Pediatric Heart Failure: Cardiac Ejection Fraction with Cardiomyopathy Decreased to 21% in Iron Deficient from 37% in Iron Sufficient Children

Introduction: The overall aim of our study was to determine if iron deficiency has harmful effects on cardiac function in children with chronic heart failure. Heart failure in children is a complex, heterogeneous disorder leading to a final common pathway of cardiomyocyte dysfunction and attrition. Cellular, animal, and human studies have shown that iron deficiency causes cardiomyocyte dysfunction that can be reversed with iron treatment. Cellular studies of human iron-deficient cardiomyocytes have shown that supplemental iron restores impaired contractility and relaxation. Animal studies have found that cardiomyocyte-specific deletions or alterations of critical iron proteins (transferrin receptor 1, hepcidin, ferroportin) produce cardiomyocyte iron deficiency (without anemia) and result in ultimately fatal cardiac dysfunction that can be rescued with intravenous (IV) iron. Over half of adults with chronic heart failure are iron deficient. Meta-analysis of small randomized clinical trials has shown that IV iron significantly reduces recurrent hospitalization, cardiovascular mortality, and all-cause mortality in iron deficient adults with heart failure. European Society of Cardiology, American College of Cardiology and American Heart Association guidelines recommend consideration of IV iron therapy for adult iron-deficient patients with heart failure.

The prevalence and consequences of iron deficiency in children with heart failure have not been established. Previously, two small retrospective studies of children with heart failure have reported that 56% to 96% were iron deficient, with increased morbidity and mortality. The goals of our study of children with heart failure were to determine (i) how often iron status is assessed, (ii) the prevalence of iron deficiency, and (iii) the effects of iron deficiency on cardiac function in patients with cardiomyopathy.

Methods: We retrospectively reviewed electronic medical records to identify pediatric patients ages 1-21 years old seen at Columbia University Irving Medical Center Pediatric Heart Failure clinic with absolute iron deficiency during 2010-2020. Heart failure was defined as presence of symptoms or systolic dysfunction by echocardiography. Patients were excluded with a history of heart transplant, isolated diastolic failure, or renal failure requiring dialysis. In adults with heart failure, a transferrin saturation <20% has a sensitivity of 94% and a specificity of 84% in identifying absolute iron deficiency, as determined from a bone marrow aspirate, and iron stores were present in 100% of patients with a transferrin saturation ≥30% (Circ Heart Fail. 2018;11:e0045). In children with heart failure, we used these criteria to define absolute iron deficiency as a transferrin saturation <20% and iron sufficiency as a transferrin saturation ≥30%.

Patients with an intermediate transferrin saturation are likely a mixture of absolute and functional iron deficiency, and of iron sufficiency and were excluded from our analysis of cardiomyopathy. Cardiac ejection fraction was evaluated by an echocardiogram performed within 3 months of measurement of transferrin saturation.

Results: Of 579 patients with heart failure, only 159 (27%) had any type of laboratory iron studies. Of patients with iron studies, 81 (51%) were evaluated as outpatients; 49% as inpatients. The cause of heart failure was cardiomyopathy (52%), congenital heart disease (34%), acute myocarditis (6%), and other (8%).

In the 82 patients with heart failure due to cardiomyopathy, 39 (48%) were iron deficient and 16 (20%) iron sufficient. In the iron deficient children with cardiomyopathy, the left ventricular ejection fraction was lower than in the iron sufficient patients (median 21% vs. 37%; p=0.03 (Mann-Whitney); Figure). The groups did not differ significantly with respect to hemoglobin (Figure), sex, age, or New York Heart Association class.

Conclusion: We report a clinically important decrease in cardiac ejection fraction in children with heart failure due to cardiomyopathy who have absolute iron deficiency. Potentially, iron treatment could safely and effectively reverse the harmful effect of iron deficiency on heart function and prospective randomized trials of oral and intravenous iron therapy are urgently needed. Measurement of iron status should routinely be included in the evaluation of children with heart failure.

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