Cardiac troponin T

Big Tests in Little People

Can laboratory tests that are routinely used in adult patients also be used in pediatric patients? Does the current literature support the routine use of troponin, brain natriuretic peptide, D-dimer, and lactate in children? Adult problems such as acute coronary syndrome and pulmonary embolism are rare in pediatrics, and there is a paucity of literature on how blood tests commonly used to help diagnose these conditions in adults play a role in the diagnosis and management of children. This article presents the literature about 4 common blood tests and examines the clinical applications of each.

Evaluation of clinical utility of serum enzymes and troponin-T in the early stages of acute myocardial infarction

Laboratory infarction diagnostics are based on the detection of elevated serum activities of total Creatine Kinase (CK), Creatine Kinase isoensyme MB, (CKMB), Lactate dehydrogenase (LDH), isoenzyme forms of LDH and transaminases. Determination of these cardiac marker enzymes permits a highly sensitive diagnosis of transmural myocardial infarction. In such patients the diagnosis of acute myocardial infarction can be confirmed by the clinical, symptoms, and changes in the ECG in addition to the enzyme assays. The 50 AMI patients selected in the present study were those admitted to the ICCU of Shri Krishna Hospital, Karamsad. The blood samples were taken at the time of admission (ie. within four hours of the start of chest pain). The samples were analyzed for CK, CKMB, SGOT, (Serum glutamate oxaloactate transaminase) αHBDH α-hydroxybutyrate dehydrogenase and troponin T. The serum CKMB activity in AMI showed an increase only 5-6 hours after the commencement of chest pain. The elevation in SGOT and αHBDH was still delayed. At the same time we could observe that the cardiac Troponin T (cTnT) was elevated at the time of admission of the patient itself. This increase of cTnT in AMI patients was 20 times higher than the normal blood donors. The controls included 25 normal blood donors and 25 patients with polytraumatic injuries with no chest contusion. The study shows that cTnT estimation could serve in the early diagnosis of AMI. The increase of cardiac troponin T in AMI patients was 20 times higher than the normal blood donors in AMI patients at the time of admission. Cardiac troponin T in serum appears to be a more sensitive indicator of myocardial cell injury than CKMB activity and its detection in the circulation may be a useful prognostic indicator in patients with unstable angina as well. When the blood of normal blood donors or that of patients with polytraumatic injury was analysed the troponin T values were well within the normal range in both the above categories showing that cardiac troponin T is highly specific for heart tissue. Although CKMB and cardiac troponin T are released soon after the myocardial injury, the release of cardiac troponin T is much earlier than CKMB thereby invalidating the important role of cardiac troponin T in diagnosing AMI. Cardiac troponin T has been shown to be highly sensitive for cardiac injury and not elevated in any other trauma, heavy exercise or skeletal muscle injury. Cardiac troponin T is ordinarily undetectable in healthy individuals, and so its measurement can serve as a powerful tool in the diagnosis of AMI.

Cardiac troponins in renal insufficiency and other non-ischemic cardiac conditions

The emergence of cardiac troponins has been an interesting step in the diagnosis of ACS. It has clearly helped us to better triage patients toward a more aggressive posture in performing early cardiac catheterization, and in some cases, early use of adjunctive Gp IIb/IIIa antagonists and percutaneous or surgical myocardial revascularization. However, with this step forward has come uncertainty and many cardiology consults regarding positive cardiac troponins in patients without ACS or myocardial infarction. In general, increased cardiac troponins imply a worse prognosis. This is clearly true of patients with ESRD and advanced heart failure. It is also true of patients with severe, noncardiac illnesses. In other situations, such as acute pericarditis and cardiac surgery, slightly elevated cardiac troponins do not seem to predict a worse prognosis, and can probably be disregarded. The elevation of cardiac troponins after successful percutaneous coronary interventions is not unexpected, and the level of cardiac troponin release seems to predict problems, but lively controversy persists. Last, monitoring cardiac troponins in cardiac transplant recipients and those receiving certain cardiotoxic chemotherapies may be of some diagnostic value, but clearly more experience and clinical research are needed.

