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Proteomics and Protein Markers |
1 Division of Cardiovascular Diseases and Internal Medicine and2 Department of Clinical Biochemistry and Immunology, Mayo Clinic Rochester, MN.
aAddress correspondence to this author at: Mayo Clinic, 200 First Street SW, Rochester, MN 55905. Fax 507-266-9142; e-mail miller.wayne{at}mayo.edu.
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Abstract |
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Methods: NT-proBNP and BNP were measured in a nonconsecutive patient cohort receiving clinically indicated intravenous nesiritide. Blood samples were drawn before, at 6 and 24 h during, and at 6 h after infusion. A reduction in NT-proBNP was defined as a decrease from baseline during infusion ("infusion responders") of >3 SD of the variability of the assay measurement (
20%). Patients with decreases >20% in both NT-pro BNP and BNP at 6 h post infusion were designated "biochemical responders".
Results: Forty patients [27 males; mean (SE) age, 68 (2) years; mean (SE) left ventricular ejection fraction, 25 (1.4)%] were studied. All patients improved clinically. Overall, the changes in NT-proBNP were a 18 (4.6)% [mean (SE)] and 19.8% (median) decrease from baseline at 24 h of infusion and a 22 (6.0)% and 17.8% decrease at 6 h post infusion (P <0.001 compared with baseline). In a large number of patients, decreases in NT-proBNP were, however, within the variability of the assay. Subgroup analysis showed that 22 of 40 patients were infusion responders with a >20% decrease from baseline in NT-proBNP during nesiritide infusion, whereas only 12 patients were biochemical responders with >20% decreases from baseline postinfusion for both NT-proBNP and BNP.
Conclusions: In this study, many patients had decreased NT-proBNP and BNP values after therapy with nesiritide, but the majority of patients did not demonstrate biochemically significant decreases in analytes despite a clinical response. Until we know more about the responses of natriuretic peptides to therapies such as nesiritide, a strategy of monitoring NT-proBNP and BNP to guide therapy cannot be universally advocated.
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Materials and Methods |
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Blood samples were drawn in EDTA before nesiritide infusion, at 6 and 24 h during infusion, and at 6 h after completion of infusion. Blood samples were immediately stored on ice, processed, and subsequently stored at –70 °C until batch analysis was performed. Standard nesiritide infusion therapy doses were used: 2 µg/kg intravenous push over 1–2 min followed by continuous infusion at 0.01 µg · kg–1 · min–1. The duration of infusion was intended to be at least 24 h, and patient vital signs were monitored initially every 15 min for the first hour and every 60 min thereafter for the duration of infusion unless otherwise ordered as per clinical care protocol. Outpatient baseline oral medications were continued, but diuretic regimens were adjusted and nitrates were discontinued as determined for each patient by the primary clinical service. No patients received concomitant intravenous positive inotropic therapy.
NT-proBNP [76 amino acid residues; mean (SE) half-life, 69.6 (10.8) min (12)] was measured by a sandwich electrochemiluminescence immunoassay on the Roche Elecsys® 2010 Analyzer (Roche Diagnostics; lower limit of detection, 5 µg/L with inter- and intraassay CVs of 3.1% and 2.5%, respectively). BNP [32 amino acid residues; half-life, 20 min (13)] was measured by the Shionoria assay method [mean (SE) inter- and intraassay variability of 7.2 (1.7) µg/L and 8.0 (1.4) µg/L, respectively; reference interval in plasma of 12 (4) µg/L] in the laboratory of John C. Burnett, Jr., at the Mayo Clinic. cGMP was measured by RIA in the laboratory of Doctor Burnett (upper cutoff of the reference interval 
1.7 nmol/L; inter- and intraassay CVs of 4.2% and 2.5%, respectively) so that analysis of the signaling response to nesiritide could be assessed. Troponin T (cutoff value for limit of detection 0.01 µg/L, with CV of 10% at 0.035 µg/L) was measured on the Roche Elecsys 2010 Analyzer. This was done so that if a differential response was noted, we could assess the extent to which cardiac injury was implicated. We determined renal function at baseline and during and after infusion by estimation of glomerular filtration rate (GFR; mL/min) by the modified Cockcroft–Gault formula (14), using serum creatinine, age, body weight, and gender. Urine output was measured before, during, and after nesiritide infusion.
