More reasons why men and women are not the same (gender differences in electrophysiology and arrhythmias)

The Cardiovascular Impact of Obstructive Sleep Apnea in Women: Current Knowledge and Future Perspectives

Overall, cardiovascular diseases have many sex-related differences in prevalence, clinical presentation, and outcomes. A considerable amount of evidence suggests that obstructive sleep apnea (OSA) increases the risk for several cardiovascular diseases. Only recently, the sex-related differences in cardiovascular outcomes gained interest in the literature. In this review, the authors discuss the current evidence addressing the cardiovascular impact of OSA in women. Particular attention is devoted to hypertension, target-organ damage, heart failure, atrial fibrillation, and cardiovascular events (including mortality). A research agenda is proposed to increase the understanding of the relevance of OSA in women from the Cardiology perspective.

Sex Related Differences in Electrocardiography

Since its implementation into the clinical medicine by Willem Einthoven electrocardiography had become one of crucial diagnostic method in cardiology. In spite of this fact effects of gender differences on parameters of electrocardiographic recordings started to be studied only recently. Sex related differences in physiological ECG are only minimal in childhood but there are developing during adolescence reflecting rapidly evolving differences particularly in hormonal secretion and activity of an autonomic nervous system. The heart rate is approximately 7 % higher in women than in men, PQ and QRS intervals are longer in men while QT interval is longer in women. The ST segment in females is flatter but generally the sex-related differences in ST-T waveform patterns are relatively very small with higher level of ST segment and taller T wave in men. The effects of sex-related differences, including sex hormones, on cardiac cell injury and death and their influence in determining rhythmogenesis and action potential configuration and conduction play an important role in clinics. Women have a higher prevalence of sick sinus syndrome, inappropriate sinus tachycardia, atrioventricular nodal reentry tachycardia, idiopathic right ventricular tachycardia, and arrhythmic events in the long QT syndrome. In contrast, men have a higher prevalence of atrioventricular block, carotid sinus syndrome, atrial fibrillation, supraventricular tachycardia due to accessory pathways, Wolff-Parkinson-White syndrome, reentrant ventricular tachycardia, ventricular fibrillation and sudden death, and the Brugada syndrome.

Sex differences on outcomes of catheter ablation of ventricular tachycardia in patients with structural heart disease: A real-world systematic review and meta-analysis

Background

Sex differences have diversely affected cardiac diseases. Little is known whether these differences impact outcomes of catheter ablation of ventricular tachycardia (VT).

Objectives

To assess the impact of sex differences on outcomes of catheter ablation of VT.

Methods

Databases were searched from inception through December 2021. Effect estimates from individual studies were extracted and combined using the random-effects, generic inverse variance method of DerSimonian and Laird. The outcomes of interest included VT recurrence rates, all-cause mortality, and composite outcomes of mortality, left ventricular assistant device use, and heart transplantation following VT ablation.

Results

Our analysis included 22 observational studies. There were 10,206 patients, of which 12.8% were women. We found no statistical difference between sexes for VT recurrence rate (pooled hazard ratio [HR] 1.04, P = .57, I ² = 14.9%). Similarly, there was statistical difference in neither all-cause mortality nor composite outcomes (pooled HR 0.93, P = .75, I ² = 59.1% and pooled HR 0.9, P = .33, I ² = 0%, respectively). There was a trend toward an increase in women undergoing VT ablation in the recent registries (P = .071).

Conclusion

Our contemporary analysis suggests that sex may have no impact on clinical outcomes of catheter ablation of VT in patients with structural heart disease, though women are the underrepresented. However, recent VT ablation registries have involved more women in their studies. Future studies with a higher proportion of women are encouraged to verify the current perception.

Sex Differences in Incidence, Clinical Characteristics and Outcomes in Children and Young Adults Hospitalized for Clinically Suspected Myocarditis in the Last Ten Years-Data from the MYO-PL Nationwide Database

There is a widespread lack of systematic knowledge about myocarditis in children and young adults in European populations. The MYO-PL nationwide study aimed to evaluate sex differences in the incidence, clinical characteristics, management and outcomes of all young patients with a clinical diagnosis of myocarditis, hospitalized in the last ten years. The study involved data (from the only public healthcare insurer in Poland) of all (n = 3659) patients aged 0–20 years hospitalized for myocarditis in the years 2011–2019. We assessed clinical characteristics, management and five-year outcomes. Males comprised 75.4% of the study population. The standardized incidence rate of myocarditis increased over the last ten years and was, on average, 7.8 and 2.5 (in males and females, respectively). It was the highest (19.5) in males aged 16–20 years. The highest rates of hospital admissions occurred from late autumn to early spring. Most myocarditis-directed diagnostic procedures, including laboratory tests, echocardiography, coronary angiography, cardiac magnetic resonance and endomyocardial biopsy, were performed in a low number of patients, particularly in females. Most patients required rehospitalization for cardiovascular reasons. The results of this large epidemiological study showed an increasing incidence of myocarditis hospitalizations in young patients over last ten years and that it was sex-, age- and season-dependent. Survival in young patients with myocarditis was age- and sex-related and usually it was worse than in the national population. The general management of myocarditis requires significant improvement.

Gender differences in patients with structural heart disease undergoing VT ablation

INTRODUCTION

This study sought to examine gender differences in patients with structural heart disease (SHD) referred for ablation of ventricular tachycardia (VT).

