In this review, we provide a comprehensive analysis of the functional contribution of non-coding RNAs, primarily microRNAs, to the normal configuration of the cardiac action potential, as well as their association to distinct types of arrhythmogenic cardiac diseases.

The Impact of Testosterone on the QT Interval: A Systematic Review

Humans and mammals have sex-specific differences in cardiac electrophysiology, linked to the action of sex hormones in the cardiac muscle. These hormones can upregulate or downregulate the expression of ionic channels modulating the cardiac cycle through genomic and non-genomic interactions. Systematic search in PubMed, Medline and EMBASE including keywords pertaining to testosterone and QT interval. Included experimental studies and observation studies and case reports presenting the results of testosterone administration, excess or deficiency in humans and animals. Testosterone has been shown to shorten the action potential duration, by enhancing the expression of K⁺ channels and downregulating I_CaL increasing the repolarization reserve of the cardiac muscle. This effect has been observed in both genders and animals. Testosterone deficient states can promote arrhythmogenesis. The evidence in this paper may be used to guide clinical considerations, such as increased clinical surveillance of patients in testosterone deficient states using ECG.

Common Genetic Variants Modulate the Electrocardiographic Tpeak-to-Tend Interval

Sudden cardiac death is responsible for half of all deaths from cardiovascular disease. The analysis of the electrophysiological substrate for arrhythmias is crucial for optimal risk stratification. A prolonged T-peak-to-Tend (Tpe) interval on the electrocardiogram is an independent predictor of increased arrhythmic risk, and Tpe changes with heart rate are even stronger predictors. However, our understanding of the electrophysiological mechanisms supporting these risk factors is limited. We conducted genome-wide association studies (GWASs) for resting Tpe and Tpe response to exercise and recovery in ∼30,000 individuals, followed by replication in independent samples (∼42,000 for resting Tpe and ∼22,000 for Tpe response to exercise and recovery), all from UK Biobank. Fifteen and one single-nucleotide variants for resting Tpe and Tpe response to exercise, respectively, were formally replicated. In a full dataset GWAS, 13 further loci for resting Tpe, 1 for Tpe response to exercise and 1 for Tpe response to exercise were genome-wide significant (p ≤ 5 × 10^-8). Sex-specific analyses indicated seven additional loci. In total, we identify 32 loci for resting Tpe, 3 for Tpe response to exercise and 3 for Tpe response to recovery modulating ventricular repolarization, as well as cardiac conduction and contraction. Our findings shed light on the genetic basis of resting Tpe and Tpe response to exercise and recovery, unveiling plausible candidate genes and biological mechanisms underlying ventricular excitability.

Testosterone, myocardial function, and mortality

The cardiovascular system is particularly sensitive to androgens, but some controversies exist regarding the effect of testosterone on the heart. While among anabolic abusers, cases of sudden cardiac death have been described, recently it was reported that low serum level of testosterone was correlated with increased risk of cardiovascular diseases (CVD) and mortality rate. This review aims to evaluate the effect of testosterone on myocardial tissue function, coronary artery disease (CAD), and death. Low testosterone level is associated with increased incidence of CAD and mortality. Testosterone administration in hypogonadal elderly men and women has a positive effect on cardiovascular function and improved clinical outcomes and survival time. Although at supraphysiologic doses, androgen may have a toxic effect, and at physiological levels, testosterone is safe and exerts a beneficial effect on myocardial function including mechanisms at cellular and mitochondrial level. The interaction with free testosterone and estradiol should be considered. Further studies are necessary to better understand the interaction mechanisms for an optimal androgen therapy in CVD.

Withdrawal of prenylamine: perspectives on pharmacological, clinical and regulatory outcomes following the first QT-related casualty

Prenylamine, an antianginal agent marketed since early 1960, became the first casualty of QT interval related proarrhythmias in 1988 when it was withdrawn from the market. The period of its synthesis and marketing is of particular interest since it antedated, first, any serious clinical safety concern regarding drug-induced prolongation of the QT interval which was, in fact, believed to be an efficient antiarrhythmic mechanism; second, the first description of torsade de pointes as a unique proarrhythmia, typically associated with prolonged QT interval; and third, the discovery and recognition of calcium antagonism as an important cardiovascular therapeutic strategy. This review, 30 years almost to the day following its withdrawal, provides interesting perspectives on clinical, pharmacological and regulatory outcomes that followed. Prenylamine underscored torsadogenic potential of other early antianginal drugs on the market at that time and identified QT-related proarrhythmias as a much wider major public health issue of clinical and regulatory concern. This resulted in various guidelines for early identification of this potentially fatal risk. Application of these guidelines would have readily identified its proarrhythmic potential. Prenylamine also emphasized differences in drug responses between men and women which subsequently galvanized extensive research into sex-related differences in pharmacology. More importantly, however, investigations into the mechanisms of its action paved the way to developing modern safe and effective calcium antagonists that are so widely used today in cardiovascular pharmacotherapy.

