a Department of Cardiovascular Research, Istituto di Ricerche Farmacologiche Mario Negri,Milan, Italy
b Cardiology Section, V.A. Medical Centre,Minneapolis, Minnesota, USA
c Novartis Pharmaceuticals Corporation,East Hanover, New Jersey, USA
d Cardiovascular Division, Department of Medicine, University of Minnesota Medical School,Minneapolis, Minnesota, USA
e Centro Studi ANMCO,Florence, Italy
* Correspondence to: Dr. Roberto Latini, Istituto di Ricerche Farmacologiche Mario Negri, Via Eritrea 62, 20157 Milan, Italy. Tel: +39.0239014454; Fax: +39 0233200049
E-mail address: latini{at}marionegri.it
Received 29 January 2003;
revised 1 October 2003;
accepted 30 October 2003
See page 281, for the editorial comment on this article
Abstract
Aims Plasma levels of individual neurohormones (NH) have been proposed as reliable indicators for risk stratification of patients with heart failure (HF). Mainly because of small sample size, the predictive value of different NH has never been compared, while taking into account demographic, clinical and echocardiographic markers of risk in HF.
Methods and results Plasma brain natriuretic peptide (BNP), norepinephrine (NE), renin activity (PRA), aldosterone (aldo) and endothelin were measured in 4300 patients before randomization in Val-HeFT. Univariate and multivariate Cox proportional hazard analyses were performed to investigate the relationship between NH and two primary study outcomes, mortality and combined mortality and morbidity (M/M). Higher baseline values for all NH were related to mortality and M/M, with univariate hazard ratios ranging from 1.13 [95% CI 0.991.30] (aldo) to 2.47 [2.132.87] (BNP) for mortality, and from 1.24 [1.111.39] (aldo) to 2.56 [2.282.89] (BNP) for M/M. In multivariate analyses, BNP had the strongest association with outcome, followed by NE and PRA. Patients with more activation of renin-angiotensin-aldosterone system tended to show greater benefit from valsartan; but the trend was not statistically significant.
Conclusion All the NHs evaluated in 4300 patients with stable moderate to severe HF were found to be significant markers of outcome, despite therapy with ACEi, BB and randomization to an angiotensin receptor blocker or placebo. Several of these markers have been implicated as contributors to progression of HF, but BNP, which is thought to be protective, was the most powerful indicator for poor outcome.
Key Words: Heart failure Neurohormones Outcome Brain natriuretic peptide Norepinephrine Aldosterone Renin Endothelin
1. Introduction
Activation of different neurohormone (NH) systems, especially the sympathetic and renin-angiotensin-aldosterone systems (RAAS), plays a central role in the progression of heart failure (HF).1High circulating concentrations of several NHs have been found in patients with HF, in particular norepinephrine (NE), natriuretic peptides (ANP, BNP), plasma renin activity (PRA), aldosterone (aldo) and endothelin-1 (ET-1).26Based on these observations, and the seminal prognostic study on NE,7plasma levels of different NHs have been proposed as reliable indicators for risk stratification of patients with HF.810
Few data are available on the relative, independent contribution of each individual NH to predict outcome in HF when compared directly in the same population of patients, the most representative studies being those on V-HeFT II,9SOLVD Treatment11and SOLVD Registry.12In Val-HeFT13six different NH (NE, BNP, aldo, PRA, Big ET-1 and ET-1) were assayed at baseline in more than 4300 out of the 5010 patients randomized with stable HF of class IIIV severity. Since follow-up was for a median of 23 months, this was an ideal and unique setting in which to test comparatively the prognostic value of the different NHs.
2. Methods
2.1. Patients
Val-HeFT was a randomized, placebo-controlled, double-blind, parallel-arm multicentre trial. Five thousand and ten patients with stable, symptomatic HF, who were on prescribed HF therapy, with left ventricular (LV) ejection fraction <40% and LV internal diameter in diastole adjusted for body surface area (LVIDd/BSA) >2.9cm/m2, were enrolled from March 1997 to April 1999 at 302 clinical centres in 16 countries. All patients provided written informed consent before enrolment in the study. Study design and protocol have been presented in details previously.14
2.2. Blood sampling and assays
Blood for NH assays was sampled before randomization. Patients were supine for at least 30min before collection using an indwelling venous cannula. Blood was centrifuged at 4°C within 10min, the plasma aliquoted, shipped on dry ice and stored at 70°C until assayed in one of the two core laboratories, University of Minnesota for the US centres and Mario Negri Institute, Milan, Italy for the non-US centres.
