Baseline values, serial measurements, or both of multiple biomarkers (copeptin, a peptide co-secreted with arginine vasopressin; hyponatremia; B-type natriuretic peptide [BNP]; and cardiac troponin T [cTnT]) may improve risk stratification in outpatients with chronic heart failure. A cohort of 157 patients with class III or IV heart failure was prospectively evaluated every 3 months over 2 years with regard to biomarker levels and risk for death or cardiac transplantation. Copeptin ≥40 pmol/L (cohort fourth quartile value), hyponatremia (≤135 mEq/L), BNP >3 times the upper range limitation of normal adjusted for age and gender, and cTnT ≥0.01 ng/ml were pre hoc determined cut points. After multivariate time-dependent regression analysis, copeptin (hazard ratio [HR] 2.26, 95% confidence interval [CI] 1.2 to 4.3, p = 0.014) and BNP (HR 1.89, 95% CI 1.0 to 3.5, p = 0.047), but not hyponatremia, were associated with the primary end point of death or cardiac transplantation. In contrast to univariate prediction of mortality and transplantation, hyponatremia (HR 1.74, 95% CI 0.9 to 3.4, p = 0.099) and cTnT ≥0.01 ng/ml (HR 1.89, 95% CI 1.0 to 3.7, p = 0.064) were not predictive in multivariate models. Interaction models of copeptin with hyponatremia, adjusted for BNP and cTnT, improved the predictive capacity of serial measurements (HR 4.20, 95% CI 1.6 to 8.9, p = 0.004). In conclusion, marked elevations of copeptin, particularly in serial measurements, are independent predictors of poor outcomes. The combination of elevated copeptin with hyponatremia, when adjusted for BNP and cTnT, is an even stronger predictor. These markers appear to reflect activation of the arginine vasopressin system present even in the absence of overt clinical changes. A strategy of serial monitoring of copeptin in combination with hyponatremia may be valuable in identifying higher risk patients with heart failure.
The syndrome of heart failure (HF) is characterized by the activation of multiple neurohormonal mechanisms that include the arginine vasopressin (AVP) system. This is often accompanied by hyponatremia, which is also a marker of mortality risk in patients with chronic HF. Copeptin (CT-pro-vasopressin) is synthesized together with AVP and released from the posterior pituitary gland. Copeptin may serve as a highly measurable surrogate analyte for monitoring AVP activity. Copeptin levels have been shown to be elevated in patients with chronic systolic HF and to have prognostic value. In this study we hypothesized that markedly elevated plasma copeptin concentrations (≥40 pmol/L) would show an association with hyponatremia (sodium ≤135 mEq/L) in ambulatory outpatients with HF by predicting increased risk for death or need for cardiac transplantation. We also tested whether copeptin and hyponatremia enhanced risk stratification over and above that of a model including the more established biomarkers B-type natriuretic peptide (BNP) and cardiac troponin T (cTnT).
Methods
A cohort of 170 patients with New York Heart Association class III or IV left ventricular systolic HF was prospectively enrolled from June 2001 to January 2004. Patients referred to the Mayo Heart Failure Clinic were recruited, with informed consent obtained after a primary medical evaluation. Patients were excluded if cardiac revascularization was anticipated within 6 months of enrollment, if they were awaiting cardiac transplantation, or if they had experienced episodes of acute HF decompensation within 30 days. Patients were followed at prespecified intervals of 3 months ± 3 weeks, with biomarker measurements for 24 months. The study was approved by the Mayo Foundation Institutional Review Board and included only patients who provided written consent as required by Minnesota Statute 144.335/Code of Federal Regulations 21 (Part 50).
Blood samples were collected in ethylenediaminetetraacetic acid, immediately placed on ice, processed, and stored at −70°C until batch analysis was performed. The left ventricular ejection fraction was derived by echocardiography performed <3 months before enrollment. An updated patient history, including interim clinical status, routine clinically indicated blood studies, and physical examination, was completed at each 3-month follow-up visit. The mean follow-up duration was 19.1 ± 7.7 months.