Electro-mechanical dysfunction in long QT syndrome: Role for arrhythmogenic risk prediction and modulation by sex and sex hormones

Long QT syndrome (LQTS) is a congenital arrhythmogenic channelopathy characterized by impaired cardiac repolarization. Increasing evidence supports the notion that LQTS is not purely an "electrical" disease but rather an "electro-mechanical" disease with regionally heterogeneously impaired electrical and mechanical cardiac function. In the first part, this article reviews current knowledge on electro-mechanical (dys)function in LQTS, clinical consequences of the observed electro-mechanical dysfunction, and potential underlying mechanisms. Since several novel imaging techniques - Strain Echocardiography (SE) and Magnetic Resonance Tissue Phase Mapping (TPM) - are applied in clinical and experimental settings to assess the (regional) mechanical function, advantages of these non-invasive techniques and their feasibility in the clinical routine are particularly highlighted. The second part provides novel insights into sex differences and sex hormone effects on electro-mechanical cardiac function in a transgenic LQT2 rabbit model. Here we demonstrate that female LQT2 rabbits exhibit a prolonged time to diastolic peak - as marker for contraction duration and early relaxation - compared to males. Chronic estradiol-treatment enhances these differences in time to diastolic peak even more and additionally increases the risk for ventricular arrhythmia. Importantly, time to diastolic peak is particularly prolonged in rabbits exhibiting ventricular arrhythmia - regardless of hormone treatment - contrasting with a lack of differences in QT duration between symptomatic and asymptomatic LQT2 rabbits. This indicates the potential added value of the assessment of mechanical dysfunction in future risk stratification of LQTS patients.

Cardiotoxic Electrophysiological Effects of the Herbicide Roundup(®) in Rat and Rabbit Ventricular Myocardium In Vitro

Roundup (R), a glyphosate (G)-based herbicide (GBH), containing unknown adjuvants is widely dispersed around the world. Used principally by farmers, intoxications have increasingly been reported. We have studied R effects (containing 36 % of G) on right ventricular tissues (male Sprague-Dawley rats, up to 20,000 ppm and female New Zealand rabbits, at 25 and 50 ppm), to investigate R cardiac electrophysiological actions in vitro. We tested the reduced Ca(++) intracellular uptake mechanism as one potential cause of the electrical abnormalities after GBH superfusion, using the Na(+)/K(+)-ATPase inhibitor ouabain or the 1,4-dihydropyridine L-type calcium channel agonist BAY K 8644 which increases I Ca. R concentrations were selected based on human blood ranges found after acute intoxication. The study showed dose-dependent V max, APD50 and APD90 variations during 45 min of R superfusion. At the highest concentrations tested, there was a high incidence of conduction blocks, and 30-min washout with normal Tyrode solution did not restore excitability. We also observed an increased incidence of arrhythmias at different doses of R. Ouabain and BAY K 8644 prevented V max decrease, APD90 increase and the cardiac inexcitability induced by R 50 ppm. Glyphosate alone (18 and 180 ppm) had no significant electrophysiological effects. Thus, the action potential prolonging effect of R pointing to I Ca interference might explain both conduction blocks and proarrhythmia in vitro. These mechanisms may well be causative of QT prolongation, atrioventricular conduction blocks and arrhythmias in man after GBH acute intoxications as reported in retrospective hospital records.

Effects of Gender on Electrocardiography in Subjects with Shortened Ventricular Depolarization (QRS)

BACKGROUND

Distinctions between electrocardiograms of female and male subjects have been recognized for many years. Due to these differences, arrhythmias in each gender have a tendency to differ. In our study, we aimed to compare electrocardiography intervals between men and women with short QRS durations.

METHODS

Subjects with a QRS interval of ≤80 ms were included in the study. Patients were grouped by gender and the parameters were compared. Patients with diseases that might affect QRS interval and/or who were on medications were excluded. The electrocardiogram intervals of the subjects were measured, Holter monitors were placed, and parameters of time-based heart rate variation were analyzed.

RESULTS

A total of 100 patients (55% female) were included in the study. According to statistical analysis, no significant difference between the genders was observed in the heart rate or in the parameters, such as QT, JT, JTp, and TpTe intervals or heart rate-corrected QTc, JTc, JTpc, and TpTec intervals, which affect repolarization and are known to be arrhythmia precursors by shortening or elongation. No statistically significant difference was found between the two groups for the parameters of heart rate variability time measures (SDNN, SDANN, rMSSD, and pNN50).