Appropriate within- and between-laboratory controls were performed for each analyte. NE was assayed by high performance liquid chromatography with electrochemical detection,15BNP with an IRMA (Shionogi, Schering CIS, Milan, Italy), PRA with a RIA (PerkinElmer Life Sciences, Boston, USA), aldo with a non-extractive RIA (DiaSorin, Saluggia, Italy), ET-1 with an extractive RIA (Peninsula, San Carlos, USA) for samples of patients randomized in US centres only, and Big ET-1 with a non-extractive ELISA (Biomedica, Vienna, Austria) for samples of patients randomized in non-US centres only.
The study was conducted in accordance with the Declaration of Helsinki as revised in 1996, and in all participating centres the local ethics committees had approved the research protocol prior to the study.
2.3. Statistical methods
Correlations between different NH were done by non-parametric Spearman method. Univariate (simple regression) and multivariate (multiple regression) Cox proportional hazard analyses were performed to investigate the relationship between NH activation at baseline and the two primary study outcomes, mortality and combined mortality and morbidity (M/M), which was defined as cardiac arrest with resuscitation, hospitalization for heart failure or administration of intravenous inotropic or vasodilator drugs for 4h or more without hospitalization. Both end-points had been validated by an independent Endpoint Committee, blind to study treatment.13Patients were classified on the basis of the median levels of each neurohoromone at the time of randomization. All tests were made at a two-sided, 5% significance level. The univariate analysis (simple-regression) consisted of a Cox proportional hazard model with one baseline NH as the sole independent variable. Two multivariate analyses (multiple regression) were performed. In the first, the baseline NH values (for BNP, NE, PRA, and aldo) were used as independent variables; baseline ET-1 and Big ET-1 were not used in this multivariate analysis, since there were no patients for whom both endothelins were measured. In the second analysis, the demographic, clinical and echocardiographic variables that had a univariate relationship with outcome with a P<0.05 for either outcome were also included: age, gender, randomized treatment, NYHA class, aetiology, ejection fraction, LVIDd/BSA, sitting SBP, sitting HR, body-mass index, serum creatinine and bilirubin at baseline, concomitant therapy at baseline with beta-blockers (BB), diuretics or digoxin. In order to check for possible biases due to the arbitrary choice of cut-offs of NH concentration, the same Cox multivariate analysis was done on continuous variables. To ease the interpretability of its results, hazard ratios have been computed for intervals of 10pg/ml of aldosterone, BNP and NE, or 10ng/ml/h of PRA. The assumption of linear relationship between the end-points and NHs expressed as continuous variables has been assessed by plotting the log of the odds for death or M/M for each decile of NH concentration.
Since ACEi and BB favourably modulate NH activation in heart failure, we tested their possible interaction with NH at baseline in outcome prediction, with all the caution due to the non-randomized assignment to the subgroups. BreslowDay chi-square test was used to test for significance of interaction between ACEi or BB and NH at baseline.
Results of Cox proportional hazard models are presented in order of increasing complexity to compare the prognostic value of baseline NH in different models, and to evaluate consistency of the data. Different models have been compared by means of the 2logL statistics and the likelihood ratio test has been considered. An increment in 2
3.84 (P<0.05) was used to assess the contribution of individual NHs to the model including clinical and echocardiographic variables in predicting higher risk of death or of M/M.
To explore whether NH concentrations at baseline predict the response to valsartan, hazard ratios (valsartan vs placebo) were computed for each of the two primary end-points in patients with NH concentrations at baseline below and above or equal to the median value. BreslowDay chi square test was adopted to test for significance of interaction between randomized treatment and baseline NH concentrations on outcome.