BACKGROUND

Female patients are often underrepresented in large studies. Significant differences in the clinical presentation, treatment, and prognosis of female patients have been described in previous studies.

METHODS AND RESULTS

We investigated 88 female patients with SHD undergoing VT ablation (mean age 59 years, 56% nonischemic cardiomyopathy, mean left ventricular ejection fraction 35%, 82% in electrical storm). A case-control study with 88 male patients was performed and the results regarding clinical and procedural characteristics, acute and long-term results of the two groups were compared. The female patients had more arrhythmogenic substrate, as they more commonly presented with electrical storm (p = .016) and had a higher number of inducible VT morphologies during the procedure (p = .018). Moreover, the female patients were less likely to have an optimized heart failure medical treatment at baseline (p = .030) and required more time from the first manifestation of the VT to ablation referral (p = .034). Although fewer epicardial ablations were performed in female patients (p = .019), the two groups showed similar results regarding VT noninducibility as ablation endpoint (p = .844), major procedure-related complications (p = .719) and freedom from VT during follow-up (p = .268). Moreover, the overall mortality in the two groups was similar (p = .176). Advanced NYHA class was associated with worse transplant and assist-device-free survival in the female group.

CONCLUSION

Female patients presenting for VT ablation had more arrhythmogenic substrate and were less likely to have an optimized heart failure medical treatment. Nevertheless, the procedural acute and long-term outcomes between the two genders were similar.

Sex Differences in Drug-Induced Arrhythmogenesis

The electrical activity in the heart varies significantly between men and women and results in a sex-specific response to drugs. Recent evidence suggests that women are more than twice as likely as men to develop drug-induced arrhythmia with potentially fatal consequences. Yet, the sex-specific differences in drug-induced arrhythmogenesis remain poorly understood. Here we integrate multiscale modeling and machine learning to gain mechanistic insight into the sex-specific origin of drug-induced cardiac arrhythmia at differing drug concentrations. To quantify critical drug concentrations in male and female hearts, we identify the most important ion channels that trigger male and female arrhythmogenesis, and create and train a sex-specific multi-fidelity arrhythmogenic risk classifier. Our study reveals that sex differences in ion channel activity, tissue conductivity, and heart dimensions trigger longer QT-intervals in women than in men. We quantify the critical drug concentration for dofetilide, a high risk drug, to be seven times lower for women than for men. Our results emphasize the importance of including sex as an independent biological variable in risk assessment during drug development. Acknowledging and understanding sex differences in drug safety evaluation is critical when developing novel therapeutic treatments on a personalized basis. The general trends of this study have significant implications on the development of safe and efficacious new drugs and the prescription of existing drugs in combination with other drugs.

Effects of genetic background, sex, and age on murine atrial electrophysiology

AIMS

Genetically altered mice are powerful models to investigate mechanisms of atrial arrhythmias, but normal ranges for murine atrial electrophysiology have not been robustly characterized.

METHODS AND RESULTS

We analyzed results from 221 electrophysiological (EP) studies in isolated, Langendorff-perfused hearts of wildtype mice (114 female, 107 male) from 2.5 to 17.7 months (mean 7 months) with different genetic backgrounds (C57BL/6, FVB/N, MF1, 129/Sv, Swiss agouti). Left atrial monophasic action potential duration (LA-APD), interatrial activation time (IA-AT), and atrial effective refractory period (ERP) were summarized at different pacing cycle lengths (PCLs). Factors influencing atrial electrophysiology including genetic background, sex, and age were determined. LA-APD70 was 18 ± 0.5 ms, atrial ERP was 27 ± 0.8 ms, and IA-AT was 17 ± 0.5 ms at 100 ms PCL. LA-APD was longer with longer PCL (+17% from 80 to 120 ms PCL for APD70), while IA-AT decreased (-7% from 80 to 120 ms PCL). Female sex was associated with longer ERP (+14% vs. males). Genetic background influenced atrial electrophysiology: LA-APD70 (-20% vs. average) and atrial ERP (-25% vs. average) were shorter in Swiss agouti background compared to others. LA-APD70 (+25% vs. average) and IA-AT (+44% vs. average) were longer in 129/Sv mice. Atrial ERP was longer in FVB/N (+34% vs. average) and in younger experimental groups below 6 months of age.

CONCLUSION

This work defines normal ranges for murine atrial EP parameters. Genetic background has a profound effect on these parameters, at least of the magnitude as those of sex and age. These results can inform the experimental design and interpretation of murine atrial electrophysiology.

Prolonged care delivery time and reduced rate of electrophysiological procedures during the lockdown period due to Covid-19 outbreak

OBJECTIVES

The aim of this study is to demonstrate how Electrophysiology activity has been impacted by the pandemic Coronavirus disease 2019 (COVID-19).

METHODS

In this multicenter retrospective study, we analyze all consecutive patients admitted for electrophysiological procedures during the COVID-19 lockdown in the Tuscany region of Italy, comparing them to patients hospitalized in the corresponding period of the previous year.

RESULTS

The impact of COVID-19 on cardiac arrhythmia management was impressive, with a reduction of more than 50% in all kinds of procedures. A gender gap was observed, with a more relevant reduction for female patients. Arrhythmic urgencies requiring a device implant showed a reduced time from symptoms to first medical contact but the time from first medical contact to procedure was significantly prolonged.

