The prognostic significance of immunoradiometric CK-MB assay (IRMA) diagnosis of myocardial infarction in patients with low total CK and elevated MB isoenzymes

Serum Creatine Kinase-MB Isoenzyme Activity among Subjects with Uncomplicated Essential Hypertension: Any Sex Differences

Hypertension (high blood pressure) is a major health challenge and more women than men are affected by the condition. Complications as a result of this condition often lead to disabilities and premature death. The objective of this study was to evaluate creatine kinase-MB (CK-MB) activity in uncomplicated hypertension and to know whether sex differences exist in the activity of the enzyme. Serum creatine kinase-MB isoenzyme activity, troponin I, and lipid profile were evaluated in 140 male and 100 female Nigerians with hypertension. The control group was comprised of 100 (50 males and 50 females) normotensive subjects. Measured parameters were assayed using Selectra Pros chemistry analyzer. The means were compared between males and females using Students't-test. The mean CK-MB activity of the female hypertensive subjects was significantly higher (p < 0.001) than the males. Similarly, the mean cardiac troponin I (cTnI) of the female hypertensive subjects was significantly higher (p < 0.001) than the males. Conversely, the mean CK-MB activity of the female normotensive subjects was significantly lower (p < 0.001) than the male counterparts. There was no difference in the levels of cTnI between male and female normotensive subjects. Serum CK-MB activity was higher in female than male hypertensive subjects. In the light of these results, cardiac markers should be routinely done in the evaluation of hypertensive subjects and sex-specific consideration may be recognized in the management of these patients.

Sensitive troponin assays

Sensitive troponin assays have been developed to meet the diagnostic goals set by the universal definition of myocardial infarction (MI). The analytical advantages of sensitive troponin assays include improved analytical imprecision at concentrations below the 99th percentile and the ability to define a reference distribution fully. Clinically, the improved sensitivity translates into the ability to diagnosis MI earlier, possibly within 3 h from admission and the ability to use the rate of change of troponin (Δ troponin) for diagnosis. Very sensitive assays may, in appropriately selected populations (perhaps with the addition of Δ troponin), allow diagnosis on hospital admission or within 1–2 h of admission. An elevated troponin level occurring in patients without suspected acute coronary syndromes has, in all studies to date in which outcome has been examined, been shown to indicate an adverse prognosis whatever the underlying clinical diagnosis. Failure of elevation means a good prognosis allowing early, safe hospital discharge, whereas a raised value requires investigation and should help prevent clinically significant pathology being overlooked. Sensitive troponins do present a challenge to the laboratory and the clinician. For the laboratory, the diagnosis of MI requires a change in troponin value. For the clinician, the challenge is to shift from a simplistic yes/no diagnosis of MI based on a single troponin value to a diagnosis that utilises early troponin changes as part of the clinical picture, and to relate the new class of detectable troponin elevation in patients with ischaemic myocardial disease to existing clinical guidelines and trial evidence.

Elevated creatine kinase-MB with normal creatine kinase predicts worse outcomes in patients with acute coronary syndromes: results from 4 large clinical trials

BACKGROUND

The degree to which elevated creatine kinase (CK)-MB in the presence of normal CK is predictive of outcome is not well understood despite having been studied for decades. This analysis examined whether normal CK with elevated CK-MB in patients with non-ST-segment elevation acute coronary syndrome (NSTE ACS) is an independent predictor of worse outcomes. A concomitant goal was to contribute insight to the debate over how patients with NSTE ACS should be managed.

METHODS

Data for 25,960 patients from the GUSTO IIb, PARAGON A and B, and PURSUIT trials were analyzed. Of these patients, 6402 were excluded from primary analysis because of missing (unmeasured) biomarkers. Patients with complete laboratory data (n = 19,558) were grouped by CK and CK-MB results. To confirm the primary analysis results, data from patients with missing biomarkers were used in an imputation model.

RESULTS

Patients were categorized in 1 of 4 groups: normal CK + normal CK-MB; normal CK + elevated CK-MB; elevated CK + normal CK-MB; or elevated CK + elevated CK-MB. For the primary outcome, 180-day death, or myocardial infarction, Kaplan-Meier estimates were 14.9%, 20.8%, 14.5%, and 18.2%, respectively. Regardless of total CK, elevated CK-MB was associated with a 25% to 49% increased relative risk of worse outcomes. Findings from the analyses were verified by the multivariable model.

