Gender-related differences in exercise ventricular function among healthy subjects and patients

Sex and gender differences in myocarditis and dilated cardiomyopathy: An update

In the past decade there has been a growing interest in understanding sex and gender differences in myocarditis and dilated cardiomyopathy (DCM), and the purpose of this review is to provide an update on this topic including epidemiology, pathogenesis and clinical presentation, diagnosis and management. Recently, many clinical studies have been conducted examining sex differences in myocarditis. Studies consistently report that myocarditis occurs more often in men than women with a sex ratio ranging from 1:2-4 female to male. Studies reveal that DCM also has a sex ratio of around 1:3 women to men and this is also true for familial/genetic forms of DCM. Animal models have demonstrated that DCM develops after myocarditis in susceptible mouse strains and evidence exists for this progress clinically as well. A consistent finding is that myocarditis occurs primarily in men under 50 years of age, but in women after age 50 or post-menopause. In contrast, DCM typically occurs after age 50, although the age that post-myocarditis DCM occurs has not been investigated. In a small study, more men with myocarditis presented with symptoms of chest pain while women presented with dyspnea. Men with myocarditis have been found to have higher levels of heart failure biomarkers soluble ST2, creatine kinase, myoglobin and T helper 17-associated cytokines while women develop a better regulatory immune response. Studies of the pathogenesis of disease have found that Toll-like receptor (TLR)2 and TLR4 signaling pathways play a central role in increasing inflammation during myocarditis and in promoting remodeling and fibrosis that leads to DCM, and all of these pathways are elevated in males. Management of myocarditis follows heart failure guidelines and there are currently no disease-specific therapies. Research on standard heart failure medications reveal important sex differences. Overall, many advances in our understanding of the effect of biologic sex on myocarditis and DCM have occurred over the past decade, but many gaps in our understanding remain. A better understanding of sex and gender effects are needed to develop disease-targeted and individualized medicine approaches in the future.

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.

Mitogen-activated protein kinases contribute to temperature-induced cardiac remodelling in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) live in environments where water temperatures range between 4 °C and 20 °C. Laboratory studies demonstrate that cold and warm acclimations of male trout can have oppositional effects on cardiac hypertrophy and the collagen content of the heart. The cellular mechanisms behind temperature-induced cardiac remodelling are unclear, as is why this response differs between male and female fish. Studies with cultured trout cardiac fibroblasts suggests that collagen deposition is regulated, at least in part, by mitogen-activated protein kinase (MAPK) cell signalling pathways. We, therefore, hypothesized that temperature-dependent cardiac remodelling is regulated by these signalling pathways. To test this, male and female trout were acclimated to 18 °C (warm) in the summer and to 4 °C (cold) in the winter and the activation of MAPK pathways in the hearts were characterized and compared to that of control fish maintained at 12 °C. In addition, cardiac collagen content, cardiac morphology and the expression of gene transcripts for matrix metalloproteinases (MMP) -9, MMP-2, tissue inhibitor of matrix metalloproteinases and collagen 1α were characterized. p38 MAPK phosphorylation increased in the hearts of female fish with cold acclimation and the phosphorylation of extracellular signal-regulated kinase increased in the hearts of male fish with warm acclimation. However, there was no effect of thermal acclimation on cardiac morphology or collagen content in either male or female fish. These results indicate that thermal acclimation has transient and sex-specific effects on the phosphorylation of MAPKs but also how variable the response of the trout heart is to thermal acclimation.

Sex-dependent vulnerability of fetal nonhuman primate cardiac mitochondria to moderate maternal nutrient reduction

Poor maternal nutrition in pregnancy affects fetal development, predisposing offspring to cardiometabolic diseases. The role of mitochondria during fetal development on later-life cardiac dysfunction caused by maternal nutrient reduction (MNR) remains unexplored. We hypothesized that MNR during gestation causes fetal cardiac bioenergetic deficits, compromising cardiac mitochondrial metabolism and reserve capacity. To enable human translation, we developed a primate baboon model (Papio spp.) of moderate MNR in which mothers receive 70% of control nutrition during pregnancy, resulting in intrauterine growth restriction (IUGR) offspring and later exhibiting myocardial remodeling and heart failure at human equivalent ∼25 years. Term control and MNR baboon offspring were necropsied following cesarean-section, and left ventricle (LV) samples were collected. MNR adversely impacted fetal cardiac LV mitochondria in a sex-dependent fashion. Increased maternal plasma aspartate aminotransferase, creatine phosphokinase (CPK), and elevated cortisol levels in MNR concomitant with decreased blood insulin in male fetal MNR were measured. MNR resulted in a two-fold increase in fetal LV mitochondrial DNA (mtDNA). MNR resulted in increased transcripts for several respiratory chain (NDUFB8, UQCRC1, and cytochrome c) and adenosine triphosphate (ATP) synthase proteins. However, MNR fetal LV mitochondrial complex I and complex II/III activities were significantly decreased, possibly contributing to the 73% decreased ATP content and increased lipid peroxidation. MNR fetal LV showed mitochondria with sparse and disarranged cristae dysmorphology. Conclusion: MNR disruption of fetal cardiac mitochondrial fitness likely contributes to the documented developmental programming of adult cardiac dysfunction, indicating a programmed mitochondrial inability to deliver sufficient energy to cardiac tissues as a chronic mechanism for later-life heart failure.

