Enzymatic estimation of myocardial infarct size when early creatine kinase values are not available

Methods of creatine kinase-MB analysis to predict mortality in patients with myocardial infarction treated with reperfusion therapy

BACKGROUND

Larger infarct size measured by creatine kinase (CK)-MB release is associated with higher mortality and has been used as an important surrogate endpoint in the evaluation of new treatments for ST-segment elevation myocardial infarction (STEMI). Traditional approaches to quantify infarct size include the observed CK-MB peak and calculated CK-MB area under the curve (AUC). We evaluated alternative approaches to quantifying infarct size using CK-MB values, and the relationship between infarct size and clinical outcomes.

METHODS

Of 1,850 STEMI patients treated with reperfusion therapy in the COMplement inhibition in Myocardial infarction treated with Angioplasty (COMMA) (percutaneous coronary intervention (PCI)-treated) and the COMPlement inhibition in myocardial infarction treated with thromboLYtics (COMPLY) (fibrinolytic-treated) trials, 1,718 (92.9%) (COMMA, n = 868; COMPLY, n = 850) had at least five of nine protocol-required CK-MB measures. In addition to traditional methods, curve-fitting techniques were used to determine CK-MB AUC and estimated peak CK-MB. Cox proportional hazards modeling assessed the univariable associations between infarct size and mortality, and the composite of death, heart failure, shock and stroke at 90 days.

RESULTS

In COMPLY, CK-MB measures by all methods were significantly associated with higher mortality (hazard ratio range per 1,000 units increase: 1.09 to 1.13; hazard ratio range per 1 standard deviation increase: 1.41 to 1.62; P <0.01 for all analyses). In COMMA, the associations were similar but did not reach statistical significance. For the composite outcome of 90-day death, heart failure, shock and stroke, the associations with all CK-MB measures were statistically significant in both the COMMA and COMPLY trials.

CONCLUSIONS

Sophisticated curve modeling is an alternative to infarct-size quantification in STEMI patients, but it provides information similar to that of more traditional methods. Future studies will determine whether the same conclusion applies in circumstances other than STEMI, or to studies with different frequencies and patterns of CK-MB data collection.

Quantitative evaluation of the amount of delayed myocardial enhancement as a predictor of systolic dysfunction

30 patients with delayed contrast enhancement in patterns suggestive of myocardial infarctions were reviewed. Infarct mass was quantitatively measured using short axis images obtained in the delayed phase of gadopentetate administration. Left ventricular mass and ejection fraction were measured using short axis, steady state free precession images. A relationship is drawn between increased mass of infarction and decreased left ventricular ejection fraction. For each gram of infarct, there is a 0.5 % reduction in ejection fraction (EF = 50 - (0.48 x gm infarcted myocardium); r²= 0.49). For each % increase of infarcted myocardium, there is a 0.67 % reduction in ejection fraction (EF = 50 - (0.67 x percent of infarcted myocardium); r²= 0.39). Left ventricular ejection fraction correlates inversely with the mass of myocardium with delayed enhancement on cardiac MRI.

Troponin-I concentration 72 h after myocardial infarction correlates with infarct size and presence of microvascular obstruction

OBJECTIVES

The aim of this study was to use late gadolinium hyper-enhancement cardiac magnetic resonance (LGE-CMR) imaging to determine if a 72-h troponin-I measurement would provide a more accurate estimation of infarct size and microvascular obstruction (MVO) than serial creatine kinase (CK) or early troponin-I values.

METHODS

LGE-CMR was performed 3.7+/-1.4 days after medical treatment for acute ST elevation or non-ST elevation myocardial infarction. Infarct size and MVO were measured and correlated with serum troponin-I concentrations, which were sampled 12 h and 72 h after admission, in addition to serial CK levels.

RESULTS

Ninety-three patients, of whom 71 had received thrombolysis for ST elevation myocardial infarction, completed the CMR study. Peak CK, 12-h troponin-I, and 72-h troponin-I were related to infarct size by LGE-CMR (r = 0.75, p<0.0001; r = 0.56, p = 0.0003; r = 0.62, p<0.0001 respectively). Serum biomarkers demonstrated higher values in the group with MVO compared with those without MVO (Peak CK 3085+/-1531 vs 1471+/-1135, p<0.001; 12-h troponin-I 58.3+/-46.9 vs 33.4+/-40.0, p = 0.13; 72-h troponin-I 11.5+/-9.9 vs 5.5+/-4.6, p<0.005). The correlation between the extent of MVO and 12-h troponin-I was not significant (r = 0.16), in contrast to the other serum biomarkers (peak CK r = 0.44, p<0.0001; 72-h troponin-I r = 0.46, p = 0.0002).

CONCLUSION

A single measurement of 72-h troponin-I is similar to serial CK measurements in the estimation of both myocardial infarct size and extent of MVO, and is superior to 12-h troponin-I measurements.

