Prognostic utility of novel biomarkers of cardiovascular stress: the Framingham Heart Study

BACKGROUND

Biomarkers for predicting cardiovascular events in community-based populations have not consistently added information to standard risk factors. A limitation of many previously studied biomarkers is their lack of cardiovascular specificity.

METHODS AND RESULTS

To determine the prognostic value of 3 novel biomarkers induced by cardiovascular stress, we measured soluble ST2, growth differentiation factor-15, and high-sensitivity troponin I in 3428 participants (mean age, 59 years; 53% women) in the Framingham Heart Study. We performed multivariable-adjusted proportional hazards models to assess the individual and combined ability of the biomarkers to predict adverse outcomes. We also constructed a "multimarker" score composed of the 3 biomarkers in addition to B-type natriuretic peptide and high-sensitivity C-reactive protein. During a mean follow-up of 11.3 years, there were 488 deaths, 336 major cardiovascular events, 162 heart failure events, and 142 coronary events. In multivariable-adjusted models, the 3 new biomarkers were associated with each end point (P<0.001) except coronary events. Individuals with multimarker scores in the highest quartile had a 3-fold risk of death (adjusted hazard ratio, 3.2; 95% confidence interval, 2.2-4.7; P<0.001), 6-fold risk of heart failure (6.2; 95% confidence interval, 2.6-14.8; P<0.001), and 2-fold risk of cardiovascular events (1.9; 95% confidence interval, 1.3-2.7; P=0.001). Addition of the multimarker score to clinical variables led to significant increases in the c statistic (P=0.005 or lower) and net reclassification improvement (P=0.001 or lower).

CONCLUSION

Multiple biomarkers of cardiovascular stress are detectable in ambulatory individuals and add prognostic value to standard risk factors for predicting death, overall cardiovascular events, and heart failure.

Direct tissue evaluation via immunofluorescence: in the diagnosis of hereditary transthyretin cardiac amyloidosis

Multiple precursor proteins have been shown to cause cardiac amyloidosis. The most common forms are due either to immunoglobulin light chains or to transthyretin proteins (either wild-type or mutant forms). Correct subclassification of the amyloid is paramount because treatment differs in accordance with the type of amyloidosis. Indirect diagnostic methods, including serologic analysis, can lead to misdiagnosis. Definitive diagnosis often requires analysis of amyloid in the tissue. We present a case of a woman who was diagnosed with hereditary transthyretin cardiac amyloidosis by means of immunofluorescence and genetic analysis. This case highlights the importance-in the diagnostic algorithm of cardiac amyloidosis-of direct evaluation of the tissue with immunofluorescence and of genetic testing.

Reference limits for N-terminal-pro-B-type natriuretic peptide in healthy individuals (from the Framingham Heart Study)

N-terminal pro-B-type natriuretic peptide (NT-pro-BNP) is a commonly measured cardiovascular biomarker in ambulatory and hospital settings. Nonetheless, there are limited data regarding "normal" ranges for NT-pro-BNP in healthy subjects, despite the importance of such information for interpreting natriuretic peptide measurements. In this study, a healthy reference sample free of cardiovascular disease from the Framingham Heart Study Generation 3 cohort was examined; there were 2,285 subjects (mean age 38 years, 56% women). Plasma NT-pro-BNP levels were measured using the Roche Diagnostics Elecsys 2010 assay, and reference values (2.5th, 50th, and 97.5th quantiles) were determined using empiric and quantile regression methods. Gender, age, blood pressure, and body mass index accounted for approximately 33% of the interindividual variability in NT-pro-BNP in the reference sample. NT-pro-BNP values were substantially higher in women compared to men at every age, and levels increased with increasing age for both genders. Using quantile regression, the upper reference values (97.5th quantile) for NT-pro-BNP were 42.5 to 106.4 pg/ml in men (depending on age) and 111.0 to 215.9 pg/ml in women. Intraindividual variability was assessed in an additional 12 healthy subjects, who had serial NT-pro-BNP measurements over 1 month. Intraclass correlation was 0.85, indicating that most of the variability in NT-pro-BNP concentrations was among rather than within subjects. However, the reference change value was 100%, suggesting that small proportional differences in NT-pro-BNP could be attributable to analytic variability. In conclusion, the reference limits obtained from this large, healthy, community-based sample may aid in the evaluation of NT-pro-BNP concentrations measured for clinical and research purposes.