Testing the wrong hypothesis: the failure to recognize the limitations of troponin assays

Association of NTproBNP and cTnI with outpatient sudden cardiac death in hemodialysis patients: the Choices for Healthy Outcomes in Caring for ESRD (CHOICE) study

BACKGROUND

Sudden cardiac death (SCD) is the most common etiology of death in hemodialysis patients but not much is known about its risk factors. The goal of our study was to determine the association and risk prediction of SCD by serum N-terminal prohormone of brain natriuretic peptide (NTproBNP) troponin I (cTnI) in hemodialysis patients.

METHODS

We measured NTproBNP and cTnI in 503 hemodialysis patients of a national prospective cohort study. We determined their association with SCD using Cox regression, adjusting for demographics, co-morbidities, and clinical factors and risk prediction using C-statistic and Net Reclassification Improvement (NRI).

RESULTS

Patients' mean age was 58 years and 54 % were male. During follow-up (median 3.5 years), there were 75 outpatient SCD events. In unadjusted and fully-adjusted models, NTproBNP had a significant association with the risk of SCD. Analyzed as a continuous variable, the risk of SCD increased 27 % with each 2-fold increase in NTproBNP (HR, 1.27 per doubling; 95 % CI, 1.13-1.43; p < 0.001). In categorical models, the risk of SCD was 3-fold higher in the highest tertile of NTproBNP (>7,350 pg/mL) compared with the lowest tertile (<1,710 pg/mL; HR for the highest tertile, 3.03; 95 % CI, 1.56-5.89; p = 0.001). Higher cTnI showed a trend towards increased risk of SCD in fully adjusted models, but was not statistically significant (HR, 1.17 per doubling; 95 % CI, 0.98-1.40; p = 0.08). Sensitivity analyses using competing risk models showed similar results. Improvement in risk prediction by adding cardiac biomarkers to conventional risk factors was greater with NTproBNP (C-statistic for 3-year risk: 0.810; 95 % CI, 0.757 to 0.864; and continuous NRI: 0.270; 95 % CI, 0.046 to 0.495) than with cTnI.

CONCLUSIONS

NTproBNP is associated with the risk of SCD in hemodialysis patients. Further research is needed to determine if biomarkers measurement can guide SCD risk prevention strategies in dialysis patients.

Troponin I as a prognostic marker of cardiac events in asymptomatic hemodialysis patients using a sensitive troponin I assay

Elevated troponin T is known to be a prognostic marker for long-term cardiac events and mortality in asymptomatic end-stage renal disease patients. There are conflicting data in this regard with respect to troponin I (TnI). We recently showed a high incidence of elevated TnI levels in asymptomatic hemodialysis (HD) patients using a new generation sensitive TnI assay. The aim of this pilot study was to explore the prognostic value of TnI, as measured with this new assay, as a marker for outcomes in HD patients over a 2-year follow-up period. Fifty-one asymptomatic HD patients were enrolled, and pre-dialysis TnI levels were checked once monthly over 3 consecutive months. Patients were considered to be in the TnI positive group if TnI level on any of the three draws was ≥0.035 ng/ml. All patients were followed for a period of 2 years. The primary end points were acute coronary syndrome, coronary revascularization, sudden death, or cardiac arrest. The secondary end point was all-cause mortality. Elevated TnI levels were found in 51% (26/51) of patients in our cohort. One TnI positive patient was subsequently lost to follow up. There were 6 cardiac events over 2 years, all of which were in the troponin positive group (6/25 or 24%). The presence of a positive TnI at baseline was significantly associated with future cardiac events (p=0.022). A prior history of coronary artery disease (CAD) was also significantly related to future cardiac events (p=0.010). No patient with negative TnI at baseline developed a cardiac event, while 45.5% of those with both a positive TnI and a history of CAD had an event. Fourteen deaths occurred over 2 years, 8 in TnI positive and 6 in the negative group. All-cause mortality was not associated with elevated TnI levels at baseline. We found a significant association between positive TnI and subsequent cardiac events in asymptomatic HD patients followed for 2 years. TnI levels, as measured with a sensitive assay, may be useful in assessing cardiac risk in asymptomatic HD patients. This needs further confirmation in a larger cohort.

Cardiac troponins in renal failure - time for an optimistic consensus?