Effectiveness of testosterone therapy in hypogonadal patients and its controversial adverse impact on the cardiovascular system

Testosterone is the major male hormone produced by testicles which are directly associated with man's appearance and secondary sexual developments. Androgen deficiency starts when the male hormonal level falls from its normal range though, in youngsters, the deficiency occurs due to disruption of the normal functioning of pituitary, hypothalamus glands, and testes. Thus, testosterone replacement therapy was already known for the treatment of androgen deficiency with lesser risks of producing cardiovascular problems. Since from previous years, the treatment threshold in the form of testosterone replacement therapy has effectively increased to that extent that it was prescribed for those conditions which it was considered as inappropriate. However, there are some research studies and clinical trials available that proposed the higher risk of inducing cardiovascular disease with the use of testosterone replacement therapy. Thus under the light of these results, the FDA has published the report of the increased risk of cardiovascular disease with the increased use of testosterone replacement therapy. Nevertheless, there is not a single trial available or designed that could evaluate the risk of cardiovascular events with the use of testosterone replacement therapy. As a result, the use of testosterone still questioned the cardiovascular safety of this replacement therapy. Thus, this literature outlines the distribution pattern of disease by investigating the data and link between serum testosterone level and the cardiovascular disease, also the prescription data of testosterone replacement therapy patients and their tendency of inducing cardiovascular disease, meta-analysis and the trials regarding testosterone replacement therapy and its connection with the risks of causing cardiovascular disease and lastly, the possible effects of testosterone replacement therapy on the cardiovascular system. This study aims to evaluate the available evidence regarding the use of testosterone replacement therapy when choosing it as a treatment plan for their patients.

Sex Differences in Cardiac Flow Dynamics of Healthy Volunteers

Purpose

The purpose of this study was to further understand the relationship between cardiac function and flow, on the basis of sex, by quantifying cardiac flow characteristics and relating them to cardiac muscle performance in young adults.

Materials and Methods

In this cross-sectional study, cardiac four-dimensional flow (4D flow) magnetic resonance imaging (MRI) and two-dimensional cine MRI were performed on 20 male and 19 female volunteers aged 20-35. Velocity-based metrics of flow, kinetic energy, vorticity, and efficiency indices were quantified, as well as cardiac strain metrics.

Results*

Peak systolic blood kinetic energy (male: 4.76 ± 2.66 mJ; female: 3.36 ± 1.43 mJ; p=0.047) was significantly higher in the male left ventricle (LV) than in the female LV. Peak systolic vorticity index (male: 0.008 ± 0.005 rad-m²/ml-s; female: 0.014 ± 0.007 rad-m²/ml-s; p=0.007), peak diastolic vorticity index (male: 0.007 ± 0.006 rad-m²/ml-s; female: 0.014 ± 0.010 rad-m²/ml-s; p=0.015), and cycle-average vorticity (male: 0.006 ± 0.001 rad-m²/ml-s; female: 0.011 ± 0.002 rad/s; p=0.001) were all significantly higher in the LV of women than they were in the LV of men. Radial, circumferential, and long-axis strain metrics were significantly higher in the female LV than in the male LV (p<0.05). Circumferential systolic and diastolic strain rates displayed moderate correlation to peak systolic (r=-0.38, p=0.022) and diastolic vorticity (r=0.40, p=0.015) values, respectively. *Results are reported as mean ± standard deviation.

Conclusion

Left ventricular vorticity metrics were observed to be higher in women than in men and displayed moderate correlation to cardiac strain metrics. The methods and results of this study may be used to further understand the sex-based cardiac efficiency relationship between cardiac function and flow.

Testosterone replacement therapy and cardiovascular risk

Testosterone is the main male sex hormone and is essential for the maintenance of male secondary sexual characteristics and fertility. Androgen deficiency in young men owing to organic disease of the hypothalamus, pituitary gland or testes has been treated with testosterone replacement for decades without reports of increased cardiovascular events. In the past decade, the number of testosterone prescriptions issued for middle-aged or older men with either age-related or obesity-related decline in serum testosterone levels has increased exponentially even though these conditions are not approved indications for testosterone therapy. Some retrospective studies and randomized trials have suggested that testosterone replacement therapy increases the risk of cardiovascular disease, which has led the FDA to release a warning statement about the potential cardiovascular risks of testosterone replacement therapy. However, no trials of testosterone replacement therapy published to date were designed or adequately powered to assess cardiovascular events; therefore, the cardiovascular safety of this therapy remains unclear. In this Review, we provide an overview of epidemiological data on the association between serum levels of endogenous testosterone and cardiovascular disease, prescription database studies on the risk of cardiovascular disease in men receiving testosterone therapy, randomized trials and meta-analyses evaluating testosterone replacement therapy and its association with cardiovascular events and mechanistic studies on the effects of testosterone on the cardiovascular system. Our aim is to help clinicians to make informed decisions when considering testosterone replacement therapy in their patients.