Diagnostic efficiency of rejection monitoring after heart transplantation with cardiac troponin T is improved in specific patient subgroups

Cardiac troponin T (cTnT) is a cardio-specific myofibrillar protein known to be elevated early after heart transplantation and during cardiac allograft rejection. cTnT determination in heart allograft recipients showed elevated levels in patients with higher degrees of graft rejection (International Society for Heart and Lung Transplantation grades >/=3A-4). Subgroup analyses revealed demographic patient characteristics markedly improving the diagnostic efficiency of cTnT measurement for rejection monitoring, including male recipient gender, recipient age <60 yr, female donor gender and donor age >/= 33 yr. The clinical utility of these parameters was confirmed by longitudinal patient data and may help to select recipients most likely to benefit from cTnT rejection surveillance.

Non-invasive assessment of rejection in pediatric transplant patients: serologic and echocardiographic prediction of biopsy-proven myocardial rejection

BACKGROUND

Cardiac allograft rejection is a multifocal immune process that is currently assessed using biopsy-guided histologic classification systems (International Society for Heart and Lung Transplantation). Cardiac troponin T and I are established serologic markers of global myocyte damage. The use of load-independent measures of contractility have also been shown to accurately assess the presence of ventricular dysfunction. Little is known about their utility in accurately predicting rejection in the pediatric age group. We undertook the present study to compare rejection grade with echocardiographic and serologic estimates of transplant rejection-related myocardial damage.

METHODS

We compared histologic rejection grades (0 to 4) with patient characteristics, echocardiographic measurements, catheterization measurements, and biochemical markers for 86 evaluations in 37 transplant recipients at Children's Hospital.

RESULTS

In univariate analyses, biopsy scores correlated (p < 0.05) inversely with left ventricular systolic function (shortening fraction) and contractility (stress velocity index, SVI), and directly with mitral E-wave amplitude. In multivariate analyses, lower contractility and higher mitral E-wave amplitude remained significantly (p < or = 0.01) associated with rejection (SVI, p = 0.002, odds ratio = 0.393; E wave, p = 0.0002, odds ratio = 228). Most rejection episodes were associated with elevation of biochemical markers of myocardial injury. Although troponin I was weakly associated with differences between rejection grades (p = 0.034), troponin T, creatine kinase-MB fraction, and C-reactive protein did not differ with biopsy-rejection scores. Serum markers had a poor predictive capacity for biopsy-detected rejection. Troponin T and I did correlate with increased left ventricular wall thickness and mass.

CONCLUSION

Progressively depressed left ventricular contractility and diastolic function are found with worsening pediatric heart transplant rejection-biopsy score; however, sensitive and specific serum markers do not correspond to the degree of active myocardial injury. The use of echocardiographic measures of contractility is associated with a specificity of 91.8% but low sensitivity of 66.7%. Overall we found poor concordance between serum markers and grade of rejection. It is unclear whether myocardial injury as assessed by serum markers, echocardiography, or histologic scoring is more important for assessment of acute rejection or long-term outcome, but it does not appear that serum and tissue markers of rejection can be used interchangeably.

Elevated serum concentrations of cardiac troponin T in acute allograft rejection after human heart transplantation

OBJECTIVES

This study evaluates the concept and diagnostic efficacy of using serum troponin T for the detection of cardiac graft rejection.

BACKGROUND

Cardiac troponin T is a cardiospecific myofibrillar protein, which is only detectable in the circulation after cardiac myocyte damage. It might be expected to be released during acute heart allograft rejection, allowing noninvasive rejection diagnosis.

METHODS

In 35 control subjects and in 422 samples from 95 clinically unremarkable heart allograft recipients more than 3 months postoperatively, troponin T serum concentrations were compared to the histological grade of acute graft rejection in concurrent endomyocardial biopsies.