CONCLUSION

Hospitals need to consider how outbreaks may affect health systems beyond the immediate infection. Routine activity should be based on a risk assessment between the prompt performance of procedure and its postponement. Retrospective observational analysis such as this study could be decisive in evidence-based medicine of any future pathogen outbreak.Nonstandard Abbreviations and Acronyms PM= pacemakerICD= implantable cardioverter defibrillatorECV= electrical cardioversionEPS= electrophysiological studyAP= ablations proceduresCIED= cardiac implantable electronic devicesWCD= wearable cardioverter defibrillatorEP Lab= Electrophysiology LaboratoriesAVNRT =atrioventricular nodal reentry tachycardiaAVRT= atrioventricular reentry tachycardiaAFL= atrial flutterAF= atrial fibrillationVT= ventricular tachycardiaAT= atrial tachycardia.

Sex-Related Differences in Heart Failure With Preserved Ejection Fraction

BACKGROUND

To describe characteristics and outcomes in women and men with heart failure with preserved ejection fraction.

METHODS

Baseline characteristics (including biomarkers and quality of life) and outcomes (primary outcome: composite of first heart failure hospitalization or cardiovascular death) were compared in 4458 women and 4010 men enrolled in CHARM-Preserved (Candesartan in Heart failure: Assessment of Reduction in Mortality and morbidity) (EF≥45%), I-Preserve (Irbesartan in heart failure with Preserved ejection fraction), and TOPCAT-Americas (Treatment of Preserved Cardiac Function Heart Failure with an Aldosterone Antagonist trial).

RESULTS

Women were older and more often obese and hypertensive but less likely to have coronary artery disease or atrial fibrillation. Women had more symptoms and signs of congestion and worse quality of life. Despite this, the risk of the primary outcome was lower in women (hazard ratio, 0.80 [95% CI, 0.73-0.88]), as was the risk of cardiovascular death (hazard ratio, 0.70 [95% CI, 0.62-0.80]), but there was no difference in the rate for first hospitalization for heart failure (hazard ratio, 0.92 [95% CI, 0.82-1.02]). The lower risk of cardiovascular death in women, compared with men, was in part explained by a substantially lower risk of sudden death (hazard ratio, 0.53 [0.43-0.65]; P<0.001). E/A ratio was lower in women (1.1 versus 1.2).

CONCLUSIONS

There are significant differences between women and men with heart failure with preserved ejection fraction. Despite worse symptoms, more congestion, and lower quality of life, women had similar rates of hospitalization and better survival than men. Their risk of sudden death was half that of men.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT00853658, NCT01035255.

Association Between HDL Cholesterol and QTc Interval: A Population-Based Epidemiological Study

Previous experimental studies showed that increasing high-density lipoprotein cholesterol (HDL) cholesterol shortens cardiac ventricular repolarization and the QT interval corrected for heart rate (QTc). However, little is known about the epidemiological relationship between HDL and QTc. The potential antiarrhythmic effect of HDL cholesterol remains a speculative hypothesis. In this cross-sectional population based study in adults living in the Italian-speaking part of Switzerland, we aimed to explore the association between HDL cholesterol and the QTc interval in the general population. A total of 1202 subjects were screened. electrocardiogram (ECG) recordings, measurements of lipid parameters and other laboratory tests were performed. QTc was corrected using Bazett’s (QTc_Baz) and Framingham (QTc_Fram) formulas. HDL was categorized according to percentile distributions: <25th (HDL-1; ≤1.39 mmol/L); 25th–<50th (HDL-2; 1.40–1.69 mmol/L); 50th–<75th (HDL-3; 1.69–1.99 mmol/L); and ≥75th (HDL-4; ≥2.0 mmol/L). After exclusion procedures, data of 1085 subjects were analyzed. Compared with the HDL reference group (HDL-1), HDL-2 and HDL-3 were associated with a reduction of QTc_Baz and QTc_Fram duration in crude (HDL-2, QTc_Baz/QTc_Fram: β-11.306/–10.186, SE 4.625/4.016; p = 0.016/0.012; HDL-3, β-12.347/–12.048, SE 4.875/4.233, p = 0.012/<0.001) and adjusted (HDL-2: β-11.697/–10.908, SE 4.333/4.151, p < 0.001/0.010; HDL-3 β-11.786/–11.002, SE 4.719/4.521, p = 0.014/0.016) linear regression models in women. In adjusted logistic regression models higher HDL, were also associated with lower risk of prolonged QTc_Baz/QTc_Fram (HDL-2: OR 0.16/0.17, CI 0.03–0.83/0.47–0.65; HDL-3: OR 0.10/0.14, CI 0.10–0.64/0.03–0.63) in women. Restricted cubic spline analysis confirmed a non linear association (p < 0.001). The present findings indicate an epidemiological association between HDL cholesterol and QTc duration. To draw firm conclusions, further investigations in other populations and with a prospective cohort design are needed.