CONCLUSION

We observed that when the QRS interval gets shorter, repolarization differences between the genders disappear. New studies are required on this subject.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

QT Prolongation and Oncology Drug Development

Many pharmaceutical agents interact with cardiac ion channels resulting in abnormal ventricular repolarization and prolongation of the QT interval. In rare circumstances, this has resulted in the development of the potentially life-threatening arrhythmia, torsades de pointes. It is recognized, however, that accurate measurement of the QT interval is challenging, and it is a poor predictor for the development of this arrhythmia. Nevertheless, QT interval monitoring is an essential part of pharmaceutical development, and significant increases in the QT interval may prevent a drug from gaining approval.

How do sex hormones modify arrhythmogenesis in long QT syndrome? Sex hormone effects on arrhythmogenic substrate and triggered activity

Gender differences in cardiac repolarization and the arrhythmogenic risk of patients with inherited and acquired long QT syndromes are well appreciated clinically. Enhancing our knowledge of the mechanisms underlying these differences is critical to improve our therapeutic strategies for preventing sudden cardiac death in such patients. This review summarizes the effects of sex hormones on the expression and function of ion channels that control cardiac cell excitation and repolarization as well as key proteins that regulate Ca(2+) dynamics at the cellular level. Moreover, it examines the role of sex hormones in modifying the dynamic spatiotemporal (regional and transmural) heterogeneities in action potential duration (eg, the arrhythmogenic substrate) and the susceptibility to (sympathetic) triggered activity at the tissue, organ, and whole animal levels. Finally, it explores the implications of these effects on the management of patients with LQTS.

Absence of gender-based differences in the atrial and pulmonary vein substrate: a detailed electroanatomic mapping study

BACKGROUND

Gender-based differences in the clinical nature of cardiac arrhythmias such as atrial fibrillation (AF) are well established.

OBJECTIVE

The purpose of this study was to identify any such gender-based differences in the underlying pulmonary vein and atrial substrate.

METHODS AND RESULTS

Thirty-eight patients with no history of AF undergoing catheter ablation for supraventricular tachycardia (SVT) and 55 with paroxysmal or persistent AF undergoing catheter ablation of AF underwent detailed electroanatomic mapping of the pulmonary veins and atria. Refractory periods in multiple locations, sinus node function, endocardial bipolar voltage, pulmonary vein and atrial conduction, and bipolar electrogram complexity were analyzed. There were no significant between-gender differences in age or other clinical variables known to impact on the atrial or pulmonary vein substrate. In neither the AF nor the non-AF cohorts were there any significant differences in atrial or pulmonary vein refractoriness, sinus node function, any measure of PV electrophysiology, or any measure of atrial electrophysiology.

CONCLUSION

No systematic between-gender differences were observed in the PV or atrial substrate either in those with or without a history of AF, with a similar prevalence of the cardiovascular comorbidities frequently associated with atrial remodeling and AF seen in both male and female groups.

Use of QT intervals for a more accurate diagnose of syncope and evaluation of syncope severity

BACKGROUND

This study aimed to evaluate the use of QT intervals, their diagnostic predictive value in patients with syncope and their relationship with syncope severity.

METHODS

One hundred and forty nine patients with a diagnosis of syncope were admitted to Internal Medicine departments at the University of Palermo, Italy, between 2006 and 2012, and 140 control subjects hospitalised for other causes were enrolled. QT maximum, QT minimum, QTpeak, QT corrected, QT dispersion and Tpeak-to-Tend interval were compared between two groups. The paper medical records were used for scoring with San Francisco Syncope Rule (SFSR), Evaluation of Guidelines in SYncope Study (EGSYS) score and Osservatorio Epidemiologico sulla Sincope nel Lazio (OESIL) risk score.

RESULTS

Mean QTc (p < 0.0005), mean QTmax (p < 0.0005), mean QTdisp (p < 0.0005), mean QTpeak (p = 0.005) and mean TpTe (p = 0.018) were significantly longer in patients with syncope compared with control subjects. A QTc > 424.8 ms (sensibility: 81.88 - specificity: 57.86) showed the greatest predictive value for diagnosis of syncope. On the EGSYS score and on the OESIL score, QTc was significantly prolonged in high-risk patients compared with low-risk patients. On the San Francisco Syncope Rule, QTc and QTdisp were significantly prolonged in high-risk patients compared with low-risk patients.

CONCLUSION

Mean QTc, mean QTdisp, mean TpTe, mean QTmax and mean QTpeak were significantly longer in patients with syncope compared with control subjects. Furthermore, prolonged QTc and QTdisp were associated with major severe syncope according to San Francisco Syncope Rule, EGSYS and OESIL risk scores.