RESULTS

Mean troponin T serum concentrations were identical in control subjects (23.2 +/- 1.4 ng/liter) and in heart transplant recipients without graft rejection (International Society for Heart and Lung Transplantation [ISHLT] grade 0; 22.4 +/- 1.7 ng/liter). Mean troponin T concentrations increased in parallel with the severity of graft rejection (ISHLT grade 1: 27.8 +/- 1.8 ng/liter; grade 2: 33.2 +/- 2.7 ng/liter; grade 3A: 54.6 +/- 6.5 ng/liter; grade 3B and 4: 105.4 +/- 53.7 ng/liter; p < 0.001 for grades 3 and 4 vs. grades 0 and 1). The proportion of positive samples also increased in parallel with rejection severity, reaching 100% in rejections of grade 3B and 4. Sensitivity and specificity for the detection of significant graft rejection (ISHLT grade 3/4) were 80.4% and 61.8%, respectively. The negative predictive value was most remarkable with 96.2%. Intraindividual longitudinal analysis of troponin T levels and biopsy results in 15 patients during long-term follow-up confirmed these findings.

CONCLUSIONS

The present data demonstrate that acute allograft rejection after human heart transplantation is often associated with increased serum concentrations of troponin T. All cases of serious forms of graft rejection would have been detected before the development of clinical symptoms. Measurement of troponin T levels may become a useful ancillary parameter for noninvasive rejection diagnosis, being most valuable in the exclusion of severe cardiac graft rejection.

Troponin T, creatine kinase MB mass, and creatine kinase MB isoform ratio in the detection of myocardial damage during non-surgical coronary revascularization

The presence of myocardial injury during non-surgical coronary revascularization has been evaluated by means of highly specific and sensitive biochemical markers. Troponin T, creatine kinase-MB isoenzyme mass concentration, and creatine kinase MB2/MB1 isoform ratio have been determined in 80 patients who underwent coronary revascularization with percutaneous transluminal coronary angioplasty (PTCA). Forty-five patients underwent balloon angioplasty, 15 rotational atherectomy, 10 directional atherectomy, and 10 elective coronary stenting. Serum concentration of the evaluated markers did not increase significantly after 57 uncomplicated revascularization procedures, including 15 rotablation procedures, nor after 8 PTCAs complicated by localized coronary type B and C dissections. Significant elevation of all markers above the upper limits of the reference interval (P < 0.05) was detected after occlusion of small side branches (< 0.5 mm diameter) in 5 patients. Creatine kinase MB2/MB1 isoform ratio was the earliest marker to increase. After recanalization of occluded vessels in 8/10 patients with 6-60 days old myocardial infarction only troponin T concentrations increased from a baseline of 0.28 microgram/l to a median peak of 0.80 microgram/l. This increase was statistically not significant (P = 0.12). In conclusion, myocardial damage was not detected following uncomplicated non-surgical revascularization obtained with different techniques. Markers of myocardial injury provide high sensitivity after small side branch occlusion.

Cardiac troponin T levels for risk stratification in acute myocardial ischemia. GUSTO IIA Investigators

BACKGROUND

The prognosis of patients hospitalized with acute myocardial ischemia is quite variable. We examined the value of serum levels of cardiac troponin T, serum creatine kinase MB (CK-MB) levels, and electrocardiographic abnormalities for risk stratification in patients with acute myocardial ischemia.

METHODS

We studied 855 patients within 12 hours of the onset of symptoms. Cardiac troponin T levels, CK-MB levels, and electrocardiograms were analyzed in a blinded fashion at the core laboratory. We used logistic regression to assess the usefulness of baseline levels of cardiac troponin T and CK-MB and the electrocardiographic category assigned at admission-ST-segment elevation, ST-segment depression, T-wave inversion, or the presence of confounding factors that impair the detection of ischemia (bundle-branch block and paced rhythms)-in predicting outcome.

RESULTS

On admission, 289 of 801 patients with base-line serum samples had elevated troponin T levels (> 0.1 ng per milliliter). Mortality within 30 days was significantly higher in these patients than in patients with lower levels of troponin T (11.8 percent vs. 3.9 percent, P < 0.001). The troponin T level was the variable most strongly related to 30-day mortality (chi-square = 21, P < 0.001), followed by the electrocardiographic category (chi-square = 14, P = 0.003) and the CK-MB level (chi-square = 11, P = 0.004). Troponin T levels remained significantly predictive of 30-day mortality in a model that contained the electrocardiographic categories and CK-MB levels (chi-square = 9.2, P = 0.027).