Clinical characteristics of patients with sustained ventricular arrhythmias after sacubitril/valsartan initiation

Our aim was to describe the clinical profile of patients presenting sustained ventricular arrhythmias after sacubitril/valsartan (SV) initiation. All cases of sustained ventricular arrhythmias in patients receiving SV were consecutively recorded in two centers. Nineteen patients had sustained ventricular arrhythmias after SV. All were men and were previously receiving angiotensin-converting enzyme inhibitors, or angiotensin II receptor blockers before SV initiation. Fifteen patients (78.9%) had electrical stability in the previous 6 months. Nine patients (47.4%) initiated SV at the lowest available dose (24/26 mg). Globally, in all but five patients alive at discharge, SV was discontinued after the event. Six patients presented new arrhythmic events after discontinuation of SV. Two deaths and three heart transplants occurred (one due to heart failure and the other two due to persistent ventricular arrhythmias). All patients had a high arrhythmic risk, and 17 (89.5%) had an implanted cardioverter defibrillator. No specific triggers for the arrhythmic event were found. Male sex and previous episodes of ventricular arrhythmias could be associated with an increased risk of sustained ventricular tachycardia after SV initiation. Discontinuation of the drug might be an additional approach to enable a better control of ventricular arrhythmias in some 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 differences in cardiac electrophysiology

Women have a longer QT interval than men, which appears to evolve after puberty suggesting that sex hormones have an influence on cardiac electrophysiology. Sex hormones do in fact regulate cardiac ion channels via genomic and nongenomic pathways. Women are at greater risk for life-threatening arrhythmias under conditions that prolong the QT interval. In addition, women exhibit greater sensitivity to QT interval–prolonging drugs. Female sex has also an impact on propensity to cardiovascular disease, including atrial fibrillation. However, ex vivo recorded atrial action potentials (APs) from female and male patients in atrial fibrillation did not exhibit significant differences in shape, except that APs from women had slower upstroke velocity. It is concluded that sex-related differences should be taken into account not only in the clinics, but also in basic research.

Estradiol up-regulates L-type Ca2+ channels via membrane-bound estrogen receptor/phosphoinositide-3-kinase/Akt/cAMP response element-binding protein signaling pathway

BACKGROUND

In long QT syndrome type 2, women are more prone than men to the lethal arrhythmia torsades de pointes. We previously reported that 17β-estradiol (E2) up-regulates L-type Ca²⁺ channels and current (I_Ca,L) (∼30%) in rabbit ventricular myocytes by a classic genomic mechanism mediated by estrogen receptor-α (ERα). In long QT syndrome type 2 (I_Kr blockade or bradycardia), the higher Ca²⁺ influx via I_Ca,L causes Ca²⁺ overload, spontaneous sarcoplasmic reticulum Ca²⁺ release, and reactivation of I_Ca,L that triggers early afterdepolarizations and torsades de pointes.

OBJECTIVE

The purpose of this study was to investigate the molecular mechanisms whereby E2 up-regulates I_Ca,L, which are poorly understood.

METHODS

H9C2 and rat myocytes were incubated with E2 ± ER antagonist, or inhibitors of downstream transcription factors, for 24 hours, followed by western blots of Cav1.2α1C and voltage-clamp measurements of I_Ca,L.

RESULTS

Incubation of H9C2 cells with E2 (10-100 nM) increased I_Ca,L density and Cav1.2α1C expression, which were suppressed by the ER antagonist ICI182,780 (1 μM). Enhanced I_Ca,L and Cav1.2α1C expression by E2 was suppressed by inhibitors of phosphoinositide-3-kinase (Pi3K) (30 μM LY294002; P <.05) and Akt (5 μM MK2206) but not of mitogen-activated protein kinase (5 μM U0126) or protein kinase A (1 μM KT5720). E2 incubation increased p-CREB via the Pi3K/Akt pathway, reached a peak in 20 minutes (3-fold), and leveled off to 1.5-fold 24 hours later. Furthermore, a CREB decoy oligonucleotide inhibited E2-induced Cav1.2α1C expression, whereas membrane-impermeable E2 (E2-bovine serum albumin) was equally effective at Cav1.2α1C up-regulation as E2.

CONCLUSION

Estradiol up-regulates Cav1.2α1C and I_Ca,L via plasma membrane ER and by activating Pi3K, Akt, and CREB signaling. The promoter regions of the CACNA1C gene (human-rabbit-rat) contain adjacent/overlapping binding sites for p-CREB and ERα, which suggests a synergistic regulation by these pathways.

Atrial fibrillation with a structurally normal heart in pregnancy: An international survey on current practice

BACKGROUND

Little evidence exists for the optimal management of atrial fibrillation with a structurally normal heart in pregnancy.

METHODS

A survey was sent to members of two associations to obtain input on optimal management of atrial fibrillation in pregnancy. The survey presented four cases with respect to (1) baseline investigations; (2) rate versus rhythm control; (3) chemical versus electrical cardioversion; and (4) anticoagulation.

RESULTS

Sixty-one responders from 11 countries participated. High agreement was noted for baseline investigations. A quarter (25%) of participants chose elective cardioversion even with a reversible precipitant. Electrical cardioversion was preferred over chemical (p < 0.05). Anticoagulation strategies were heterogeneous except in the presence of a left atrial appendage thrombus.

DISCUSSION

This study revealed that there was little consensus in current practice in pregnancy beyond basic investigations. An adaptation of established guidelines to the pregnant population would require a meeting of Cardiologists with input from colleagues in Obstetric Medicine.

[Sudden cardiac death: Are women different?]

Sudden cardiac death is a major public health problem with around 40,000 cases per year in France. Epidemiological, clinical and prognostic differences according to gender have been described in most cardiovascular diseases, including sudden cardiac death. In this article, we will review gender differences in sudden cardiac death incidence, circumstance of occurrence, management, and prognosis.

