The weight of the evidence to date seem to suggest that non-blood group O may be associated with non-valvular atrial fibrillation (NVAF)-related peripheral cardioembolic complications, myocardial infarction (MI) and ischemic stroke. ^1-4

A 2015 retrospective Mayo Clinic study involving patients with NVAF adjusted for CHADS₂ score found significantly lower rate of peripheral embolization in those with blood group O compared to those with other blood groups combined (3% vs 2%, O.R. 0.66, 95% CI, 0.5-0.8); rates of cerebral thromboembolic events were not significantly different between the 2 groups, however. ¹

A 2008 systematic review and meta-analysis of studies spanning over 45 years reported a significant association between non-O blood group and MI, peripheral vascular disease, cerebral ischemia of arterial origin, and venous thromboembolism.² Interestingly, the association was not significant for angina pectoris or for MI when only prospective studies were included.  Some studies have reported that the association between von Willebrand factor (VWF) and the risk of cardiovascular mortality may be independent of blood group. ^5,6

Although the apparent lower risk of thromboembolic conditions in O blood group patients may be due to lower levels of VWF and factor VIII in this population ^1,4, other pathways likely  play a role.⁷  

As for why the rate of peripheral (but not cerebral) thromboembolic events in NVAF is affected by blood group, one explanation is that because of their size, larger clots (facilitated by lower VWF levels) may bypass the carotid and vertebral orifices in favor of their continuation downstream to the “peripheral bed”.¹

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References

1. Blustin JM, McBane RD, Mazur M, et al. The association between thromboembolic complications and blood group in patients with atrial fibrillation. Mayo Clin Proc 2015;90;216-23. https://www.sciencedirect.com/science/article/abs/pii/S002561961401043X
2. Wu O, Bayoumi N, Vickers MA, et al. ABO (H) groups and vascular disease: a systematic review and meta-analysis. J Thromb Haemostasis 2008;6:62-9. https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1538-7836.2007.02818.x
3. Medalie JH, Levene C, Papier C, et al. Blood groups, myocardial infarction, and angina pectoris among 10,000 adult males. N Engl J Med 1971;285:1348-53. https://www.nejm.org/doi/pdf/10.1056/NEJM197112092852404
4. Franchini M, Capra F, Targher G, et al. Relationship between ABO blood group and von Willebrand factor levels: from biology to clinical implications. Thrombosis Journal 2007, 5:14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2042969/
5. Meade TW, Cooper JA, Stirling Y, et al. Factor VIII, ABO blood group and the incidence of ischaemic heart disease. Br J Haematol 1994;88:601-7. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2141.1994.tb05079.x
6. Jager A, van Hinsbergh VW, Kostense PJ, et al. von Willebrand factor, C-reactive protein, and 5-year mortality in diabetic and nondiabetic subjects: the Hoorn Study. Arterioscl Thromb Vasc Biol 1999;19:3071-78. https://www.researchgate.net/publication/12709043_von_Willebrand_Factor_C-Reactive_Protein_and_5-Year_Mortality_in_Diabetic_and_Nondiabetic_Subjects_The_Hoorn_Study
7. Sode BF, Allin KH, Dahl M, et al. Risk of venous thromboembolism and myocardial infarction associated with factor V Leiden and prothrombin mutations and blood type. CMAJ 2013.DOI:10.1503/cmaj.121636. https://www.ncbi.nlm.nih.gov/pubmed/23382263