CONCLUSIONS

The cardiac troponin T level is a powerful, independent risk marker in patients who present with acute myocardial ischemia. It allows further stratification of risk when combined with standard measures such as electrocardiography and the CK-MB level.

Factors associated with the release of cardiac troponin T following percutaneous transluminal coronary angioplasty

BACKGROUND

Recent studies have suggested that immunoassay of cardiac troponin T (cTnT) provides a more sensitive measurement of myocardial necrosis than creatine kinase MB (CK-MB) mass concentration.

HYPOTHESIS

The purpose of this study was to compare the release of cTnT and CK-MB isoenzyme in patients undergoing percutaneous coronary angioplasty, and to investigate the clinical, procedural, and angiographic correlates of abnormal elevations of both of these markers.

METHODS

Total creatine kinase (total CK), CK-MB, and cTnT levels were measured immediately before and 12 h following intervention in 110 patients, including 100 consecutive patients undergoing coronary angioplasty and 10 control patients undergoing diagnostic cardiac catheterization. All patients had normal levels of all three markers at baseline. A postintervention total CK level > 225 U/l, an increase in CK-MB > 5.0 ng/ml, and/or an increase in cTnT > 0.04 ng/ml were considered indicative of myocardial injury.

RESULTS

Coronary angioplasty was successfully performed in all 100 patients without emergency bypass surgery or death, although six patients required emergent placement of an intracoronary stent for threatened closure. Eight patients demonstrated an abnormal increase in total CK, including six who were undergoing primary angioplasty for an acute myocardial infarction. One of these patients sustained a Q-wave infarction. Post angioplasty, 18 patients had elevations of both CK-MB and cTnT, 23 had elevations of only cTnT, and the remaining 59 patients had elevations of neither. All patients with CK-MB elevation also had cTnT elevation. Neither serologic marker increased in the diagnostic catheterization control patients. In comparison with patients without postintervention cTnT rise, patients with abnormal cTnT levels had a higher incidence of complex lesion morphology (p < 0.01) and intracoronary thrombus (p < or = 0.0001) prior to coronary angioplasty, and a higher incidence of coronary dissection (p < or = 0.01), abrupt closure (p < or = 0.05), and side-branch occlusion (p < or = 0.01) during angioplasty. In patients with elevation of both cTnT and CK-MB, postintervention CK-MB levels were 12-fold higher and cTnT levels were 21-fold higher than in patients with isolated elevation of only cTnT (p < 0.01).

CONCLUSIONS

These data indicate that > 40% of patients undergoing coronary angioplasty have evidence of minor degrees of myocardial damage, as evidenced by cTnT release. High-risk coronary lesions and both minor and major complications of angioplasty are associated with cTnT release. cTnT appears to be a more sensitive marker of myocardial injury than CK-MB under these circumstances. In comparison with isolated cTnT rise, elevation of both CK-MB and cTnT may be indicative of greater levels of myocardial injury.

Prognostic significance of admission troponin T concentrations in patients with myocardial infarction

BACKGROUND

New, highly specific cardiac structural proteins can now be measured. The early presence of one of these proteins, troponin T, has been found to have important prognostic significance in patients with unstable angina pectoris. The prognostic significance of its presence on admission was assessed in patients with myocardial infarction.

METHODS AND RESULTS

Two hundred forty patients admitted with myocardial infarction were studied and followed prospectively for a median of 3 years. The prognostic significance of an admission troponin T concentration > or = 0.2 ng/mL for subsequent cardiac death and/or reinfarction was assessed and compared with other variables in a regression model. Any detectable troponin T on admission was associated with a worse prognosis on follow-up. An admission concentration of > or = 0.2 ng/mL was associated with a higher risk of subsequent cardiac death (chi 2, 13.3; P = .0002) and death or nonfatal reinfarction (chi 2, 16; P = .00006). The excess risk was seen primarily in patients with admission ECG ST-segment elevation (cardiac death chi 2, 9.7; P = .001; death or nonfatal reinfarction chi 2, 10.3; P = .001). In a stepwise regression model for cardiac death or nonfatal reinfarction, troponin T was superior to most of the other variables entered in both myocardial infarction subgroups.