The Role of 17β-Estradiol and Estrogen Receptors in Regulation of Ca2+ Channels and Mitochondrial Function in Cardiomyocytes

Numerous epidemiological, clinical, and animal studies showed that cardiac function and manifestation of cardiovascular diseases (CVDs) are different between males and females. The underlying reasons for these sex differences are definitely multifactorial, but major evidence points to a causal role of the sex steroid hormone 17β-estradiol (E2) and its receptors (ER) in the physiology and pathophysiology of the heart. Interestingly, it has been shown that cardiac calcium (Ca²⁺) ion channels and mitochondrial function are regulated in a sex-specific manner. Accurate mitochondrial function and Ca²⁺ signaling are of utmost importance for adequate heart function and crucial to maintaining the cardiovascular health. Due to the highly sensitive nature of these processes in the heart, this review article highlights the current knowledge regarding sex dimorphisms in the heart implicating the importance of E2 and ERs in the regulation of cardiac mitochondrial function and Ca²⁺ ion channels, thus the contractility. In particular, we provide an overview of in-vitro and in-vivo studies using either E2 deficiency; ER deficiency or selective ER activation, which suggest that E2 and ERs are strongly involved in these processes. In this context, this review also discusses the divergent E2-responses resulting from the activation of different ER subtypes in these processes. Detailed understanding of the E2 and ER-mediated molecular and cellular mechanisms in the heart under physiological and pathological conditions may help to design more specifically targeted drugs for the management of CVDs in men and women.

Sex-based differences in myocardial gene expression in recently deceased organ donors with no prior cardiovascular disease

Sex differences in the development of the normal heart and the prevalence of cardiomyopathies have been reported. The molecular basis of these differences remains unclear. Sex differences in the human heart might be related to patterns of gene expression. Recent studies have shown that sex specific differences in gene expression in tissues including the brain, kidney, skeletal muscle, and liver. Similar data is limited for the heart. Herein we address this issue by analyzing donor and post-mortem adult human heart samples originating from 46 control individuals to study whole-genome gene expression in the human left ventricle. Using data from the genotype tissue expression (GTEx) project, we compared the transcriptome expression profiles of male and female hearts. We found that genes located on sex chromosomes were the most abundant ones among the sexually dimorphic genes. The majority of differentially expressed autosomal genes were those involved in the regulation of inflammation, which has been found to be an important contributor to left ventricular remodeling. Specifically, genes on autosomal chromosomes encoding chemokines with inflammatory functions (e.g. CCL4, CX3CL1, TNFAIP3) and a gene that regulates adhesion of immune cells to the endothelium (e.g., VCAM1) were identified with sex-specific expression levels. This study underlines the relevance of sex as an important modifier of cardiac gene expression. These results have important implications in the understanding of the differences in the physiology of the male and female heart transcriptome and how they may lead to different sex specific difference in human cardiac health and its control.

Genomic upregulation of cardiac Cav1.2α and NCX1 by estrogen in women

Background

Women have a higher risk of lethal arrhythmias than men in long QT syndrome type 2 (LQTS2), but the mechanisms remain uncertain due to the limited availability of healthy control human tissue. We have previously reported that in female rabbits, estrogen increases arrhythmia risk in drug-induced LQTS2 by upregulating L-type Ca²⁺ (I_Ca,L) and sodium-calcium exchange (I_NCX) currents at the base of the epicardium by a genomic mechanism. This study investigates if the effects of estrogen on rabbit I_Ca,L and I_NCX apply to human hearts.

Methods

Postmortem human left ventricular tissue samples were probed with selective antibodies for regional heterogeneities of ion channel protein expression and compared to rabbit myocardium. Functionally, I_Ca,L and I_NCX were measured from female and male cardiomyocytes derived from human induced pluripotent stem cells (iPS-CMs) with the voltage-clamp technique from control and estrogen-treated iPS-CMs.

Results

In women (n = 12), Cav1.2α (primary subunit of the L-type calcium channel protein 1) and NCX1 (sodium-calcium exchange protein) levels were higher at the base than apex of the epicardium (40 ± 14 and 81 ± 30%, respectively, P < 0.05), but not in men (n = 6) or postmenopausal women (n = 6). Similarly, in cardiomyocytes derived from female human iPS-CMs, estrogen (1 nM, 1–2 days) increased I_Ca,L (31%, P < 0.05) and I_NCX (7.5-fold, − 90 mV, P < 0.01) and their mRNA levels (P < 0.05). Moreover, in male human iPS-CMs, estrogen failed to alter I_Ca,L and I_NCX.

