Serum iron concentration, but not hemoglobin, correlates with TIMI risk score and 6-month left ventricular performance after primary angioplasty for acute myocardial infarction

Abstract

Objective: Anemia is associated with high mortality and poor prognosis after acute coronary syndrome (ACS). Increased red cell distribution width (RDW) is a strong independent predictor for adverse outcomes in ACS. The common underlying mechanism for anemia and increased RDW value is iron deficiency. It is not clear whether serum iron deficiency without anemia affects left ventricular (LV) performance after primary angioplasty for acute myocardial infarction (AMI). We investigated the prognostic value of serum iron concentration on LV ejection fraction (EF) at 6 months and its relationship to thrombolysis in myocardial infarction (TIMI) risk score in post MI patients.

Methods: We recruited 55 patients who were scheduled to undergo primary coronary balloon angioplasty after AMI and 54 age- and sex-matched volunteers. Serum iron concentration and interleukin-6 levels were measured before primary angioplasty. LVEF was measured by echocardiography at baseline and after 6 months. TIMI risk score was calculated for risk stratification.

Results: Serum iron concentration was significantly lower in those in whom LVEF had not improved ≥ 10% from baseline (52.7 ± 24.1 versus 80.8 ± 50.8 µg/dl, P = 0.016) regardless of hemoglobin level, and was significantly lower in the AMI group than in the control group (62.5 ± 37.7 versus 103.0 ± 38.1 µg/dl, P<0.001). Trend analysis revealed that serum iron concentration decreased as TIMI risk score increased (P = 0.002). In addition, lower serum iron concentrations were associated with higher levels of inflammatory markers. Multiple linear regression showed that baseline serum iron concentration can predict LV systolic function 6 months after primary angioplasty for AMI even after adjusting for traditional prognostic factors.

Conclusion: Hypoferremia is not only a marker of inflammation but also a potential prognostic factor for LV systolic function after revascularization therapy for AMI, and may be a novel biomarker for therapeutic intervention.

Figure 1. The relationships between serum iron concentration and TIMI risk scores after primary angioplasty for AMI.

The AMI patients were divided into four subgroups according to TIMI risk score for STEMI: Group 1 (TIMI risk score 1, n = 8); Group 2 (TIMI risk score 2, n = 15); Group 3 (TIMI risk score 3, n = 19); and Group 4 (TIMI risk score ≥4, n = 13). Trend analysis with Jonckheere-Terpstra test found that serum iron concentration significantly decreased as TIMI risk score rose (P = 0.002).

Figure 2. The relationship between serum iron concentration and IL-6 levels in all enrolled subjects.

The result indicated that the serum iron concentration was negatively correlated with circulating IL-6 concentration in all study subjects. The linear relationship was well described by Serum iron = 95.994−1.246 (IL-6), R² = 0.133 and P<0.001.

Figure 3. Trend analysis showed serum iron concentration was inversely proportional to IL-6 concentration in STEMI patients.

AMI patients were divided into three subgroups according to circulating IL-6 concentration tertile: group 1, IL-6 concentration ≤10.48 pg/ml (n = 19); group 2, IL-6 concentration between 10.49–19.67 pg/ml (n = 20); group 3, IL-6 concentration ≥19.68 pg/ml (n = 16). Trend analysis showed serum iron concentration was inversely proportional to IL-6 concentration. (Jonckheere-Terpstra test, P = 0.043).