Pneumatic Distension of Ventricular Mural Architecture Validated Histologically

Abstract

▼Purpose: There are ongoing arguments as to how cardiomyocytes are aggregated together within the ventricular walls. We used pneumatic distension through the coronary arteries to exaggerate the gaps between the aggregated cardiomyocytes, analyzing the pattern revealed using computed tomography, and validating our findings by histology. Methods: We distended 10 porcine hearts, arresting 4 in diastole by infusion of cardioplegic solutions, and 4 in systole by injection of barium chloride. Mural architecture was revealed by computed tomography, measuring also the angulations of the long chains of cardiomyocytes. We prepared the remaining 2 hearts for histology by perfusion with formaldehyde. Results: Increasing pressures of pneumatic distension elongated the ventricular walls, but produced insignificant changes in mural thickness. The distension exaggerated the spaces between the aggregated cardiomyocytes, compartmenting the walls into epicardial, central, and endocardial regions, with a feathered arrangement of transitions between them. Marked variation was noted in the thicknesses of the parts in the different ventricular segments, with no visible anatomical boundaries between them. Measurements of angulations revealed intruding and extruding populations of cardiomyocytes that deviated from a surface-parallel alignment. Scrolling through the stacks of tomographic images revealed marked spiraling of the aggregated cardiomyocytes when traced from base to apex. Conclusion: Our findings call into question the current assumption that cardiomyocytes are uniformly aggregated together in a tangential fashion. There is marked heterogeneity in the architecture of the different ventricular segments, with the aggregated units never extending in a fully transmural fashion.This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.

What is the clinical significance of ventricular mural antagonism?

“…The ventricular walls are composed of chains of cardiomyocytes connected together in end-to-end fashion. In combination with the dense endomysium, myocytic branches serve to aggregate the individual cardiomyocytes into units described as lamellae, or sheets [13,[16][17][18][19][20][21][22][23][24][25][26][27]29]. These aggregated units of cardiomyocytes are markedly heterogeneous in dimensions and shape [25][26][27]],…”

“…So as to further assess the global nature of this variability, we injected compressed air through the coronary arteries of porcine and bovine hearts, thus pneumatically distending the loose perimysial spaces and making the aggregated units and their associated myocytic connecting branches clearly discernible. When imaged using computed tomography, and the short-axis slices (tomograms) viewed sequentially [28,29], a complex structural pattern is observed. Ascending sub-epicardial and descending subendocardial aggregates are connected by a heterogeneously distributed circumferential zone in between.…”

Antagonism of contractile forces in left ventricular hypertrophy: a diagnostic challenge for better pathophysiological and clinical understanding

“…During the last 50 years, morphological research unanimously has shown that the parallel alignment of the myocardial fibres based on Frank's understanding must be replaced by associations of sequentially splitted myocytes forming a continuous spatial network of endless chains of myocytes with no origin or insertion (figure 2). [27][28][29][30][31][32][33][34] Less than a hundred chains are bundled and surrounded by connective tissue to form aggregates with muscle fibres of different orientation 35 (figure 3). Smaller fibres of endless chains form the connection between respective aggregates as a strong network between two adjacent entities.…”