Gender differences in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy: Clinical manifestations, electrophysiological properties, substrate characteristics, and prognosis of radiofrequency catheter ablation

BACKGROUND

Gender differences in the penetrance and clinical expression of genetic mutations have been reported in patients with arrhythmogenic right ventricular (RV) dysplasia/cardiomyopathy (ARVD/C). Our study aimed at clarifying the impact of gender on ventricular substrates and clinical outcomes after radiofrequency catheter ablation (RFCA).

METHODS

Patients with ARVD/C underwent RFCA for drug-refractory ventricular arrhythmias (VAs) were consecutively enrolled. Baseline characteristics, electrocardiograms, ventricular substrates, and VA recurrences after RFCA were extracted for comparison between genders.

RESULTS

A total of 70 consecutive unselected patients with definite ARVD/C (36 men [51%], age 45±14years) were studied. Male patients had a higher incidence of sustained ventricular tachycardia and ventricular fibrillation or sudden cardiac arrest as initial manifestations. Electroanatomical mapping demonstrated that men with ARVD/C had a larger epicardial RV unipolar low-voltage zone, a larger endocardial and epicardial area with late potentials, and longer local abnormal ventricular activity. Cox regression analysis demonstrated that gender and late potential area predicted the recurrences of VAs.

CONCLUSION

Patients with ARVD/C displayed different characteristics of VAs and substrate properties between men and women. Male gender and the presence of larger area of abnormal electrograms independently predicted VA recurrences after RFCA.

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/.

Atrial Fibrillation: The Science behind Its Defiance

Atrial fibrillation (AF) is the most prevalent arrhythmia in the world, due both to its tenacious treatment resistance, and to the tremendous number of risk factors that set the stage for the atria to fibrillate. Cardiopulmonary, behavioral, and psychological risk factors generate electrical and structural alterations of the atria that promote reentry and wavebreak. These culminate in fibrillation once atrial ectopic beats set the arrhythmia process in motion. There is growing evidence that chronic stress can physically alter the emotion centers of the limbic system, changing their input to the hypothalamic-limbic-autonomic network that regulates autonomic outflow. This leads to imbalance of the parasympathetic and sympathetic nervous systems, most often in favor of sympathetic overactivation. Autonomic imbalance acts as a driving force behind the atrial ectopy and reentry that promote AF. Careful study of AF pathophysiology can illuminate the means that enable AF to elude both pharmacological control and surgical cure, by revealing ways in which antiarrhythmic drugs and surgical and ablation procedures may paradoxically promote fibrillation. Understanding AF pathophysiology can also help clarify the mechanisms by which emerging modalities aiming to correct autonomic imbalance, such as renal sympathetic denervation, may offer potential to better control this arrhythmia. Finally, growing evidence supports lifestyle modification approaches as adjuncts to improve AF control.

Incidence, Characteristics, Risk Factors, and Outcomes of Takotsubo Cardiomyopathy With and Without Ventricular Arrhythmia

Takotsubo cardiomyopathy (TC) is a medical entity mimicking an acute coronary syndrome (ACS). Ventricular arrhythmia (VA) in TC has been reported in small studies, leading to uncertain knowledge of its incidence. We sought to describe the characteristics, incidence, predictive factors, and outcomes of VA in patients presenting with TC. Over a 12-year period, we reviewed all patients (n = 5,484) referred to our coronary care unit for a suspicion of ACS. TC was diagnosed in 90 patients according to the Mayo Clinic criteria. Incidence of VA among TC was 10%. In multivariate analysis, the factors significantly associated with an increased risk of VA were syncope (p = 0.007), age <55 years (p = 0.008), atypical TC (p = 0.04), a troponin I peak >7 μg/L (p = 0.04), and dobutamine use during hospitalization (p = 0.04). During follow-up, there was no significant difference in mortality rate between patients with or without VA. In conclusion, VA occurred in 10% of patients at the acute phase of TC and independent predictive factors of VA were syncope, atypical pattern of TC, high troponin peak, dobutamine use, and a relatively young age in a female and menopausal population. During the acute phase, identification of high-risk patients with VA allows better management, with electrocardiographic monitoring and therapeutic intervention in the coronary care unit.

Primary Prevention Implantable Cardioverter Defibrillator (ICD) Therapy in Women-Data From a Multicenter French Registry

BACKGROUND

There are limited data describing sex specificities regarding implantable cardioverter defibrillators (ICDs) in the real-world European setting.

METHODS AND RESULTS

Using a large multicenter cohort of consecutive patients referred for ICD implantation for primary prevention (2002-2012), in ischemic and nonischemic cardiomyopathy, we examined the sex differences in subjects' characteristics and outcomes. Of 5539 patients, only 837 (15.1%) were women and 53.8% received cardiac resynchronization therapy. Compared to men, women presented a significantly higher proportion of nonischemic cardiomyopathy (60.2% versus 36.2%, P<0.001), wider QRS complex width (QRS >120 ms: 74.6% versus 68.5%, P=0.003), higher New York Heart Association functional class (≥III in 54.2%♀ versus 47.8%♂, P=0.014), and lower prevalence of atrial fibrillation (18.7% versus 24.9%, P<0.001). During a 16 786 patient-years follow-up, overall, fewer appropriate therapies were observed in women (hazard ratio=0.59, 95% CI 0.45-0.76; P<0.001). By contrast, no sex-specific interaction was observed for inappropriate shocks (odds ratio ♀=0.84, 95% CI 0.50-1.39, P=0.492), early complications (odds ratio=1.00, 95% CI 0.75-1.32, P=0.992), and all-cause mortality (hazard ratio=0.87 95% CI 0.66-1.15, P=0.324). Analysis of sex-by- cardiac resynchronization therapy interaction shows than female cardiac resynchronization therapy recipients experienced fewer appropriate therapies than men (hazard ratio=0.62, 95% CI 0.50-0.77; P<0.001) and lower mortality (hazard ratio=0.68, 95% CI 0.47-0.97; P=0.034).

