Single Cardiac Troponin Research Articles

Uniform or Sex-Specific Cardiac Troponin Thresholds to Rule Out Myocardial Infarction at Presentation

BackgroundMyocardial infarction can be ruled out in patients with a single cardiac troponin measurement. Whether use of a uniform rule-out threshold has resulted in sex differences in care remains unclear. ObjectivesThe purpose of this study was to evaluate implementation of a uniform rule-out threshold in females and males with possible myocardial infarction, and to derive and validate sex-specific thresholds. MethodsThe implementation of a uniform rule-out threshold (<5 ng/L) with a high-sensitivity cardiac troponin I assay was evaluated in consecutive patients presenting with possible myocardial infarction. The proportion of low-risk patients discharged from the emergency department and incidence of myocardial infarction or cardiac death at 30 days were determined. Sex-specific thresholds were derived and validated, and proportion of female and male patients were stratified as low-risk compared with uniform threshold. ResultsIn 16,792 patients (age 58 ± 17 years; 46% female) care was guided using a uniform threshold. This identified more female than male patients as low risk (73% vs 62%), but a similar proportion of low-risk patients were discharged from the emergency department (81% for both) with fewer than 5 (<0.1%) patients having a subsequent myocardial infarction or cardiac death at 30 days. Compared with a uniform threshold of <5 ng/L, use of sex-specific thresholds would increase the proportion of female (61.8% vs 65.9%) and reduce the proportion of male (54.8% vs 47.8%) patients identified as low risk. ConclusionsImplementation of a uniform rule-out threshold for myocardial infarction was safe and effective in both sexes. Sex-specific rule-out thresholds should be considered, but their impact on effectiveness and safety may be limited.

Troponin in early presenters to rule out myocardial infarction.

Whether a single cardiac troponin measurement can safely rule out myocardial infarction in patients presenting within a few hours of symptom onset is uncertain. The study aim was to assess the performance of troponin in early presenters. In patients with possible myocardial infarction, the diagnostic performance of a single measurement of high-sensitivity cardiac troponin I at presentation was evaluated and externally validated in those tested ≤3, 4-12, and >12 h from symptom onset. The limit-of-detection (2 ng/L), rule-out (5 ng/L), and sex-specific 99th centile (16 ng/L in women; 34 ng/L in men) thresholds were compared. In 41 103 consecutive patients [60 (17) years, 46% women], 12 595 (31%) presented within 3 h, and 3728 (9%) had myocardial infarction. In those presenting ≤3 h, a threshold of 2 ng/L had greater sensitivity and negative predictive value [99.4% (95% confidence interval 99.2%-99.5%) and 99.7% (99.6%-99.8%)] compared with 5 ng/L [96.5% (96.2%-96.8%) and 99.3% (99.1%-99.4%)]. In those presenting ≥3 h, the sensitivity and negative predictive value were similar for both thresholds. The sensitivity of the 99th centile was low in early and late presenters at 71.4% (70.6%-72.2%) and 92.5% (92.0%-93.0%), respectively. Findings were consistent in an external validation cohort of 7088 patients. In early presenters, a single measurement of high-sensitivity cardiac troponin I below the limit of detection may facilitate the safe rule out of myocardial infarction. The 99th centile should not be used to rule out myocardial infarction at presentation even in those presenting later following symptom onset.

Single troponin measurement to rule-out acute myocardial infarction in early presenters