Conclusions

The results show that estrogen upregulates cardiac I_Ca,L and I_NCX in women through genomic mechanisms that account for sex differences in Ca²⁺ handling and spatial heterogeneities of repolarization due to base-apex heterogeneities of Cav1.2α and NCX1. By analogy with rabbit studies, these effects account for human sex-difference in arrhythmia risk.

Acute exposure to progesterone attenuates cardiac contraction by modifying myofilament calcium sensitivity in the female mouse heart

Acute application of progesterone attenuates cardiac contraction, although the underlying mechanisms are unclear. We investigated whether progesterone modified contraction in isolated ventricular myocytes and identified the Ca²⁺ handling mechanisms involved in female C57BL/6 mice (6-9 mo; sodium pentobarbital anesthesia). Cells were field-stimulated (4 Hz; 37°C) and exposed to progesterone (0.001-10.0 μM) or vehicle (35 min). Ca²⁺ transients (fura-2) and cell shortening were recorded simultaneously. Maximal concentrations of progesterone inhibited peak contraction by 71.4% (IC₅₀ = 160 ± 50 nM; n = 12) and slowed relaxation by 75.4%. By contrast, progesterone had no effect on amplitudes or time courses of underlying Ca²⁺ transients. Progesterone (1 µM) also abbreviated action potential duration. When the duration of depolarization was controlled by voltage-clamp, progesterone attenuated contraction and slowed relaxation but did not affect Ca²⁺ currents, Ca²⁺ transients, sarcoplasmic reticulum (SR) content, or fractional release of SR Ca²⁺ Actomyosin MgATPase activity was assayed in myofilaments from hearts perfused with progesterone (1 μM) or vehicle (35 min). While maximal responses to Ca²⁺ were not affected by progesterone, myofilament Ca²⁺ sensitivity was reduced (EC₅₀ = 0.94 ± 0.01 µM for control, n = 7 vs. 1.13 ± 0.05 μM for progesterone, n = 6; P < 0.05) and progesterone increased phosphorylation of myosin binding protein C. The effects on contraction were inhibited by lonaprisan (progesterone receptor antagonist) and levosimendan (Ca²⁺ sensitizer). Unlike results in females, progesterone had no effect on contraction or myofilament Ca²⁺ sensitivity in age-matched male mice. These data indicate that progesterone reduces myofilament Ca²⁺ sensitivity in female hearts, which may exacerbate manifestations of cardiovascular disease late in pregnancy when progesterone levels are high.

NEW & NOTEWORTHY

We investigated myocardial effects of acute application of progesterone. In females, but not males, progesterone attenuates and slows cardiomyocyte contraction with no effect on calcium transients. Progesterone also reduces myofilament calcium sensitivity in female hearts. This may adversely affect heart function, especially when serum progesterone levels are high in pregnancy.Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/acute-progesterone-modifies-cardiac-contraction/.

Sexual dimorphism in the expression of mitochondria-related genes in rat heart at different ages

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Moreover, sex and age are considered major risk factors in the development of CVDs. Mitochondria are vital for normal cardiac function, and regulation of mitochondrial structure and function may impact susceptibility to CVD. To identify potential role of mitochondria in sex-related differences in susceptibility to CVD, we analyzed the basal expression levels of mitochondria-related genes in the hearts of male and female rats. Whole genome expression profiling was performed in the hearts of young (8-week), adult (21-week), and old (78-week) male and female Fischer 344 rats and the expression of 670 unique genes related to various mitochondrial functions was analyzed. A significant (p<0.05) sexual dimorphism in expression levels of 46, 114, and 41 genes was observed in young, adult and old rats, respectively. Gene Ontology analysis revealed the influence of sex on various biological pathways related to cardiac energy metabolism at different ages. The expression of genes involved in fatty acid metabolism was significantly different between the sexes in young and adult rat hearts. Adult male rats also showed higher expression of genes associated with the pyruvate dehydrogenase complex compared to females. In young and adult hearts, sexual dimorphism was not noted in genes encoding oxidative phosphorylation. In old rats, however, a majority of genes involved in oxidative phosphorylation had higher expression in females compared to males. Such basal differences between the sexes in cardiac expression of genes associated with energy metabolism may indicate a likely involvement of mitochondria in susceptibility to CVDs. In addition, female rats showed lower expression levels of apoptotic genes in hearts compared to males at all ages, which may have implications for better preservation of cardiac mass in females than in males.

