Large scale analysis of atrial structure and geneexpression in patients with atrial fibrillationCitation for published version (APA):

Winters, J. (2021). Large scale analysis of atrial structure and gene expression in patients with atrialfibrillation. Maastricht University. https://doi.org/10.26481/dis.20211208jw

Document status and date:Published: 01/01/2021

DOI:10.26481/dis.20211208jw

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Download date: 15 Mar. 2022

APPENDIX B

IMPACT PARAGRAPH

B

Impact | 159

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and is associated with increased mortality4-6. Moreover, AF increases the risk for several cardiovascular or cerebral complications. Aging of the population and better treatment of acute heart disease resulted in more cases of AF, posing a challenge to contemporary health care management1,

2. The number of AF patients in Europe is expected to increase to 13 million patients in the EU by 20303. Irregular electrical activation of the heart results in symptoms of palpitations, shortness of breath, fatigue, cognitive impairment and dementia. Furthermore, AF is associated with cardiac comorbidities such as heart failure7 and significantly increase stroke risk8, 9, ultimately resulting in a high hospitalization rate4, 10 .

Typically, AF patients seek medical care as a consequence of symptomatic burden. One of the main goals of AF therapy is therefore to alleviate symptomatic burden by controlling heart rate and restoring normal sinus rhythm. Another important therapeutic strategy focusses on reducing stroke risk by administering anticoagulants. These therapeutic options are not always targeting the mechanisms that initially trigger AF or that are required to sustain the arrhythmia. AF patients could benefit from mechanism-based therapeutic models. Therefore, we need to improve our ability to recognize pro-arrhythmic mechanisms in individual patients. The development of mechanism-based therapeutic models thus relies on accurate characterization of individual disease mechanisms in AF patients and the translation of these mechanisms into functional parameters that can be measured non-invasively in the clinic.

This thesis offers stepping stones for a better understanding of the molecular processes ongoing in the myocardium of the left and right atria, focusing on gene expression changes associated with persistent AF and on careful assessment of tissue structure. Therefore, we applied state-of-the-art next generation sequencing technology, which allows for direct analysis of expression changes in the atrial transcriptome, the collection of mRNA molecules expressed from the genes. Doing so, we significantly improved our understanding of the transcriptomic differences between left and right atria and showed that these differences could be involved in AF and heart failure pathophysiology. Moreover, we identified 33 novel transcripts that are differentially expressed in persistent AF patients, independent of heart failure status. We also note that heart failure had a much stronger effect on the atrial transcriptome than AF in our data, but that the interaction of heart failure and AF does not result in even more alterations of the transcriptome. These results aid our understanding of the genetic background underlying AF.

In the second part of the thesis, we focused on accurate visualization of fibrosis, the thickening of connective tissue in the atrial tissue. Fibrosis is often described as a reparative response following injury to the myocardium and cell death. Fibrosis can, however, also be a reactive process following increased stress or pressure on the myocardial tissue. In the last chapters of this dissertation, we studied fibrosis in between cardiomyocytes, endomysial fibrosis. Prior research suggested that this type of fibrosis could cause conduction disturbances, a pro-arrhythmic process. Unfortunately, frequently used methods used to visualize and analyze fibrosis are not sensitive enough to clearly contrast fibrotic tissue from cardiomyocytes. Consequently, large areas of fibrosis can be studied, but endomysial fibrosis in between cardiomyocytes is often not adequately visualized. We therefore developed a technique

160 | Appendix B

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to clearly visualize various types of fibrosis and automatically analyze the obtained images in a standardized way. This technique proved successful in identifying endomysial fibrosis independent of the observer and can be used to simultaneously study other structural characteristics in the myocardium. Therefore, this technique could be applied in many future studies to analyze multiple structural features in the atria in the context of AF or other pathologies. Our algorithm is used to explore histological changes in cardiac tissue also outside the CATCH-ME study. Examples are the RACE V consortium in the Netherlands (https://race-v.org) and the recently funded EU consortium MAESTRIA (https://cordis.europa.eu/project/id/965286).

