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Proteomics and Protein Markers |
1 Division of Critical Care, Fujita Health University Graduate School of Health Sciences, 2 Department of Internal Medicine, Fujita Health University School of Medicine, 3 Department of Joint Research Laboratory of Clinical Medicine, Fujita Health University Hospital, and 4 Department of Clinical Chemistry, Fujita Health University School of Health Sciences, Toyoake 470-1192, Japan.
aAddress correspondence to this author at: Division of Critical Care, Fujita Health University Graduate School of Health Sciences, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake 470-1192, Japan. Fax 81-562-93-2315; e-mail jishii{at}fujita-hu.ac.jp.
| Abstract |
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Methods: We measured serum cTnT, plasma BNP, and left ventricular ejection fraction (LVEF) on admission for worsening CHF [New York Heart Association (NYHA) functional class III to IV] and 2 months after initiation of treatment to stabilize CHF (n = 100; mean age, 68 years).
Results: Mean (SD) concentrations of cTnT [0.023 (0.066) vs 0.063 (0.20) µg/L] and BNP [249 (276) vs 753 (598) ng/L], percentage increased cTnT (>0.01 µg/L; 35% vs 60%), NYHA functional class [2.5 (0.6) vs 3.5 (5)], and LVEF [43 (13)% vs 36 (12)%] were significantly (P <0.01) improved 2 months after treatment compared with admission. During a mean follow-up of 391 days, there were 44 cardiac events, including 12 cardiac deaths and 32 readmissions for worsening CHF. On a stepwise Cox regression analysis, increased cTnT and BNP were independent predictors of cardiac events (P <0.001). cTnT >0.01 µg/L and/or BNP >160 ng/L 2 months after initiation of treatment were associated with increased cardiac mortality and morbidity rates.
Conclusion: The combination of cTnT and BNP measurements after initiation of treatment may be highly effective for risk stratification in patients with CHF.
| Introduction |
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The combination of cTnT, a marker for ongoing myocardial damage (1)(2)(3)(4), and B-type natriuretic peptide (BNP), a marker for left ventricular overload (10)(11), might effectively stratify patients with CHF. Recently we measured cTnT and BNP concentrations on admission in 98 consecutive patients hospitalized for worsening CHF and monitored these individuals for adverse outcome during a mean follow-up period of 451 days after admission. We showed that cTnT >0.033 µg/L and/or BNP >440 ng/L on admission could reliably stratify the patients into low-, intermediate-, and high-risk groups for cardiac mortality and morbidity (12). Accordingly, this study was prospectively designed to determine whether the combination of measuring cTnT and BNP concentrations after additional medical treatment for CHF could stratify patients with CHF.
| Materials and Methods |
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study protocol
Venous blood samples were obtained for measurements of cTnT and BNP concentrations on admission and 2 months after treatment had been initiated to stabilize each patients condition. At the same time, two-dimensional echocardiography was performed by experts blinded to the study, and left ventricular ejection fraction (LVEF) was calculated by use of the modified Simpson rule.
All patients underwent clinical follow-up for a mean period of 391 days (range, 16884 days). Cardiac events, which were judged by researchers blinded to the biochemistry results, were defined as cardiac death (death from worsening CHF, fatal myocardial infarction, or sudden death) and readmission for worsening CHF or myocardial infarction. Myocardial infarction was defined by a combination of two of three characteristics: typical symptoms, time-dependent changes in serum creatine kinase MB activity, and a typical electrocardiographic pattern involving the development of Q waves. The diagnosis of worsening CHF was established by researchers blinded to biochemistry results on the basis of symptoms, physical findings, and evidence of pulmonary congestion on chest radiography. All patients who did not have a cardiac event underwent clinical follow-up for >12 months.
Physicians blinded to the results of the biochemical tests independently selected the appropriate therapy and managed the patients according to standard protocols using outcome measures such as improvement in symptoms, physical findings, and evidence of pulmonary congestion on chest radiography (13). Diuretics were given in flexible dosages on the basis of body weight and daily diuresis. Spironolactone was administered as 25 or 50 mg/day. Angiotensin-converting enzyme inhibitor, angiotensin II receptor blocker, and beta-blocker were gradually increased to the maximum dosage possible for 2 months. The maximum dosages were 5 mg/day for enalapril, 5 mg/day for imidapril, 2 mg/day for temocapril, 50 mg/day for losartan, and 20 mg/day for carvedilol.
measurements of biochemical markers
Blood samples for measuring serum cTnT were centrifuged at 4 °C for 15 min at 1000g and stored at -70 °C until assayed. A third-generation Enzymun Test Troponin T assay was used, based on a prototype of the new electrochemiluminescence-based Elecsys system (Roche Diagnostics, Tokyo, Japan). The lower limit of detection of the assay for cTnT was 0.01 µg/L. The imprecision for cTnT assay was 14% at 0.012 µg/L and 8.7% at 0.024 µg/L. cTnT was not detectable in 100 healthy adult volunteers.
