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Implications of serial measurements of natriuretic peptides in heart failure: insights from BIOSTAT‐CHF

Natriuretic peptides [NP, including B-type natriuretic peptide (BNP) and amino-terminal prohormone of BNP (NT-proBNP)] are the gold-standard biomarkers in heart failure (HF) management,1 with NP levels at presentation/admission routinely used for diagnostic and prognostic purposes.2 NP levels at discharge/follow-up also show association with outcomes,3 and NP levels following HF treatment add further value to tailoring risk.4 However, the usefulness of NP serial measurements beyond conventional HF treatment in clinical practice still remains a matter of controversy.3,5 A cohort with current HF guideline-based treatment would provide an ideal setting to revisit usefulness of NP serial measurements in risk stratification of HF patients, including the role of recently identified BNP molecular forms.6 The European multi-national BIOlogy Study to TAilored Treatment in Chronic Heart Failure (BIOSTAT-CHF) provides an opportunity for the aforementioned analysis, being a European cohort in which serial sampling of NPs was done before and after titration of HF medications according to current European guidelines in a multi-centre, observational, real-world setting.7 The aims of the present study were to investigate the association with HF outcomes, effects of HF guideline treatment, and the implications of NP serial measurement in the BIOSTAT-CHF cohort.7 From the total cohort, 757 patients with available plasma samples at baseline (V1) and at follow-up (V2, approximately 9 months apart) were measured for BNP and BNP molecular form, BNP 5–326 (see Table 1 for methods on measurements). NT-proBNP measurement was only available at baseline (V1); therefore, analyses related to this peptide were limited to baseline (V1). The primary endpoints were all-cause mortality and a composite of mortality with HF rehospitalisation (mortality/HF) at 3 years, and overall from baseline (V1). Changes in dosage titrations and response of peptide levels were investigated by splitting the population into two groups based on treatment up-titration, as previously reported (see online supplementary material).7 Demographics and clinical measurements are described in Table 1. At baseline (V1), NP levels (BNP, NT-proBNP, and BNP 5–32) were strongly correlated with each other (rs = 0.635–0.904, P< 0.001). Cox regression modelling showed baseline BNP levels to be associated with mortality [hazard ratio (HR) 1.99, 95% confidence interval (CI) 1.23–3.23; P = 0.005] and mortality/HF (HR 1.72, 95% CI 1.25–2.37; P = 0.001). NT-proBNP and detection of BNP 5–32 were similarly associated with mortality (HR ≥1.85, 95% CI 1.15–3.20; P≤ 0.012) and mortality/HF [HR ≥1.54, 95% CI 1.14–3.22; P≤ 0.015) after adjustment for the BIOSTATCHF compact model7 (Table 2). All three NPs retained their associations with outcomes after further adjustment with additional NP confounders (online supplementary Table S1A). With regard to the effect of HF treatment, significantly reduced BNP levels were observed only when at least one medication was up-titrated, whereas BNP 5–32 was reduced regardless of drug up-titration (Table 3). A general linear model analysis for repeated measures confirmed these findings (online supplementary Table S1B). For serial measurements (Table 4), when BNP baseline (V1) and follow-up (V2) levels were compared, follow-up (V2) measurements were more strongly associated with all causemortality than baseline (V1) (chi-square: 67.1 vs. 16.0). However, even if the combination of baseline (V1) and follow-up (V2) measurements were significant (chi-square: 66.7, P< 0.001), there was no added value to the follow-up (V2) measurement alone, as the role of the baseline (V1) measurement was not preponderant (P = 0.878). Similarly, follow-up BNP 5–32 measurement showed a stronger association with all-cause mortality than the baseline value (chi-square: 64.3 vs. 18.8); however, the combination of baseline (V1) and follow-up (V2) measurements was significantly better (chi-square: 69.8), with the baseline (V1) level providing additional value (chi-square: 5.5, P = 0.017) to follow-up (V2) measurement alone. Furthermore, in patients that did not achieve ≥50% dose treatment but still showed BNP 5–32 to decrease from detectable to undetectable levels (or high-low for BNP) exhibited better outcomes than those who displayed increased levels at follow-up (online supplementary Figures S1 and S2). There are three main findings of the present investigation. Firstly, baseline NP levels were independently associated with adverse outcomes, with comparable results for BNP, NT-proBNP, and BNP 5–32. Secondly, response to HF guideline treatment up-titration was associated with a decrease in both BNP and BNP 5–32 levels. Finally, even if both BNP and BNP 5–32 showed stronger association with all-cause mortality at follow-up measurement compared to baseline, combination of baseline and follow-up measurements did not add value for BNP beyond follow-up alone, whereas BNP 5–32 did. The recent North American GUIDE-IT trial8 showed guideline-directed medical therapy (GDMT) guided by NT-proBNP levels was not superior to GDMT alone and that GDMT intensity was associated with lower NT-proBNP levels and further that low NP levels at follow-up (NT-proBNP levels ≤1000 pg/mL during GDMT) were associated with