Very interesting read. On the quiz it mentioned PE was unlikely as the clots only tend to form in the left atrium. Is there any reason for this? I’d always assumed it could form in either.
This is a very interesting question. We know that the prevalence of atrial thrombosis is significantly higher in the left atrium compared to the right atrium.
Generally, the reasons for atrial thrombogenesis in AF are:
1) activation of the clotting system
2) low blood flow
3) endothelial damage [1]
As per the Assessment of Cardioversion Using Transesophageal Echocardiography (ACUTE) trial [2]:
- Atrial thrombosis is the most common complication of AF (up to 13% of AF cases)
- 88.2% of thrombi localised in the LAA (left atrial appendage)
- 11.8% of thrombi localised in the RA/RAA (right atrium/ right atrial appendage)
The reasons why there is a difference in the prevalence of thrombogenesis between the right and left atrium are not well understood. However, there is evidence for the following:
1) THE RIGHT ATRIUM HAS BETTER FLOW:
In a 2016 study, 3D structures of the right atrial appendage (RAA) and left atrial appendage (LAA) were created. They concluded that the RAA appears to be suited for a more favorable blood flow, which may explain why the thrombus formation is less common in RAA than in LAA. [3]
2) THERE IS A PRO-COAGULABLE STATE IN THE LEFT ATRIUM IN AF:
In another study, they found that there is impaired protein C activation on the left atrial endocardium attributable to low thrombomodulin expression. [4]
Remember the role of protein C, which is to regulate coagulation, by inactivating the procoagulation factors Va (FVa) and VIIIa (FVIIIa), that promote the generation of thrombin from its precursor molecule prothrombin. Therefore, protein C activation leads to thrombin inactivation; therefore, protein C INHIBITS blood clotting (and protein C is inhibited in the left atrium more than the right atrium in AF).
So in LAA, protein C is inhibited, therefore blood clotting is PROMOTED.
I hope this answer gave you some insight into why there is a difference in the prevalence of blood clot formation between the RA and LA. Check out the references below to find out more:
Thanks for reading!
References:
1) Bukowska, A., Hammwöhner, M., Corradi, D. et al. Atrial thrombogenesis in atrial fibrillation. Herzschr Elektrophys 29, 76–83 (2018). https://doi.org/10.1007/s00399-017-0543-x
2) Degiovanni, A, Carassia, C, De Vecchi, S, Erbetta, R, Patti, G. Atrial thrombosis: Not only left, think also about right!. J Clin Ultrasound. 2022; 50(8): 1194-1201. doi:10.1002/jcu.23311
3) Shinoda K, Hayashi S, Fukuoka D, Torii R, Watanabe T, Nakano T. Structural Comparison between the Right and Left Atrial Appendages Using Multidetector Computed Tomography. Biomed Res Int. 2016;2016:6492183. doi: 10.1155/2016/6492183. Epub 2016 Nov 9. PMID: 27900330; PMCID: PMC5120179.
4) Cerveró J, Montes R, España F, Esmon CT, Hermida J. Limited ability to activate protein C confers left atrial endocardium a thrombogenic phenotype: a role in cardioembolic stroke? Stroke. 2011 Sep;42(9):2622-4. doi: 10.1161/STROKEAHA.111.614420. Epub 2011 Jun 23. PMID: 21700937; PMCID: PMC3178262.
Very interesting read. On the quiz it mentioned PE was unlikely as the clots only tend to form in the left atrium. Is there any reason for this? I’d always assumed it could form in either.
This is a very interesting question. We know that the prevalence of atrial thrombosis is significantly higher in the left atrium compared to the right atrium.
Generally, the reasons for atrial thrombogenesis in AF are:
1) activation of the clotting system
2) low blood flow
3) endothelial damage [1]
As per the Assessment of Cardioversion Using Transesophageal Echocardiography (ACUTE) trial [2]:
- Atrial thrombosis is the most common complication of AF (up to 13% of AF cases)
- 88.2% of thrombi localised in the LAA (left atrial appendage)
- 11.8% of thrombi localised in the RA/RAA (right atrium/ right atrial appendage)
The reasons why there is a difference in the prevalence of thrombogenesis between the right and left atrium are not well understood. However, there is evidence for the following:
1) THE RIGHT ATRIUM HAS BETTER FLOW:
In a 2016 study, 3D structures of the right atrial appendage (RAA) and left atrial appendage (LAA) were created. They concluded that the RAA appears to be suited for a more favorable blood flow, which may explain why the thrombus formation is less common in RAA than in LAA. [3]
2) THERE IS A PRO-COAGULABLE STATE IN THE LEFT ATRIUM IN AF:
In another study, they found that there is impaired protein C activation on the left atrial endocardium attributable to low thrombomodulin expression. [4]
Remember the role of protein C, which is to regulate coagulation, by inactivating the procoagulation factors Va (FVa) and VIIIa (FVIIIa), that promote the generation of thrombin from its precursor molecule prothrombin. Therefore, protein C activation leads to thrombin inactivation; therefore, protein C INHIBITS blood clotting (and protein C is inhibited in the left atrium more than the right atrium in AF).
So in LAA, protein C is inhibited, therefore blood clotting is PROMOTED.
I hope this answer gave you some insight into why there is a difference in the prevalence of blood clot formation between the RA and LA. Check out the references below to find out more:
Thanks for reading!
References:
1) Bukowska, A., Hammwöhner, M., Corradi, D. et al. Atrial thrombogenesis in atrial fibrillation. Herzschr Elektrophys 29, 76–83 (2018). https://doi.org/10.1007/s00399-017-0543-x
2) Degiovanni, A, Carassia, C, De Vecchi, S, Erbetta, R, Patti, G. Atrial thrombosis: Not only left, think also about right!. J Clin Ultrasound. 2022; 50(8): 1194-1201. doi:10.1002/jcu.23311
3) Shinoda K, Hayashi S, Fukuoka D, Torii R, Watanabe T, Nakano T. Structural Comparison between the Right and Left Atrial Appendages Using Multidetector Computed Tomography. Biomed Res Int. 2016;2016:6492183. doi: 10.1155/2016/6492183. Epub 2016 Nov 9. PMID: 27900330; PMCID: PMC5120179.
4) Cerveró J, Montes R, España F, Esmon CT, Hermida J. Limited ability to activate protein C confers left atrial endocardium a thrombogenic phenotype: a role in cardioembolic stroke? Stroke. 2011 Sep;42(9):2622-4. doi: 10.1161/STROKEAHA.111.614420. Epub 2011 Jun 23. PMID: 21700937; PMCID: PMC3178262.