Gender Differences in the Effect of Auditory Stimuli on Ventricular Repolarization in Healthy Subjects

Maximum QTc on Holter electrocardiography in children

BACKGROUND

Corrected QT interval (QTc) on electrocardiography (ECG) at rest and after exercise in a short daytime recording period may be insufficient for the diagnosis and management of long QT syndrome (LQTS), especially for LQTS type 2 and 3. Therefore, examination of QTc on Holter ECG is important. We designed a method of analyzing QTc on Holter ECG that can be performed in daily clinical practice by combining automatic and manual measurements.

METHODS

We reviewed the charts of healthy children (n = 210) and LQTS patients (n = 35) aged <16 years and analyzed QTc at rest and after exercise, and the maximum QTc on Holter ECG.

RESULTS

The QTc (Fridericia's correction) of most controls and LQTS patients reached the maximum at night or early in the morning. QTc differed according to sex and age. In the control group, QTc on ECG of all three types tended to lengthen with age. QTc after exercise was slightly longer than QTc at rest, and the maximum QTc on Holter ECG was much longer than both, reaching >450 ms in boys and 500 ms in girls. In most LQTS type 1 patients, QTc after exercise and that on Holter ECG tended to be long. In most LQTS type 2 and 3 patients, QTc at rest and that after exercise was long, and that on Holter ECG tended to be much longer.

CONCLUSIONS

The present method of analyzing QTc on Holter ECG, in which automatic and manual measurements are combined, is practical and may be useful for diagnosis and risk stratification of LQTS.

Bridging the gender gap in atrial fibrillation

Women have a similar lifetime prevalence of non-valvular atrial fibrillation (NVAF) compared with that of men. Given the significant morbidity and potential mortality associated with NVAF, it is crucial to understand gender differences with NVAF. Women can be more symptomatic than men. Despite a higher baseline stroke risk, they are less likely to be on anticoagulation. Women have a greater risk of thromboembolism and a similar rate of bleeding risk compared with men on anticoagulation. Initial experience suggests that novel oral anticoagulants have similar safety and efficacy profile in men and women. Although women can have more adverse reactions from antiarrhythmic therapies, they are often referred later than men for ablation. As a group, a mitigating factor in ablation referral is that women also have a higher incidence of procedural complications from catheter ablation. This review summarizes the available literature highlighting significant gender-based differences and also highlights areas for research to improve NVAF outcomes in women.

Sex and gender aspects in antiarrhythmic therapy

Although cardiac arrhythmia had long been considered a predominantly male syndrome, it is now clear that arrhythmia is also a primary cause of mortality in women. Notably, the manifestation of specific arrhythmia syndromes appears to be gender specific. In particular, female sex is an independent risk factor for development of torsade de pointes (TdP) arrhythmias not only in congenital long QT syndromes but also in acquired long QT syndromes which occur as adverse effects of existing drugs. Males, on the other hand, are more likely to develop Brugada syndrome. Recent clinical and experimental studies suggest that these differences may stem from intrinsic sex differences in cardiac tissue. These include fundamental electrical differences resulting from variable ion channel expression and diverse sex hormonal regulation via long-term genomic and acute nongenomic pathways, and sex differences in drug responses and metabolisms. Undoubtedly, determining the effect of gender on cardiac function will be difficult and require sophisticated methodologies. However, gender differences underlying predilection to distinct arrhythmia syndromes must be revealed so that new therapeutic strategies that take gender into account can be applied to at-risk patients.

hERG K+ Channels: Structure, Function, and Clinical Significance

The human ether-a-go-go related gene (hERG) encodes the pore-forming subunit of the rapid component of the delayed rectifier K+ channel, Kv11.1, which are expressed in the heart, various brain regions, smooth muscle cells, endocrine cells, and a wide range of tumor cell lines. However, it is the role that Kv11.1 channels play in the heart that has been best characterized, for two main reasons. First, it is the gene product involved in chromosome 7-associated long QT syndrome (LQTS), an inherited disorder associated with a markedly increased risk of ventricular arrhythmias and sudden cardiac death. Second, blockade of Kv11.1, by a wide range of prescription medications, causes drug-induced QT prolongation with an increase in risk of sudden cardiac arrest. In the first part of this review, the properties of Kv11.1 channels, including biogenesis, trafficking, gating, and pharmacology are discussed, while the second part focuses on the pathophysiology of Kv11.1 channels.