Blood samples for measuring plasma BNP were collected in chilled tubes containing EDTA, disodium salt, and aprotinin (500 IU/mL). The plasma was separated by centrifugation at 4 °C for 15 min at 1000g and then stored at -70 °C until analysis. BNP concentrations were measured by a commercial RIA for human BNP (Shiono RIA BNP assay; Shionogi Co., Ltd.). The lower limit of detection and the upper limit of the reference interval were 2 and 18.4 ng/L, respectively, for the BNP assay. The intraassay and interassay CV for BNP assay were 5.2% and 6.1%, respectively.
data analysis
Continuous variables were analyzed using the MannWhitney U-test, Wilcoxon paired sign-rank test, or linear regression analysis, and the data are expressed as mean (SD). Values below the lower detection limit of the assay were defined as zero. Categorical variables were compared by the
2 test. Univariate and stepwise multivariate Cox regression analyses were used to evaluate the prognostic value of variables. Cardiac event-free survival was determined according to the KaplanMeier method, and comparison of cardiac event-free survival between subgroups was performed using the log-rank test. ROC curves were used to determine the cutoff values of the biochemical markers for predicting cardiac events (14). P values <0.05 were considered significant.
| Results |
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Follow-up was complete in all study patients. During the follow-up period, there were 2 noncardiac deaths (1 gastric cancer and 1 pneumonia) and 44 (44%) cardiac events, including 12 cardiac deaths and 32 readmissions for worsening CHF. The causes of cardiac death were worsening CHF in 9 patients and sudden death in 3 patients.
At 2 months after the start of treatment, cTnT and BNP concentrations, NYHA functional class, and LVEF were significantly better than at the time of admission (Table 1
). The percentage of increased cTnT (>0.01 µg/L) was significantly decreased at 2 months compared with on admission (35% vs 60%; P <0.001). At 2 months after treatment, cTnT was detectable in 11 (19%) of 57 patients in NYHA class II and in 24 (56%) of 43 patients in NYHA class III or class IV. There was a significant but weak correlation between cTnT and log BNP concentrations 2 months after initiation of treatment (r = 0.24; P <0.05).
Patients who died from a cardiac cause were older (P <0.05); had higher concentrations of cTnT, BNP, and creatinine (P <0.01); had a higher NYHA class (P <0.05); and had a lower LVEF (P <0.05) after treatment was established compared with those who did not die from a cardiac cause (Table 1
). Patients who had a cardiac event were older (P <0.05); had higher concentrations of cTnT, BNP, and creatinine (P <0.01); had a higher NYHA class (P <0.01); and had a lower LVEF (P <0.01) after establishment of treatment (Table 1
). However, the number of patients with IHD and the treatment regimens were similar in the two groups.
The areas under the ROC curves for cTnT and BNP after treatment was initiated [0.73; 95% confidence interval (CI), 0.630.83 for cTnT; 0.72; 95% CI, 0.600.84 for BNP] did not differ significantly from each other (Fig. 1
). The optimal values of cTnT and BNP for predicting cardiac events were defined as the concentration with the largest sum of sensitivity plus specificity for each of the curves; for cTnT, the optimal concentration was 0.01 µg/L, and for BNP, it was 160 ng/L. The sensitivity, specificity, positive and negative predictive values, and overall accuracy for predicting cardiac death and cardiac events in patients with a serum cTnT >0.01 µg/L were 100% (12 of 12) and 61% (27 of 44), 74% (65 of 88) and 86% (48 of 56), 34% (12 of 35) and 77% (27 of 35), 100% (65 of 65) and 74% (48 of 65), and 77% (77 of 100) and 75% (75 of 100), respectively. The corresponding sensitivity, specificity, positive and negative predictive values, and overall accuracy in patients with a plasma BNP >160 ng/L were 83% (10 of 12) and 73% (32 of 44), 57% (50 of 88) and 71% (40 of 56), 21% (10 of 48) and 67% (32 of 48), 96% (50 of 52) and 77% (40 of 52), and 60% (60 of 100) and 72% (72 of 100), respectively.
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The univariate and multivariate predictors of cardiac event and cardiac death are summarized in Table 2
. On a stepwise Cox regression analysis including age, sex, etiology, NYHA class, LVEF, creatinine, cTnT, and BNP, only cTnT (P = 0.0001) and BNP (P = 0.0005) concentrations after treatment were independent predictors of cardiac events. In addition, when cTnT >0.01 µg/L and BNP >160 ng/L after treatment were included in a multivariate model as continuous variables, cTnT >0.01 µg/L (P = 0.0009) and BNP >160 ng/L (P = 0.013) were independent predictors of cardiac events.