study endpoints
We monitored several general clinical and hemodynamic indices that are used to gauge patient response and constitute diuresis/renal function responses to nesiritide infusion reflecting clinical improvement, such as improved symptoms and New York Heart Association class, effective diuresis, weight reduction, increased urine output, stable/improved systemic blood pressure, and the associated predictive assessment of plasma biomarker concentrations. Significant decreases in NT-proBNP and BNP concentrations were defined as changes >3 SD of the variability of the assay measurement, which is 20%. This definition ensures that the sequential values are different analytically from each other (15). Patients meeting the criterion of a >20% decrease in NT-proBNP from baseline during nesiritide infusion were designated as "infusion responders" for the purposes of stratifying patients. Those patients whose NT-proBNP and BNP concentrations both decreased by >20% during the postinfusion period (6 h post infusion) were designated as "biochemical responders". This definition was again predicated on the analytic variability of the measurements and was used to identify a group of responders for analysis. We also evaluated whether the responses in NT-proBNP and BNP were related to cGMP response or the pattern of troponin T release. The study was not powered as an outcomes study, but in- and posthospital cardiac-related mortalities were determined for all patients. The mean (SE) posthospital follow-up was 10 (1.1) months.
data analysis
Continuous variable data are reported as the mean (SE) and the median with 25–75% interquartile ranges. Categorical variables are presented as percentages of the group total. Primary comparisons were analyzed by paired t-test analysis and signed-rank analysis to compare medians of values with nonparametric distributions, with statistical difference accepted for P <0.05. We assessed associations between each of the biomarkers at baseline and subsequent hemodynamic variables by the Spearman rank correlation. Study design decisions with regard to the amount of change from baseline that would be considered a response to nesiritide were made before the report of Wu et al. (16), which suggested that even larger changes from baseline in NT-proBNP and BNP concentrations are required to be assured of responses over biological variability. Accordingly, we examined larger percentage changes as well.
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Results |
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. The majority of patients had an ischemic etiology of their heart failure with previous myocardial infarction, moderate renal insufficiency, mild anemia, diabetes, hypertension, and hypercholesterolemia and were receiving an appropriate antifailure medical regimen. Shown in Table 2
and Fig. 1
are the baseline plasma values for NT-proBNP, BNP, troponin T, cGMP, and additional clinical indices with their changes during the nesiritide infusion at 6 and 24 h as well as 6 h post infusion for the group as a whole. Statistically significant increases from baseline were noted in BNP during the nesiritide infusion. Decreases in NT-proBNP were observed at 24 h of infusion [mean (SE), –18 (4.6)%; median, –19.8% from baseline; P <0.001] and at 6 h postinfusion [mean, –22 (6)%; median, –17.8%; P <0.001]. These decreases were, however, near the analytic variability of the assay measurements (±20%). Troponin T concentrations were increased (>0.03 µg/L) at baseline and increased further during infusion (6 h), but although still increased after nesiritide infusion, values were not different from baseline. cGMP was increased relative to baseline values at 6 and 24 h of infusion and returned essentially to baseline after the infusion. Estimated glomerular filtration rate (GFR) was unchanged, although urine output increased after 24 h of nesiritide infusion. Eighty-five percent of patients received intravenous furosemide, and the remaining 15% responded to oral diuretics during the period of nesiritide infusion and did not require intravenous diuretic therapy.
