Advanced Structure–Function Imaging of Cardiac Trans-Scar Electrical Conduction

• Applicants: Dr. Leonardo Sacconi; Dr. Callum Michael Zgierski-Johnston
• Subject Area: Cardiology, Angiology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 502822458

Cardiac scars were once seen as non-excitable barriers to electrical conduction (‘dead tissue’). However, trans-scar conduction (TSC) of electrical excitation has been confirmed in basic and clinical settings, challenging some of our established concepts of cardiac electrophysiology and arrhythmogenesis. Surviving cardiomyocytes (CM) inside scars are likely to underlie TSC, but it is unclear whether TSC occurs via strands of CM only, or via pathways formed by interconnected CM and non-myocytes (NM). In the latter setting, NM would act as passive conductors of action potentials (AP). Such electrotonic AP conduction would be possible over limited distances only (<<1 mm), due to the loss in electrical signal amplitude in NM. This is in contrast to published experimental observations of TSC in native tissue (>1 cm). We hypothesise that surviving CM in cardiac scars act as electrical ‘repeater stations’, locally generating new AP, and thus effectively resetting the otherwise limited maximum distance of passive NM-mediated conduction.Altering TSC is of potential translational relevance. This could involve making lesions electrically more (e.g. to reduce arrhythmogenesis after ventricular scarring) or less conductive (e.g. to make atrial ablation lines permanently non-conductive). Assessment of this potential requires an improved understanding of TSC. Currently, mechanisms and modifiers of TSC are ill-explored, in part due to our inability (i) to perform large-scale cellular resolution reconstructions of scars and (ii) to interrelate this with whole heart electrophysiology data.Here, we will develop and apply a new framework for correlation of functional information, such as AP shape and propagation, with 3D structural data, to quantify post-lesion cardiac remodelling over extended tissue volumes with better-than-single-cell resolution. Hearts will first be electrophysiologically characterised, then fixed, optically cleared, immuno-stained, and 3D-imaged using a novel dual-light-sheet approach. Structural data will be used to interpret electrical propagation using a one-to-one (same heart) correlative paradigm. Implementation requires a concerted technological effort where advances in imaging methods and tissue preparation will be combined with novel software strategies for analysis, processing, and correlation of structural and functional data. This will be applied initially to mouse hearts with ischaemia-reperfusion, permanent ligation or cryo-injury scars, using lines that overexpress Cx43 in CM or NM. The lesion models differ in CM/NM ratios, and the murine models in hetero-cellular connectivity, allowing us to decipher mechanisms and modulators of TSC. Our research and development activities will support not only quantitative assessment of structure and function with high enough throughput for discovering insight into basic mechanisms underlying TSC in the heart, but also form a novel foundation for cell-to-organ studies by other researchers.

• DFG Programme: Research Grants