BackgroundA single high-sensitive cardiac troponin (hs-cTn) can be used to rule-out acute myocardial infarction (MI) in patients presenting >3 hours (3 h) after chest pain onset to the emergency department. This study aimed to investigate the safety of ruling-out MI in early presenters with chest pain ≤3 h using a single hs-cTnI at admission. MethodsWe prospectively enrolled patients presenting with chest pain suggestive of MI. Hs-cTnI (Siemens ADVIA Centaur TNIH, Limit of detection: 2.2 ng/L) was measured at admission. Two physicians adjudicated final diagnosis. A diagnostic cut-off value <3 ng/L was used to rule-out MI. Patients were classified as early (chest pain ≤3 h) or late presenters (>3 h). ResultsWe included 1370 patients with available admission hs-cTnI results: median (Q1–Q3) age 65 (52–74), female sex: 43%, previous MI: 22%. We confirmed MI in 118 (8.6%) patients. Overall, 470 (34%) patients were classified as early, 770 (56%) as late presenters, and 130 (9%) patients had unknown onset. When applying the diagnostic cut-off value, MI was correctly ruled-out at admission in 370 (27%) patients: 134 (29%) early presenters, 206 (27%) late presenters and 30 (23%) patients with unknown onset. This resulted in an overall negative predictive value of 100% (95% CI: 99.0–100%), with both 100% (97.3–100%) for early and 100% (98.2–100%) for late presenters, respectively. Sensitivity was similarly high in the two groups. ConclusionMI could be safely ruled-out in all patients presenting with chest pain ≤3 h when using a single hs-cTnI value <3 ng/L as diagnostic cut-off. Trial registration numberNCT03634384.

Diagnostic Reclassification by a High-Sensitivity Cardiac Troponin Assay

Our objective is to describe the rates of diagnostic reclassification between conventional cardiac troponin I (cTnI) and high-sensitivity cardiac troponin T (hs-cTnT) and between combined and sex-specific hs-cTnT thresholds in adult emergency department (ED) patients in the United States. We conducted a prospective, single-center, before-and-after, observational study of ED patients aged 18 years or older undergoing single or serial cardiac troponin testing in the ED for any reason before and after hs-cTnT implementation. Conventional cTnI and hs-cTnT results were obtained from a laboratory quality assurance database. Combined and sex-specific thresholds were the published 99th percentile upper reference limits for each assay. Cases underwent physician adjudication using the Fourth Universal Definition of Myocardial Infarction. Diagnostic reclassification occurred when a patient received a diagnosis of myocardial infarction or myocardial injury with one assay but not the other assay. Our primary outcome was diagnostic reclassification between the conventional cTnI and hs-cTnT assays. Diagnostic reclassification probabilities were assessed with sample proportions and 95% confidence intervals for binomial data. We studied 1,016 patients (506 men [50%]; median age 60 years [25th, 75th percentiles 49, 71]). Between the conventional cTnI and hs-cTnT assays, 6 patients (0.6%; 95% confidence interval 0.2% to 1.3%) underwent diagnostic reclassification regarding myocardial infarction (5/6 reclassified as no myocardial infarction) and 166 patients (16%; 95% confidence interval 14% to 19%) underwent diagnostic reclassification regarding myocardial injury (154/166 reclassified as having myocardial injury) by hs-cTnT. Compared with conventional cTnI, the hs-cTnT assay resulted in no clinically relevant change in myocardial infarction diagnoses but substantially more myocardial injury diagnoses.

Ultrarapid Rule-out for Acute Myocardial Infarction Using the Generation 5 Cardiac Troponin T Assay: Results From the REACTION-US Study

We determine how well a new Food and Drug Administration-approved single cardiac troponin T (cTnT) Generation 5 baseline measurement below the level of quantification (6 ng/L) and a novel study-derived baseline and 30-minute cTnT Generation 5 algorithm might adequately exclude acute myocardial infarction in patients with suspected acute coronary syndrome in a US emergency department (ED). Patients presenting with any symptoms suspicious for acute coronary syndrome were enrolled at a single US ED. Baseline and 30-minute blood samples were obtained and cTnT Generation 5 levels were later batch analyzed in an independent core laboratory. Acute myocardial infarction diagnosis was adjudicated by a cardiologist and an emergency physician. Of the 569 study patients, 44 (7.7%) had an acute myocardial infarction diagnosis. One hundred sixty-four patients (28.8%) had a presentation cTnT Generation 5 level less than 6 ng/L, and none of these individuals had an acute myocardial infarction (negative predictive value of 100% [95% confidence interval 97.8% to 100.0%] and sensitivity of 100% [95% confidence interval 92.0% to 100.0%]). A baseline cTnT Generation 5 value of less than 8 ng/L and a 30-minute Δ of less than 3 ng/L were present in 221 patients (41.0%), and none had acute myocardial infarction (negative predictive value of 100% [95% confidence interval 98.3% to 100.0%] and sensitivity of 100% [95% confidence interval 92.0% to 100.0%]). In a single US ED, a single baseline cTnT Generation 5 measurement less than 6 mg/L and values at baseline less than 8 ng/L and a 30-minute Δ of less than 3 ng/L ruled out acute myocardial infarction in 28.8% and 41.0% of patients, respectively. Additional multicenter US studies evaluating these ultrarapid acute myocardial infarction rule-out guidelines are needed, especially to narrow the confidence intervals.