The quantification of infarct size

We sought to summarize the published evidence regarding the measurement of infarct size by serum markers, technetium-99m sestamibi single-photon emission computed tomography (SPECT) myocardial perfusion imaging, and magnetic resonance imaging. The measurement of infarct size is an attractive surrogate end point for the early assessment of new therapies for acute myocardial infarction. For each of these three approaches, we reviewed reports published in English providing the clinical validation for the measurement of infarct size and the relevant clinical trial experience. The measurement of infarct size by serum markers has multiple theoretical and practical limitations. The measurement of troponin is promising, but the available data validating this marker are limited. Sestamibi SPECT imaging has five separate lines of published evidence supporting its validity and has received extensive study in multicenter trials. Magnetic resonance imaging has great promise but has less clinical validation and no multicenter trial experience. Therefore, SPECT sestamibi imaging is currently the best available technique for the quantitation of infarct size to assess the incremental treatment benefit of new therapies in multicenter trials of acute myocardial infarction.

Indices of reperfusion in patients with acute myocardial infarction using characteristics of the CK-MB time-activity curve

The purpose of this study was to identify indices of coronary artery reperfusion in patients treated with thrombolytic therapy for acute myocardial infarction (AMI) by means of characteristics from the serum creatine kinase (CK) isoenzyme MB time-activity curve. Frequent blood sampling as performed in three groups with a first AMI: 29 patients treated with intravenous thrombolytic therapy who had a patent infarct-related artery with normal flow (TIMI-3) at acute catheterization (reperfusion group); four patients with a persistently closed infarct-related artery (no reperfusion group); and 44 patients who did not receive any therapy aimed at coronary reperfusion (no thrombolytic therapy group). In the latter group we prospectively estimated that 25% would have spontaneous reperfusion. A physiologically based computer-calculated multi-compartment method was used to determine the characteristics of the serum CK-MB time-activity curve. In addition to demonstrating an earlier increase, a shorter time to peak of serum CK-MB and a lower estimated infarct size in the reperfusion group (p = 0.025 to 0.00001), the appearance rate constant (k1) and time from estimated initial increase to peak of CK-MB in the blood stream (tRP) were significantly different from those values in the no thrombolytic therapy group (p less than 00001). A cutoff level indicating reperfusion if k1 was greater than 0.185 or tRP was less than 16.5 hours demonstrated overlapping values between these two groups in only four patients (k1), two patients (tRP), and six patients with a combination.(ABSTRACT TRUNCATED AT 250 WORDS)

Frequency, characteristics and significance of supraventricular tachyarrhythmias detected by 24-hour electrocardiographic recording in the late hospital phase of acute myocardial infarction

The incidence, characteristics and clinical significance of supraventricular tachyarrhythmias occurring in the late hospital phase of acute myocardial infarction (AMI) were assessed in 209 consecutive patients. Arrhythmias were quantified by 24-hour electrocardiographic recording 16 +/- 3 days after AMI, and were classified according to the degree of complexity in 5 classes. Class 0 = less than 5 premature beats/hr; class 1 = between 5 and 100/hr; class 2 = greater than 100/hr or repetitive premature beats; class 3 = atrial-junctional tachycardia; class 4 = atrial flutter-fibrillation. Supraventricular tachyarrhythmias classes 1 to 2 always occurred in the absence of symptoms in 86 patients (41%); supraventricular tachyarrhythmias classes 3 to 4 (paroxysmal, self-limiting, brief) occurred in 27 patients (13%), symptomatically in 6. The presence of supraventricular tachyarrhythmias classes 2 to 3 was related to age over 55 years and complex ventricular tachyarrhythmias (greater than 20 premature beats/hr, ventricular tachycardia) (both p less than 0.05). Increasing complexity of supraventricular tachyarrhythmias was significantly associated with presence and entity of cardiac enlargement and left ventricular dysfunction (both p less than 0.01). Patients with class 4 showed the most severe cardiac deterioration. During the 2 years after AMI, patients with classes 2, 3 and 4 had a higher incidence of acute pulmonary edema, New York Heart Association functional classes III to IV for congestive heart failure (both p less than 0.005) and a greater need of digitalis and diuretics (p = 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

Rate of disappearance of creatine kinase-MB after acute myocardial infarction: clinical determinants of variability

The apparent rate of disappearance (Kd) of creatine kinase (CK)-MB is used in the calculation of the size of acute myocardial infarction (AMI), but little is known about the determinants of variability of this parameter. We therefore evaluated the relationship between clinical characteristics and apparent Kd in 328 patients with AMI without evidence of recurrent infarction. Patients with a history of cigarette smoking within 6 months had higher rates of disappearance of CK-MB, but no relationship was found between renal function and apparent Kd. Slower rates of disappearance of CK-MB were correlated with longer times from the onset of symptoms to peak CK-MB value (p less than 0.001), while higher peak CK-MB levels were not correlated with apparent rates of enzyme clearance. Decreased rates of disappearance of CK-MB were found in patients who had congestive heart failure during or after the hospitalization (both p less than 0.05), and who died during the hospitalization or during study follow-up (both p less than 0.05). Slower rates of disappearance were also significantly correlated with lower ejection fractions on radionuclide ventriculography at 10 days (p less than 0.001) and at 3 months (p less than 0.05) after AMI. These data suggest that patients with slower rates of disappearance of CK-MB may have poorer prognoses, perhaps reflecting continuing necrosis and enzyme release from jeopardized myocardium.

