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N-terminal pro-brain natriuretic peptide has an established role in the diagnosis and prognosis of heart failure. In Fontan patients, this peptide is often increased, but its diagnostic value in this particular non-physiologic, univentricular circulation is unclear. We investigated whether N-terminal pro-brain natriuretic peptide represents ventricular function or other key variables in Fontan patients.
Methods and results:
Ninety-five consecutive Fontan patients ≥10 years old who attended the outpatient clinic of the Center for Congenital Heart Diseases in 2012–2013 were included. Time since Fontan completion was 16 ± 9 years. Median N-terminal pro-brain natriuretic peptide was 114 (61–264) ng/l and was higher than gender-and age-dependent normal values in 54% of the patients. Peptide Z-scores were higher in patients in NYHA class III/IV compared to those in class I/II, but did not correlate with ventricular function assessed by MRI and echocardiography, nor with peak exercise capacity. Instead, peptide Z-scores significantly correlated with follow-up duration after Fontan completion (p < 0.001), right ventricular morphology (p = 0.004), indexed ventricular mass (p = 0.001), and inferior caval vein diameter (p < 0.001) (adjusted R2 = 0.615).
Conclusions:
N-terminal pro-brain natriuretic peptide levels in Fontan patients correlate with functional class, but do not necessarily indicate ventricular dysfunction. Increased peptide levels were associated with a longer existence of the Fontan circulation, morphologic ventricular characteristics, and signs of increased systemic venous congestion. Since the latter are known to be key determinants of the performance of the Fontan circulation, these findings suggest increase in N-terminal pro-brain natriuretic peptide levels to indicate attrition of the Fontan circulation, independent of ventricular function.
Elastic modulus and residual stress in freestanding ultrathin films (<100 nm) are characterized using bilayer cantilevers. The cantilevers comprise a test film and a well-characterized reference material (SU-8). When released from the substrate, residual stresses in the bilayer cantilever cause it to deflect with measurable curvatures, allowing the determination of both stiffness and residual stress of the test film. The technique does not require sophisticated mechanical test equipment and serves as a useful metrology tool for characterizing coatings immediately after fabrication in a clean room assembly line. The measured biaxial modulus and residual strain of 75 nm copper films are 211 ± 19 GPa and (7.05 ± 0.22) × 10−3, respectively. Additional experiments on the freestanding structures yield a mean Young’s modulus of 115 GPa. These properties are in close agreement with those measured from additional residual stress–driven structures developed on the same coatings by the authors.