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Fontan survivors have depressed cardiac index that worsens over time. Serum biomarker measurement is minimally invasive, rapid, widely available, and may be useful for serial monitoring. The purpose of this study was to identify biomarkers that correlate with lower cardiac index in Fontan patients.
Methods and results
This study was a multi-centre case series assessing the correlations between biomarkers and cardiac magnetic resonance-derived cardiac index in Fontan patients ⩾6 years of age with biochemical and haematopoietic biomarkers obtained ±12 months from cardiac magnetic resonance. Medical history and biomarker values were obtained by chart review. Spearman’s Rank correlation assessed associations between biomarker z-scores and cardiac index. Biomarkers with significant correlations had receiver operating characteristic curves and area under the curve estimated. In total, 97 cardiac magnetic resonances in 87 patients met inclusion criteria: median age at cardiac magnetic resonance was 15 (6–33) years. Significant correlations were found between cardiac index and total alkaline phosphatase (−0.26, p=0.04), estimated creatinine clearance (0.26, p=0.02), and mean corpuscular volume (−0.32, p<0.01). Area under the curve for the three individual biomarkers was 0.63–0.69. Area under the curve for the three-biomarker panel was 0.75. Comparison of cardiac index above and below the receiver operating characteristic curve-identified cut-off points revealed significant differences for each biomarker (p<0.01) and for the composite panel [median cardiac index for higher-risk group=2.17 L/minute/m2 versus lower-risk group=2.96 L/minute/m2, (p<0.01)].
Higher total alkaline phosphatase and mean corpuscular volume as well as lower estimated creatinine clearance identify Fontan patients with lower cardiac index. Using biomarkers to monitor haemodynamics and organ-specific effects warrants prospective investigation.
Hemoglobinopathies, including the thalassemia syndromes and sickle cell disease, are complex disorders with protean manifestations. Their pathophysiology is influenced by environmental and genetic factors in addition to the pleiotropic effects of the globin gene mutations themselves. The erythrocyte membrane plays a critical role in these disorders because of the effects of its structural and functional perturbations and alterations in ion and water homeostasis regulated by membrane proteins. The first portion of this chapter reviews the structural and functional characteristics of the erythrocyte membrane; this is followed by a review of the alterations in ion and water homeostasis observed in the erythrocytes of sickle cell disease and thalassemia.
MEMBRANE STRUCTURE AND FUNCTION
The erythrocyte membrane is a complex, multifunctional structure. Although providing a protective layer between hemoglobin and other intracellular components and the external environment, it provides the erythrocyte with the deformability and stability required to withstand its travels through the circulation. The erythrocyte is subjected to high sheer stress in the arterial system, dramatic changes in size in the microcirculation, and wide variations in tonicity, pH, and pO2 as it travels throughout the body. It facilitates the transport of cations, anions, urea, water and other small molecules in and out of the cell, but denies entry to larger molecules, particularly if charged. A unique anucleate cell, the erythrocyte has a limited capacity for self-repair.
The erythrocyte membrane is composed of a lipid bilayer linked to an underlying cortical membrane skeleton.
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