Early Exclusion of Major Adverse Cardiac Events in Emergency Department Chest Pain Patients: A Prospective Observational Study

BackgroundThe current evaluation of patients with chest pain presenting to an emergency department (ED) with suspected acute coronary syndrome (ACS) is a lengthy process involving serial measurements of troponin. ObjectiveWe aimed to validate the diagnostic accuracy of a Thrombolysis in Myocardial Infarction (TIMI) score with single high-sensitive cardiac troponin T (hs-cTnT) for early rule out of 30-day major adverse cardiac events (MACE), and to compare the TIMI score with combinations of heart-type fatty acid binding protein (H-FABP) and a modified HEART (history, electrocardiogram, age, risk factors, troponin) score. MethodsWe recruited 602 consecutive adult patients with chest pain and suspected ACS in the ED. Each patient had TIMI and HEART scores, and a point-of-care H-FABP test. ResultsMACE occurred in 42 (7.0%) patients within 30 days. A low risk for 30-day MACE was identified by a modified TIMI score of 0 in 65 (11%) patients, and by a HEART score ≤ 2 in 96 (16%) patients. No MACE occurred in these groups, giving both scores a sensitivity of 100% (95% confidence interval [CI] 91.6–100%), and specificity of 11.6% (95% CI 9.2–14.5%) and 17.1% (95% CI 14.2–20.5%), respectively. Use of combined TIMI and HEART scores improved the specificity further to 22.0% (95% CI 18.7–25.6%) without lowering sensitivity. Early H-FABP measurement > 7 μg/L had a sensitivity of 41.5% (95% CI 27.8–56.6%) and a specificity of 91.1% (95% CI 88.4–93.2%) for predicting 30-day MACE. ConclusionsA modified TIMI score of 0 or a HEART score of ≤ 2, incorporating a single hs-cTnT level, will identify patients with low risk of 30-day MACE for early discharge within 2 h of ED arrival.

Best Practices for Monitoring Cardiac Troponin in Detecting Myocardial Injury.

Cardiac troponin [cardiac troponin I (cTnI) and cTnT] has become globally recognized as the standard biomarker for the diagnosis of acute myocardial infarction (AMI).8 With improvements in the analytical characteristics of cardiac troponin assays, particularly imprecision at low measurable concentrations, high-sensitivity cardiac troponin (hs-cTn) assays are now being implemented worldwide; but not in the US since the Food and Drug Administration has not yet cleared them for clinical use. With the implementation of hs-cTn assays, improvements in clinical care are beginning to be observed in the peer-reviewed literature. These improvements include early rule out (early hospital discharge) and rule in (right bed for appropriate patient) for MI and improved risk stratification for patients presenting with symptoms suggestive of ischemia, with improved short- and long-term outcomes. Further hs-cTn assays have been part of solidifying the definition of myocardial injury, based on an increased cardiac troponin concentration above the 99th percentile upper reference limit. The high-sensitivity assays have improved the clinical understanding that not all cardiac troponin increases are MI and that patients with nonischemic disease also have increases in cardiac troponin that must be managed accordingly. This Q&A provides the opportunity for 3 cardiologists, 2 laboratory medicine scientists, and 1 emergency medicine physician to share their experiences with the evolving role of cardiac troponin testing in their practices. Ideally, the messages they share will assist in better harmonizing the appropriate utilization of high-sensitivity assays worldwide as we transition away from contemporary cardiac troponin assays. Should all medical centers have a uniform serial order set to assist in ruling in/out AMI? Should a single cardiac troponin order be available? What would your ideal serial order set (timing) be? Allan S. Jaffe: Medical centers would benefit from developing consistent, uniform serial orders to rule in/out AMI. These serial orders should be agreed …

