Identification of the atrioventricular conduction axis and its positional relationship with anatomical landmarks of a heart with tricuspid atresia.
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ABSTRACT:
SUBMITTER: Wada Y
PROVIDER: S-EPMC9390617 | biostudies-literature | 2021 Dec
REPOSITORIES: biostudies-literature
Publications
Identification of the atrioventricular conduction axis and its positional relationship with anatomical landmarks of a heart with tricuspid atresia.
Wada Yuson Y Matsuhisa Hironori H Oshima Yoshihiro Y Yoshimura Naoki N
JTCVS open 20211026
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Project description:In this study, we aimed to differentiate atrioventricular (AV) canal-like cardiomyocytes (AVCM) from hiPSCs to facilitate the study of disorders that affect the AV conduction axis. hiPSC-derived AVCM preferentially expressed AV canal-associated genes MSX2, TBX2 and TBX3. Single cell RNA sequencing and comparative analysis with mouse heart further validated their AV canal-like identity. In addition, hiPSC-AVCM demonstrated sensitivity to ivabradine and carbachol, indicating the presence of key nodal currents If and IKACh. To model the AV conduction axis, we created an organoid-based tissue model. These so-called “assembloids” consisted of atrial, AVC, and ventricular organoids, which exhibited spontaneous contractions and unidirectional conduction with impulses initiated predominantly at the atrial end. Remarkably, we observed slower conduction in the AVC region of the assembloid, effectively recapitulating the “fast-slow-fast” conduction pattern found in the early heart tube. Our results demonstrate that hiPSC-derived AVCM recapitulate molecular and electrophysiological properties of in vivo AV canal cardiomyocytes and tissue models incorporating this cell type enhance our ability to evaluate complex cardiac conduction disorders.
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Project description:The atrioventricular (AV) conduction axis provides electrical continuity between the atrial and ventricular chambers. The "nodal" cardiomyocytes populating this region (AV canal in the embryo, AV node from fetal stages onward) propagate impulses slowly, ensuring sequential contraction of the chambers. Dysfunction of AV nodal tissue causes severe disturbances in rhythm and contraction, and human models that capture its salient features are limited. Here, we report an approach for the reproducible generation of AV canal cardiomyocytes (AVCMs) with in vivo-like gene expression and electrophysiological profiles. We created the so-called "assembloids" composed of atrial, AVCM, and ventricular spheroids, which effectively recapitulated unidirectional conduction and the "fast-slow-fast" activation pattern typical for the vertebrate heart. We utilized these systems to reveal intracellular calcium mishandling as the basis of LMNA-associated AV conduction block. In sum, our study introduces novel cell differentiation and tissue construction strategies to facilitate the study of complex disorders affecting heart rhythm.
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Project description:Background and significance The specialized conduction system (SCS) of the heart was extensively studied to understand the synchronization of atrial and ventricular contractions, the large atrial to His bundle (A-H) delay through the atrioventricular node (AVN), and delays between Purkinje (P) and ventricular (V) depolarization at distinct junctions (J), PVJs. Here, we use optical mapping of perfused rabbit hearts to revisit the mechanism that explains A-H delay and the role of a passive electrotonic step-delay at the boundary between atria and the AVN. We further visualize how the P anatomy controls papillary activation and valve closure before ventricular activation. Methods Rabbit hearts were perfused with a bolus (100–200 µl) of a voltage-sensitive dye (di4ANEPPS), blebbistatin (10–20 µM for 20 min) then the right atrial appendage and ventricular free-wall were cut to expose the AVN, P fibers (PFs), the septum, papillary muscles, and the endocardium. Fluorescence images were focused on a CMOS camera (SciMedia) captured at 1K-5 K frames/s from 100 × 100 pixels. Results AP propagation across the AVN-His (A-H) exhibits distinct patterns of delay and conduction blocks during S1–S2 stimulation. Refractory periods were 81 ± 9, 90 ± 21, 185 ± 15 ms for Atrial, AVN, and His, respectively. A large delay (>40 ms) occurs between atrial and AVN activation that increased during rapid atrial pacing contributing to the development of Wenckebach periodicity followed by delays within the AVN through slow or blocked conduction. The temporal resolution of the camera allowed us to identify PVJs by detecting doublets of AP upstrokes. PVJ delays were heterogeneous, fastest in PVJ that immediately trigger ventricular APs (3.4 ± 0.8 ms) and slow in regions where PF appear insulated from the neighboring ventricular myocytes (7.8 ± 2.4 ms). Insulated PF along papillary muscles conducted APs (>2 m/s), then triggered papillary muscle APs (<1 m/s), followed by APs firing of septum and endocardium. The anatomy of PFs and PVJs produced activation patterns that control the sequence of contractions ensuring that papillary contractions close the tricuspid valve 2–5 ms before right ventricular contractions. Conclusions The specialized conduction system can be accessed optically to investigate the electrical properties of the AVN, PVJ and activation patterns in physiological and pathological conditions.
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