Modeling gender effects on electrical activity of single ventricular myocytes

In this study we investigate the mechanisms underlying gender differences in the generation of arrhythmias in the long QT and Brugada syndromes. Simulations were conducted at the single myocyte level using a detailed mathematical model of human ventricular myocytes. Given the scarce human data on the gender-related differences in single cardiac cells, we assumed gender-related differences in five ionic-current systems: fast sodium current (INa), slowly inactivating late sodium current (INal), transient outward potassium current (Ito), slow delayed rectifier potassium current (IKs), and calcium current through the L-type channel (ICa(L)), based on experimental results obtained in canine myocytes. Our modeling results suggest that in left ventricular myocytes, enhanced INal under conditions of reduced repolarization reserve results in sex-dependent development of early afterdepolarizations (EADs) in the post-pause action potentials (APs). Moreover, this modeling study demonstrates increased propensity for the development of the loss of the AP dome in male epicardial myocytes of the right ventricle compared with other types of myocytes from the left and right ventricles. Finally, we also found a slight effect of INal on gender-dependent loss of AP dome in epicardial right ventricular myocytes. In conclusion, at the cellular level, gender differences in the development of EADs and the propensity to develop the loss of the AP dome can be attributed to male/female related differences in INa, INal, Ito, IKs, and ICa(L).

ICH E14 Q & A (R1) document: perspectives on the updated recommendations on thorough QT studies

The International Conference on Harmonization (ICH) guidance ICH E14 provides recommendations, focusing on a clinical 'thorough QT/QTc (TQT) study', to evaluate the QT liability of a drug during its development. An Implementation Working Group (IWG) was also established to assist the sponsors with any uncertainties and clarify any ambiguities. In April 2012, the IWG updated its June 2008 version of the Questions and Answers document to address additional issues. These include the gender of the study population, a reasonable approach to evaluating QTc changes in late stage clinical development and the recommended approach to correcting the measured QT interval. This commentary provides our observations and, when appropriate, recommendations, on these issues. We review briefly evidence that suggests that (i) the greater QT effect observed in females is not entirely related to differences in drug exposure and (ii) the Fridericia correction of measured QT interval is adequate for a majority of TQT studies. Until further evidence suggests otherwise, we recommend balanced gender representation in TQT studies, unless warranted otherwise, and for positive studies, subgroup analysis of key data by common demographic variables including the gender and ethnicity. We provide a general scheme for ECG monitoring in late phase clinical trials and consider that while intensive monitoring and centralized reading of ECGs in late phase clinical trials is the norm when a TQT study is positive, there are other circumstances that also call for high quality ECG reading. Therefore, locally read ECGs should only be acceptable as long as accurate high quality ECG data can be guaranteed.

Sex differences in cardiac autonomic regulation and in repolarisation electrocardiography

The review summarises the present knowledge on the sex differences in cardiac autonomic regulations and in related aspects of electrocardiography with particular attention to myocardial repolarisation. Although some of the sex differences are far from fully established, multitude of observations show consistent differences between women and men. Despite more pronounced parasympathetic cardiac regulation, women have higher resting heart rate and lower baroreflex sensitivity. Of the electrocardiographic phenomena, women have longer QT interval duration, repolarisation sequence more synchronised with the inverse of the depolarisation sequence, and likely increased regional heterogeneity of myocardial repolarisation. Studies investigating the relationship of these sex disparities to hormonal differences led frequently to conflicting results. Although sex hormones seem to play a key role by influencing both autonomic tone and electrophysiological properties at the cellular level, neither the truly relevant hormones nor their detailed actions are known. Physiologic usefulness of the described sex differences is also unknown. The review suggests that new studies are needed to advance the understanding of the physiologic mechanisms responsible for these inequalities between women and men and provides key methodological suggestions that need to be followed in future research.

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.

Frequency-dependent acceleration of cardiac repolarization by progesterone underlying its cardiac protection against drug-induced proarrhythmic effects in female rabbits

Concurrent supplement of estradiol and progesterone has been shown to reduce the cardiac sensitivity to class III antiarrhythmic agent-induced arrhythmias in ovariectomized rabbits. To understand the underlying cardiac electrophysiological mechanisms of the hormones, present study explored the modulation of progesterone and estradiol on repolarization and its frequency dependence in papillary muscles of female rabbit right ventricles by glass microelectrode technique. Results showed that progesterone shortened action potential duration for 90% repolarization (APD(90)) whereas estradiol prolonged APD(90) and those actions on APD(90) were concentration-dependent for both hormones at 1.0-30 μM (P<0.05 or P<0.01). Further, the action of both hormones on APD(90) was found to be dependent on stimulation frequencies (0.2-3.3Hz). The shortening of APD(90) by progesterone (10 μM) was enhanced with the increase in frequencies reaching a statistic significance at frequencies ≥1.0 Hz, whereas the prolongation of APD(90) by estradiol (3 μM) was weakened with the increase in frequencies and the significant change was observed at frequencies ≤2.0 Hz (P<0.05 or P<0.01). More interestingly, the relative change of APD(90) and the incidence of early afterdepolarization induced after by dofetilide (0.1 μM), a class III antiarrhythmic agent, were significantly less or lower in the papillary muscles pretreated with progesterone than in those pretreated with estradiol (P<0.01 or P<0.05). In conclusion, progesterone has a reverse modulating affect on cardiac repolarization to that of estradiol. By acceleration of ventricular repolarization, progesterone may reduce the susceptibility of females to class III antiarrhythmic agents-induced proarrhythmic affection.