Testosterone modulates cardiac contraction and calcium homeostasis: cellular and molecular mechanisms

The incidence of cardiovascular disease rises dramatically with age in both men and women. Because a woman's risk of cardiovascular disease rises markedly after the onset of menopause, there has been growing interest in the effect of estrogen on the heart and its role in the pathophysiology of these diseases. Much less attention has been paid to the impact of testosterone on the heart, even though the levels of testosterone also decline with age and low-testosterone levels are linked to the development of cardiovascular diseases. The knowledge that receptors for all major sex steroid hormones, including testosterone, are present on individual cardiomyocytes suggests that these hormones may influence the heart at the cellular level. Indeed, it is well established that there are male-female differences in intracellular Ca(2+) release and contraction in isolated ventricular myocytes. Growing evidence suggests that these differences arise from effects of sex steroid hormones on processes involved in intracellular Ca(2+) homeostasis. This review considers how myocardial contractile function is modified by testosterone, with a focus on the impact of testosterone on processes that regulate Ca(2+) handling at the level of the ventricular myocyte. The idea that testosterone regulates Ca(2+) handling in the heart is important, as Ca(2+) dysregulation plays a key role in the pathogenesis of a variety of different cardiovascular diseases. A better understanding of sex hormone regulation of myocardial Ca(2+) homeostasis may reveal new targets for the treatment of cardiovascular diseases in all older adults.

Sex differences in SR Ca(2+) release in murine ventricular myocytes are regulated by the cAMP/PKA pathway

Previous studies have shown that ventricular myocytes from female rats have smaller contractions and Ca(2+) transients than males. As cardiac contraction is regulated by the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway, we hypothesized that sex differences in cAMP contribute to differences in Ca(2+) handling. Ca(2+) transients (fura-2) and ionic currents were measured simultaneously (37°C, 2Hz) in ventricular myocytes from adult male and female C57BL/6 mice. Under basal conditions, diastolic Ca(2+), sarcoplasmic reticulum (SR) Ca(2+) stores, and L-type Ca(2+) current did not differ between the sexes. However, female myocytes had smaller Ca(2+) transients (26% smaller), Ca(2+) sparks (6% smaller), and excitation-contraction coupling gain in comparison to males (23% smaller). Interestingly, basal levels of intracellular cAMP were lower in female myocytes (0.7±0.1 vs. 1.7±0.2fmol/μg protein; p<0.001). Importantly, PKA inhibition (2μM H-89) eliminated male-female differences in Ca(2+) transients and gain, as well as Ca(2+) spark amplitude. Western blots showed that PKA inhibition also reduced the ratio of phospho:total RyR2 in male hearts, but not in female hearts. Stimulation of cAMP production with 10μM forskolin abolished sex differences in cAMP levels, as well as differences in Ca(2+) transients, sparks, and gain. To determine if the breakdown of cAMP differed between the sexes, phosphodiesterase (PDE) mRNA levels were measured. PDE3 expression was similar in males and females, but PDE4B expression was higher in female ventricles. The inhibition of cAMP breakdown by PDE4 (10μM rolipram) abolished differences in Ca(2+) transients and gain. These findings suggest that female myocytes have lower levels of basal cAMP due, in part, to higher expression of PDE4B. Lower cAMP levels in females may attenuate PKA phosphorylation of Ca(2+) handling proteins in females, and may limit positive inotropic responses to stimulation of the cAMP/PKA pathway in female hearts.

Sex and gender differences in myocarditis and dilated cardiomyopathy

Heart failure due to nonischemic dilated cardiomyopathy (DCM) contributes significantly to the global burden of cardiovascular disease. Myocarditis is, in turn, a major cause of acute DCM in both men and women. However, recent clinical and experimental evidence suggests that the pathogenesis and prognosis of DCM differ between the sexes. This seminar provides a contemporary perspective on the immune mediators of myocarditis, including interdependent elements of the innate and adaptive immune response. The heart's acute response to injury is influenced by sex hormones that appear to determine the subsequent risk of chronic DCM. Preliminary data suggest additional genetic variations may account for some of the differences in epidemiology, left ventricular recovery, and survival between men and women. We highlight the gaps in our knowledge regarding the management of women with acute DCM and discuss emerging therapies, including bromocriptine for the treatment of peripartum cardiomyopathy.

Sex differences in mechanisms of cardiac excitation-contraction coupling

The incidence and expression of cardiovascular diseases differs between the sexes. This is not surprising, as cardiac physiology differs between men and women. Clinical and basic science investigations have shown important sex differences in cardiac structure and function. The pervasiveness of sex differences suggests that such differences must be fundamental, likely operating at a cellular level. Indeed, studies have shown that isolated ventricular myocytes from female animals have smaller and slower contractions and underlying calcium transients compared to males. Recent evidence suggests that this arises from sex differences in components of the cardiac excitation–contraction coupling pathway, the sequence of events linking myocyte depolarization to calcium release from the sarcoplasmic reticulum and subsequent contraction. The concept that sex hormones may regulate intracellular calcium at the level of the cardiomyocyte is important, as levels of these hormones decline in both men and women as the incidence of cardiovascular disease rises. This review focuses on the impact of sex on cardiac contraction, in particular at the cellular level, and highlights specific components of the excitation–contraction coupling pathway that differ between the sexes. Understanding sex hormone regulation of calcium homeostasis in the heart may reveal new avenues for therapeutic strategies to treat cardiac dysfunction and cardiovascular diseases.