Weekly and 90-Minute Biological Variations in Cardiac Troponin T and Cardiac Troponin I in Hemodialysis Patients and Healthy Controls

Myocardial infarction (MI) is diagnosed by the finding of a single cardiac troponin value above the 99th percentile and a significant time-dependent change in cardiac troponin concentration. The aim of this study was to determine the 90-min and weekly biological variations, the reference change value (RCV), and the index of individuality (II) of high-sensitivity cardiac troponin T (hs-cTnT) (Roche Diagnostics) and hs-cTnI (Abbott Diagnostics) in patients receiving hemodialysis (HD) and in healthy individuals. Blood samples were collected from 19 HD patients (on an HD-free day) and 20 healthy individuals at 90-min intervals over a 6-h period (between 08:30 and 14:30) and before the midweek HD treatment for 10 weeks. The within-person variation (CVi), between-person variation, RCV, and II were calculated. During the 6-h sampling period, the concentrations of hs-cTnT (both groups) and hs-cTnI (HD patients only) decreased on average by 0.8% to 1.7% per hour, respectively. These declining trends were included in the calculation of a 90-min asymmetric RCV: -8%/+5% in HD patients (hs-cTnT), -18%/+21% in HD patients (hs-cTnI), -27%/+29% in healthy individuals (hs-cTnT), and -39%/+64% in healthy individuals (hs-cTnI). The II was low in both groups for both assays. The weekly CVi values were approximately 8% (hs-cTnT) and 15% (hs-cTnI) in both groups. When using a cardiac troponin change of 20%-50% to diagnose an MI, the false-positive rate is likely to be lower for the hs-cTnT assay than for the hs-cTnI assay. The low II suggests that use of a diagnostic cutoff value can be omitted.

Early discharge using single cardiac troponin and copeptin testing in patients with suspected acute coronary syndrome (ACS): a randomized, controlled clinical process study.

AimsThis randomized controlled trial (RCT) evaluated whether a process with single combined testing of copeptin and troponin at admission in patients with low-to-intermediate risk and suspected acute coronary syndrome (ACS) does not lead to a higher proportion of major adverse cardiac events (MACE) than the current standard process (non-inferiority design).Methods and resultsA total of 902 patients were randomly assigned to either standard care or the copeptin group where patients with negative troponin and copeptin values at admission were eligible for discharge after final clinical assessment. The proportion of MACE (death, survived sudden cardiac death, acute myocardial infarction (AMI), re-hospitalization for ACS, acute unplanned percutaneous coronary intervention, coronary artery bypass grafting, or documented life threatening arrhythmias) was assessed after 30 days. Intention to treat analysis showed a MACE proportion of 5.17% [95% confidence intervals (CI) 3.30–7.65%; 23/445] in the standard group and 5.19% (95% CI 3.32–7.69%; 23/443) in the copeptin group. In the per protocol analysis, the MACE proportion was 5.34% (95% CI 3.38–7.97%) in the standard group, and 3.01% (95% CI 1.51–5.33%) in the copeptin group. These results were also corroborated by sensitivity analyses. In the copeptin group, discharged copeptin negative patients had an event rate of 0.6% (2/362).ConclusionAfter clinical work-up and single combined testing of troponin and copeptin to rule-out AMI, early discharge of low- to intermediate risk patients with suspected ACS seems to be safe and has the potential to shorten length of stay in the ED. However, our results need to be confirmed in larger clinical trials or registries, before a clinical directive can be propagated.