Field and action potential recordings in heart slices: correlation with established in vitro and in vivo models

BACKGROUND AND PURPOSE

Action potential (AP) recordings in ex vivo heart preparations constitute an important component of the preclinical cardiac safety assessment according to the ICH S7B guideline. Most AP measurement models are sensitive, predictive and informative but suffer from a low throughput. Here, effects of selected anti-arrhythmics (flecainide, quinidine, atenolol, sotalol, dofetilide, nifedipine, verapamil) on field/action potentials (FP/AP) of guinea pig and rabbit ventricular slices are presented and compared with data from established in vitro and in vivo models.

EXPERIMENTAL APPROACH

Data from measurements of membrane currents (hERG, I(Na) ), AP/FP (guinea pig and rabbit ventricular slices), AP (rabbit Purkinje fibre), haemodynamic/ECG parameters (conscious, telemetered dog) were collected, compared and correlated to complementary published data (focused literature search).

KEY RESULTS

The selected anti-arrhythmics, flecainide, quinidine, atenolol, sotalol, dofetilide, nifedipine and verapamil, influenced the shape of AP/FP of guinea pig and rabbit ventricular slices in a manner similar to that observed for rabbit PF. The findings obtained from slice preparations are in line with measurements of membrane currents in vitro, papillary muscle AP in vitro and haemodynamic/ECG parameters from conscious dogs in vivo, and were also corroborated by published data.

CONCLUSION AND IMPLICATIONS

FP and AP recordings from heart slices correlated well with established in vitro and in vivo models in terms of pharmacology and predictability. Heart slice preparations yield similar results as papillary muscle but offer enhanced throughput for mechanistic investigations and may substantially reduce the use of laboratory animals.

The effects of supplementation with omega-3 polyunsaturated Fatty acids on cardiac rhythm: anti-arrhythmic, pro-arrhythmic, both or neither? It depends…

Supplementation of omega-3 fatty acids (Ω-3) has been associated with a decreased cardiovascular risk, thereby concentrating attention on a potentially preventive effect regarding tachyarrhythmias and sudden cardiac death. However, recent randomized controlled trials challenge the efficacy of the additional application of Ω-3 and its anti-arrhythmic effect under certain clinical conditions. The present paper reflects the results of earlier and recent clinical studies with respect to the individual background conditions that may determine the clinical outcome of Ω-3 supplementation and thereby explain apparently conflicting clinical results. It is concluded that the efficacy of Ω-3 supplementation to prevent cardiac arrhythmias strongly depends on the underlying clinical and pharmacological conditions, a hypothesis that also is supported by data from experimental animal studies and by molecular interactions of Ω-3 at the cellular level.

Concurrent supplement of estradiol and progesterone reduces the cardiac sensitivity to D,L-sotalol-induced arrhythmias in ovariectomized rabbits

BACKGROUND

Although the difference in the modulation of estradiol and dihydrotesterone on ventricular repolarization has been intensively studied, little information is available concerning the role of the different ovarian hormones in the modulation of repolarization in the female.

METHODS

The chronic modulation of female hormones, estradiol, and progesterone, on cardiac repolarization and the susceptibility to d,l-sotalol, a class III antiarrhythmic agent, were studied in female rabbits by ovariectomy and hormone replacement therapy (HRT) through recording and analyzing of electrocardiograms.

RESULTS

The corrected QT interval (QTc) measured 2 weeks after ovariectomy was not significantly different from that in the time-matched control rabbits. After 2 weeks of HRT, the QTc in the ovariectomized rabbits treated with estradiol alone (group E) was not significantly different from that in the control (group C); whereas in the ovariectomized rabbits treated with estradiol plus progesterone (group E + P), it was significantly shorter than those in groups E (P < .05) and C (P < .01), respectively. The corrected Tpeak-end interval (Tpec), an indicator of global dispersion of ventricular repolarization, was also significantly reduced in group E + P compared with that of group C (P < .01). In group E, d,l-sotalol-induced prolongation of QTc and the rate and the severity of arrhythmias were significantly higher, while the dose of sotalol to initiate arrhythmias was significantly lower than those in groups C or E + P, respectively (P < .05 or P < .01).