CONCLUSIONS

CK-MB remains a reliable marker for myocardial necrosis and a strong predictor of worse prognosis. All patients with ACS should have CK-MB measurement to search for cardiac ischemia. Patients with elevated CK-MB should receive aggressive management commensurate with their increased risks.

Cardiovascular outcome in hospitalized patients with minimal troponin I elevation and normal creatine phosphokinase

BACKGROUND

Among patients with acute coronary syndrome, elevated cardiac troponin and creatine phosphokinase MB fraction levels have both prognostic and diagnostic values. However, in hospitalized patients, cardiac biomarkers are measured in a variety of clinical situations including but not limited to acute coronary syndrome. Moreover, these patients may have elevated troponin levels with no increase in creatine phosphokinase MB fraction levels.

OBJECTIVE

To evaluate the cardiovascular outcome of acutely ill, hospitalized patients with minimal troponin I increase with normal creatine phosphokinase MB fraction.

METHODS

We identified 64 patients retrospectively from our database with minimal troponin I increase and normal creatine phosphokinase MB fraction hospitalized between November 1998 and April 2000. Discharged patients were questioned about re-hospitalization for myocardial infarction, unstable coronary syndrome, congestive heart failure and percutaneous coronary intervention by means of a structured questionnaire. For those patients who died during hospitalization, data were collected from hospital records. For patients who died at home or at a different institution, a surviving relative completed the questionnaire. Primary outcomes were death, myocardial infarction and the need for revascularization or re-hospitalization.

RESULTS

Composite endpoint of death, myocardial infarction, percutaneous coronary intervention or coronary artery bypass grafting and re-hospitalization for cardiac cause occurred in 35.95% of patients within 1 year.

CONCLUSIONS

There is a significant composite event rate of death, myocardial infarction or re-hospitalization for cardiac causes in acutely ill, hospitalized patients with normal creatine phosphokinase MB fraction and minimally elevated troponin I, regardless of the cause for hospitalization.

Measurement of cardiac troponins

The cardiac troponins form part of the regulatory mechanism for muscle contraction. Specific cardiac isoforms of cardiac troponin T and cardiac troponin I exist and commercially available immunoassay systems have been developed for their measurement. A large number of clinical and analytical studies have been performed and the measurement of cardiac troponins is now considered the 'gold standard' biochemical test for diagnosis of myocardial damage. There have been advances in understanding the development and structure of troponins and their degradation following myocardial cell necrosis. This has contributed to the understanding of the problems with current assays. Greater clinical use has also highlighted areas of analytical and clinical confusion. The assays are reviewed based on manufacturers' information, current published material as well as the authors' in-house experience.

Cardiac markers in the diagnosis of acute coronary syndromes

Evolution of the role of cardiac markers has ranged from the diagnosis of acute myocardial infarction in patients with nondiagnostic electrocardiograms to prognostic risk stratification and to guide therapy. The technology to provide rapid, real time measurements by immunoassay has provided the laboratory and clinician with a range of test options. The principal changes have been the use of rapid serial marker measurements of well-recognized cardiac markers, and the development of immunoassays for the cardiac structural proteins. Measurement of cardiac troponins has generated a new diagnostic paradigm in patients with suspected acute coronary syndromes. There is now a new gold standard biochemical test for myocardial infarction. A range of interventions can be guided by troponin measurement. The use of troponin measurements is central to management of patients with suspected acute coronary syndromes. Future developments in this field will focus on the role of existing and novel markers of inflammation and ischemia.

Normal CK, elevated MB predicts complications in acute coronary syndromes

The implications of an elevated Creatine kinase (CK)-MB isoenzyme (MB) in suspected acute coronary syndromes, with a normal total CK, is not well established. Despite many guidelines on managing patients with acute coronary ischemia, none indicates strategies for patients with elevated MB and with a normal CK. The outcome consequence of this result is not firmly established. Our objective was to prospectively evaluate outcomes in patients with suspected acute coronary syndromes, normal initial total CK, and increased MB. All Emergency Department patients with suspected acute coronary syndromes and creatinine < 2.0 mg/dL were eligible for study entry. Serial CK and MB fractions were measured on arrival in the Emergency Department, then 8 and 16 h postpresentation. A composite outcome of death, Q-wave myocardial infarction, or revascularization was defined at the index visit and 6 months later. Outcomes were determined by blinded record review and by telephone contact. In the 698 patients entered, the acute composite outcome rate was 25% (175) and 6.3% (44) at 6 months. Acute and 6 month adverse outcome rates were statistically the same for all patients with an elevated MB fraction, regardless of the total CK level. An elevated MB conferred a higher event rate than did a normal MB. We conclude that the adverse event rate for patients with suspected acute coronary syndromes and an elevated MB is the same whether or not the total CK is elevated. These patients should be considered as having had an acute coronary syndrome.