CONCLUSIONS

The presence of admission troponin T in patients with myocardial infarction defines a subgroup, particularly those with ST-segment elevation, at increased risk of subsequent cardiac events and identifies a group that may benefit from alternative early management strategies.

Cardiac troponin T and creatine kinase MB mass concentrations in children receiving anthracycline chemotherapy

Anthracyclines (doxorubicin, daunorubicin, and derivatives) are among the most effective antineoplastic drugs for pediatric cancer with dose-limiting acute and long-term cardiotoxicity. The exact mechanism of the development of cardiomyopathy is still not clear. Anthracyclines may induce subclinical acute myocardial injury leading to lysis of a limited number of myocytes. Alternatively, myocytes may experience a transient loss of cytoplasmic membrane integrity. Both conditions may lead to a transient efflux of small amounts of cytoplasmic enzymes and other proteins specific to the heart muscle fibers. To test these hypotheses we assayed plasma creatine kinase (CK) MB mass and cardiac specific troponin T (TnT). CKMB may be released even in case of reversible cell membrane injury, while prolonged elevation of TnT is the most sensitive and specific marker of limited myocardial necrosis. Thirty-five anthracycline-containing chemotherapy courses in 22 children with cancer were analyzed. CKMB mass and TnT concentrations were within the normal range in all children before anthracycline therapy. Within 72 hours from anthracycline therapy no increment of one of these two marker proteins was detected (ANOVA for repeated measures, P = 0.94 [TnT] and 0.25 [CKMB]). We conclude that only minimal if any acute necroses of cardiac myocytes occur after anthracycline therapy. Even membrane integrity appears to be maintained within the first 3 days after anthracycline therapy, in the absence of electrocardiographic or echocardiographic signs of acute cardiotoxicity.

Comparison of two strategies for myocardial management during coronary artery operations

Despite the current trend for using blood cardioplegia, ventricular fibrillation with intermittent ischemia is still used as a strategy to manage the myocardium with impressive results. These two methods of myocardial management were compared in 40 patients undergoing elective coronary artery operations using creatine kinase MB isoforms and troponin T assays. Each patient was randomized to have either cold blood cardioplegia (n = 20) or ventricular fibrillation with intermittent ischemia (n = 20) for myocardial management during the construction of distal anastomoses. Until recently, the comparison of different methods of myocardial management has been hindered by the lack of a specific and sensitive marker of myocardial damage. Analysis of creatine kinase MB isoforms (MB2, cardiac tissue form; MB1, plasma-modified form) and cardiac-specific troponin T (a structural protein) has been shown to improve the sensitivity for the detection of myocardial damage. There were no significant differences between the two groups in age, sex ratio, extent of disease, or left ventricular function. Blood samples for analysis were collected before cross-clamp application and at time intervals up to 48 hours after. Median peak creatine kinase MB2 activity was found to be significantly higher in the blood cardioplegia group compared with ventricular fibrillation (26.5 U/L versus 19.5 U/L, respectively, p = 0.04). Although median peak troponin T concentration was higher in the blood cardioplegia group, the difference failed to reach significance (2.2 ng/mL versus 1.6 ng/mL, p = 0.15).(ABSTRACT TRUNCATED AT 250 WORDS)

Intermittent ischaemic arrest and cardioplegia in coronary artery surgery: coming full circle?

OBJECTIVE

To compare the cardioprotective efficacy of cold crystalloid cardioplegia and intermittent ischaemic arrest in patients undergoing elective coronary artery surgery.

DESIGN

Prospective randomised trial.

SETTING

London teaching hospital.

SUBJECTS

20 patients with at least moderately good left ventricular function undergoing elective coronary artery surgery by one experienced surgeon and needing at least two bypass grafts.

INTERVENTIONS

Patients were randomised to cold crystalloid cardioplegia or intermittent ischaemic arrest.

MAIN OUTCOME MEASURES

The primary determinant of the efficacy of myocardial protection was serial measurement (before and at 1, 6, 24, and 72 hours after the end of cardiopulmonary bypass) of cardiac troponin T (cTnT), a highly sensitive and specific marker of myocardial damage.

