Ferric carboxymaltose has a higher distribution into myocardium than gadobutrol - a quantitative T1 mapping study in healthy volunteers

ObjectivesThe dynamic tissue distribution of the clinically available intravenous iron substitution agent ferric carboxymaltose (FCM) is largely unknown. We aimed to evaluate and quantify the dynamic tissue distribution of FCM using cardiovascular magnetic resonance (CMR). Materials and methodsT1 mapping was prospectively performed to determine T1 and the partition coefficient (lambda) in myocardium, liver, spleen and skeletal muscle up to 60 minutes after onset of a 15-minute-long infusion of 20 ml (50 mg iron/ml) FCM in healthy male volunteers. For comparison, myocardial lambda for gadobutrol (0.2 mmol/kg) was measured in a separate group of age-matched healthy male volunteers. The t-test was used for group comparisons. ResultsA total of 25 healthy males (mean{+/-}SD age 27{+/-}3 years) underwent CMR with intravenous FCM (n=8) or gadobutrol (n=17). T1 values decreased in myocardium, blood, liver, spleen and skeletal muscle following FCM infusion (p < 0.001 for all). Lambda for FCM in myocardium and spleen remained constant over time after injection of FCM (mean{+/-}SEM 64{+/-}8% and 81{+/-}20%, respectively, at 30 minutes), while liver and skeletal muscle lambda increased. Myocardial lambda for FCM was higher than myocardial lambda for gadobutrol (64{+/-}8 vs 45{+/-}1%, p=0.003). ConclusionsT1 mapping can detect and quantify the dynamic tissue distribution of iron from FCM in the myocardium, liver, spleen, and skeletal muscle. Higher myocardial lambda for FCM compared to gadobutrol, indicating that FCM distributes to a greater extent into the myocardium than extracellular contrast agents, most likely due to additional distribution into the intracellular space. Key pointsO_LIUnderstanding iron physiology in heart failure is crucial, as intravenous iron therapy by ferric carboxymaltose (FCM) improves cardiac function. C_LIO_LIT1 mapping effectively measures FCM in myocardium, showing higher myocardial distribution than gadobutrol, likely due to additional intracellular distribution. C_LIO_LIThis technique offers new insights into myocardial iron physiology in both healthy and diseased hearts. C_LI