Elevated cardiac troponin concentrations are now accepted as the gold standard biochemical markers for the diagnosis of myocardial damage in patients with unstable coronary syndromes, having also a demonstrated value in early risk stratification and in adopting different therapeutic strategies. The specificity and sensitivity of cardiac troponins for diagnosis of acute coronary diseases in renal failure have been a point of confusion over the past decade, mainly because of moderate elevations of these cardiac biomarkers, commonly observed in patients with chronic renal dysfunction and without any significant myocardial damage. This review discusses the cardiac troponins, their biochemistry, their currently accepted cut-off values and their real significance in chronic renal failure (CRF), concluding that troponins maintain their diagnostic and prognostic values in patients with CRF, being predictive not only of cardiovascular mortality but also of general mortality in this patient group.

Prognostic value of low-level cardiac troponin-I elevations in patients without definite acute coronary syndromes

BACKGROUND

Low-level cardiac troponin-I (cTn-I) elevations predict adverse cardiovascular outcomes in patients with definite acute coronary syndromes (ACS), as defined by the presence of chest pain accompanied by ischemic electrocardiographic changes. However, their prognostic value in other clinical situations remains unclear.

METHODS

We studied 366 patients with suspected myocardial infarction (MI) but without definite ACS, including 57 patients with low-level cTn-I elevations (1.0 to 3.0 ng/mL) and 309 patients with cTn-I <1.0 ng/mL. All cTn-I measurements were made with the Dade Stratus II analyzer. We determined the adjusted 1-year risk of nonfatal MI or death from coronary heart disease (CHD death) in each group by using Cox proportional hazards models.

RESULTS

Among patients with cTn-I elevations between 1.0 and 3.0 ng/mL, 6 (11%) had a nonfatal MI or CHD death at 1 year compared with 12 (4%) patients in the cTn-I <1.0 ng/mL group [hazard ratio (HR), 3.5; 95% CI, 1.4 to 8.8]. After adjusting for baseline clinical characteristics, cTn-I levels between 1.0 and 3.0 ng/mL remained strongly associated with nonfatal MI or CHD death (adjusted HR, 3.4; 95% CI, 1.3 to 9.4). This association persisted even in the 215 patients who presented without chest pain (adjusted HR, 4.3; 95% CI, 1.4 to 13).

CONCLUSIONS

Low-level cTn-I elevations identify a subset of patients at increased risk for future cardiovascular events, even when obtained outside the context of definite ACS or presentation with chest pain.

Markers to define ischemia: are they ready for prime time use in patients with acute coronary syndromes?

Optimal treatment of patients who present with chest pain is predicated on accurate identification of those patients with a cardiac etiology of their discomfort. Serial troponins and electrocardiograms are very sensitive for the detection of myocardial infarction but they are insensitive for the detection of ischemia. There are many analytes that are being actively evaluated for routine use to facilitate the identification of patients with myocardial ischemia. At present, only one assay is US Food and Drug Administration-approved for the exclusion of ischemia; many other analytes are under clinical evaluation and are briefly reviewed. At present, none of these analytes are yet appropriate for routine clinical use.

Beckman Access versus the Bayer ACS:180 and the Abbott AxSYM cardiac Troponin-I real-time immunoassays: an observational prospective study

Background

Reliability of cardiac troponin-I assays under real-time conditions has not been previously well studied. Most large published cTnI trials have utilized protocols which required the freezing of serum (or plasma) for delayed batch cTnI analysis. We sought to correlate the presence of the acute ischemic coronary syndrome (AICS) to troponin-I values obtained in real-time by three random-mode analyzer immunoassay systems: the Beckman ACCESS (BA), the Bayer ACS:180 (CC) and the Abbott AxSYM (AX).

Methods

This was an observational prospective study at a university tertiary referral center. Serum from a convenience sampling of telemetry patients was analyzed in real-time for troponin-I by either the BA-CC (Arm-1) or BA-AX (Arm-2) assay pairs. Presence of the AICS was determined retrospectively and then correlated with troponin-I results.

Results

100 patients were enrolled in Arm-1 (38 with AICS) and 94 in Arm-2 (48 with AICS). The BA system produced 51% false positives in Arm-1, 44% in Arm-2, with negative predictive values of 92% and 100% respectively. In Arm-1, the BA and the CC assays had sensitivities of 97% and 63% and specificities of 18% and 87%. In Arm-2, the BA and the AX assays had sensitivities of 100% and 83% and specificities of 11% and 78%.

