Effects of long-term hormone replacement therapy on QT and corrected QT dispersion during resting and peak exercise electrocardiography in post-menopausal women

Sex differences in heart: from basics to clinics

Sex differences exist in the structure and function of human heart. The patterns of ventricular repolarization in normal electrocardiograms (ECG) differ in men and women: men ECG pattern displays higher T-wave amplitude and increased ST angle. Generally, women have longer QT duration because of reduced repolarization reserve, and thus, women are more susceptible for the occurrence of torsades de pointes associated with drugs prolonging ventricular repolarization. Sex differences are also observed in the prevalence, penetrance and symptom severity, and also in the prognosis of cardiovascular disease. Generally, women live longer, have less clinical symptoms of cardiac diseases, and later onset of symptoms than men. Sex hormones also play an important role in regulating ventricular repolarization, suggesting that hormones directly influence various cellular functions and adrenergic regulation. From the clinical perspective, sex-based differences in heart physiology are widely recognized, but in daily practice, cardiac diseases are often underdiagnosed and untreated in the women. The underlying mechanisms of sex differences are, however, poorly understood. Here, we summarize sex-dependent differences in normal cardiac physiology, role of sex hormones, and differences in drug responses. Furthermore, we also discuss the importance of human induced pluripotent stem cell-derived cardiomyocytes in further understanding the mechanism of differences in women and men.

The Effects of Female Sex Hormones on Ventricular Premature Beats and Repolarization Parameters in Physiological Menstrual Cycle

BACKGROUND

The effects of gender difference on cardiac electrophysiology have been well studied. In this study, we aimed to evaluate the effects of estradiol and progesteron changes occuring in physiological menstrual cycle on ventricular premature beats (VPBs) and cardiac repolarization parameters.

METHODS

Women of reproductive age with VPBs were included into the study group and healthy women were recruited as the control group. During the menstruation period, a 12-lead electrocardiography, blood samples, and 24-hour rhythm Holter were applied to the study group. Similarly, all tests were repeated in the estimated ovulation period (12-14 days before menstruation) by all cases.

RESULTS

The study group consisted of 20 women patients with VPB, and the control group of 18 healthy women. While the number of VPB in the menstruation period was 210 beats/day (interquartile range [IQR]: 1,144), it decreased to 86 beats/day (IQR: 251) in the ovulation period with statistical significance (P < 0.05). Average heart rate in the menstruation period was 81.4 ± 10 beats/min and it significantly increased to 84.6 ± 8 beats/min in the ovulation period (P < 0.05). There were no differences in cardiac repolarization parameters in both menstruation and ovulation periods between the study and control groups. Comparing the menstruation and the ovulation periods, J-Tpeak interval, which reflects early repolarization, was shorter in the ovulation period (193 ± 27.7 ms and 201.1 ± 28.6 ms, respectively; P < 0.05). Other repolarization parameters did not show any significant difference.

CONCLUSION

VPB frequency decreases with estradiol peak in the ovulation period. This suggests that estrogen may have protective effects against ventricular arrhythmias.

Six-minute walk test in non-insulin-dependent diabetes mellitus patients living in Northwest Africa

INTRODUCTION

International recommendations of the exploration of non-insulin-dependent diabetes mellitus (NIDDM) are focused on deficiency and not incapacity.

AIMS

(1) To estimate the incapacity of NIDDM patients through the 6-minute walk test (6MWT) data. (2) To determine their 6-minute walk distance (6MWD) influencing factors (3) To compare data of NIDDM patient group (PG; n = 100) with those of two control groups (CG): CG1 (n = 174, healthy nonobese and nonsmoker); CG2 (n = 55, obese nondiabetic free from comorbidities).

POPULATION AND METHODS

The anthropometric, socioeconomic, clinical, metabolic, and 6MWT data of 100 NIDDM patients (45 females) were collected.

