Abstract
Despite increasing awareness of cardiovascular sexual dimorphism, the mechanisms underlying sex differences in cardiovascular physiology and pathology remain poorly understood. Most studies, often relying on animal models, have produced inconsistent findings. My study aims to address this gap by investigating sex differences in human myocardial structure and function. I hypothesized that female cardiac muscle would exhibit reduced fibrosis and higher relative myocyte content, leading to enhanced cardiac function compared to males.
Right atrial appendages were obtained from consenting (postmenopausal) biological female and male (~65 years) cardiac surgery patients at Dunedin Hospital. Trabeculae muscles were dissected, mounted on a force transducer, and electrically stimulated to contract. Force production was measured under varying conditions, including different stimulation frequencies and external calcium concentrations. Histological analysis using phalloidin and wheat germ agglutinin (WGA) staining assessed cardiomyocyte and fibrotic areas in the trabeculae samples, respectively. Structural data was integrated with functional parameters to examine the influence of fibrosis and cardiomyocyte area on myocardial performance between sexes. Clinical information from the patients was also incorporated to contextualize the findings.
Contrary to the hypothesis, no significant differences in myocardial function between males and females were observed at baseline, under increased calcium, or at different stimulation frequencies. However, muscles from females did show a significantly greater increase in contraction and relaxation rates after rest periods compared to males. Additionally, no significant differences were found in the relative proportions of cardiomyocyte and fibrotic areas between sexes.
The subtle sex differences found in myocardial function provide an important foundation for further in-depth sex-specific myocardial research, which is critical to understanding the increased risk of cardiovascular disease in post-menopausal women. Moreover, it underscores the need for greater inclusion of female subjects in cardiovascular research.