Developmental changes in sinus node function in growing children: an updated analysis

Female cardiovascular biology and resilience in the setting of physiological and pathological stress

For years, females were thought of as smaller men with complex hormonal cycles; as a result, females have been largely excluded from preclinical and clinical research. However, in the last ten years, with the increased focus on sex as a biological variable, it has become clear that this is not the case, and in fact, male and female cardiovascular biology and cardiac stress responses differ substantially. Premenopausal women are protected from cardiovascular diseases, such as myocardial infarction and resultant heart failure, having preserved cardiac function, reduced adverse remodeling, and increased survival. Many underlying biological processes that contribute to ventricular remodeling differ between the sexes, such as cellular metabolism; immune cell responses; cardiac fibrosis and extracellular matrix remodeling; cardiomyocyte dysfunction; and endothelial biology; however, it is unclear how these changes afford protection to the female heart. Although many of these changes are dependent on protection provided by female sex hormones, several of these changes occur independent of sex hormones, suggesting that the nature of these changes is more complex than initially thought. This may be why studies focused on the cardiovascular benefits of hormone replacement therapy in post-menopausal women have provided mixed results. Some of the complexity likely stems from the fact that the cellular composition of the heart is sexually dimorphic and that in the setting of MI, different subpopulations of these cell types are apparent. Despite the documented sex-differences in cardiovascular (patho)physiology, the underlying mechanisms that contribute are largely unknown due to inconsistent findings amongst investigators and, in some cases, lack of rigor in reporting and consideration of sex-dependent variables. Therefore, this review aims to describe current understanding of the sex-dependent differences in the myocardium in response to physiological and pathological stressors, with a focus on the sex-dependent differences that contribute to post-infarction remodeling and resultant functional decline.

Cavotricuspid isthmus ablation and subcutaneous monitoring device implantation in a 2-year-old baby with 2 SCN5A mutations, sinus node dysfunction, atrial flutter recurrences, and drug induced long-QT syndrome: a tricky case of pediatric overlap syndrome?

We describe the case of 2-year-old baby with compound heterozygosity for paternal and maternal alleles mutation of α-subunit of the cardiac sodium channel (SCN5A), sinus node dysfunction, atrial flutter recurrences, and drug induced long-QT syndrome. In this setting, we chose at first to perform linear ablation of cavotricuspid isthmus resulting in a bidirectional isthmus block. As a second step, we decided to implant a miniaturized loop recorder that, with a minimally invasive procedure, permits us to follow the development of the disease in order to define the future strategy. After 8 months follow-up, automatic daily loop-recorder transmissions disclose the complete absence of any arrhythmia along with asymptomatic ventricular pauses due to sinus node dysfunction. Echocardiography shows normal findings, in particular no left ventricular dysfunction.

Gender differences in the phosphorus content of the sino-atrial nodes and other cardiac regions of monkeys

To examine whether there were gender differences in the sino-atrial node (SAN), the authors investigated the gender difference in the SAN using monkey hearts by direct chemical analysis from a viewpoint of element contents. The used rhesus and Japanese monkeys consisted of 30 males (average age=6.5±7.5 years) and 30 females (average age=12.2±10.3 years), ranging in age from newborn to 30 years. The SAN tissues were removed from the anatomical position of monkey hearts and were confirmed by means of histological observation. After ashing with nitric acid and with perchloric acid, element contents of the SANs, such as Ca, P, S, Mg, Zn, Fe, and Na, were determined by inductively coupled plasma-atomic emission spectrometry. In addition, gender differences in the right atrial walls, left ventricular walls, mitral valves, and left coronary arteries of monkeys were also investigated as controls. It was found that the P content was significantly higher in females than in males in the SANs of monkeys, but the other six element contents, Ca, S, Mg, Zn, Fe, and Na, were not significantly different between males and females in the SANs of monkeys. Regarding the P content, a similar finding was also obtained in both the right atrial walls and the left ventricular walls of monkeys, but it was not obtained in the mitral valves and the left coronary arteries of monkeys. The P content of tissue is mostly determined by the nucleic acid (DNA and RNA) content and the phospholipid content of tissue. Nucleic acids in the cell nucleus and the cytosol, and phospholipids in the cell membrane are all indicators of metabolically active cells. It is reasonable to presume that the P content in the SAN indicates the active cell density, namely, the number of active cells per volume. Therefore, there is a possibility that the active cell density of the SAN is significantly higher in females than in males.