Complex relationship between iron status and outcomes of STEMI: hypothesis-generating study

Iron deficiency (ID) is common amongst patients with ST-elevation myocardial infarction (STEMI). Its impact on outcomes remains contested. Previous studies reported favourable or adverse impacts depending on outcome measures, sampling timepoints, ID definition and follow-up duration. This study systematically characterises the prognostic impact of iron status on short-term, mid-term and long-term outcomes, and evaluates the effect of sampling timepoint and ID definition on these prognostic relationships.

We performed an observational cohort study in patients with acute STEMI (n = 167) and no prior heart failure (HF). Iron markers were sampled at presentation, and successive timepoints thereafter. Cardiac Magnetic Resonance was performed at 2 days and 6 months. Major adverse cardiovascular events (MACE), consisting of new-onset HF, recurrent MI or cardiac death were recorded over 4.5 years. Mechanisms were evaluated in a preclinical model of MI.ID was common at presentation, affecting between 44.9% and 67%, depending on ID definition. Tsat <20%, serum iron<13μM, or European Society of Cardiology's definition, but not ferritin<100μg/L, independently predicted lower risk of MACE. Lower Tsat at presentation predicted attenuated infarct and non-infarct T1, and smaller left ventricular volumes at 2 days. This prognostic effect was weakened by delayed sampling. Lower Tsat and serum iron in the post-acute timepoints, but not at presentation, predicted lower myocardial salvage at 6 months. In mice, MI triggered an acute myocardial labile iron storm and early LV remodelling, progressing to HF. Baseline ID and acute iron chelation averted these effects.

This study gives rise to the hypothesis that ID at presentation with STEMI improves long-term outcomes by attenuating myocardial injury. It reconciles previous conflicting reports by revealing the confounding effects of delayed sampling, and non-interchangeability of different ID definitions. It suggests iron chelation in the acute stage, followed by post-acute iron repletion might improve long-term outcomes.