What is the fine-grained topic of the following text: Due to the lack of significant association between ABO system versus significant association of Rh system with myocardial infarction in this study and given the findings of the other studies with no substantial evidence, further studies including more samples and other antigens of Rh system are recommended. Only return the topic.
The association between ABO and Rh blood systems and myocardial infarction.