RESULTS

Total sample means ± standard deviation of age, weight, and height were 54 ± 8 years, 81 ± 14 kg, and 1.64 ± 0.09 m. (1) Measured 6MWD (566 ± 81 m) was significantly lower than the theoretical 6MWD (90% ± 12%). The profile of the PG carrying the 6MWT, was as follows: 23% had an abnormal 6MWD; at the end of the 6MWT, 21% and 12% had, respectively, a low heart rate and a high dyspnea (>5/10), and 4% had desaturation during the walk. The estimated "cardiorespiratory and muscular chain" age (68 ± 16 years) was significantly higher than the chronological age. (2) The factors that significantly influenced the 6MWD (r(2) = 0.58) are included in the following equation: 6MWD (m) = -73.94 × gender (0, male; 1, female) - 3.25 × age (years) + 7.33 × leisure activity score - 35.57 × obesity (0, no; 1, yes) + 32.86 × socioeconomic level (0, low; 1, high) - 27.67 × cigarette use (0, no; 1, yes) + 8.89 × resting oxyhemoglobin saturation - 105.48. (3) Compared to the CGs, the PG had a significantly (P < 0.05) lower 6MWD (100%+9% and 100%+8%, respectively, for the CG1 and CG2).

CONCLUSION

NIDDM seems to accelerate the decline of the submaximal aerobic capacity evaluated through the 6MWD.

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.

Estrogen contributes to gender differences in mouse ventricular repolarization

RATIONALE

Fast-transient outward K(+) (I(to,f)) and ultrarapid delayed rectifier K(+) currents (I(K,slow), also known as I(Kur)) contribute to mouse cardiac repolarization. Gender studies on these currents have reported conflicting results.

OBJECTIVE

Key missing information in these studies is the estral stage of the animals. We revisited gender-related differences in K(+) currents, taking into consideration the females' estral stage. We hypothesized that changes in estrogen levels during the estral cycle could play a role in determining the densities of K(+) currents underlying ventricular repolarization.

METHODS AND RESULTS

Peak total K(+) current (I(K,total)) densities (pA/pF, at +40 mV) were much higher in males (48.6+/-3.0) versus females at estrus (27.2+/-2.3) but not at diestrus-2 (39.1+/-3.4). Underlying this change, I(to,f) and I(K,slow) were lower in females at estrus versus males and diestrus-2 (I(K,slow): male 21.9+/-1.8, estrus 14.6+/-0.6, diestrus-2 20.3+/-1.4; I(to,f): male 26.8+/-1.9, estrus 14.9+/-1.6, diestrus-2 22.1+/-2.1). Lower I(K,slow) in estrus was attributable to only I(K,slow)(1) reduction, without changes in I(K,slow)(2). Estrogen treatment of ovariectomized mice decreased I(K,total) (46.4+/-3.0 to 28.4+/-1.6), I(to,f) (26.6+/-1.6 to 12.8+/-1.0) and I(K,slow) (22.2+/-1.6 to 17.2+/-1.4). Transcript levels of Kv4.3 and Kv1.5 (underlying I(to,f) and I(K,slow), respectively) were lower in estrus versus diestrus-2 and male. In ovariectomized mice, estrogen treatment resulted in downregulation of Kv4.3 and Kv1.5 but not Kv4.2, KChIP2, or Kv2.1 transcripts. K(+) current reduction in high estrogenic conditions were associated with prolongation of the action potential duration and corrected QT interval.

CONCLUSION

Downregulation of Kv4.3 and Kv1.5 transcripts by estrogen are one mechanism defining gender-related differences in mouse ventricular repolarization.

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.

Relationship between QT interval and cardiovascular risk factors in healthy young subjects

A prolongation of QT interval increases the risk for coronary heart disease, ventricular arrhythmias, and sudden death in diabetic patients, after myocardial infarction, and in the elderly. An association between QT prolongation and cardiovascular risk factors has been demonstrated in middle-aged and elderly subjects. Aims of this study were to evaluate the prevalence of a prolonged corrected QT interval (QTc) in a healthy young population (n=170, age 22-25 years, 84 males) and to investigate the association of QTc and QT dispersion (QTd) with cardiovascular risk factors (body mass index, blood pressure, fasting blood glucose and cholesterol, smoking habits, and hypertensive familiarity). A prolonged QTc was observed in 10% of female and 5% of male subjects; in multiple regression analysis, QTc showed a significant positive relationship with blood glucose in females (P=0.04) and systolic blood pressure in male subjects (P=0.03), while QTd was not significantly related with any of the factors. In conclusion, the association between QTc length, glucose levels, and blood pressure is present also in young healthy subjects. QT measurement may represent a useful marker in the screening of young subjects for cardiovascular prevention. Journal of Human Hypertension (2005) 19, 623-627. doi:10.1038/sj.jhh.1001874; published online 19 May 2005.

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.