RESULTS

There was no significant difference in age, ejection fraction, number of grafts, bypass times, or cross clamp times between the two groups. One patient in the cardioplegia group had a perioperative infarct and was excluded from further study. In both groups there was a significant increase in cTnT, with peak concentrations being reached 6 hours after the end of cardiopulmonary bypass and remaining significantly high at 72 hours. At 6 hours the median (75% interquartile range) concentrations of cTnT were similar in both groups (1.8 (1.0-3.6) micrograms/l for cardioplegia v 1.9 (1.0-3.5) micrograms/l for intermittent ischaemic arrest).

CONCLUSION

This trial shows that intermittent ischaemic arrest, even without systemic cooling or venting of the left ventricle, provides a similar level of myocardial protection to cardioplegia in patients with moderate left ventricular function and short ischaemic times.

Lack of cardioprotective efficacy of allopurinol in coronary artery surgery

OBJECTIVE

To examine the cardioprotective efficacy of allopurinol in patients undergoing elective coronary artery surgery.

DESIGN

Prospective randomised trial.

SETTING

London teaching hospital.

PATIENTS

Twenty patients with at least moderately good left ventricular function undergoing elective coronary artery surgery and requiring at least two bypass grafts.

INTERVENTIONS

Patients were randomised to receive allopurinol (1200 mg in two divided doses) or to act as controls.

MAIN OUTCOME MEASURE

The primary determinant of the efficacy of myocardial protection was serial measurement (preoperatively and subsequently at one, six, 24, and 72 hours after the end of cardiopulmonary bypass) of cardiac troponin T (cTnT) a highly sensitive and specific marker of myocardial damage. Additional evidence was provided by serial measurement of the MB-isoenzyme of creatine kinase (CK-MB) and myoglobin, ECG changes, and clinical outcome.

RESULTS

There was no significant difference in age, ejection fraction, number of grafts, bypass times, or cross clamp times between the two groups. In both groups there was a highly significant (p < 0.01) rise in cTnT, CK-MB, and myoglobin. Peak concentrations were reached between one (CK-MB and myoglobin) and six hours (cTnT) after the end of cardiopulmonary bypass. At 72 hours cTnT concentrations were six times higher than baseline concentrations whereas CK-MB and myoglobin were approximately double baseline concentrations. There was no significant difference in cTnT, CK-MB, or myoglobin between the allopurinol and control groups at any time. There was no diagnostic ECG evidence of perioperative infarction in any patient.

CONCLUSION

Unlike previous reports this study did not show that allopurinol had a cardioprotective effect in patients with good left ventricular function undergoing elective coronary artery surgery.

Diagnostic performance and prognostic value of serum troponin T in suspected acute myocardial infarction

Cardiac troponin T (TnT) is a new serological marker for use as a diagnostic tool for myocardial damage. A blinded prospective multicentre study representing 298 patients suspected of having acute myocardial infarction (AMI), and admitted to the coronary care units of six Scandinavian Hospitals was undertaken to assess the diagnostic performance and prognostic efficacy of a new cardiospecific TnT immunoassay. We used a discriminator TnT value of 0.20 microgram l-1. One hundred and fifty five patients (52%) had definite AMI, based on WHO criteria (all had peak S-TnT values of > or = 0.20 micrograms l-1); 127 patients (43%) had ischaemic heart disease (IHD) without AMI; and 16 patients (5%) had non-IHD (all had peak S-TnT values of < 0.20 microgram l-1). The 127 IHD-patients without definite AMI could be subdivided into a group of 44 patients with S-TnT peak values of > or = 0.20 microgram l-1, and a group of 83 patients with TnT below this level. An equal identification of these patients among the centres was seen (mean +/- SD 35 +/- 13%; range 20-55%). A follow-up study was able to define the clinical significance of these findings. The cumulative 6 months probability of suffering cardiac death or AMI was significantly higher in the subgroup with increased TnT values (14% (6/44)) as compared to the other subgroup (4% (3/83)) (Log-rank test, p = 0.025). The probability of cardiac events was 15% for the patients with definite AMI.(ABSTRACT TRUNCATED AT 250 WORDS)