The Anatomical Arrangement of the Cardiomyocytes Within the Ventricular Walls

Over the course of the twentieth century, and during the initial decades of the twenty-first century, the anatomical arrangement of the cardiomyocytes making up the ventricular walls has become a highly contentious topic. At the beginning of the twentieth century, it was customary to assess the cardiac muscle in the context of skeletal muscles, describing origins and insertions of discrete components. Even at that early stage, it had been suggested that the ventricular mass could be unwrapped as a continuous band. Subsequent to the introduction of histological investigation, it emerged that the individual cardiomyocytes were aggregated together within a supporting fibrous matrix. The precise details of such aggregation, however, have still to be agreed. Detailed investigations were made to assess the angulation of the aggregated entities within the walls, with debates emerging as to whether the aggregates could be transmural. Suggestions were made that the cardiomyocytes could be grouped together in a laminar fashion, with the aggregates described as sheets, or sheetlets. Others revisited the notion that the ventricular mass was best assessed on the basis of a continuous helical band. In this review, we assess these various concepts of mural architecture in light of our own extensive studies. We emphasize that the working unit of the myocardium is the sarcomeric array of the individual cardiomyocyte. The cardiomyocytes themselves are aggregated together within the supporting fibrous matrix to form a three-dimensional mesh. Although the majority of the aggregates are then aligned in a relatively tangential fashion, a significant population are orientated in a transmural fashion. It is the inter-relationship of the tangential and transmural population within the three-dimensional mesh that likely underscores the mural antagonism now known to exist during ventricular contraction.