Detection of myocardial injury during transvenous implantation of automatic cardioverter-defibrillators

OBJECTIVES

The present study was designed to assess the extent of myocardial injury in patients undergoing transvenous implantation of an automatic implantable cardioverter-defibrillator (ICD) using cardiac troponin I (cTNI), which is a highly specific marker of structural cardiac injury.

BACKGROUND

During ICD implantation, repetitive induction and termination of ventricular fibrillation (VF) via endocardial direct current shocks is required to demonstrate the correct function of the device. Transthoracic electrical shocks can cause myocardial cell injury.

METHODS

Measurements of total creatine kinase (CK), CK-MB, myoglobin, cardiac troponin T (cTNT) and cTNI were obtained before and after ICD implantation in 49 consecutive patients. Blood samples were drawn before and 2, 4, 8, and 24 h after implantation.

RESULTS

Elevations of CK, CK-MB, myoglobin, cTNT and cTNI above cut-off level were found in 25%, 6%, 76%, 37% and 14% of patients, respectively, with peak cTNI concentrations ranging from 1.7 to 5.5 ng/ml. Cumulative defibrillation energy (DFE), mean DFE, cumulative VF time, number of shocks as well as prior myocardial infarction (MI) were found to be significantly related to a rise of cTNI. Mean DFE > or = 18 J and a recent MI were identified as strong risk factors for cTNI rise.

CONCLUSIONS

During transvenous ICD implantation myocardial injury as assessed by cTNI rise occurs in about 14% of the patients. Peak cTNI concentrations are only minimally elevated reflecting subtle myocardial cell damage. Patients with a recent MI and a mean DFE > or = 18 J seem to be prone to cTNI rise.

Prognostic influence of elevated values of cardiac troponin I in patients with unstable angina

BACKGROUND

Elevations of the MB isoform of creatine kinase (CK) and cardiac troponin T seem to confer an adverse prognosis in unstable angina. We examined whether this prognostic influence is also present for cardiac troponin I (cTnI), a new and even more specific marker of myocardial injury.

METHODS AND RESULTS

We studied 106 patients with the clinical diagnosis of unstable angina showing chest discomfort at rest within 48 hours of admission, ECG evidence of myocardial ischemia, and normal values of total CK over the initial 16 hours of observation. The primary end point was death or nonfatal myocardial infarction (MI) at 30 days; the secondary end point was the incidence of cardiac events at 1 year. Blood was drawn every 8 hours for 3 days. Thirteen patients were excluded because of increased CK-MB mass concentrations within 16 hours of admission (non-Q-wave MI) and 2 because of inadequate blood sampling. Of the remaining 91 patients, 22 had cTnI elevations on admission (n=7) or after 8 hours (n=15). At 30 days, no deaths (0%) and 4 MIs (5.8%) occurred in the 69 patients with normal cTnI compared with 2 deaths (9.1%) and 4 MIs (18.2%) in the 22 patients with elevated cTnI. The combined incidence of death and nonfatal MI was 5.8% and 27.3%, respectively (P=.02). At 1 year, only 68% of patients with elevated cTnI were free of cardiac events, compared with 90% of those without elevations (P=.01).

CONCLUSIONS

These data indicate that cTnI is an important prognostic variable in patients with unstable angina. Elevations of cTnI predict an adverse short- and long-term prognosis.

Cardiac-specific troponin I levels to predict the risk of mortality in patients with acute coronary syndromes

BACKGROUND

In patients with acute coronary syndromes, it is desirable to identify a sensitive serum marker that is closely related to the degree of myocardial damage, provides prognostic information, and can be measured rapidly. We studied the prognostic value of cardiac troponin I levels in patients with unstable angina or non-Q-wave myocardial infarction.

METHODS

In a multicenter study, blood specimens from 1404 symptomatic patients were analyzed for cardiac troponin I, a serum marker not detected in the blood of healthy persons. The relation between mortality at 42 days and the level of cardiac troponin I in the specimen obtained on enrollment was determined both before and after adjustment for baseline characteristics.