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The relative percentage changes from baseline for the entire patient cohort during and after nesiritide infusion are shown in Fig. 2
. BNP was increased during infusion as expected [at 6 h of infusion, mean (SE), 213 (42)%; median, 110%; P <0.001] and returned to below baseline values in the postinfusion period [mean, –2 (12.8)%; median, –23.6%; P = 0.05]. NT-proBNP concentrations were statistically different from baseline at 24 h of infusion and 6 h after infusion for the patient cohort as a whole. We found no relationship between duration (hours) of nesiritide infusion and 6 h postinfusion percentage changes from baseline for NT-proBNP or BNP.
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Of the entire cohort of 40 patients, 22 patients (Table 3
) were designated as infusion responders, as defined by a change greater than the analytic variability of sequential values in NT-proBNP between baseline and 6 and/or 24 h of nesiritide infusion. The remaining 18 patients were nonresponders. The clinical responses of each of these patients are shown in Table 3
. Shown in Table 4
are the percentage changes from baseline for cGMP, troponin T, BNP, and NT-proBNP for infusion responders and nonresponders during and after nesiritide infusion therapy. NT-proBNP concentrations decreased in infusion responders during and after the infusion. cGMP concentrations were significantly increased in both infusion responders and nonresponders. Troponin T was increased from baseline with nesiritide infusion in both infusion responders and nonresponders. Initial (6 h) BNP concentrations were somewhat higher in infusion responders, but none of the differences were statistically significant between infusion responders and nonresponders.
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Patients whose NT-proBNP and BNP values were not lower after the infusion might not be expected to show decreases in NT-proBNP during the infusion. Accordingly, we examined a subgroup of patients whose postinfusion NT-proBNP and BNP values both were decreased by >20% below baseline (the subgroup was designated as biochemical responders). Twelve patients met this criterion (Figs. 3
and 4
). The clinical characteristics of these patients are also shown in Table 3
. NT-proBNP was unchanged from baseline to 6 h of infusion but decreased significantly at 24 h of infusion [mean, –39 (5)%; median, –39%; P <0.01] and showed an additional decrease post infusion [mean, –59 (6)%; median, –61%; P <0.001]. BNP was increased significantly [mean, 177 (45)%; median, 116%; P <0.01] during nesiritide infusion, but decreased at 6 h post-nesiritide infusion to below the baseline value [mean, –51 (7)%; median, –46%; P <0.001]. The maximum individual decrease in BNP was 89% below baseline.
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We observed no relationships between the estimated GFR at baseline or during nesiritide infusion (range, 28–109 mL/min), or in the duration of the infusion or in changes in NT-proBNP that would contribute to an explanation of the more prominent biochemical response to nesiritide in these 12 patients compared with the remainder of the patient cohort. cGMP concentrations were increased in response to nesiritide infusion [mean, 118 (45)%; median, 46%; P <0.01] in these 12 patients and remained increased into the postinfusion period [128 (99)%; median, 28%; P <0.05]. Troponin T was increased from baseline values during [mean, 14 (9)%; median, 1%; P = 0.06] and after nesiritide infusion [35 (19)%; median, 8%; P = 0.08] but only marginally.