CONCLUSIONS

In our real-life registry, women account for the minority of ICD recipients and presented with a different clinical profile. Whereas female cardiac resynchronization therapy recipients had a lower incidence of appropriate ICD therapies and all-cause death than their male counterparts, the observed rates of inappropriate shocks and early complications in all ICD recipients were comparable.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov/. Unique identifier: NCT01992458.

Gender differences in electrophysiological characteristics of idiopathic ventricular tachycardia originating from right ventricular outflow tract

It has become increasingly apparent in recent years that there are important differences of many cardiovascular disorders including ventricular tachycardias in men and women. Nevertheless, so far just few studies have addressed possible gender differences in electrophysiological characteristics of idiopathic ventricular tachycardia from right ventricular outflow tract (RVOT-VT), other than epidemiological ones. This study explored possible gender differences in electrophysiological characteristics and catheter ablation outcome in RVOT-VT patients. Ninety-three patients (mean age 38.7+/-15.5 years, 30 males) with idiopathic RVOT-VT were enrolled and analyzed in our study. Male patients had longer QRS width (99.9+/-19.4 ms vs. 88.4+/-20.7 ms, p=0.02). Female patients had lower right ventricular mean voltage (3.0+/-0.7 mV vs. 3.7+/-0.9 mV, p=0.03), and more low voltage zone over the right ventricular outflow tract free wall (27.0 % vs. 6.7 %, p=0.02). Eighty-one patients passed catheter ablation (23 males). The acute success rate, repeated catheter ablation rate and VT recurrence rate were similar in both genders. The present study provides evidence of the gender differences in electrophysiological findings in patients with idiopathic RVOT-VT. Studies on gender-specific differences in arrhythmia could lead to a better understanding of its mechanism(s) and provide valuable information for the development of optimal treatment strategies.

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.

Cardiac contraction, calcium transients, and myofilament calcium sensitivity fluctuate with the estrous cycle in young adult female mice

This study established conditions to induce regular estrous cycles in female C57BL/6J mice and investigated the impact of the estrous cycle on contractions, Ca2+ transients, and underlying cardiac excitation-contraction (EC)-coupling mechanisms. Daily vaginal smears from group-housed virgin female mice were stained to distinguish estrous stage (proestrus, estrus, metestrus, diestrus). Ventricular myocytes were isolated from anesthetized mice. Contractions and Ca2+ transients were measured simultaneously (4 Hz, 37°C). Interestingly, mice did not exhibit regular cycles unless they were exposed to male pheromones in bedding added to their cages. Field-stimulated myocytes from mice in estrus had larger contractions (∼2-fold increase), larger Ca2+ transients (∼1.11-fold increase), and longer action potentials (>2-fold increase) compared with other stages. Larger contractions and Ca2+ transients were not observed in estrus myocytes voltage-clamped with shorter action potentials. Voltage-clamp experiments also demonstrated that estrous stage had no effect on Ca2+ current, EC-coupling gain, diastolic Ca2+, sarcoplasmic reticulum (SR) Ca2+ content, or fractional release. Although contractions were largest in estrus, myofilament Ca2+ sensitivity was lowest (EC50 values ∼1.15-fold higher) in conjunction with increased phosphorylation of myosin binding protein C in estrus. Contractions were enhanced in ventricular myocytes from mice in estrus because action potential prolongation increased SR Ca2+ release. These findings demonstrate that cyclical changes in reproductive hormones associated with the estrous cycle can influence myocardial electrical and contractile function and modify Ca2+ homeostasis. However, such changes are unlikely to occur in female mice housed in groups under conventional conditions, since these mice do not exhibit regular estrous cycles.

Estrogen receptor 1 gene (TA)n polymorphism is associated with lone atrial fibrillation in men

Aim

To determine the association between the number of thymine-adenine (TA)n dinucleotide repeats in the promoter region of the gene coding for the estrogen receptor alpha (ESR1) and the prevalence of lone atrial fibrillation (AF) in men.

Methods

We conducted a case-control study involving 89 men with lone AF and 166 healthy male controls. The ESR1 genotype was established by polymerase chain reaction and capillary electrophoresis. To assess the association of ESR1 genotype with AF, logistic regression models were built with AF as outcome.

Results

Men with lone AF had significantly greater number of (TA)n repeats of single alleles than controls (mean ± standard deviation, 19.2 ± 4.2 vs 18 ± 4.3, P = 0.010). After adjustment for other factors, a unit-increase in (TA)n repeat number was associated with a significantly greater likelihood of AF (odds ratio 1.069; 95% confidence interval 1.024-1.116, P = 0.002).

Conclusions

Our results indicate that a greater number of (TA)n repeats in the promoter region of ESR1 is associated with a significantly increased likelihood of lone atrial fibrillation in men.

