with implications that may extend to cardiovascular disease in general.
In the study involving more than 900 patients with PH, investigators at seven U.S. centers determined the prevalence of iron deficiency by two separate definitions and assessed its associations with functional measures and quality of life (QoL) scores.
An iron deficiency definition used conventionally in heart failure (HF) – ferritin less than 100 g/mL or 100-299 ng/mL with transferrin saturation (TSAT) less than 20% – failed to discriminate patients with reduced peak oxygen consumption (peakVO2), 6-minute walk test (6MWT) results, and QoL scores on the 36-item Short Form Survey (SF-36).
But an alternative definition for iron deficiency, simply a TSAT less than 21%, did predict such patients with reduced peakVO2, 6MWT, and QoL. It was also associated with an increased mortality risk. The study was published in the European Heart Journal.
“A low TSAT, less than 21%, is key in the pathophysiology of iron deficiency in pulmonary hypertension” and is associated with those important clinical and functional characteristics, lead author Pieter Martens MD, PhD, said in an interview. The study “underscores the importance of these criteria in future intervention studies in the field of pulmonary hypertension testing iron therapies.”
A broader implication is that “we should revise how we define iron deficiency in heart failure and cardiovascular disease in general and how we select patients for iron therapies,” said Dr. Martens, of the Heart, Vascular & Thoracic Institute of the Cleveland Clinic.
Iron’s role in pulmonary vascular disease
“Iron deficiency is associated with an energetic deficit, especially in high energy–demanding tissue, leading to early skeletal muscle acidification and diminished left and right ventricular (RV) contractile reserve during exercise,” the published report states. It can lead to “maladaptive RV remodeling,” which is a “hallmark feature” predictive of morbidity and mortality in patients with pulmonary vascular disease (PVD).
Some studies have suggested that iron deficiency is a common comorbidity in patients with PVD, their estimates of its prevalence ranging widely due in part to the “absence of a uniform definition,” write the authors.
Dr. Martens said the current study was conducted partly in response to the increasingly common observation that the HF-associated definition of iron deficiency “has limitations.” Yet, “without validation in the field of pulmonary hypertension, the 2022 pulmonary hypertension guidelines endorse this definition.”
As iron deficiency is a causal risk factor for HF progression, Dr. Martens added, the HF field has “taught us the importance of using validated definitions for iron deficiency when selecting patients for iron treatment in randomized controlled trials.”
Moreover, some evidence suggests that iron deficiency by some definitions may be associated with diminished exercise capacity and QoL in patients with PVD, which are associations that have not been confirmed in large studies, the report notes.
Therefore, it continues, the study sought to “determine and validate” the optimal definition of iron deficiency in patients with PVD; document its prevalence; and explore associations between iron deficiency and exercise capacity, QoL, and cardiac and pulmonary vascular remodeling.