RESULTS

The mortality rate at 42 days was significantly higher in the 573 patients with cardiac troponin I levels of at least 0.4 ng per milliliter (21 deaths, or 3.7 percent) than in the 831 patients with cardiac troponin I levels below 0.4 ng per milliliter (8 deaths, or 1.0 percent; P < 0.001). There were statistically significant increases in mortality with increasing levels of cardiac troponin I (P < 0.001). Each increase of 1 ng per milliliter in the cardiac troponin I level was associated with a significant increase (P = 0.03) in the risk ratio for death after adjustment for the base-line characteristics that were independently predictive of mortality (ST-segment depression and age > or = 65 years).

CONCLUSIONS

In patients with acute coronary syndromes, cardiac troponin I levels provide useful prognostic information and permit the early identification of patients with an increased risk of death.

Clinical and angiographic correlates of normal creatine kinase with increased MB isoenzymes in possible acute myocardial infarction

A retrospective study of patients with possible acute myocardial infarction was conducted over a 2-year period to evaluate the clinical characteristics, angiographic findings, and in-hospital prognosis in patients with normal total creatine kinase (CK) activity and increased MB isoenzyme activity (CK-MB). Thirty-nine cases were identified (study group) and compared with cases of Q-wave (n = 77) and non-Q-wave (n = 60) infarctions. Compared with the Q-wave group, study group patients were older (67.5 +/- 9.0 vs 60.8 +/- 11.5 years; p < 0.01) and more often had previous diagnoses of coronary disease (52.6% vs 18.2%; p < 0.01) and peripheral vascular disease (28.9% vs 10.4%; p = 0.02). Angina (92.2% vs 65.8%; p < 0.01) and ST elevation (81.8% vs 13.2%; p < 0.01) were more common in the Q-wave group. Nearly identical clinical profiles and electrocardiographic findings were observed in the study and non-Q-wave groups. Angiographic analysis revealed a higher frequency of multivessel disease in the study group (89.6%) than in the Q-wave group (48.6%, p < 0.01) but no difference between the study group and the non-Q-wave group (79.6%; p not statistically significant). Left ventricular function and in-hospital complications were similar among groups. It is concluded that patients with normal total CK activity and increased CK-MB concentration represent a subgroup of patients with non-Q-wave infarction with a high prevalence of multivessel coronary disease.

The diagnosis of acute myocardial infarction

Changes in the economic and therapeutic environment have altered the time frame in which an accurate diagnosis of acute myocardial infarction (AMI) must be made. The advent of effective reperfusion therapies and the increasing emphasis on reducing cost produce an environment in which rapid diagnosis can reduce morbidity and mortality while simultaneously reducing overall cost by avoiding unnecessary hospitalization and intervention. The first element of a diagnostic strategy remains a brief, directed history and physical examination. The orientation of this phase is to identify important causes of symptoms other than AMI, while rapidly leading to more definitive evaluation for myocardial ischemia when another diagnosis is not found. The ECG provides the most rapid definitive diagnosis, but the diagnosis remains equivocal in many patients with nondiagnostic ECGs. In this group, the use of cardiac enzyme measurements early in the course holds promise in directing intensive care at high-risk patients while avoiding unnecessary intervention in low-risk patients. A protocolized approach to patient evaluation should become a part of standard practice patterns in every hospital.

Use of rapid serial sampling of creatine kinase MB for very early detection of myocardial infarction in patients with acute chest pain

To determine how early myocardial infarction can be detected, serial creatine kinase MB concentrations were sampled in 313 patients during triage of acute (less than 12 hours) chest pain. Serum was sampled on hospital arrival (baseline) and hourly for 3 hours (total of four samples). Creatine kinase MB concentrations were subsequently analyzed for their ability to detect infarction. Infarction was present in 70 patients (22%) and was diagnosable from the index electrocardiograms in 27 of these (39%). Sensitivity and specificity for detection of infarction were 76% and 72%, respectively, as determined from baseline MB values only and increased with each additional sample to a maximum of 92% and 96%, respectively, in all four samples. Analysis of two serum samples taken 2 hours apart showed a sensitivity of 94% and a specificity of 91%. If these results are confirmed, improved initial diagnostic accuracy with this rapid assay technique in acute chest pain may (1) conserve resources when initial suspicion of infarction is low, (2) identify patients with infarction appropriate for early intervention, and (3) avoid premature hospital discharge of patients with infarction.