Mitochondrial distribution in tachycardiomyopathy

Moritz Mayer (Regensburg)1, L.-M. Köhler (Regensburg)1, M. Paulus (Regensburg)1, S. Iberl (Regensburg)1, S. Wagner (Regensburg)1, C. Brochhausen-Delius (Mannheim)2, L. S. Maier (Regensburg)1, A. Dietl (Regensburg)1

1Universitätsklinikum Regensburg Klinik und Poliklinik für Innere Med. II, Kardiologie Regensburg, Deutschland; 2Universitätsklinikum Mannheim Allgemeine Pathologie und Pathologische Anatomie Mannheim, Deutschland


Introduction: Tachycardiomyopathy is induced by high ventricular rate, leads to reversible systolic dysfunction and signs of heart failure. It entails a specific metabolic fingerprint, setting it apart from ischemic and dilated cardiomyopathy. In animal models as in patients, the mitochondrial network shifts to the intercalated discs (enrichment of mitochondria at intercalated discs, EMID), accompanied by a specific pattern of dysfunctions. In pathology, EMID sign has relied on investigator-based grading so far and subtle alterations may have been missed by eye-balling, as an objective software tool has been missing hitherto.

Study aim: We set out to create a novel software tool for the quantitative assessment of mitochondrial allocation in tachycardiomyopathy to overcome qualitative analyses.

Methods: Permanent pacemakers were implanted in rabbits. Tachypacing was performed progressively with frequencies up to 380 bpm for 30 days (T-CM, n=4). In sham operated animals (SHAM, n = 6), pacemakers remained inactive. Right and left ventricular specimens were harvested. Confocal microscopy visualized mitochondrial allocation (HSP60) with relation to the intercalated discs (N-Cadherin). Images were analyzed for histogram, grey-level co-occurrence matrix derived and dislocation parameters using a novel in-house Matlab script. Mitochondrial ultrastructure was scrutinized by transmission electron microscopy. 

Results: T-CM animals showed systolic dysfunction (T-CM vs. SHAM, fractional shortening 19.5 vs. 34.6%, p=0.001) and developed heart failure syndrome (pleural and pericardial effusion, ascites). Confocal microscopy showed EMID sign in T-CM (Figure, A). Intensity of mitochondrial signals (HSP60) decreased in both ventricles of T-CM compared to SHAM (LV: Mean IntensityT-CM = 6792, Mean IntensitySHAM = 10258, p < 0.0001). Mitochondria formed giant agglomerations in T-CM as visualized by transmission electron microscopy. A novel tool based on grey-level co-occurrence matrix analyses derived descriptors for heterogeneity in texture showed precise measures of mitochondrial agglomeration, which were in good accordance with transmission electron microscopy (Figure, B). Distances of mitochondria to the intercalated discs decreased in T-CM (Figure, C), supporting the visual EMID sign.

Conclusion: The presented findings illustrate that quantitative descriptors of texture and distribution can measure the displacement of mitochondria in tachycardiomyopathy. Further evaluation for sensitivity and potential diagnostic use in human tachycardiomyopathy are subjected to future studies.

Figure description: Analyses of mitochondrial distribution in left ventricular specimens of tachycardiomyopathy (T-CM) versus sham (SHAM) based on confocal microscopy 

(A) Negative image of HSP60 staining in T-CM group (left) and SHAM (right, red circle = nucleus, yellow line = intercalated disc) (B) Receiver-Operating-Characteristic (ROC) plot for grey-level Co-occurrence matrix (GLCM) derived descriptor Angular Second Moment of HSP60 stained images in T-CM and SHAM (C) Results of quantitative parameter of dislocation to the intercalated disc (ID) in T-CM and SHAM 

T-CM: tachycardiomyopathy

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