3. Results
Of the 5010 patients randomized in Val-HeFT, baseline plasma concentrations of NH were available for about 4300 patients for NE, BNP, aldosterone and PRA, whereas Big ET-1 and ET-1 levels were available for 2359 non-US and 1934 US patients, respectively. Baseline characteristics of patients with and without neurohormonal data are overall comparable, except for small, but significant differences in ethnicity (white: 90.6 vs 88.7%), LVIDd/BSA (3.6±0.5 vs 3.7±0.5cm/m2), diuretics (85.0 vs 88.7%) and BB (35.9 vs 29.1%). These differences suggest that patients without neurohormonal data were slightly more severely ill; however, their 23-month outcome was not different for either mortality (19.3 vs 20.8%) or morbidity and mortality (30.4 vs 30.5%).
Plasma concentrations of the six NHs are reported in Table 1for the overall population, and by background therapy with ACEi and/or BB. Plasma aldosterone at baseline was maximal in patients receiving neither an ACEi nor a beta-blocker at randomization, and minimal in those taking both ACEi and BB at entry. PRA was highest in patients receiving ACEi, but when a beta-blocker was co-administered, PRA was reduced (4.38 vs 6.84ng/ml/h). ET-1 was lower in patients receiving BB at entry than in those not on BB. Concentrations of NE and Big ET-1 at randomization were unaffected by concomitant therapy.
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3.2. Baseline neurohormones and outcome Cox multiple regression analysis
When the hazard ratios for higher values of BNP, NE, PRA, or aldo were adjusted for each of the other three NHs, aldosterone was no longer predictive of mortality whereas the other three NHs were still significantly associated with increased mortality, with hazard ratios ranging from 1.51 [95% CI 1.301.74] (NE) to 2.48 [95% CI 2.132.88] (BNP) (Fig. 2a). The same analysis showed association of all four NHs to combined M/M, with hazard ratios ranging from 1.12 [95% CI 1.001.25] (aldo) to 2.55 [95% CI 2.262.87] (BNP) (Fig. 2b).
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3.4. Baseline neurohormones and outcome combination of several neurohormones
Although BNP proved to be the strongest NH predictor of outcome, even after adjusting for baseline demographic, clinical and echocardiographic variables, also NE and PRA provided additive prognostic value for death, whereas only BNP and NE contributed to prediction of M/M (Table 3, Fig. 4). In both cases, BNP provided the largest increase in prognostic information.
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The individual baseline NHs evaluated in patients with moderate to severe, stable HF in the present study were found to be significant markers of mortality and morbidity as previously reported in several studies.710,17,18The main new finding of this study is that BNP is the most powerful indicator of outcome in this large and representative population of HF patients, treated with background therapy that included ACEi and BB in addition to digoxin and diuretics. BNP proved to be the strongest predictor of mortality and morbidity, but NE and PRA were found to have independent prognostic value and to significantly increase the predictability of outcome when added to BNP assay. Valsartan did not significantly modify the predictive value of neurohormonal activation.
Patients in Val-HeFT were treated with background drug therapy and half were randomized to receive valsartan. ACEi, prescribed to 93% of the population, are known to raise PRA levels and reduce NE and BNP.8,9,19BB may reduce PRA2022and, may23or may not22,24reduce BNP. In Val-HeFT, lowest baseline PRA in patients on BB supports the view that these drugs modulate not only the adrenergic, but also the renin-angiotensin system. The lower baseline concentrations of BNP in patients on BB in Val-HeFT might be partly due to lower severity of the disease in this subgroup. The lower levels of aldosterone in patients on ACEi compared to those not on ACEi suggests the absence of complete aldosterone escape.25Valsartan was shown in Val-HeFT to reduce NE and BNP.16Nonetheless, baseline hormone levels remained highly predictive of subsequent mortality and morbidity. Thus the confounding influence of NH inhibiting therapy for HF does not appear, in general, to obscure the relationship between hormone levels and outcome. However, an exception needs to be pointed out: the prognostic value of aldosterone was very low, if any, in all patients, but aldosterone above the median at baseline was a significant marker of worse outcome in the minority of patients (7%) not on ACEi at randomization. The lower concentrations of aldosterone at baseline found in patients on ACEi in Val-HeFT (132±2pg/ml vs 190±11pg/ml, ACEi yes vs no, P<0.0001) might explain the lack of relation with outcome in this group. However, the limitation of any post-hoc analysis and that due to uneven distribution of non-randomized treatments (i.e. 113 patients not on ACEi with aldo < median and 194 patients with aldo median) should be pointed out. On the other hand, neither ACEi nor BB affected the prognostic value of PRA at baseline. Thus PRA, even in the presence of ACEi which increase its levels, still remains a prognostic marker in Val-HeFT.