Early or late intervention in high-risk non-ST-elevation acute coronary syndromes: results of the ELISA-3 trial

To compare an early to a delayed invasive strategy in high-risk patients with NSTE-ACS. In this prospective multicentre trial, 542 patients hospitalised with NSTE-ACS were randomised to either an immediate (angiography and revascularisation if appropriate <12 hr) or a delayed invasive strategy (>48 hr after randomisation). Patients were eligible if they had two of the following three high-risk characteristics: evidence of extensive myocardial ischaemia on ECG, elevated biomarkers for myocardial necrosis (TropT >0.10 μg/L), and an age above 65 years. Primary endpoint of the study was the combined incidence of death, reinfarction and/or recurrent ischaemia at 30-day follow-up. Secondary endpoints were enzymatic infarct size as assessed by a single cardiac troponin T, at 72-96 hours after admission or at discharge, and the percentage of patients without a rise in CKMB during admission. Median age was 71.9 (interquartile range [IQR] 64.5-78.4) years. Median time between randomisation and start of angiography was 2.6 (IQR 1.2-6.2) hours in the immediate and 54.9 (44.2-74.5) hours in the delayed intervention group. The composite of death, reinfarction and/or recurrent ischaemia at 30 days occurred in 12% of patients and was not significantly different between the two groups (9.9% and 14.2%, respectively, p=0.135). All secondary endpoints and bleeding complications were comparable. Hospital duration was two days shorter in the immediate intervention group (4 days [IQR 2-10] vs. 6 days [IQR 4-12]). Although no definitive conclusion can be drawn due to a lower than expected prevalence of the primary endpoint, an immediate invasive strategy was safe and feasible but not superior to a delayed invasive strategy in terms of the combined primary endpoint of death, reinfarction and/or recurrent ischaemia at 30 days. These results are consistent with previous randomised trials which studied the effect of timing of angiography in patients with NSTE-ACS. ISRCTN Register 9230163.

Predicting microvascular obstruction with cardiac troponin T after acute myocardial infarction: a correlative study with contrast-enhanced magnetic resonance imaging

The presence of microvascular obstruction (MVO) is associated with more severely impaired left ventricular function and adverse prognosis. The aim of this study was to evaluate whether a single cardiac troponin T-value (cTnT) was able to predict the presence of MVO and whether cTnT is an independent predictor of MVO as compared to usual risk factors. Sixty-one consecutive patients with reperfused ST-elevation myocardial infarction (STEMI) were enrolled in the study. cTnT was measured serially at admission and after 24, 48, 72 and 96 h. Contrast-enhanced cardiac magnetic resonance imaging (CE-MRI) was performed on a 1.5T MR-scanner 4 +/- 1 days after STEMI. cTnT-time concentration kinetics in the presence of MVO differs from cTnT release in the absence of MVO showing a higher peak and a slower release. At single point measurement 24 h-cTnT correlates at least as well with the presence of MVO (P < 0.001) as peak cTnT (P = 0.0016) and sampling over 96 h (P < 0.001). Using ROC analysis, at single measurement a cTnT concentration >2.52 microg/l at 24 h was a predictor for MVO (AUC 0.91) with a sensitivity of 100% and a specificity of 80% with a positive predictive value of 76% and a negative predictive value of 100%. In multivariate regression analysis 24 h-cTnT remained independent predictor for MVO. In STEMI, a single 24 h-cTnT value is an independent predictor for MVO and a convenient and inexpensive way to help define this important risk parameter in clinically routine.