CONCLUSION

Estradiol potentiates QTc prolonging effects of d,l-sotalol and increases the susceptibility to d,l-sotalol-induced arrhythmias without significantly altering QTc itself, whereas progesterone may accelerate the process of repolarization and protect the females from drug-induced arrhythmias, thus counteracting the effect of estradiol.

Alteration of the cardiac sympathetic innervation is modulated by duration of diabetes in female rats

To evaluate the sympathetic innervation of the female diabetic heart, resting heart rate and sympathetic tone were assessed in vivo, and effect of tyramine on spontaneous beating rate, norepinephrine atrial concentrations, uptake, and release were determined in vitro in streptozotocin- (STZ-) treated rats and respective controls aged 3 months to 2 years. Resting bradycardia, decreased sympathetic tone, deceleration of spontaneous beating rate, and slightly declining carrier-mediated, but preserved exocytotic norepinephrine release from the atria were found in younger diabetic rats while the reactivity of the right atria to tyramine was not affected with age and disease duration. Diabetic two-year-old animals displayed symptoms of partial spontaneous recovery including normoglycemia, increased plasma insulin concentrations, fully recovered sympathetic tone, but putative change, in releasable norepinephrine tissue stores. Our data suggested that female diabetic heart exposed to long-lasting diabetic conditions seems to be more resistant to alteration in sympathetic innervation than the male one.

How is electrocardiogram influenced by electroconvulsive therapy in males and females?

OBJECTIVES

We aimed to investigate and compare the P duration and P dispersion (Pd) between male and female patients with a primary diagnosis of chronic schizophrenia disorder before and after the electroconvulsive therapy (ECT) period.

METHODS

We obtained electrocardiograms of 50 healthy young volunteers which included 25 female (group F, n = 25) and 25 male patients (group M, n = 25). We measured minimum and maximum P wave durations (Pmin, Pmax) and Pd in milliseconds. Electrocardiography was performed before electroconvulsive therapy (ECT) and immediately after the ECT period after awakening. A 12-lead surface electrocardiogram was obtained from each subject in the supine position.

RESULTS

The post-ECT P duration was significantly longer than the pre-ECT P duration in groups F and M (P = 0.01 and P = 0.008, respectively). The post-ECT Pd was significantly longer than the pre-ECT Pd in groups F and M (P = 0.0001 in both groups). A higher correlation (r) in group M was observed between the pre-ECT Pd and post-ECT P duration than in group F (r = 0.538, P = 006 in group M; r = 0.349, P = 08 in group F). There was no significant difference between the groups regarding hemodynamics.

CONCLUSIONS

Electroconvulsive therapy in both sexes may influence atrial conduction as evidenced by the significantly prolonged Pmax and Pd in patients with a primary diagnosis of schizophrenia disorder.

Diverse modulating effects of estradiol and progesterone on the monophasic action potential duration in Langendorff-perfused female rabbit hearts

This study aimed to comparatively investigate the acute modulating effects of oestrogen and progesterone on the repolarization and the susceptibility of female rabbits to class III anti-arrhythmic agents. The acute influence of estradiol and progesterone on the cardiac repolarization and the drug sensitivity of the rapidly activating delayed rectifier K(+) channel to sotalol was comparatively studied in Langendorff-perfused rabbit hearts at pharmacological concentrations through recording of epicardial monophasic action potentials. In Langendorff-perfused rabbit hearts, estradiol (1-30 μm) concentration-dependently prolonged the monophasic action potential durations (MAPD(30) and MAPD(90) ) (P < 0.05); while the effects of progesterone on MAPD were biphasic: it prolonged MAPD(30) and MAPD(90) at lower concentrations (1-3 μm) but shortened MAPD(30) and MAPD(90) at higher concentrations (10-30 μm). Sotalol-induced prolongation of MAPD(90) was significantly less in the hearts pretreated with progesterone than those treated with estradiol (P < 0.05). The incidence of the pro-arrhythmic events induced by sotalol in the hearts pretreated with progesterone was also significantly lower than those pretreated with estradiol (P < 0.05). In conclusion, estradiol and progesterone have different modulating effects on cardiac repolarization: estradiol can concentration-dependently prolong the cardiac repolarization time and thus may reduce the repolarization reserve and increase the susceptibility of female rabbits to sotalol-induced arrhythmias, whereas progesterone may shorten the cardiac repolarization time at concentrations above 10 μm, thus protecting the heart from drug-induced arrhythmias.

Circadian and gender effects on repolarization in healthy adults: a study using harmonic regression analysis

BACKGROUND

Sudden cardiac death and myocardial infarction have a circadian variation with a peak incidence in the early morning hours. Increased dispersion of repolarization facilitates the development of conduction delay necessary to induce sustained arrhythmia. Both QT-dispersion and T-wave peak to T-wave end (TpTe) have been proposed as markers of dispersion of myocardial repolarization.

