Myocardial fibrosis activity following ST-segment elevation myocardial infarction

Abstract Background Myocardial fibrosis following myocardial infarction (MI) is a key healing mechanism and involves widespread fibroblast activation. Once activated, fibroblasts express fibroblast activation protein (FAP) (1). Hybrid positron emission tomography (PET) imaging of radiolabelled fibroblast activation protein inhibitor (FAPI) fused with cardiovascular magnetic resonance (68Ga-FAPI PET/MR) is an emerging method for assessing myocardial fibrosis activity that may provide additional insights into the recovery of the heart following MI. Methods Forty patients with acute (<4 weeks), 19 with recent (12 weeks), and 19 with prior established ST-segment elevation MI (>12 months), and 20 healthy volunteer participants underwent 68Ga-FAPI PET/MR. Participants were imaged 30 min after administration of 100-200 MBq 68Ga-FAPI-04. Image analysis was performed using FusionQuant (Cedars Sinai, Los Angeles, California). 68Ga-FAPI uptake was quantified by maximum standardised uptake value (SUVmax) and tissue-to-background ratio (TBRmax) correcting for blood-pool activity in the left ventricle. Comparisons between were assessed with one-way ANOVA with Tukey-Kramer post-hoc testing where significant differences were detected. A 2-sided p-value of <0.05 denoted statistical significance. Results Participants were predominantly middle-aged men with similar sized infarcts (peak plasma cardiac troponin concentrations and post-MI left ventricular ejection fraction) (Table). Blood pool tracer activity was also similar between groups. Focal myocardial 68Ga-FAPI uptake localised to areas of the infarct and peri-infarct zones on magnetic resonance late gadolinium enhancement imaging (Figure). Both myocardial SUVmax and TBRmax varied between infarcts of different ages, being highest in acute (TBRmax 4.1±1.2) and lowest in those with prior established MI (2.1±0.7, Table and Figure). Conclusions Fibrosis activity is greatest in the immediate aftermath of acute MI with a step-wise reduction in the weeks and years that follow. Fibrosis activity continues for many months and years after acute infarction.FigureTable