Serial increased cardiac troponin T predicts mortality in asymptomatic patients treated with chronic haemodialysis

A single detectable cardiac troponin predicts mortality in patients treated with dialysis. There are limited data on changes in troponin concentration over time and the clinical implications of serial troponin measurement. Serial cardiac troponin T (cTnT) was assayed five times over 12 months in a prospective cohort study of patients with end-stage kidney disease treated with haemodialysis. A concentration of cTnT > or = 0.04 microg/L was considered increased. Mortality and cardiovascular events were analysed by survival analysis, according to the serial troponin results. From 100 patients who provided a baseline sample for cTnT, 81 completed five serial measurements. The analysis of patients who completed serial cTnT measurements demonstrated that 28 patients (35%) had normal cTnT concentrations in all five samples, 20 patients (24%) had between one and four increased cTnT measurements and 33 patients (41%) had increased concentrations of cTnT in all five samples. The 1.7-y patient survival was 100%, 90% and 78% for patients with zero, one to four, or five out of five concentrations of cTnT increased, respectively (P = 0.037), and the corresponding cardiovascular event-free survival was 100%, 91% and 78%, respectively (P = 0.027). Serial measurements of cTnT concentration were frequently increased in patients receiving haemodialysis. The number of abnormal measurements over time predicted mortality and cardiovascular adverse events.

Will the Universal Definition of Myocardial Infarction Criteria Result in an Overdiagnosis of Myocardial Infarction?

The Universal Definition of Myocardial Infarction (acute myocardial infarction [AMI]) requires detection of increasing or decreasing cardiac biomarkers (preferably cardiac troponin) with >or=1 value >99(th) percentile, together with either clinical symptoms, new ischemic electrocardiographic changes, or typical imaging findings indicative of myocardial necrosis as diagnostic criteria for AMI. However, a small cardiac troponin elevation together with ST-T segment abnormalities may also occur in clinically stable populations. Accordingly, 0.6% of elderly subjects from a community sample (PIVUS Study) and 6.7% of patients stabilized after an acute coronary syndrome (FRISC II Study) would have been labeled AMI following the Universal Definition of AMI when diagnostic classification had been based on a single cardiac troponin I result. In conclusion, our results emphasized the importance of a significant change in cardiac troponin to avoid misdiagnosis of AMI.

Single histidine-substituted cardiac troponin I confers protection from age-related systolic and diastolic dysfunction

Contractile dysfunction associated with myocardial ischaemia is a significant cause of morbidity and mortality in the elderly. Strategies to protect the aged heart from ischaemia-mediated pump failure are needed. We hypothesized that troponin I-mediated augmentation of myofilament calcium sensitivity would protect cardiac function in aged mice. To address this, we investigated transgenic (Tg) mice expressing a histidine-substituted form of adult cardiac troponin I (cTnI A164H), which increases myofilament calcium sensitivity in a pH-dependent manner. Serial echocardiography revealed that Tg hearts showed significantly improved systolic function at 4 months, which was sustained for 2 years based on ejection fraction and velocity of circumferential fibre shortening. Age-related diastolic dysfunction was also attenuated in Tg mice as assessed by Doppler measurements of the mitral valve inflow and lateral annulus Doppler tissue imaging. During acute hypoxia, cardiac contractility significantly improved in aged Tg mice made evident by increased stroke volume, end systolic pressure, and +dP/dt compared with non-transgenic mice. This study shows that increasing myofilament function by means of a pH-responsive histidine button engineered into cTnI results in enhanced baseline heart function in Tg mice over their lifetime, and during acute hypoxia improves survival in aged mice by maintaining cardiac contractility.

Kinetic analysis of cardiac troponin I release is no more accurate than a single 24-h measurement in predicting in-hospital outcome after cardiac surgery