Copeptin concentrations were measured from ethylenediaminetetraacetic acid plasma by immunoluminometric assays (CT-proAVP LIA [copeptin]) provided by BRAHMS Aktiengesellschaft (Henningsdorf, Germany) on a Berthold LB952 Auto CliniLumat Luminescence analyzer. Copeptin (inter- and intra-assay coefficients of variation <10%) was measured with coated tube immunoluminometric assays. The details for BNP and cTnT measurements for this study have been previously reported. The pre hoc definitions of elevated biomarker levels for the purpose of this study were chosen in an attempt to ensure the identification of patients with marked activation of the AVP and natriuretic peptide systems, who should be at highest risk. For copeptin, an elevated value was defined as ≥40 pmol/L (corresponding approximately to the 70th to 80th percentiles in patients with decompensated HF in previous evaluations, including our own ). Normal copeptin levels are typically <7.1 pmol/L in women and <9.4 pmol/L in men. For BNP, elevated levels were defined as ≥3 times the 95th percentile of the upper range limitation of normal adjusted for age and gender using the Shinogi method. Serum sodium levels were determined by standard clinical assay, with hyponatremia defined pre hoc as values ≤135 mEq/L. Cut points for elevated cTnT levels were defined as values ≥0.01 ng/ml (i.e., greater than the 99th percentile of normal) using the fourth-generation assay on the Roche Elecsys analyzer (Roche Diagnostics, Indianapolis, Indiana). This maximized the predictive value of cTnT in this cohort. Renal function was determined at study enrollment and every 3 months by calculation of estimated glomerular filtration rate (GFR) using the Modification of Diet in Renal Disease (MDRD) equation.
Continuous variables are reported as mean ± SD and medians with 25th and 75th percentile interquartile ranges. Categorical variables are reported as frequencies of total values. Student’s t test and Pearson’s chi-square test were used to evaluate differences between patients who had elevated copeptin at baseline and those who did not. The variables that were significant univariately were used to develop a multivariate logistic regression model to determine variables associated with an elevated copeptin value. The coefficients from the logistic regression were used to calculate the propensity score for each subject, which was used for covariate adjustment in subsequent models. The study end point was the time until death or cardiac transplantation. The goal was to evaluate the relations over time (2 years) between the primary end point and elevated copeptin levels in relation to serum sodium, plasma BNP, and cTnT values. Modeling was done with Cox proportional-hazards models. We categorized each of the biomarkers dichotomously as either elevated or not elevated (for copeptin, BNP, and cTnT) and low sodium or normal sodium on the basis of the definitions described previously. Results are reported as hazard ratios (HRs) with corresponding 95% confidence intervals (CIs). Time-dependent Cox multivariate models were used to allow for the changes (normal to elevated and elevated to normal) in biomarkers at each of the 3-month follow-up periods. In the time-dependent Cox multivariate models, patients were included in the initial proper risk set but allowed to move between risk sets (high and low risk) over time. Sodium values were available for baseline measurements only and therefore viewed as unchanged in the time-dependent analyses. All clinical variables were also based on values at study enrollment. Kaplan-Meier survival curves were used to summarize follow-up outcomes and account for changes in biomarker levels during the study period. Differences in survival curves were evaluated using log-rank tests. Analyses were done using SAS version 9 software (SAS Institute Inc., Cary, North Carolina).
Results
Table 1 shows the clinical and demographic characteristics of the outpatient study cohort with chronic HF. Of the 200 patients enrolled, 13 had insufficient biomarker data, and 30 had nonischemic and nonidiopathic dilated cardiomyopathy and for the purposes of this analysis were included; therefore, results are reported for 157 participants. The average duration of HF at the time of enrollment was 44.2 ± 43.8 months (median 33). Six patients (4%) went on to cardiac transplantation, and 44 patients (28%) died during the study period.