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A cTnT concentration >0.01 µg/L and/or BNP >160 ng/L 2 months after initiation of treatment correlated with an incremental increase in cardiac mortality and cardiac morbidity rates (Fig. 2
). With this combination, patients with or without BNP >160 ng/L could be further classified into two different risk groups for cardiac events (group II vs group IV, P <0.01; group I vs group III, P <0.1) and cardiac death (group II vs group IV, P <0.01; group I vs group III, P <0.05). In addition, patients with or without cTnT >0.01 µg/L could be further classified into two different risk groups for cardiac event (group III vs group IV, P <0.1; group I vs group II, P <0.1). Thus the combination of cTnT and BNP concentrations after additional treatment appeared to improve the ability to stratify risk in patients with CHF over the individual use of these markers, especially BNP alone. KaplanMeier analysis showed that this combination could be used to stratify the patients into the four groups for cardiac events (Fig. 3
).
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| Discussion |
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Serum cTnT after treatment was initiated decreased in parallel with the decrease in BNP concentrations, improvement in LVEF, and symptom reduction, suggesting that ongoing myocardial damage may be partly suppressed by the treatment of CHF. Serum cTnT was still measurable 2 months after initiation of treatment in 35% of clinically stable patients with CHF. Such patients were at increased risk for cardiac death and cardiac events. cTnT was detectable after treatment was begun in all 12 patients who died of a cardiac death, and the cTnT concentration after initiation of treatment was an independent predictor of cardiac morbidity. These findings suggested that ongoing myocardial damage may play an important role in the progression of CHF and lead to an adverse outcome (1)(2)(3)(4)(5)(6)(7).
In the present study, the combination of cTnT and BNP after treatment was able to stratify these clinically stable patients into four groups for adverse outcomes. The weak correlation between cTnT and BNP concentrations suggests that markers specific for ongoing myocardial damage and left ventricular overload reflect different aspects of the pathophysiology of CHF and may identify different groups of patients at risk. It is reasonable to expect that patients who have both ongoing myocardial damage and left ventricular overload are at greatest risk.
The authors of a recent study reported that amino-terminal proBNP-guided treatment of heart failure reduced total cardiovascular events and delayed time to first event compared with intensive clinically guided treatment (17). In the present study, the combination of cTnT and BNP concentrations after additional treatment appeared to improve the ability to stratify risk in patients with CHF over the use of these markers individually, particularly BNP alone. Thus, our results indicate that the combination of cTnT and BNP might be used to guide the treatment of patients with CHF. When patients are categorized as group II or especially IV after additional treatment, further treatment and intensive care might improve the prognosis. When patients are rated as group III after additional treatment, even in the absence of high concentrations of BNP, further treatment to decrease the cTnT concentrations might be needed to reduce cardiac events. Additional studies are needed before treatment decisions can be based on these measurements.
The multivariate analysis showed that LVEF tended to be an independent predictor of cardiac events. These findings indicate that combinations of LVEF and cTnT, LVEF and BNP, or of both biochemical markers together with LVEF might effectively stratify patients with CHF. Further studies are needed to clarify the utility of these combinations in patients with CHF.
It is difficult to completely exclude the possibility that increased concentrations of BNP and, particularly, cTnT might be related to ischemic cell injury attributable to ACS. We therefore investigated the association of adverse outcome with these markers 2 months after initiation of treatment, when patients were in stable clinical condition. We also ruled out patients who had clinical or electrocardiographic evidence suggestive of ACS or those who received coronary revascularization for 2 months after the initiation of treatment. We believe that this strategy can minimize the possibility that increased concentrations of these markers after treatment are caused by ischemic cell injury attributable to ACS.
Recent studies have shown that increased concentrations of cTnT (18)(19)(20)(21) and BNP (22)(23) may be independently associated with poor prognosis in patients undergoing chronic hemodialysis. It would be interesting to determine whether our findings might apply to patients with severe renal failure. However, to minimize the effects of renal clearance, we excluded patients with serum creatinine concentrations >30 mg/L.
In the present study, there was a relatively small number of cardiac events (n = 44) for every putative predictor (n = 8) included in multivariate models. In addition, we could not use multivariate models to determine independent predictors of cardiac mortality because of the low number of cardiac deaths (n = 12). Thus, additional studies should be carried out in a larger CHF population to confirm our results.
Threshold values derived from the ROC curves are highly dependent on the study population and might have been different in another set of patients. Thus, the threshold values for cTnT and BNP that were used in the present study should be confirmed in larger follow-up studies. In addition, in the present study treatments were not randomized. Thus, it was difficult to evaluate the effects of specific drugs for CHF on adverse outcomes.
In conclusion, the combination of cTnT and BNP measurements after initiation of treatment may be highly effective for risk stratification in patients with CHF.
| Acknowledgments |
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| Footnotes |
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| References |
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