A single cardiac troponin I (cTnI) 24-h measurement is an independent predictor of short- and long-term adverse outcome after coronary surgery. We compared a single cTnI 24-h measurement and kinetic analysis of cTnI release in predicting in-hospital outcome in unselected cardiac surgery patients. Consecutive patients (n = 184) undergoing cardiac surgery with cardiopulmonary bypass were included and divided into two groups according to the time course of postoperative peak serum cTnI (6 or 24 h after surgery). Serial measurements of cTnI were performed the day before surgery, at the end of surgery and 6, 24 and 120 h after surgery in all patients. The total amount of cTnI released (integrated area under the curve), postoperative major adverse cardiac events (ventricular arrhythmias, myocardial infarction and congestive heart failure) and in-hospital death were recorded. Data are expressed as median (95% CI). In all, 152 (83%) patients had an early peak cTnI (6 h after surgery) and 32 (17%) patients had a late peak cTnI (24 h after surgery). The integrated area under the curve differed between both groups: 159 (142-178) vs. 321 (255-590), respectively, P < 0.001. Major adverse cardiac events and/or death (22 vs. 9%, P = 0.04) was greater in patients with a late peak cTnI. The integrated area under the curve and the peak value of cTnI were no more accurate than a single 24-h measurement in predicting the occurrence of major adverse cardiac events and/or death. Kinetic analysis of cTnI release was no more accurate than a single 24-h measurement in predicting in-hospital poor outcome.

Single and serial measurements of cardiac troponin I in asymptomatic patients on chronic hemodialysis.

Coronary artery disease is the major cause of death in patients with end-stage renal failure on dialysis. This study aimed to assess the predictive value of a single cardiac troponin I (cTnI), and also the kinetics of serial values. Since cTnI is a potential biomarker of cardiac outcome, the present study examined single cTnI measurements (n = 88 patients) and its predictive value for future cardiac events, and a kinetic substudy of serial weekly cTnI measured for 8 weeks (n = 57) in a group of patients on hemodialysis. Single cTnI measurements: 9 patients (10.2%) had a detectable cTnI at baseline and 79 patients (89.8%) had a negative baseline cTnI. There were no significant differences in age, sex, history of ischemic heart disease, diabetes, smoking or dyslipidemia between patients with detectable and negative cTnI. At the end of 9 months, the rate of combined primary endpoints, which included myocardial infarction, cardiac death and cardiac revascularization, was significantly higher in the patients with a detectable baseline cTnI (55.6%), compared to patients with a negative cTnI (6.3%) (p = 0.0007). Serial weekly cTnI measurements: significant fluctuations in cTnI were noted over time; 27% of patients with an undetectable cTnI measured at baseline had subsequent detectable levels in the serial follow-up. A single detectable cTnI in asymptomatic patients on hemodialysis defines patients at high risk of future cardiac events. However, the incidence of detectable cTnI levels is markedly increased when serial weekly measurements are performed. The clinical significance of detectable serial measurements of cTnI is the focus of ongoing studies.

The Key to Unraveling the Mystery of Mortality in Heart Failure

Heart failure (HF) is a growing public health problem in the United States. Nearly 5 million Americans suffer from HF, and an estimated 550 000 new cases of HF are diagnosed each year.1 HF is the No. 1 discharge diagnosis in patients ≥65 years of age and results in a substantial burden on healthcare expenditures. It is estimated that in 2001, more than $24 billion was spent as direct cost for the care of patients with HF.1 Furthermore, HF is associated with a significant increase in morbidity and mortality. See p 1764 Although considerable progress has been made in our approach to the pharmacological management of patients with HF, most patients remain at increased risk of cardiac death. To further improve outcomes in patients with HF, newer therapeutic modalities, including devices such as biventricular pacemaker, automatic internal cardioverter-defibrillators (AICDs), and left ventricular assist devices, have been increasingly utilized. Several recent randomized controlled trials have shown that such devices can indeed further improve the outcome in patients with HF.2–4 However, these devices are expensive, and their widespread or injudicious application in unselected patients with HF is likely to have a substantial impact on healthcare expenditures. On the other hand, appropriate use of device therapy in properly selected patients (who are at high risk of mortality) is essential to improve clinical outcome. Thus, there is a need to develop a strategy to accurately identify those patients with HF who are at increased risk of mortality. The paper by Vrtovec and associates5 in the present issue of Circulation provides such a strategy by showing that routinely available diagnostic tests, such as measurement of QT interval on 12-lead ECG and measurement of B-type natriuretic peptide (BNP), can indeed identify the HF patients who are at increased risk of overall mortality, …

Cardiac Troponin T Variants Produced by Aberrant Splicing of Multiple Exons in Animals with High Instances of Dilated Cardiomyopathy