better outcomes.9 Consistent with this, the present study based on a European real-world cohort showed that follow-up values after guideline-based treatment were more associated with outcomes for both BNP and BNP 5–32 (online supplementary Figures S3 and S4). In this context, analysis of the NP response in the BIOSTAT-CHF cohort, with medications optimised according to HF guidelines, confirmed the association of baseline NP levels (BNP, NT-proBNP and BNP 5–32) with adverse outcomes, and follow-up levels after treatment to show better association with adverse outcomes when compared to baseline levels, consistent with previous reports.1,2,4,10,11 This is in line with a previous finding in another real-world cohort conducted in the UK in which the measurement of follow-up NT-proBNP, after optimisation of pharmacotherapy, although preceding current guidelines, provided more value than baseline measurements alone.10 The difference in added value of combined


Implications of serial measurements of natriuretic peptides in heart failure: insights from BIOSTAT-CHF
Natriuretic peptides [NP, including B-type natriuretic peptide (BNP) and amino-terminal prohormone of BNP (NT-proBNP)] are the gold-standard biomarkers in heart failure (HF) management, 1 with NP levels at presentation/admission routinely used for diagnostic and prognostic purposes. 2 NP levels at discharge/follow-up also show association with outcomes, 3 and NP levels following HF treatment add further value to tailoring risk. 4 However, the usefulness of NP serial measurements beyond conventional HF treatment in clinical practice still remains a matter of controversy. 3,5 A cohort with current HF guideline-based treatment would provide an ideal setting to revisit usefulness of NP serial measurements in risk stratification of HF patients, including the role of recently identified BNP molecular forms. 6 The European multi-national BIOlogy Study to TAilored Treatment in Chronic Heart Failure (BIOSTAT-CHF) provides an opportunity for the aforementioned analysis, being a European cohort in which serial sampling of NPs was done before and after titration of HF medications according to current European guidelines in a multi-centre, observational, real-world setting. 7 The aims of the present study were to investigate the association with HF outcomes, effects of HF guideline treatment, and the implications of NP serial measurement in the BIOSTAT-CHF cohort. 7 From the total cohort, 757 patients with available plasma samples at baseline (V1) and at follow-up (V2, approximately 9 months apart) were measured for BNP and BNP molecular form, BNP 5-32 6 (see Table 1 for methods on measurements). NT-proBNP measurement was only available at baseline (V1); therefore, analyses related to this peptide were limited to baseline (V1). The primary endpoints were all-cause mortality and a composite of mortality with HF rehospitalisation (mortality/HF) at 3 years, and overall from baseline (V1). Changes in dosage titrations and response of peptide levels were investigated by splitting the population into two groups based on treatment up-titration, as previously reported (see online supplementary material). 7 Demographics and clinical measurements are described in Table 1. At baseline (V1), NP levels (BNP,  were strongly correlated with each other (r s = 0.635-0.904, P < 0.001). Cox regression modelling showed baseline BNP levels to be associated with mortality [hazard ratio (HR) 1.99, 95% confidence interval (CI) 1.23-3.23; P = 0.005] and mortality/HF (HR 1.72, 95% CI 1.25-2.37; P = 0.001). NT-proBNP and detection of BNP 5-32 were similarly associated with mortality (HR ≥1.85, 95% CI 1.15-3.20; P ≤ 0.012) and mortality/HF [HR ≥1.54, 95% CI 1.14-3.22; P ≤ 0.015) after adjustment for the BIOSTAT-CHF compact model 7 ( Table 2). All three NPs retained their associations with outcomes after further adjustment with additional NP confounders (online supplementary  Table S1A). With regard to the effect of HF treatment, significantly reduced BNP levels were observed only when at least one medication was up-titrated, whereas BNP 5-32 was reduced regardless of drug up-titration ( Table 3). A general linear model analysis for repeated measures confirmed these findings (online supplementary Table S1B). For serial measurements (Table 4), when BNP baseline (V1) and follow-up (V2) levels were compared, follow-up (V2) measurements were more strongly associated with all causemortality than baseline (V1) (chi-square: 67.1 vs. 16.0). However, even if the combination of baseline (V1) and follow-up (V2) measurements were significant (chi-square: 66.7, P < 0.001), there was no added value to the follow-up (V2) measurement alone, as the role of the baseline (V1) measurement was not preponderant (P = 0.878). Similarly, follow-up BNP 5-32 measurement showed a stronger association with all-cause mortality than the baseline value (chi-square: 64.3 vs. 18.8); however, the combination of baseline (V1) and follow-up (V2) measurements was significantly better (chi-square: 69.8), with the baseline (V1) level providing additional value (chi-square: 5.5, P = 0.017) to follow-up (V2) measurement alone. Furthermore, in patients that did not achieve ≥50% dose treatment but still showed BNP 5-32 to decrease from detectable to undetectable levels (or high-low for BNP) exhibited better outcomes than those who displayed increased levels at follow-up (online supplementary Figures S1  and S2).