Why sex matters: the biological mechanisms of cardiovascular disease

Cardiovascular disease (CVD) is the leading determinant of mortality and morbidity in women. However, a full understanding of the basic and clinical aspects of CVD in women is far from being accomplished. Sexual dimorphism in CVD has been reported both in humans and experimental animals. Menopause is a risk factor for CVD due to the reduction of endogenous estrogen, although the mechanisms underlying are poorly understood. Estrogens act through binding to vascular estrogen receptors and by non-genomic mechanisms. Advances in this field are essential to improve CVD diagnostic and clinical strategies in women, and to develop sex-specific prevention plans as much as female-oriented treatment algorithms. This paper reviews pathophysiology of CVD in women and its potential clinical implications. Particular emphasis is given to biochemical markers and to indicators of cardiovascular dysfunction and damage. Estimation of these parameters, central to cardiovascular pathophysiology, could represent a particularly relevant tool in female patients. More research is needed to identify women who will profit most of early intervention.

Sex and gender differences in coronary artery disease

Significant sex differences exist between men and women with regard to coronary artery disease. Most notably, this lethal disease kills more women than men each year and remains the leading cause of death for both men and women. Women and men clearly have different risk profiles when diagnosed with coronary artery disease and fare much differently after myocardial infarction and coronary artery bypass grafting. This review summarizes the sex differences in clinical presentation, diagnosis, and the surgical treatment of coronary artery disease between men and women; and potential multifactorial reasons for sex disparities are suggested.

Oestrogen upregulates L-type Ca²⁺ channels via oestrogen-receptor- by a regional genomic mechanism in female rabbit hearts

In type-2 long QT (LQT2), adult women and adolescent boys have a higher risk of lethal arrhythmias, called Torsades de pointes (TdP), compared to the opposite sex. In rabbit hearts, similar sex- and age-dependent TdP risks were attributed to higher expression levels of L-type Ca(2+) channels and Na(+)-Ca(2+) exchanger, at the base of the female epicardium. Here, the effects of oestrogen and progesterone are investigated to elucidate the mechanisms whereby I(Ca,L) density is upregulated in adult female rabbit hearts. I(Ca,L) density was measured by the whole-cell patch-clamp technique on days 0-3 in cardiomyocytes isolated from the base and apex of adult female epicardium. Peak I(Ca,L) was 28% higher at the base than apex (P < 0.01) and decreased gradually (days 0-3), becoming similar to apex myocytes, which had stable currents for 3 days. Incubation with oestrogen (E2, 0.1-1.0 nm) increased I(Ca,L) (∼2-fold) in female base but not endo-, apex or male myocytes. Progesterone (0.1-10 μm) had no effect at base myocytes. An agonist of the α- (PPT, 5 nm) but not the β- (DPN, 5 nm) subtype oestrogen receptor (ERα/ERβ) upregulated I(Ca,L) like E2. Western blots detected similar levels of ERα and ERβ in male and female hearts at the base and apex. E2 increased Cav1.2α (immunocytochemistry) and mRNA (RT-PCR) levels but did not change I(Ca,L) kinetics. I(Ca,L) upregulation by E2 was suppressed by the ER antagonist ICI 182,780 (10 μm) or by inhibition of transcription (actinomycin D, 4 μm) or protein biosynthesis (cycloheximide, 70 μm). Therefore, E2 upregulates I(Ca,L) by a regional genomic mechanism involving ERα which is a known determinant of sex differences in TdP risk in LQT2.

Magnetic resonance imaging detects significant sex differences in human myocardial strain

BACKGROUND

The pathophysiology responsible for the significant outcome disparities between men and women with cardiac disease is largely unknown. Further investigation into basic cardiac physiological differences between the sexes is needed. This study utilized magnetic resonance imaging (MRI)-based multiparametric strain analysis to search for sex-based differences in regional myocardial contractile function.

METHODS

End-systolic strain (circumferential, longitudinal, and radial) was interpolated from MRI-based radiofrequency tissue tagging grid point displacements in each of 60 normal adult volunteers (32 females).

RESULTS

The average global left ventricular (LV) strain among normal female volunteers (n = 32) was significantly larger in absolute value (functionally better) than in normal male volunteers (n = 28) in both the circumferential direction (Male/Female = -0.19 ± 0.02 vs. -0.21 ± 0.02; p = 0.025) and longitudinal direction (Male/Female = -0.14 ± 0.03 vs. -0.16 ± 0.02; p = 0.007).

