Living myocardial slices: walking the path towards standardization

Abstract

Cardiovascular disease remains a persistent global health burden, underscoring the necessity for effective therapeutic strategies. Despite significant advances, the ability to mechanistically study human disease and predict clinical outcomes remains limited, especially in complex diseases such as heart failure. This limitation is evident through the continuous high attrition rates in drug development pipelines. To address these challenges and contribute to improved preclinical studies, there is a need for platforms that more accurately recapitulate the human heart. This need increased the interest in living myocardial slices (LMS) - thin sections of the heart of approximately 100-400 μm. LMS retain the native multicellular architecture of the heart and enable extended ex vivo culture. However, as their utilization grows, so does variability in preparation methodologies and readouts. This review provides an overview of differences in sample selection, interspecies variations, intra-cardiac differences, and potential confounding factors. Additionally, we examine culture methods, addressing electrical and mechanical stimulation differences, and medium compositions. Our review concludes by highlighting the current limitations of LMS research and offers guidelines for standardization and future applications. The ultimate aim of this review is to serve as a resource for researchers working with LMS and for those entering this field. By presenting the landscape of methodological considerations, we aim to facilitate informed decision-making in study design and execution. We advocate for accurate reporting of methodologies to promote reproducibility and comparability across studies, advancing LMS research and strengthening its role as a valuable addition to the current drug development toolbox and basic cardiovascular research.

Keywords: Disease modeling; Living myocardial slices; Mechanical and electrical stimulation; Metabolism; Translational research.

Graphical Abstract

Living myocardial slices (LMS) have become a valuable preclinical model to study cardiac (patho)physiology and therapeutic interventions. However, the rise of studies employing LMS has come with an increased experimental and methodological variation. Unlocking the full potential of this model requires standardization.

Figure 1

Overview of LMS preparation and culture conditions: A) Schematic representation of LMS generation from a ventricular biopsy, highlighting the subsequent culture setup with options for mechanical loading and electrical stimulation. B) Illustration of three distinct mechanical loading methods applied to LMS: Auxotonic, utilizing flexible poles to create a variable afterload; Isometric, with fixed poles resulting in a maximal, continuous afterload; and work loops, where an actuator adjusts length, offering the most accurate representation of natural cardiac mechanics.

Figure 2

Overview of LMS studies: species sources, intra-cardiac sample selection, and culture conditions. A PubMed search using the term “myocardial slice” was conducted. A total of 83 articles were included in this analysis, corresponding to studies reporting the preparation of LMS from different animal models and, when available, the employed culture conditions. A) Among these publications, nine different species were used to produce LMS. B) For human-based studies, there are five different intra-cardiac locations used to produce LMS: ventricles, atria, atrial appendices, LV apex, and septal myectomies. The figure illustrates the wide variability in culturing methodologies across these species, encompassing differences in mechanical loading (C & D) and electrical stimulation (C & E). This heterogeneity highlights the lack of standardized protocols in the field and underscores the necessity for standardization in myocardial slice research.