METHODS

Forty healthy adults (20 women), age 35-67 years old, with normal EKGs, echocardiograms, stress tests, and tilt-table tests were analyzed during a 27-hour hospital stay. EKGs were done at eight different time points. QT-intervals, QT-dispersion, and TpTe were measured at each time point. Harmonic regression was used to model circadian periodicity, P < 0.05 was considered significant.

RESULTS

The composite QT-interval was longer in women than in men (416 + or - 17 msec vs 411 + or - 20 msec, respectively, P = 0.006). The QT-dispersion among all leads was greater in men than women (37 + or - 13 msec vs 30 + or - 11 msec, respectively, P < 0.0001); a similar difference was found in the precordial leads. Harmonic regression showed that QT-dispersion had a significant circadian variation, primarily in men. In men, the maximum QT-dispersion occurred at 6 AM (45 + or - 15 msec). TpTe also had a significant circadian variation that was not affected by gender in the majority of leads.

CONCLUSIONS

A circadian variation exists in the dispersion of myocardial repolarization, as measured by both TpTe and QT-dispersion. Men and women have a different circadian variation pattern. Further studies regarding the mechanisms and clinical implications are needed.

Signal-averaged electrocardiogram in physically healthy, recently abstinent chronic cocaine users

OBJECTIVES

: Cocaine use is associated with cardiac arrhythmias. Markers of ventricular late potentials, which may be a precursor to malignant ventricular arrhythmias, can be detected by signal-averaged electrocardiography (SA-ECG) but not by standard ECG.

METHODS

: We evaluated SA-ECG parameters in 60 medically screened, physically healthy, recently abstinent cocaine users (53 males, mean [SD] age, 34.0 [4.6] years; 10.1 [6.0] years of use) and 54 nondrug-using controls (21 males, mean [SD] age 28.4 [7.8] years). SA-ECGs were done periodically for ≤12 weeks of monitored abstinence in 25 cocaine users. We analyzed 3 SA-ECG parameters considered markers of ventricular late potentials: duration of filtered QRS complex, duration of low-amplitude potentials during terminal 40 ms of QRS complex (LAS40), and root mean square voltage during terminal 40 ms of QRS complex (RMS40).

RESULTS

: Cocaine users differed significantly from controls in filtered QRS complex (118.5 [11.2] ms versus 111.9 [11.4] ms; P = 0.03) but not in LAS40 (28.9 [8.2] ms versus 30.8 [8.3] ms; P = 0.40) or RMS40 (40.0 [19.8] μV versus 30.2 [20.1] μV; P = 0.06) values. The proportion of subjects with abnormal SA-ECG parameters did not differ significantly between male cocaine users and male controls. There were no significant changes over time in either the mean values or proportion of subjects with abnormal values for any SA-ECG parameter. There were significant gender differences among controls but not among cocaine users.

CONCLUSION

: These findings suggest that chronic cocaine use is not associated with a higher prevalence of abnormal SA-ECG parameters in physically healthy users.

Contraceptive hormone use and cardiovascular disease

Contraceptive hormones, most commonly prescribed as oral contraceptives (OCs), are a widely utilized method to prevent ovulation, implantation, and, therefore, pregnancy. The Women's Health Initiative demonstrated cardiovascular risk linked to menopausal hormone therapy among women without pre-existing cardiovascular disease, prompting a review of the safety, efficacy, and side effects of other forms of hormone therapy. A variety of basic science, animal, and human data suggests that contraceptive hormones have antiatheromatous effects; however, relatively less is known regarding the impact on atherosclerosis, thrombosis, vasomotion, and arrhythmogenesis. Newer generation OC formulations in use indicate no increased myocardial infarction risk for current users, but a persistent increased risk of venous thromboembolism. There are no cardiovascular data available for the newest generation contraceptive hormone formulations, including those that contain newer progestins that lower blood pressure, as well as the nonoral routes (transdermal and vaginal). Current guidelines indicate that, as with all medication, contraceptive hormones should be selected and initiated by weighing risks and benefits for the individual patient. Women 35 years and older should be assessed for cardiovascular risk factors including hypertension, smoking, diabetes, nephropathy, and other vascular diseases, including migraines, prior to use. Existing data are mixed with regard to possible protection from OCs for atherosclerosis and cardiovascular events; longer-term cardiovascular follow-up of menopausal women with regard to prior OC use, including subgroup information regarding adequacy of ovulatory cycling, the presence of hyperandrogenic conditions, and the presence of prothrombotic genetic disorders is needed to address this important issue.