CONCLUSIONS

The finding of significantly larger circumferential and longitudinal LV strain among normal female volunteers suggests that baseline contractile differences between the sexes may contribute to the well-recognized divergence in cardiovascular disease outcomes. Further work is needed in order to determine the pathologic changes that occur in LV strain between women and men with the onset of cardiovascular disease.

Sex differences in mechanisms of cardiac excitation-contraction coupling in rat ventricular myocytes

Components of excitation-contraction (E-C) coupling were compared in ventricular myocytes isolated from 3-mo-old male and female rats. Ca2+ concentrations (fura-2) and cell shortening (edge detector) were measured simultaneously (37°C). Membrane potential and ionic currents were measured with microelectrodes. Action potentials were similar in male and female myocytes, but contractions were smaller and slower in females. In voltage-clamped cells, peak contractions were smaller in females than in males (5.1 ± 0.7% vs. 7.7 ± 0.8% diastolic length, P < 0.05). Similarly, Ca2+ transients were smaller in females than in males and the rate of rise of the Ca2+ transient was slower in females. Despite smaller contractions and Ca2+ transients in females, Ca2+ current density was similar in both groups. Sarcoplasmic reticulum Ca2+ content, assessed with caffeine, did not differ between the sexes. However, E-C coupling gain (rate of Ca2+ release/Ca2+ current) was smaller in females than in males (157.0 ± 15.6 vs. 338.4 ± 54.3 (nM/s)/(pA/pF), P < 0.05). To determine whether the reduced gain in female cells was due to changes in unitary Ca2+ release, spontaneous Ca2+ sparks were evaluated (fluo-4, 37°C). Spark frequencies and widths were similar in both groups, but spark amplitudes were smaller in females than in males (0.56 ± 0.01 vs. 0.64 ± 0.01 ΔF/F0, P < 0.05). Spark durations also were shorter in females than in males (full duration at half-maximum = 14.86 ± 0.17 vs. 16.25 ± 0.27 ms, P < 0.05). These observations suggest that decreases in the size and duration of Ca2+ sparks contributes to the decrease in E-C coupling gain in female myocytes. Thus, differences in cardiac contractile function arise, in part, from differences in unitary Ca2+ release between the sexes.

Molecular and cellular basis of cardiovascular gender differences

Cardiovascular diseases (CVDs), the major cause of morbidity and mortality for both men and women, occur uncommonly in premenopausal women, but their incidence rises sharply after the menopausal transition. Cardiovascular gender differences are apparent long before CVDs appear in men and women, and improved understanding of the biology underlying these differences has the potential to advance the diagnosis and treatment of CVDs in both sexes. This review considers gender differences in the molecular and cellular physiology of the heart and blood vessels in health and disease, highlighting understudied areas that can help resolve the current controversy regarding hormone replacement therapy and improve cardiovascular health in women.

The clinical use of supine left lateral leg cycle ergometry for exercise electrocardiographic testing in women, as used in exercise echocardiography

BACKGROUND

Two-dimensional exercise echocardiography is commonly performed in the supine (SUP) left lateral posture (SLL) to optimize imaging quality.

OBJECTIVES

To assess the clinical use of SLL cycle ergometry, we determined the metabolic, cardiovascular, and hemodynamic responses during graded leg cycle ergometry in women, performed in SLL, commonly used during exercise echocardiography, and compared our findings with those obtained during upright (UP) and SUP leg cycle ergometry.

METHODS

A total of 21 apparently healthy women performed leg cycle ergometry in 3 distinct postures (UP, SUP, and SLL).

RESULTS

Peak oxygen consumption and peak achieved workload during SLL cycle ergometry were significantly lower compared with UP cycle ergometry, indicating that in SLL physical work capacity would be underestimated compared with that obtained for the UP and SUP postures. The peak heart rate was significantly lower in SLL and the peak systolic blood pressure higher, compared with UP. Maximal rate pressure product was not significantly different among the postures, indicating the equivalent value of SLL with regard to augmenting myocardial oxygen demand during exercise. Stroke volume (calculated from aortic Doppler flow integral) was higher at rest, and increased to a smaller extent during exercise, in the SUP posture and SLL compared with UP. Similar peak values were attained for the 3 postures.

CONCLUSIONS

SLL is not a suitable modality for the assessment of functional status or for the derivation of target heart rates for exercise training in UP posture. However, SLL leg cycle ergometry exercise provokes a comparable stimulus for the detection of coronary artery disease, as it will increase myocardial oxygen demand to the same extent as UP leg cycle exercise.

Bioimpedance-derived Differences in Cardiac Physiology during Exercise Stress Testing in Low-risk Chest Pain Patients

BACKGROUND

Little has been written about the utility of thoracic electrical bioimpedance (TEB)-derived cardiac physiologic variables in evaluating patients with low-risk chest pain syndromes. Noninvasive bioimpedance can monitor cardiac physiology while a patient is performing an exercise stress test. In addition, the demographics of patients with chest pain, the incidence of coronary artery disease (CAD), and the methods used for evaluation have well-documented sex differences.