| Variable | Mean ± SD | Median (Interquartile Range) | n (%) |
|---|---|---|---|
| Age (yrs) | 71 ± 10 | 73 (65–79) | 157 |
| Men | 125 (80) | ||
| Caucasian/Native American | 155/2 | ||
| New York Heart Association functional class | |||
| III | 142 (90) | ||
| IV | 15 (10) | ||
| Duration of HF (mo) | 44.2 ± 43.8 | 33 (7–67) | 157 |
| Left ventricular ejection fraction (%) | 24.9 ± 9.2 | 23 (18–28) | 157 |
| Body mass index (kg/m 2 ) | 29.2 ± 6.6 | 28 (25–33) | 157 |
| Heart rate (beats/min) | 70 ± 12 | 70 (62–78) | 157 |
| Systolic blood pressure (mm Hg) | 113 ± 20 | 110 (98–124) | 157 |
| Diastolic blood pressure (mm Hg) | 62 ± 11 | 60 (58–70) | 157 |
| Hemoglobin (g/dl) | 12.6 ± 1.7 | 12.5 (11.1–13.7) | 144 |
| Serum creatinine (mg/dl) | 1.7 ± 0.6 | 1.5 (1.3–1.9) | 157 |
| GFR (ml/min/1.73 m 2 ) | 46 ± 15 | 45 (35–57) | 157 |
| Potassium (mEq/L) | 4.4 ± 0.5 | 4.4 (4.1–4.8) | 157 |
| Sodium (mEq/L) | 139 ± 3.9 | 140 (137–142) | 157 |
| Copeptin (pmol/L) | 25.1 ± 25.6 | 16.8 (7.4−31.1) | 157 |
| BNP (pg/ml) | 406 ± 422 | 304 (115–524) | 157 |
| cTnT (ng/ml) | 0.081 ± 0.539 | 0.012 (0.005–0.034) | 157 |
| Cause of HF | |||
| Ischemic | 103 (66) | ||
| Idiopathic dilated cardiomyopathy | 54 (34) | ||
| Diabetes | 57 (36) | ||
| Hypertension | 101 (64) | ||
| Hyperlipidemia | 110 (70) | ||
| Chronic obstructive pulmonary disease | 41 (26) | ||
| Past coronary artery bypass grafting | 75 (48) | ||
| Biventricular pacemaker | 10 (6) | ||
| Automatic implantable cardioverter-defibrillator | 44 (28) | ||
| Previous myocardial infarction | 86 (55) | ||
| Previous cerebrovascular accident | 10 (6) | ||
| Smokers | 102 (65) | ||
| Atrial fibrillation | 67 (43) | ||
| Aortic stenosis | 16 (10) | ||
| Aortic regurgitation | 37 (24) | ||
| Mitral regurgitation | 115 (73) | ||
| Tricuspid regurgitation | 99 (63) | ||
| Status post valve replacement surgery | 13 (8) | ||
| Medications | |||
| Angiotensin-converting enzyme inhibitors | 118 (75) | ||
| Angiotensin receptor blockers | 28 (18) | ||
| β blockers | 122 (78) | ||
| Aldosterone antagonists | 41 (26) | ||
| Digoxin | 100 (64) | ||
| Diuretics | 143 (91) | ||
| Aspirin | 99 (63) | ||
| Nitrates | 52 (33) | ||
| Antidysrhythmic agents | 33 (21) |
At study enrollment, copeptin levels were elevated (≥40 pmol/L) in 29 patients (19%). During the course of the study, another 28 patients developed new elevations in copeptin >40 pmol/L. Thus, overall, 36.3% of patients had markedly elevated copeptin levels during the course of the study. Hyponatremia (serum sodium ≤135 mEq/L) was present at study enrollment in 30 patients (20%). BNP was elevated to >3 times the upper range limitation of normal adjusted for age and gender at enrollment in 35 patients (22%). An additional 32 patients developed this level of BNP elevation during the study. Overall, 43% of patients had elevated BNP levels >3 times the upper limit of normal during the course of the study. Levels of cTnT were ≥0.01 ng/ml in 83 patients (53%), and during the study, 24 additional patients developed elevations in cTnT.
