Three-dimensional functional anatomy of the human sinoatrial node for epicardial and endocardial mapping and ablation

Heart Rate Mystery Unveiled: Sex Differences in Human Sinoatrial Node Genes and Female Tachycardia

BACKGROUND

Despite over a century of clinical electrocardiographic studies showing that females exhibit a faster resting heart rate (HR), the mechanisms underlying sex differences in HR remain unresolved. Moreover, inappropriate sinus tachycardia primarily affects females, whereas males are at a higher risk for conduction block and atrial fibrillation. We hypothesized that the sexual dimorphism of genes responsible for sinoatrial node (SAN) pacemaking and signaling pathways may contribute to the sex differences in HR and susceptibility to arrhythmias.

METHODS

Human SAN central pacemaker and right atrial tissue were isolated from nondiseased ex vivo donor hearts. Gene expressions were quantified and validated using the transcriptomic panel and quantitative polymerase chain reaction. Gene set enrichment analysis, Ingenuity Pathway Analysis, and human-specific SAN models were utilized to define regulatory mechanisms and functional impacts of sex-biased gene transcription.

RESULTS

We identified differentially expressed region- and sex-specific genes, with gene sets enriched in HR regulation (eg, TBX3, HCN1) and metabolism (eg, ADIPOQ, LEP) pathways in female SAN. In contrast, differential genes and gene sets involved in collagen biosynthetic processes, fibrogenesis (eg, EGR1), and immune response (eg, IL6, CXCL8) pathways were enriched in males SAN and right atrial. Ingenuity Pathway Analysis predicted significant roles for TBX3 and estradiol in the sex-specific expression of genes involved in SAN function. Computational simulations showed that the sex-specific SAN differences in If (HCN1) and ICa,L (CACNA1D) can explain the faster HR in females, with females having a lower threshold for inappropriate sinus tachycardia, whereas males are more vulnerable to sinus arrest.

CONCLUSIONS

The human SAN exhibits region-specific sexual dimorphism in pacemaking gene sets. Higher expression of TBX3 and HCN1 in females may underlie their faster HR and increased susceptibility to inappropriate sinus tachycardia, whereas enriched gene sets related to inflammation and collagen biosynthesis in males may predispose them to conduction impairments and atrial fibrillation risk.

Catheter Ablation in Atrial Fibrillation: Recent Advances

Atrial fibrillation (AF) is the leading cause of arrhythmia-related morbidity and mortality. Recurrent symptoms, hospitalizations, and cost burden to patients have necessitated treatments beyond antiarrhythmic drugs (AADs) for patients with AF. Catheter ablation has proven to be effective over medical therapy alone; however the recurrence rates for atrial tachyarrhythmias post-ablation remain significant, particularly in patients with persistent and long-standing persistent AF. Hence, new techniques for catheter ablation have arisen, such as non-thermal energy sources, novel catheters, electroanatomical mapping, and ablation of additional targets. In this review, we discuss the recent advances in the field of catheter ablation, including newer modalities for the prevention of adverse events and future perspectives.

Multidimensional Analysis of the Adult Human Heart in Health and Disease Using Hierarchical Phase-Contrast Tomography

Background Current clinical imaging modalities such as CT and MRI provide resolution adequate to diagnose cardiovascular diseases but cannot depict detailed structural features in the heart across length scales. Hierarchical phase-contrast tomography (HiP-CT) uses fourth-generation synchrotron sources with improved x-ray brilliance and high energies to provide micron-resolution imaging of intact adult organs with unprecedented detail. Purpose To evaluate the capability of HiP-CT to depict the macro- to microanatomy of structurally normal and abnormal adult human hearts ex vivo. Materials and Methods Between February 2021 and September 2023, two adult human donor hearts were obtained, fixed in formalin, and prepared using a mixture of crushed agar in a 70% ethanol solution. One heart was from a 63-year-old White male without known cardiac disease, and the other was from an 87-year-old White female with a history of multiple known cardiovascular pathologies including ischemic heart disease, hypertension, and atrial fibrillation. Nondestructive ex vivo imaging of these hearts without exogenous contrast agent was performed using HiP-CT at the European Synchrotron Radiation Facility. Results HiP-CT demonstrated the capacity for high-spatial-resolution, multiscale cardiac imaging ex vivo, revealing histologic-level detail of the myocardium, valves, coronary arteries, and cardiac conduction system across length scales. Virtual sectioning of the cardiac conduction system provided information on fatty infiltration, vascular supply, and pathways between the cardiac nodes and adjacent structures. HiP-CT achieved resolutions ranging from gross (isotropic voxels of approximately 20 µm) to microscopic (approximately 6.4-µm voxel size) to cellular (approximately 2.3-µm voxel size) in scale. The potential for quantitative assessment of features in health and disease was demonstrated. Conclusion HiP-CT provided high-spatial-resolution, three-dimensional images of structurally normal and diseased ex vivo adult human hearts. Whole-heart image volumes were obtained with isotropic voxels of approximately 20 µm, and local regions of interest were obtained with resolution down to 2.3-6.4 µm without the need for sectioning, destructive techniques, or exogenous contrast agents. Published under a CC BY 4.0 license Supplemental material is available for this article. See also the editorial by Bluemke and Pourmorteza in this issue.

Revisiting Cardiac Biology in the Era of Single Cell and Spatial Omics

Throughout our lifetime, each beat of the heart requires the coordinated action of multiple cardiac cell types. Understanding cardiac cell biology, its intricate microenvironments, and the mechanisms that govern their function in health and disease are crucial to designing novel therapeutical and behavioral interventions. Recent advances in single-cell and spatial omics technologies have significantly propelled this understanding, offering novel insights into the cellular diversity and function and the complex interactions of cardiac tissue. This review provides a comprehensive overview of the cellular landscape of the heart, bridging the gap between suspension-based and emerging in situ approaches, focusing on the experimental and computational challenges, comparative analyses of mouse and human cardiac systems, and the rising contextualization of cardiac cells within their niches. As we explore the heart at this unprecedented resolution, integrating insights from both mouse and human studies will pave the way for novel diagnostic tools and therapeutic interventions, ultimately improving outcomes for patients with cardiovascular diseases.