Sex-Based Differences in Cardiac Arrhythmias, ICD Utilisation and Cardiac Resynchronisation Therapy

Many important differences in the presentation and clinical course of cardiac arrhythmias are present between men and women that should be accounted for in clinical practice. In this paper, we review published data on gender differences in cardiac excitable properties, supraventricular tachycardias, ventricular tachycardias, sudden cardiac death, and the utilisation of implantable defibrillators and cardiac resynchronisation therapy. Women have a higher heart rate at rest, and a longer QT interval than men. They further have a narrower QRS complex and lower QRS voltages on the 12-lead ECG with more often non-specific repolarisation abnormalities at rest. Supraventricular tachycardias, such as AV nodal reentrant tachycardia, are twice as frequent in women compared with men. Atrial fibrillation, however, has a 1.5-fold higher prevalence in men. The triggers for idiopathic right ventricular outflow tract tachycardia (VT) initiation are gender specific, i.e. hormonal changes play an important role in the occurrence of these VTs in women. There are clear-cut gender differences in acquired and congenital LQTS. Brugada syndrome affects men more commonly and severely than women. Sudden cardiac death is less prevalent in women at all ages and occurs 10 years later in women than in men. This may be related to the later onset of clinically manifest coronary heart disease in women. Among patients who receive ICDs and CRT devices, women appear to be under-represented, while they may benefit even more from these novel therapies.

Genetic mutation in Korean patients of sudden cardiac arrest as a surrogating marker of idiopathic ventricular arrhythmia

Mutation or common intronic variants in cardiac ion channel genes have been suggested to be associated with sudden cardiac death caused by idiopathic ventricular tachyarrhythmia. This study aimed to find mutations in cardiac ion channel genes of Korean sudden cardiac arrest patients with structurally normal heart and to verify association between common genetic variation in cardiac ion channel and sudden cardiac arrest by idiopathic ventricular tachyarrhythmia in Koreans. Study participants were Korean survivors of sudden cardiac arrest caused by idiopathic ventricular tachycardia or fibrillation. All coding exons of the SCN5A, KCNQ1, and KCNH2 genes were analyzed by Sanger sequencing. Fifteen survivors of sudden cardiac arrest were included. Three male patients had mutations in SCN5A gene and none in KCNQ1 and KCNH2 genes. Intronic variant (rs2283222) in KCNQ1 gene showed significant association with sudden cardiac arrest (OR 4.05). Four male sudden cardiac arrest survivors had intronic variant (rs11720524) in SCN5A gene. None of female survivors of sudden cardiac arrest had SCN5A gene mutations despite similar frequencies of intronic variants between males and females in 55 normal controls. Common intronic variant in KCNQ1 gene is associated with sudden cardiac arrest caused by idiopathic ventricular tachyarrhythmia in Koreans.

Gender-specific differences in clinical outcome of primary prevention implantable cardioverter defibrillator recipients

OBJECTIVE

To assess differences in clinical outcome of implantable cardioverter-defibrillator (ICD) treatment in men and women.

DESIGN

Prospective cohort study.

SETTING

University Medical Center.

PATIENTS

1946 primary prevention ICD recipients (1528 (79%) men and 418 (21%) women). Patients with congenital heart disease were excluded for this analysis.

MAIN OUTCOME MEASURES

All-cause mortality, ICD therapy (antitachycardia pacing and shock) and ICD shock.

RESULTS

During a median follow-up of 3.3 years (25th-75th percentile 1.4-5.4), 387 (25%) men and 76 (18%) women died. The estimated 5-year cumulative incidence for all-cause mortality was 20% (95% CI 18% to 23%) for men and 14% (95% CI 9% to 19%) for women (log rank p<0.01). After adjustment for potential confounding covariates all-cause mortality was lower in women (HR 0.65; 95% CI 0.49 to 0.84; p<0.01). The 5-year cumulative incidence for appropriate therapy in men was 24% (95% CI 21% to 28%) as compared with 20% (95% CI 14% to 26%) in women (log rank p=0.07). After adjustment, a non-significant trend remained (HR 0.82; 95% CI 0.64 to 1.06; p=0.13).

CONCLUSIONS

In clinical practice, 21% of primary prevention ICD recipients are women. Women have lower mortality and tend to experience less appropriate ICD therapy as compared with their male peers.

Relationships between heart rate and age, bodyweight and breed in 10,849 dogs

OBJECTIVES

To evaluate relationships between heart rate and clinical variables in healthy dogs and dogs examined at a referral hospital.

METHODS

Clinical data were extracted from the electronic patient records of a first opinion group (5000 healthy dogs) and a referral hospital (5849 dogs). Univariable and multi-variable general linear models were used to assess associations between heart rate and clinical characteristics. Separate multi-variable models were constructed for first opinion and referral populations.

RESULTS

In healthy dogs, heart rate was negatively associated with bodyweight (P<0.001) but was higher in Chihuahuas. The mean difference in heart rate between a 5 and 55 kg dog was 10.5 beats per minute. In dogs presenting to a referral hospital, heart rate was negatively associated with bodyweight (P<0.001) and the following breeds; border collie, golden retriever, Labrador retriever, springer spaniel and West Highland white terrier and positively associated with age, admitting service (emergency and critical care, emergency first opinion and cardiology) and the following breeds; Cavalier King Charles spaniel, Staffordshire bull terrier and Yorkshire terrier.

CLINICAL SIGNIFICANCE

Bodyweight, age, breed and disease status all influence heart rate in dogs, although these factors account for a relatively small proportion of the overall variability in heart rate.

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.