The relationship between elevated hormone levels and poor outcome could reflect the possibility that hormonal activation is contributing to progression of HF or that the elevated levels are merely serving as markers for the severity of the disease. The renin-angiotensin-aldosterone system, the sympathetic nervous system and aldosterone have all been implicated pathophysiologically in the progression of structural remodelling of the left ventricle and vasculature.2628Indeed, drug therapy to inhibit these systems has a favourable effect on prognosis, either alone or in combination.29It is surprising, therefore, that BNP, which is thought to be protective rather than deleterious, exhibits so much more predictive value. Indeed, aldosterone provides little predictive value despite the evidence that blocking it produces a striking reduction in mortality in heart failure.30Plasma hormone levels do not by themselves describe theactivity of NH activation and it is thus possible that tissue effects and receptor sensitivity might be playing a role.31,32
Benefit from valsartan on morbidity and mortality tended to be higher in patients with higher aldosterone or PRA at baseline. Although the interaction did not reach statistical significance, these results suggest that selective Ang II blockade might be more effective when RAAS is more activated. However, the overall lack of statistical significance in tests for interaction between baseline NHs and study treatments on outcome does not encourage the assessment of NH activation to predict the response to valsartan. In CONSENSUS8and V-HeFT II9benefits from ACE inhibition were more marked in patients with elevated plasma NHs. In a study in 206 patients with ischaemic left ventricular dysfunction,33carvedilol reduced mortality and morbidity more in patients with baseline BNP above median but with plasma NE below median. In 534 post-myocardial infarction patients in the SAVE trial, captopril did not appear to modify the relationship between NH activation and outcome.34In the 450 patients in V-HeFT III, treatment with felodipine did not reduce deaths from all causes in the overall population or in the group with high ANP and NE.35From all available evidence it appears that there is no agreement on a neurohormonal predictor of response to drug therapy in HF. Furthermore, the higher risk associated with intense NH activation may render a mortality reduction in this subgroup the consequence of statistical likelihood.
The value of BNP as a sensitive guide to outcome in HF is consistent with recent publications emphasizing its value in predicting re-hospitalization and in diagnosing HF.3638It should be noted, however, that half the patients with chronic HF in Val-HeFT had BNP levels below the 100pg/ml threshold that has been used to diagnose HF.39Furthermore, the lowest quartile (<41pg/ml) was well within the normal limits for BNP.40The data suggest that a surprisingly high fraction of patients with well-established and well-controlled chronic HF may present with normal BNP levels. Nonetheless, the normal levels appear to be associated with a good prognosis.
This NH data from Val-HeFT has important potential clinical applications. Hormonal assays, particularly BNP and NE, could be useful as a prognostic marker in individual patients for therapeutic decision-making. Furthermore, in trial design aimed at reducing events, plasma hormone assays in screened patients might be used to identify a high-risk population in order to reduce the sample size required to demonstrate therapeutic efficacy on end-points. The powerful independent prognostic value of BNP, NE and PRA, after correcting for the influence of the usual clinical markers used to identify high risk, make it clear that the current criteria for clinical trial entry could be markedly enhanced by hormone assay.
All evidence from Val-HeFT confirms and extends the high predictive value of BNP concentrations, not only for death, but also for HF hospitalizations, the most frequently occurring component of the combined morbidity end-point.13These data, together with the marked and sustained decrease of BNP observed with valsartan, further supports the value of BNP as a surrogate marker41in the follow-up of patients with HF and in individualizing drug dosing.
Acknowledgments
Paola Cardano provided valuable statistical assistance; Marjorie Carlson, Noeleen De Angelis, Tarcisio Vago and Gabriella Baldi contributed effectively to neurohormonal assays in Minneapolis and Milan, respectively. This study was supported by a grant from Novartis Pharma, Basle, Switzerland.
Footnotes
References
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