OBJECTIVE

The objectives are to show that there are different cardiac physiologic responses to exercise stress test in Chest Pain Evaluation Unit patients with and without true CAD that could be used to stratify patients and that there is a sex difference in TEB results.

METHODS

Patients 18 to 65 years of age with low-risk chest pain were eligible. Patients were attached to the TEB throughout the exercise stress test procedure. Heart rate (HR) was monitored. Primary dependent variables were TEB-measured cardiac output (CO, L/min) and stroke volume (SV, ml) at peak exercise. Secondary variables were TEB-measured ejection fraction (%), end-diastolic volume (EDV, ml), ventricular ejection time (ms), and thoracic fluid index (omega) at peak exercise. Outcome variables were either proved CAD or patient sex. CAD was proved by angiography, stress scintigraphy, or stress echocardiogram. Results were compared using a Student's t test assuming equal variances, with significance considered at a P < 0.05, and 95% confidence intervals were calculated for significant results.

RESULTS

Nine patients had proved CAD, 82 patients did not. Forty-three women and 48 men were included in the study. At peak exercise, patients with CAD had a significantly smaller increase in EDV than patients without CAD (32.8 +/- 59.5 ml versus 89.3 +/- 101.8 ml) without a significant change in CO, SV, or HR. At peak exercise, women had a significantly smaller increase in CO and SV without a significant change in HR. In addition, women had a significantly smaller increase in EDV.

CONCLUSION

When compared with patients without CAD, patients with CAD have a significantly smaller increase in EDV and a trend toward the same effect in CO and SV. Women have significantly smaller increases CO, SV, and EDV compared with men. Because there were no differences in HR, using HR as the sole end point would miss these differences. TEB is a practical means of measuring these variables.

Effects of gender on the number of diseased vessels and clinical outcome in Japanese patients with acute coronary syndrome

It has been reported that women with acute myocardial infarction (AMI) have a higher short-term mortality rate than men, but the reason is unclear and it is not known if it also applies to unstable angina pectoris (UAP). In addition, most previous studies have not presented angiographic findings. In the present study, the findings from 1,408 patients with AMI (group A: 361 women, 1,047 men) and 332 patients with UAP (group B: 103 women, 229 men) who underwent coronary angiography within 30 days of onset were analyzed. In both groups, the women were older and had a higher rate of hypertension and a lower rate of smoking than the men. There was no significant difference in Killip class or the number of diseased vessels between the women and men in both groups. Interventions (coronary angioplasty and coronary artery bypass grafting) were performed less frequently in the women than in the men (87.2% vs 91.8%, p=0.04) in group A, but not in group B (80.6% vs 81.2%, NS). In both groups, the overall mortality rate during hospitalization was higher in women than in men (group A: 14.4% vs 7.4%, p<0.0001, group B: 7.8% vs 1.7%, p=0.007). Multivariate analysis revealed that female gender was an independent predictor of in-hospital mortality in group B (odds ratio (OR): 6.4, 95% confidence interval (CI) 1.1-37.0, p=0.04), but not in group A (OR: 1.7, 95%CI 0.98-2.9, p=0.06). The independent predictors of in-hospital mortality, other than female gender were age, prior congestive heart failure, prior cerebrovascular disease and a higher Killip class in group A, and in both groups a higher number of diseased vessels. In conclusion, Japanese women with acute coronary syndromes present with similar angiographic findings and hemodynamics, but have a higher in-hospital mortality than male patients. Our results suggest that older age may be a potential explanation for the higher in-hospital mortality in women with AMI, but female gender itself may be an important predictor for it among those with UAP.

Effects of gender on the sensitivity of rat cardiac muscle to extracellular Ca2+

Experiments were designed to determine if the inotropic response to increasing buffer calcium concentration differs in male and female cardiac muscle. Left atrial and papillary muscles were isolated from hearts of 3-4-month old male and female rats, bathed in Krebs-Henseleit solution (30 degrees C), and stimulated at 1.5 Hz. Isometric developed tension was monitored continuously as extracellular Ca2+ was increased in a cumulative fashion. When compared to male atrial muscle, female atrial preparations were more sensitive to the resulting positive inotropic action; EC50 values were 2.89 +/- 0.22 and 1.86 +/- 0.21 mM in male and female atria, respectively. Two-way analysis of variance (ANOVA) also indicated that there was a significant gender-associated difference in the Ca2+ dose-response curves in atrial muscle. In contrast, papillary muscle did not show a significant gender-related difference in EC50 values (0.88 +/- 0.07 and 0.74 +/- 0.06 mM in males and females); however, the Ca2+ dose-response curves obtained from male and female preparations were found to be significantly different when compared by ANOVA.