A New Quantitative Method for Assessing the Ultrastructure of Cardiomyocyte Mitochondria of the Right Atrial Appendage

The aim of this study was to develop a quantitative method for assessing the ultrastructure of cardiomyocyte mitochondria in the right atrial appendage of patients with chronic heart failure (CHF).

Materials and Methods. A single-center prospective study included 39 patients aged 67 [58; 71] years who underwent coronary artery bypass grafting. The inclusion criteria were as follows: heart failure with a left ventricular ejection fraction of <50%, atherosclerotic plaques in two or more large coronary arteries of 70% or greater, and the cardiac team’s decision to perform coronary artery bypass grafting. To perform electron microscopy, biopsy samples were collected from the right atrial appendage during coronary artery bypass grafting. Two calculated parameters were used for the analysis: “total area of interfibrillar mitochondria” and “ratio of outer to inner membrane length”. Based on these, the total index was calculated by the formula: the “total area of interfibrillar mitochondria” / the “ratio of outer to inner membrane length”.

Results. The median values of the calculated parameters characterizing the ultrastructure of cardiomyocyte mitochondria in the right atrial appendage were as follows: 43.7 [35.9; 54.3]% for the “total area of interfibrillar mitochondria”, 31 [25; 37]% for the “ratio of outer to inner membrane length”, and 1.4 [0.95; 2.00] for the total index accounting for both ultrastructural characteristics of mitochondria: the “total area of interfibrillar mitochondria” / the “ratio of outer to inner membrane length”.

To assess the clinical significance of the proposed total index, associations between the obtained values and atrial fibrillation (AF) were studied. Mitochondrial ultrastructural changes were more pronounced in patients with both AF and CHF. However, some parameters had no statistically significant differences: the total area of interfibrillar mitochondria was lower in patients with AF (42% vs 49%, p=0.224), and the ratio of outer to inner membrane length was higher in patients with AF (35% vs 31%, p=0.125). The total index was significantly lower in patients with AF (0.96 vs 1.75, p=0.021). ROC analysis was performed to identify a connection between total index and AF, and AUC was 0.773 (p=0.021).

Conclusion. The proposed total index for analyzing cardiomyocyte micrographs, calculated as the “total area of interfibrillar mitochondria” / the “ratio of outer to inner membrane length”, provides a comprehensive characterization of mitochondria that accounts not only for their number and size but also for their internal structure.

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Kuzheleva E.A., Garganeeva A.A., Tukish O.V., Syromyatnikova E.E., Dorzhieva B.B., Kondratiev M.Yu., Andreev S.L. A New Quantitative Method for Assessing the Ultrastructure of Cardiomyocyte Mitochondria of the Right Atrial Appendage. Sovremennye tehnologii v medicine 2026; 18(2): 54, https://doi.org/10.17691/stm2026.18.2.05