Objective indices of clinical improvement were also identified in this patient cohort but did not distinguish subgroups of patients (Table 3
). Decreased body weight (enrollment to study completion), increased urine output during nesiritide infusion, decreased serum creatinine (enrollment to study completion), and lower heart rate (enrollment to study completion) were selected prospectively as generally used indicators of clinical improvement in the setting of general medical management as well as nesiritide therapy. Thirty-four patients had one or more of the indices of clinical improvement; all 22 of the infusion responder patients met these criteria. There were no patients who had all of these indices and no patients who had the combination of weight reduction, decreased serum creatinine, and increased urine output. However, as shown in Table 3
, the most common responses (n = 31) to nesiritide infusion were weight reduction [overall mean reduction, 2.6 (0.5) kg] and increased urine output. Chest x-rays were also reviewed (enrollment compared with study completion or discharge, whichever was available), but no consistent response to nesiritide therapy could be delineated (several patients underwent thoracentesis, and the remainder were unchanged or moderately improved from baseline chest x-ray). There were no clinical characteristic differences between infusion responders and nonresponder patients in etiology of heart failure, left ventricular ejection fraction, presence of biventricular failure, estimated GFR, serum potassium and sodium, body mass index, gender, comorbidities, or medical therapy regimens. Troponin T values tended to increase more in the nonresponders, but the differences were not statistically significant, and their patterns were not related to the response of NT-proBNP or BNP during or after the infusion period. No inhospital mortality occurred in this patient cohort, but at completion of follow-up, cardiovascular related mortality was 40% (16 of 40). Eight of the 16 patients were in the infusion responder group, and this included 2 patients who were among the 12 patients responding most prominently to nesiritide infusion (biochemical responders).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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). When we used a more strict criterion of a 
50% decrease from baseline for both analytes, which is still below the cutoff suggested to overcome biologic variability (16), only 5 of 40 patients had lower values. Those patients had postinfusion decreases in BNP as well. Of the subset of biochemical responder patients (n = 12), 11 patients had decreases in NT-proBNP during the infusion as well. That was the pattern expected for all patients. We expected that the clinical improvement would be mirrored by changes in NT-proBNP concentrations, which should decrease if BNP secretion was inhibited by improved hemodynamics. However, because there was little posttherapy response in many of the patients, perhaps it should not be surprising that NT-proBNP concentrations did not decrease during the nesiritide infusion. On the basis of a criterion of at least a >20% change below the baseline during nesiritide infusion, 22 of 40 (55%) of the patients had a decrease in NT-proBNP. If we used the criterion of >77% change suggested by Wu et al. (16), which reflects the biological plus analytic variability of NT-proBNP (it is even greater for BNP) measurements, only two patients could be designated as infusion responders.
The reason for NT-proBNP and BNP not consistently responding to nesiritide therapy is unclear. Nesiritide is a more effective intravenous agent than nitroglycerin, to which it has been formally compared (17). cGMP was stimulated by nesiritide, and clinically these patients all benefited. All were deemed sufficiently improved to be discharged, but the secretion of BNP was only modestly inhibited 6 h after completion of infusion (Table 2
). In most patients, NT-proBNP concentrations did not decrease substantially during nesiritide infusion, although statistically absolute values were lower at 24 h of infusion. This is surprising given the relatively short half-lives of BNP and of NT-proBNP. Perhaps, the increased amounts of BNP resulting from nesiritide infusion are cleared differently, but the 76-amino acid NT leader sequence created when corin cleaves proBNP (18) to its active moiety should not be affected by maneuvers that increase active BNP. Indeed, if BNP secretion is inhibited by exogenous BNP (nesiritide), endogenous BNP and NT-proBNP concentrations should decrease.
We do not have a simple explanation for these observed effects. Many of the patients were very ill; thus, improvement might have occurred clinically that reflected some degree of compensation but not an optimal clinical response. Perhaps there was an effect from renal clearance because the estimated GFR was 51 (4) mL/min. It has been reported that conjoint congestive heart failure and renal dysfunction induce marked increases in the NT-proBNP signal (19)(20). The patients who had a lesser response were those with more abnormal renal function, but this was not a consistent finding. It also may well be that these patients were so ill that their response to therapy, although clinically beneficial, may have left many patients with substantially increased concentrations of NT-proBNP as a way of maintaining hemodynamic compensation. This might be expected more to occur in patients with chronic heart failure that is acutely exacerbated because there is very little storage of BNP and chronic stimulation is necessary to increase concentrations (21). Coincident ischemia with cardiac injury occurred but is an unlikely explanation. Increases tended to be greater in nonresponders but not to a statistically significant extent. These responses also do not reflect a lack of stimulation because cGMP concentrations were increased in both groups. The severity of illness of our cohort is supported by the very substantial posthospital follow-up mortality rate [16 patients (40%) over 22 months]. Of interest, the mortality was the same (8 of 16) in those patients who were infusion responders and nonresponders, lending support to the concept that in some patients the inability to maintain high natriuretic peptide concentrations is an adverse prognostic indicator (22).