Age of natural menopause and atrial fibrillation: the Framingham Heart Study

BACKGROUND

Early menopausal age is associated with risk of cardiovascular events including myocardial infraction, stroke, and increased mortality. Relations between menopausal age and atrial fibrillation (AF) have not been investigated. We examined the association between menopausal age and AF.

METHODS

Framingham Heart Study women ≥ 60 years old without prevalent AF and natural menopause were followed up for 10 years or until incident AF. Menopausal age was modeled as a continuous variable and by categories (<45, 45-53, and >53 years). We used Cox proportional hazards regression to determine associations between menopausal age and AF risk.

RESULTS

In 1,809 Framingham women (2,662 person-examinations, mean baseline age 71.4 ± 7.6 years, menopausal age 49.8 ± 3.6 years), there were 273 unique participants with incident AF. We did not identify a significant association between the SD of menopausal age (3.6 years) and AF (hazard ratio [HR] per SD 0.94, 95% CI 0.83-1.06; P = .29). In a multivariable model with established risk factors for AF, menopausal age was not associated with incident AF (HR per SD 0.97, 95% CI 0.86-1.09; P = .60). Examining categorical menopausal age, earlier menopausal age (<45 years) was not significantly associated with increased AF risk compared with older menopausal age >53 years (HR 1.20, 95% CI 0.74-1.94; P = .52) or menopausal age 45 to 53 years (HR 1.38, 95% CI 0.93-2.04; P = .11).

CONCLUSION

In our moderate-sized, community-based sample, we did not identify menopausal age as significantly increasing AF risk. However, future larger studies will need to examine whether there is a small effect of menopausal age on AF risk.

Atrial fibrillation in pregnancy

BACKGROUND

Physiologic changes of pregnancy can predispose women to cardiac arrhythmias. Atrial fibrillation is rare in pregnancy and usually occurs in women with underlying cardiac anomalies.

CASE

A young woman at 22 weeks of gestation presented with new-onset atrial fibrillation with rapid ventricular response. Thorough evaluation revealed atrial fibrillation with no underlying cause and ultimately required treatment with electrical cardioversion.

CONCLUSION

Lone atrial fibrillation in pregnancy requires exclusion of all possible etiologies before diagnosis. Cardioversion is the treatment of choice. Women with persistent atrial fibrillation require anticoagulation and rate control, as well as fetal growth surveillance and antenatal testing.

Gender-specific aspects in the clinical presentation of cardiovascular disease

More than a quarter of a million women die each year in the industrialized countries from cardiovascular diseases (CVD), and current projections indicate that this number will continue to rise with our ageing population. Important sex-related differences in the prevalence, presentation, management and outcomes of different CVD have discovered in the last two decades of cardiovascular research. Nevertheless, much evidence supporting contemporary recommendations for testing, prevention and treatment of CVD in women is still extrapolated from studies conducted predominantly in men. The compendium of CVD indicates that current research and strategy development must focus on gender-specific issues to address the societal burden and costs related to these incremental shifts in female gender involvement. Indeed, this significant burden of CVD in women places unique diagnostic, treatment and financial encumbrances on our society that are only further intensified by a lack of public awareness about the disease on the part of patients and clinicians alike. This societal burden of the disease is, in part, related to our poor understanding of gender-specific pathophysiologic differences in the presentation and prognosis of CVD and the paucity of diagnostic and treatment guidelines tailored to phenotypic differences in women. In this, scenario is of outmost importance to know these differences to provide the best care for female patients, because under-recognition of CVD in women may contribute to a worse clinical outcome. This review will provide a synopsis of available evidence on gender-based differences in the initial presentation, pathophysiology and clinical outcomes of women affected by CVD.

Recent advances in the management of chronic stable angina I: approach to the patient, diagnosis, pathophysiology, risk stratification, and gender disparities

The potential importance of both prevention and personal responsibility in controlling heart disease, the leading cause of death in the USA and elsewhere, has attracted renewed attention. Coronary artery disease is preventable, using relatively simple and inexpensive lifestyle changes. The inexorable rise in the prevalence of obesity, diabetes, dyslipidemia, and hypertension, often in the risk cluster known as the metabolic syndrome, drives the ever-increasing incidence of heart disease. Population-wide improvements in personal health habits appear to be a fundamental, evidence based public health measure, yet numerous barriers prevent implementation. A common symptom in patients with coronary artery disease, classical angina refers to the typical chest pressure or discomfort that results when myocardial oxygen demand rises and coronary blood flow is reduced by fixed, atherosclerotic, obstructive lesions. Different forms of angina and diagnosis, with a short description of the significance of pain and silent ischemia, are discussed in this review. The well accepted concept of myocardial oxygen imbalance in the genesis of angina is presented with new data about clinical pathology of stable angina and acute coronary syndromes. The roles of stress electrocardiography and stress myocardial perfusion scintigraphic imaging are reviewed, along with the information these tests provide about risk and prognosis. Finally, the current status of gender disparities in heart disease is summarized. Enhanced risk stratification and identification of patients in whom procedures will meaningfully change management is an ongoing quest. Current guidelines emphasize efficient triage of patients with suspected coronary artery disease. Many experts believe the predictive value of current decision protocols for coronary artery disease still needs improvement in order to optimize outcomes, yet avoid unnecessary coronary angiograms and radiation exposure. Coronary angiography remains the gold standard in the diagnosis of coronary artery obstructive disease. Part II of this two part series will address anti-ischemic therapies, new agents, cardiovascular risk reduction, options to treat refractory angina, and revascularization.

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.