There are three main findings of the present investigation. Firstly, baseline NP levels were independently associated with adverse outcomes, with comparable results for BNP, NT-proBNP, and BNP 5-32. Secondly, response to HF guideline treatment up-titration was associated with a decrease in both BNP and BNP 5-32 levels. Finally, even if both BNP and BNP 5-32 showed stronger association with all-cause mortality at follow-up measurement compared to baseline, combination of baseline and follow-up measurements did not add value for BNP beyond follow-up alone, whereas BNP 5-32 did.
The recent North American GUIDE-IT trial 8 showed guideline-directed medical therapy (GDMT) guided by NT-proBNP levels was not superior to GDMT alone and that GDMT intensity was associated with lower NT-proBNP levels and further that low NP levels at follow-up (NT-proBNP levels ≤1000 pg/mL during GDMT) were associated with better outcomes. 9 Consistent with this, the present study based on a European real-world cohort showed that follow-up values after guideline-based treatment were more associated with outcomes for both BNP and BNP 5-32 (online supplementary Figures S3 and S4). In this context, analysis of the NP response in the BIOSTAT-CHF cohort, with medications optimised according to HF guidelines, confirmed the association of baseline NP levels (BNP, NT-proBNP and BNP 5-32) with adverse outcomes, and follow-up levels after treatment to show better association with adverse outcomes when compared to baseline levels, consistent with previous reports. 1,2,4,10,11 This is in line with a previous finding in another real-world cohort conducted in the UK in which the measurement of follow-up NT-proBNP, after optimisation of pharmacotherapy, although preceding current guidelines, provided more value than baseline measurements alone. 10 The difference in added value of combined . NT-proBNP measured using the Roche NT-proBNP assay (Roche Diagnostics, Risch-Rotkreuz, Switzerland). BNP 5-32 was measured using matrix-assisted laser desorption ionisation-time of flight-mass spectrometry (MALDI-ToF-MS). 6 BNP 4-32 and BNP 3-32 were also detected in the same assay as BNP 5-32 but were not as sensitive and not comparable to BNP and NT-proBNP, and therefore omitted from analyses. a Values recorded as % detection [median (interquartile range)]. *P < 0.05.
use of baseline and follow-up measurements for association with mortality observed for BNP and BNP 5-32 in the present study may reflect different responses to treatment, with BNP levels being affected by treatment but not BNP 5-32 levels as a result of differential peptide processing in HF patients. BNP molecular forms may provide a more treatment-independent outcome biomarker. In the era of peptidase inhibitors (i.e. sacubitril/valsartan, dipeptidyl peptidase-4 inhibitors), monitoring NPs including molecular forms might allow further insight into NP processing that appear to be altered in HF. As limitations, BIOSTAT-CHF was a nonrandomised observational study, therefore it is not possible to infer causality to our findings or provide a mechanistic explanation. This study involved only European centres, and 99% of patients were Caucasian; therefore, the findings of this study may not be representative of HF patients at a global level.
In conclusion, findings from the BIOSTAT-CHF study, as a real-world cohort, support the role of serial measurement of NPs in clinical practice, with follow-up BNP and BNP  ACEi, angiotensin-converting enzyme inhibitor; BNP, B-type natriuretic peptide; V1, visit 1 (enrolment); V2, visit 2 (9-month follow-up) <50% less than 50% of optimal recommended dosage, ≥50% of optimal recommended dosage.

Research letters
Values are reported as median [interquartile range]. a BNP 5-32 values reported as a ratio of the mass spectral peak signal intensity against adrenocorticotropic hormone (internal reference standard). Additional supporting information may be found online in the Supporting Information section at the end of the article. Appendix S1. Supporting Information. Table S1. (A) Independent prediction abilities of baseline natriuretic peptides for overall outcomes of death and death/heart failure with addition of eGFR, blood pressure and past history of diabetes mellitus.
(B) General linear model for response to guideline-based treatment for BNP and BNP 5-32. Figure S1. Kaplan-Meier survival curves to show association with outcome of death/heart failure for serial changes in BNP levels in patients that did not achieve a ≥50% dose of guideline treatment up-titration. Figure S2. Kaplan-Meier survival curves to show association with outcome of death/heart failure for serial detection of BNP 5-32 in patients that did not achieve a ≥50% dose of guideline treatment up-titration. Figure S3. Kaplan-Meier survival curves to show association with outcome of death/heart failure and death for serial changes in BNP levels following guideline treatment up-titration. Figure S4. Kaplan-Meier survival curves to show association with outcome of death/heart failure and death for serial detection of BNP 5-32 following guideline treatment up-titration.