Applying our newly developed method to study structural changes in our study cohort, we confirmed that endomysial fibrosis is independently present in persistent AF patients, heart failure patients, female patients and is associated with increasing age. The presence of endomysial fibrosis in female patients was surprisingly strong, in the same order of effect as having persistent AF or heart failure. This could have implications in other studies, such as the development of realistic computer models for AF or mechanistic studies that aim at unraveling the biological differences in AF pathophysiology between men and women.

Finally, we looked at transcriptomic changes in the atria in function of the presence of endomysial fibrosis. We did not observe any individual transcripts associated with endomysial fibrosis, but were able to identify interesting pro-fibrotic patterns of gene expression. In follow-up projects mechanistic validation of identified pathways will be performed with the ambition to better understand the complexity of AF pathophysiology, to identify critical pathways that might serve as target mechanism for new therapeutic interventions and to identify new biomarkers that indicate the presence of individual disease mechanisms.

Finally, one of the main assets of this joined European effort was the collection of both left and right atrial appendages of clinically well-defined patients on a large scale. Besides AF, a broad range of AF-related comorbidities was represented in this patient population, allowing us to study molecular changes in the atria in diverse, real clinical situations. Collaborative efforts of this scale should be further stimulated in the future, as they help to increase statistical power needed to study the complexity of underlying AF mechanism in diverse subsets of patients11.

B

Impact | 161

References

1. Heijman J, Algalarrondo V, Voigt N, Melka J, Wehrens XH, Dobrev D, et al. The value of basic research insights into atrial fibrillation mechanisms as a guide to therapeutic innovation: a critical analysis. Cardiovasc Res. 2016;109(4):467-79.

2. Andrade J, Khairy P, Dobrev D, Nattel S. The clinical profile and pathophysiology of atrial fibrillation: relationships among clinical features, epidemiology, and mechanisms. Circ Res. 2014;114(9):1453-68.

3. Krijthe BP, Kunst A, Benjamin EJ, Lip GY, Franco OH, Hofman A, et al. Projections on the number of individuals with atrial fibrillation in the European Union, from 2000 to 2060. Eur Heart J. 2013;34(35):2746-51.

4. Stewart S, Hart CL, Hole DJ, McMurray JJ. A population-based study of the long-term risks associated with atrial fibrillation: 20-year follow-up of the Renfrew/Paisley study. Am J Med. 2002;113(5):359-64.

5. Miyasaka Y, Barnes ME, Bailey KR, Cha SS, Gersh BJ, Seward JB, et al. Mortality trends in patients diagnosed with first atrial fibrillation: a 21-year community-based study. J Am Coll Cardiol. 2007;49(9):986-92.

6. Benjamin EJ, Wolf PA, D’Agostino RB, Silbershatz H, Kannel WB, Levy D. Impact of atrial fibrillation on the risk of death: the Framingham Heart Study. Circulation. 1998;98(10):946-52.

7. Wang TJ, Larson MG, Levy D, Vasan RS, Leip EP, Wolf PA, et al. Temporal relations of atrial fibrillation and congestive heart failure and their joint influence on mortality: the Framingham Heart Study. Circulation. 2003;107(23):2920-5.

8. Marini C, De Santis F, Sacco S, Russo T, Olivieri L, Totaro R, et al. Contribution of atrial fibrillation to incidence and outcome of ischemic stroke: results from a population-based study. Stroke. 2005;36(6):1115-9.

9. Miyasaka Y, Barnes ME, Gersh BJ, Cha SS, Seward JB, Bailey KR, et al. Time trends of ischemic stroke incidence and mortality in patients diagnosed with first atrial fibrillation in 1980 to 2000: report of a community-based study. Stroke. 2005;36(11):2362-6.

10. Steinberg BA, Kim S, Fonarow GC, Thomas L, Ansell J, Kowey PR, et al. Drivers of hospitalization for patients with atrial fibrillation: Results from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF). Am Heart J. 2014;167(5):735-42 e2.

11. Schotten U. From translation to integration: how to approach the complexity of atrial fibrillation mechanisms. Cardiovasc Res. 2021;117(7):e88-e90.