In this study of patients with AMI and concomitant bacterial infection, the main findings were as follows: (1) In-hospital deaths and heart failure were significantly more common in AMI patients with concomitant bacterial infection compared with those without bacterial infection. (2) It is the first time to use the CRP to platelet ratio to distinguish AMI with concomitant bacterial infection from other AMI patients. The combination of CRP > 8.05 mg/L and CRP/PLA > 0.08*10− 9mg was the best hallmark of AMI complicating bacterial infections.
The leading cause of death worldwide is AMI, a systemic, lipid-driven immune inflammatory disease. Acute bacterial infections such as influenza, pneumonia, acute bronchitis, urinary tract bacterial infection and bacteremia[2–5] usually induce or accompany AMI and lead to worse outcomes and longer hospital stays. Based on previous studies, Serious bacterial infection of AMI patients was not only resulted in longer hospital stay, but also associated with significantly higher rates of 90-day death[15]. Among the possible mechanisms is an increase in inflammation in atheromatous plaques during infection [7]. When an acute bacterial infection causes a prothrombotic, procoagulant state, the risk of coronary thrombosis increases [8, 9]. The up regulation of the metabolic needs of peripheral tissues and organs[10], and the cardiac lesions that are characterized by vacuolization and loss of myocytes without accumulation of inflammatory cells caused by pneumococcal bacteremia[11].
In our research, a 4 times increased risk of in-hospital mortality of concomitant bacterial infection subjects compared with other AMI patients, and 3 times of heart failure. The percentage of heart failure in AMI with concomitant bacterial infection patients gradually increasing with age, while the mortality was no difference between age༜75 and age ≥ 75 groups maybe because of the small sample size of deaths in these two groups. After adjusting confounders (age, gender, hypertension, diabetes, anemia and some risk factors), AMI with concomitant bacterial infection was no relationship with all-cause mortality and the mortality of shock was 12 times compared to other groups. The effect of bacterial infection on mortality maybe occurred through cardiogenic shock. It is responsible for concomitant bacterial infection to a worse prognosis of AMI patients. Healthcare providers must acknowledge these risks and not dismiss the fever and the elevation of bacterial infection biomarkers as trivial events in patients with AMI. It is an urgent need to determine whether the fever and the elevation of bacterial infection biomarkers are due to the MI, to a concomitant bacterial infection, or to other causes of systemic inflammation when an AMI patient is at admission.
Leukocytes is one of the markers of bacterial infection. Acute bacterial infections are characterized by mature and immature neutrophils. But leukocytosis is only a suggestion but not a diagnosis of bacterial infection. According to the Van den Brule A’s research, the sensitivity and specificity of leukocytosis in diagnosing acute appendicitis are 62% and 75%, respectively[16, 17]. Leukocytes also play an important role in the pathophysiology of AMI, such as permeating endothelial cells, inducing the formation of micro vascularity there, and making plaques more susceptible to rupture[18]. According to the research of Hilde E. et, al, leukocyte count increased across the coronary vascular decease continuum, which mainly depended on the increase in neutrophil count[19].
A hyperactive CRP is detected during inflammatory illnesses like rheumatoid arthritis, cardiovascular disease, and bacterial infection [20, 21]. According to Healy and Freedman’s research, CRP level increased in all bacterial infection cases compared to non-bacterial infection cases. But there is no differences between the bacterial infection types[22]. So, CRP is a marker of bacterial infection and inflammation. Since that the atherosclerosis is a systematic chronic inflammatory process, it may result in detectable levels of acute phase reactants and pro-inflammatory cytokines in the blood. Myocardial infarction and unstable angina are associated with elevated CRP; high levels of these factors predict a poor outcome [23–25].
From what has been discussed above, most of the biomarkers of bacterial infection are also present high levels in AMI. So, one of the main interests of our work was to find out the best biomarker to distinguish AMI patients with concomitant bacterial infection from other AMI patients. It is the first time to use the CRP to platelet ratio (CRP/PLA) to distinguish it. Our results showed that the AUC of CRP and CRP/PLA were over 0.8. The sensitivity of CRP and the specificity of CRP/PLA were highest. The logistic regression also revealed that the two biomarkers associated with a higher risk of bacterial infection. The combination of CRP > 8.05 mg/L and CRP/PLA > 0.08*10− 9mg was the best hallmark of AMI with concomitant bacterial infection. Currently, there is no published data to confirm our results, and further prospective studies are clearly needed to better understand CRP/PLA.
Several limitations have to be acknowledged. Firstly, limited data concerning acute bacterial infection and coronary angiography characteristics were collected, as about 15% patients did not undergo coronary angiography and the symptoms of bacterial infection were not typical. Secondly, further prospective studies are needed to address the relative risk (RR) of CRP/PLA in AMI with concomitant bacterial infection. Lastly, further classification of bacterial infection should be made to detect the value of CRP/PLA in different kinds of bacterial infection.