When analyzing the patient cohort as a function of baseline copeptin levels greater than and less than 40 pmol/L, the differences identified between subgroups were age (76 ± 8 vs 70 ± 10 years, p = 0.008), creatinine (2.1 ± 0.6 vs 1.6 ± 0.5 mg/dl, p <0.001), GFR (34.1 ± 10.4 vs 48.8 ± 14.9 ml/min/1.73 m 2 , p <0.001), BNP (median 598 pg/ml [interquartile range 307 to 1,149] vs 241 pg/ml [interquartile range 96 to 455], p <0.001), and history of coronary artery bypass graft surgery (69% vs 43%, p = 0.011). All other variables as listed in Table 1 were not different between the subgroups. With propensity score analysis, only age, GFR, and history of coronary artery bypass graft surgery retained significant associations with copeptin level ≥40 pmol/L.
Univariate analysis using baseline single-point-in-time values of the biomarkers in the prediction of death or need for cardiac transplantation demonstrated elevated copeptin and cTnT to be significant predictors of the primary outcome over 2 years of follow-up ( Table 2 ). In contrast, neither elevated BNP nor hyponatremia (sodium ≤135 mEq/L) were significant predictors of outcomes.
| Variable | HR | 95% CI | p Value |
|---|---|---|---|
| Univariate model | |||
| BNP >3 times upper range limitation of normal | 1.73 | 0.95–3.17 | 0.075 |
| Copeptin ≥40 pmol/L | 2.03 | 1.09–3.76 | 0.025 |
| Sodium ≤135 mEq/L | 1.47 | 0.77–2.81 | 0.247 |
| cTnT ≥0.01 ng/ml | 2.94 | 1.58–5.46 | <0.001 |
| cTnT >0.03 ng/ml | 2.83 | 1.62–4.94 | <0.001 |
| Multivariate model | |||
| BNP >3 times upper range limitation of normal | 1.33 | 0.71–2.50 | 0.372 |
| Copeptin ≥40 pmol/L | 1.47 ∗ | 0.75–2.87 | 0.258 |
| Sodium ≤135 mEq/L | 1.51 ∗ | 0.76–3.01 | 0.237 |
| cTnT ≥0.01 ng/ml | 2.48 ∗ | 1.28–4.80 | 0.007 |
∗ Adjusted for significant univariate predictors and significant copeptin propensity score analysis variables (age, GFR, and history of coronary artery bypass graft surgery).
Univariate analysis using baseline clinical variables for the whole cohort showed an elevated risk for the following variables: increasing New York Heart Association functional class (HRo 3.59, 95% CI 1.79 to 7.20, p <0.001), presence of biventricular pacing (HR 4.22, 95% CI 1.89 to 9.44, p <0.001), history of myocardial infarction (HR 2.88, 95% CI 1.50 to 5.51, p = 0.001), and history of stroke (HR 2.49, 95% CI 1.06 to 5.86, p = 0.036). Reduced risk was associated with a nonischemic cause of HF (HR 0.46, 95% CI 0.24 to 0.90, p = 0.024) and higher GFR (HR 0.96, 95% CI 0.95 to 0.99, p <0.001). The multivariate analysis adjusted for copeptin propensity score demonstrated only elevated cTnT ≥0.01 ng/ml remaining as a significant predictor of outcomes when using single-sample baseline measurements ( Table 2 ).
Univariate time-dependent analyses of serial measurements over 2 years for the prediction of death or transplantation showed that serial elevated levels of copeptin, BNP, and cTnT were predictive of the primary end point, while hyponatremia was not predictive ( Table 3 ). Figure 1 illustrates the Kaplan-Meier survival analysis for serial copeptin levels greater than and less than 40 pmol/L. However, in multivariate analysis adjusted for propensity score, serial copeptin and BNP values were significant predictors of death or need for cardiac transplantation ( Table 3 ), while cTnT was no longer a significant predictor, and hyponatremia remained nonpredictive.