Antioxidant activity and sex differences of acute vascular effects of amiodarone in advanced atherosclerosis

Sexual dimorphisms of atherosclerosis and the susceptibility to arrhythmias and antiarrhythmic treatment have been reported. This study investigated acute effects of amiodarone on endothelium-dependent relaxation in the aorta of male and female apoE0 mice with advanced atherosclerosis. Amiodarone tissue uptake was quantified by high-performance liquid chromatography, and xanthine oxidase-dependent superoxide anion formation was investigated in vitro in presence or absence of amiodarone. Incubation with amiodarone for 30 min improved endothelium-dependent relaxation, which was associated with rapid vascular accumulation of amiodarone (P < 0.001) that was sex-dependent. In males, reduced endothelium-dependent relaxation was improved by amiodarone (from 88 +/- 3% to 100 +/- 2%, P < 0.01). Spontaneous phasic contractions, which were greater in females than in males (P < 0.001), were completely abolished by amiodarone (P < 0.0001). Amiodarone also inhibited generation of superoxide anion (P < 0.0001). These data show that amiodarone rapidly accumulates in atherosclerotic vascular tissue, abolishes vascular autorhythmicity, and improves endothelium-dependent function in atherosclerotic arteries. Antioxidant and vasodilator effects following amiodarone administration may contribute to its antiarrhythmic effects.

Signal-averaged electrocardiogram in physically healthy, chronic 3,4-methylenedioxymethamphetamine (MDMA) users

OBJECTIVES

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) use has been associated with cardiac arrhythmias. Markers of ventricular late potentials (VLP), which may be a precursor to malignant ventricular arrhythmias, can be detected by signal-averaged electrocardiography (SA-ECG), but not by standard ECG.

METHODS

We evaluated SA-ECG parameters in 21 physically healthy, recently abstinent MDMA users who also used cannabis (11 males, mean [SD] age 23.3 [4.6] years, 2.8 [2.0] years of use), 18 physically healthy cannabis users (8 males, mean [SD] age 26.6 [7.1] years, 11.2 [5.4] years of use) and 54 non-drug-using controls (21 males, mean [SD] age 28.4 [7.8] years). We analyzed three SA-ECG parameters considered markers of VLPs: duration of filtered QRS complex (fQRS), duration of low amplitude potentials during terminal 40 ms of QRS complex (LAS40), and root mean square voltage during terminal 40 ms of QRS complex (RMS40).

RESULTS

MDMA users, cannabis users, and non-drug-using controls did not differ significantly from each other in fQRS, LAS40, or RMS40 values or in the proportion of subjects with abnormal SA-ECG parameters. There were significant gender differences among controls, but not among MDMA users.

CONCLUSION

These findings suggest that chronic MDMA use is neither quantitatively nor qualitatively associated with a high prevalence of abnormal SA-ECG parameters indicative of VLP markers.

QTc and psychopharmacs: are there any differences between monotherapy and polytherapy

BACKGROUND

Some psychotropic drugs are connected with prolongation of QT interval, increased risk of cardiac arrhythmias and greater incidence of sudden death, especially when used in combination. Concomitant use of antipsychotics and antidepressants is not rare in our clinical practice. The study compares the length of QT interval in patients on monotherapy with an antipsychotic or an antidepressant and patients taking polytherapy (an antipsychotic agent combined with an antidepressant).

METHODS

Sixty-one hospitalized women who met the ICD-10 criteria for schizophrenia, schizoaffective psychosis, delusional disorder and mood disorder were included in the study. The monotherapy group was consisted of thirty-two women treated with an antipsychotic or an antidepressant while the polytherapy group was composed of twenty-nine women treated with an antipsychotic agent plus an antidepressant. Two electrocardiograms (ECGs) were obtained for each patient: the first was carried out before the treatment and the second after two weeks of treatment.Statistical analysis was carried out by SPSS program and included unpaired and paired t test and Fisher's exact test.

RESULTS

Mean baseline QTc values did not differ between the groups (439 +/- 22 ms was the same value found in the both groups; unpaired t test, p > 0.5). Mean QTc intervals after two weeks of treatment were also similar (439 +/- 24 ms in the monotherapy group and 440 +/- 20 ms in the polytherapy group; unpaired t test, p > 0.5). Fisher's exact test did not reveal significant difference in the number of patients with borderline (451-470 ms) or prolonged (> 470 ms) QTc between groups, neither before treatment nor after two weeks of treatment. Twenty two women of the total of sixty one patients (36%) had QTc > 450 ms before applying therapy.

CONCLUSION

We did not find significant QT prolongation in our patients after two weeks of treatment with antipsychotics and/or antidepressants. The QTc interval length did not differ significantly in the monotherapy and the polytherapy group. More than one third of included women exceeded the threshold value of borderline QTc interval (450 ms) before starting treatment. This finding calls for caution when prescribing drugs to female psychiatric patients, especially if they have other health problems.