Finally, we cannot exclude the possibility that samples drawn later post infusion (beyond 6 h) might have revealed greater decreases in both NT-proBNP and BNP. Wu et al. (23) reported as observational data that it often takes many days for BNP concentrations to decrease during the treatment of heart failure. Even if greater changes do occur over time, the simplistic concept that a strategy of monitoring NT-proBNP during nesiritide infusion or immediately thereafter to guide therapy does not appear to be easily applicable to all patients with congestive heart failure. It may well be that in patients who are less ill, with less advanced heart failure and more normal renal function, such an approach would be beneficial. This merits further investigation and is supported by the serial responses seen in those patients whose NT-proBNP/BNP values improved, which was the group of patients who overall did better clinically in the short term.
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Acknowledgments |
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Footnotes |
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References |
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The following articles in journals at HighWire Press have cited this article:
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  K. B. Shah, W. J. Kop, R. H. Christenson, D. B. Diercks, D. Kuo, S. Henderson, K. Hanson, S.-Y. Li, and C. R. deFilippi Natriuretic peptides and echocardiography in acute dyspnoea: implication of elevated levels with normal systolic function Eur J Heart Fail, July 1, 2009; 11(7): 659 - 667. [Abstract] [Full Text] [PDF]
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 W. L. Miller, K. A. Hartman, D. E. Grill, J. C. Burnett Jr, and A. S. Jaffe Only Large Reductions in Concentrations of Natriuretic Peptides (BNP and NT-proBNP) Are Associated with Improved Outcome in Ambulatory Patients with Chronic Heart Failure Clin. Chem., January 1, 2009; 55(1): 78 - 84. [Abstract] [Full Text] [PDF]
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M. Metra, S. Nodari, G. Parrinello, C. Specchia, L. Brentana, P. Rocca, F. Fracassi, T. Bordonali, P. Milani, R. Danesi, et al. The role of plasma biomarkers in acute heart failure. Serial changes and independent prognostic value of NT-proBNP and cardiac troponin-T Eur J Heart Fail, August 1, 2007; 9(8): 776 - 786. [Abstract] [Full Text] [PDF]
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 F. S. Apple, A. H.B. Wu, A. S. Jaffe, M. Panteghini, R. H. Christenson, NACB COMMITTEE MEMBERS, R. H. Christenson, F. S. Apple, C. P. Cannon, G. Francis, et al. National Academy of Clinical Biochemistry and IFCC Committee for Standardization of Markers of Cardiac Damage Laboratory Medicine Practice Guidelines: Analytical Issues for Biomarkers of Heart Failure Circulation, July 31, 2007; 116(5): e95 - e98. [Full Text] [PDF]
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W. L. Miller, K. A. Hartman, M. F. Burritt, D. E. Grill, R. J. Rodeheffer, J. C. Burnett Jr, and A. S. Jaffe Serial Biomarker Measurements in Ambulatory Patients With Chronic Heart Failure: The Importance of Change Over Time Circulation, July 17, 2007; 116(3): 249 - 257. [Abstract] [Full Text] [PDF]
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 P. R. Forfia, M. Lee, R. S. Tunin, M. Mahmud, H. C. Champion, and D. A. Kass Acute Phosphodiesterase 5 Inhibition Mimics Hemodynamic Effects of B-Type Natriuretic Peptide and Potentiates B-Type Natriuretic Peptide Effects in Failing But Not Normal Canine Heart J. Am. Coll. Cardiol., March 13, 2007; 49(10): 1079 - 1088. [Abstract] [Full Text] [PDF]
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A. S. Jaffe, L. Babuin, and F. S. Apple Biomarkers in Acute Cardiac Disease: The Present and the Future J. Am. Coll. Cardiol., July 4, 2006; 48(1): 1 - 11. [Abstract] [Full Text] [PDF]
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