Conclusions

In real-time analysis, the performance of the AxSYM and ACS:180 assay systems produced more accurate troponin-I results than the ACCESS system.

Prognostic value of cardiac markers in ESRD: Chronic Hemodialysis and New Cardiac Markers Evaluation (CHANCE) study

BACKGROUND

Cardiac disease is the main cause of mortality in long-term hemodialysis patients. Cardiac troponins (cTn) have been proposed to be markers of cardiac damage, but their value is still debated in hemodialysis patients. The aim of this prospective study is to assess the prognostic value of biochemical cardiac markers in long-term hemodialysis patients.

METHODS

We measured serum levels of cTn I (cTnI), cTn T (cTnT), and creatine kinase-MB (CK-MB) in 258 asymptomatic patients (mean age, 60 +/- 15 years; 150 men) before the dialysis treatment. All causes of death and major adverse cardiac events (MACEs: cardiac death, myocardial infarction, or unstable angina) were recorded at 1 and 2 years of follow-up. A Cox proportional hazard regression model was used to identify factors predictive of mortality.

RESULTS

On inclusion, 48 patients (18.6%) had cTnT levels greater than 0.1 ng/mL, 46 patients (17.8%) had cTnI levels greater than 0.15 ng/mL, and 18 patients (7.0%) had CK-MB levels greater than 3 ng/mL. Of 246 patients followed up at 2 years, 64 patients (26%) had died, including 29 patients (11.8%) of cardiac disease, and 49 patients (19.9%) experienced at least 1 MACE. MACEs were significantly greater for patients with elevated predialysis serum cTnT and CK-MB levels (>0.1 ng/mL and 3 ng/mL, respectively) than for patients with normal levels of these cardiac markers (31.9% versus 17.1%; P = 0.01; 38.9% versus 18.4%; P = 0.02, respectively). No differences were found for cTnI levels. In multivariate analysis, age (relative risk [RR], 1.04; P = 0.002), previous ischemic heart disease (RR, 2.5; P = 0.0001), and serum cTnT levels greater than 0.1 ng/mL (RR, 1.9; P = 0.04) were independent significant factors for MACEs.

CONCLUSION

Increased predialysis serum levels of cTnT and CK-MB, but not cTnI, were predictive of a high risk for overall mortality and MACEs at 2 years in asymptomatic hemodialysis patients.

Does contrast echocardiography with Optison induce myocardial necrosis in humans?

Myocardial contrast echocardiography is a promising diagnostic tool for detecting microvascular integrity. Multiple experimental laboratories have shown that diagnostic combined microbubble contrast and ultrasound exposure can cause vessel rupture and myocardial damage in laboratory animals. This study investigated the phenomenon of contrast ultrasonically induced myocardial damage in human beings. Twenty consecutive patients (mean age of 60 +/- 12 years, 14 men) underwent contrast echocardiography with intravenous Optison using a mechanical index of at least 1.4 (Vivid Five System (GE, Vingmed Ultrasound, Horton, Norway). Creatine kinase (CK), creatine kinase-isoenzyme MB (CK-MB); CK-MB mass, myoglobin, and troponin I were measured before and 2, 4, 8, and 24 hours after contrast echocardiography. There was no significant correlation concerning the response to contrast echocardiography for any pair of parameters at any time after the intervention. Only in 2 patients were there higher values for troponin I before and after contrast echocardiography without an increase of myoglobin, CK, or CK-MB mass and activity. These values were therefore interpreted as false positive because of renal failure and severe heart failure. The use of contrast echocardiography is without demonstrated risk of myocardial damage even in patients with different cardiologic entities.

The measurement of cardiac markers: where should we focus?

Cardiac markers are presently a hot topic, with active debate on their use. They now have a major role for cost-effective management of acute chest pain and suspected acute coronary syndrome. The laboratory has a pivotal role in proper selection and interpretation of available markers, depending on the creation of evidence-based knowledge about test utilization and sources of variation. This article reviews this knowledge in the field of biomarkers determination and summarizes the major analytic and clinical issues, with reference to various recent recommendations of laboratory medicine and cardiology expert groups.