Adult cardiac muscle normally expresses a single cardiac troponin T (cTnT). As a potential pathogenic mechanism for turkey dilated cardiomyopathy, the splice-out of a normally constitutive exon generates an additional low molecular weight cTnT with altered conformation and function. We further found that aberrant splicing of cTnT also occurs in several mammals correlating to dilated cardiomyopathy. Skipping of the same exon as that in the turkey was found in the canine cTnT. Splice-out of the adjacent exon 6 occurred in the guinea pig cTnT. Retention of the embryonic exon 5 was found in the cTnT of cat, dog, and guinea pig. These aberrant splicing variants significantly altered the structure of cTnT to sustain functional effects as that in the myopathic turkey cTnT. The genomic sequence of canine cTnT gene shows no specific alterations. However, the alternative splicing patterns of canine cTnT are different in developing cardiac and skeletal muscles, suggesting abnormality of trans-regulatory factors. Transgenic expression of the aberrant cTnT variants resulted in contractile changes in mouse cardiomyocytes. The findings support the hypothesis that thin filament heterogeneity due to the co-expression of alternatively spliced cTnT variants may desynchronize myocardial contraction and contribute to the pathogenesis and pathophysiology of cardiomyopathy and heart failure.

Value of a single troponin T at the time of presentation as compared to serial CK-MB determinations in patients with suspected myocardial ischemia

Background: Prior studies with cardiac markers have focused predominantly on subjects presenting to the emergency department with chest pain or unstable angina, and have relied on serial markers for the diagnosis of acute myocardial infarction. We evaluated the diagnostic utility of a single cardiac troponin T (cTnT) determination at the time of presentation as compared to serial creatine kinase (CK) MB determinations in a broad spectrum of patients with suspected myocardial ischemia. Methods: A total of 267 consecutive patients presenting to the emergency department with suspected myocardial ischemia had a single, blinded cTnT determination drawn at the time of presentation to the emergency department in addition to routine serial electrocardiographic and CK-MB determinations. Results: The specificity (93.7% vs. 87.1%; p<0.05) and positive predictive value (80.0% vs. 69.4%; p<0.05) of a single cTnT determination were superior to that of serial CK-MB determinations without compromising sensitivity. Forty-six percent of patients with confirmed myocardial infarction and an abnormal cTnT at presentation had a normal initial CK-MB determination. Conversely, 20% of patients without acute coronary syndromes had an abnormal CK-MB determination in the setting of a normal cTnT. The initial cTnT was abnormal in all patients with confirmed myocardial infarction and a symptom duration of at least 3.5 h. Conclusions: In a heterogeneous population of patients with suspected myocardial ischemia, the initial cTnT determination drawn at the time of presentation is a powerful diagnostic tool that, when used in context with symptom duration, allows for more rapid and accurate triage of patients than serial CK-MB determinations.

In vitro splicing of cardiac troponin T precursors. Exon mutations disrupt splicing of the upstream intron.

A single cardiac troponin T (cTNT) gene generates two mRNAs by including or excluding the 30-nucleotide exon 5 during pre-mRNA processing. Transfection analysis of cTNT minigenes has previously demonstrated that both mRNAs are expressed from unmodified minigenes, and mutations within exon 5 can lead to complete skipping of the exon. These results suggested a role for exon sequence in splice site recognition. To investigate this potential role, an in vitro splicing system using cTNT precursors has been established. Two-exon precursors containing the alternative exon and either the upstream exon or downstream exon were spliced accurately and efficiently in vitro. The mutations within the alternative exon that resulted in exon skipping in vivo specifically blocked splicing of the upstream intron in vitro and had no effect on removal of the downstream intron. In addition, the splicing intermediates of these two precursors have been characterized, and the branch sites utilized on the introns flanking the alternative exon have been determined. Potential roles of exon sequence in splice site selection are discussed. These results establish a system that will be useful for the biochemical characterization of the role of exon sequence in splice site selection.