Quantification of infarct size by 201Tl single-photon emission computed tomography during acute myocardial infarction in humans. Comparison with enzymatic estimates

We prospectively investigated whether 201Tl single-photon emission computed tomography (SPECT) could accurately diagnose the presence and quantify the extent of acute myocardial infarction when compared with infarct size assessed by plasma MB-creatine kinase activity. Thirty patients with enzymatic evidence of infarction were imaged within 12-36 hours of chest pain (mean, 23.4 hours). No patient had a previous infarction, and none underwent intervention seeking to restore coronary patency. Infarct size was quantified with computer-generated polar maps of the myocardial radioactivity and expressed as a percentage of the total left ventricular volume. To assess left and right ventricular performance, blood-pool gated radionuclide angiography was performed immediately after SPECT. All 30 patients had perfusion defects consistent with myocardial infarction. Scintigraphic and enzymatic estimates of infarct size correlated well for the group as a whole (r = 0.78, p less than 0.001, SEE = 9.1) but especially for those patients with anterior infarction (r = 0.91, p less than 0.001, SEE = 7.9). The poor correlation observed in patients with inferior infarction (r = 0.50, p less than 0.05, SEE = 10.0) was believed to be related to the frequent occurrence of right ventricular involvement because SPECT assessed only left ventricular damage, whereas the enzymatic method estimated the myocardial injury in both ventricles. A quantitative index of right ventricular infarct size, derived from the relation between the scintigraphic and enzymatic estimates, had a strong inverse correlation with right ventricular ejection fraction (r = -0.89, p less than 0.001, SEE = 3.6).(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of QRS scoring system to enzymatic and pathologic infarct size: the role of infarct location

A method for estimating infarct size from 12-lead ECGs has been developed but not extensively validated. To assess its accuracy, ECG scores from 62 patients admitted to the coronary care unit at Barnes Hospital were compared to infarct size calculated from plasma MB creatine kinase (MB-CK) activity. A second cohort of 29 patients enrolled in the Multicenter Investigation of the Limitation of Infarct Size (MILIS) was evaluated as a test set and to provide pathologic correlates. Patients with conduction system disease, ventricular hypertrophy, or multiple infarctions were excluded, as were those in the Barnes group who had undergone thrombolytic therapy. ECGs obtained early (days 3 to 7 in the Barnes group and day 3 in the MILIS group) or late (days 8 to 14 in the Barnes group) were scored manually and by computer. QRS scores from early ECGs of patients with anterior infarctions correlated closely with MB-CK estimates of infarct size (r = 0.71 [Barnes] and 0.85 [MILIS] and with anatomic data (r = 0.78). Enzymatic and pathologic infarct size also correlated well (r = 0.85). Correcting for body surface area by means of total CK-derived infarct size or use of QRS scores from late ECGs did not alter the correlation coefficients. Among patients with inferior infarctions QRS scores corresponded poorly with MB-CK infarct size (r = 0.28 [Barnes] and r = -0.42 [MILIS]) and pathologic infarct size (r = -0.20), despite a significant relationship between pathologic and MB-CK estimates (r = 0.62).(ABSTRACT TRUNCATED AT 250 WORDS)

High-risk subgroups of patients with non-Q wave myocardial infarction based on direction and severity of ST segment deviation

To determine the significance of the direction of ST segment deviation on admission of patients who evolved non-Q wave myocardial infarction (MI), 97 patients with initial ST segment depression were compared to 207 patients with initial ST segment elevation. Patients with ST segment depression developed smaller infarcts than those with ST segment elevation (creatine kinase MB isoenzyme 8.2 vs 13.3 gmEq/m2, p less than 0.002), but had a lower left ventricular ejection fraction on admission (44% vs 51%, p less than 0.001), more in-hospital complications, and a higher cumulative 1-year mortality (29% vs 11%, p less than 0.001) that could be accounted for by an excess of adverse baseline characteristics. Although a severity index (combining magnitude and extent of the initial ST segment deviation) was not useful for discriminating prognosis of patients with non-Q wave MI who presented with ST segment depression, it was useful in identifying a subgroup of patients with ST segment elevation with an adverse prognosis. The poor outcome of patients with non-Q wave MI presenting with either ST segment depression or severe ST segment elevation on admission suggests that patients in these subgroups should receive close surveillance and should possibly be considered for aggressive therapy.

Prognostic implications of an early peak in plasma MB creatine kinase in patients with acute myocardial infarction

To determine the prognostic implications of an early peak in plasma MB creatine kinase (MB CK) in patients with acute myocardial infarction who were not treated with an acute intervention, 342 patients with myocardial infarction confirmed by MB CK were retrospectively studied. The patients were classified into those with an early peak MB CK (less than or equal to 15 hours after the onset of symptoms, n = 84) and those with a late peak MB CK (greater than 15 hours after the onset of symptoms, n = 258). Patients with an early peak MB CK were slightly older, were more frequently female and had a higher incidence of prior myocardial infarction, congestive heart failure and arrhythmias compared with patients with a late peak MB CK. Patients with an early peak MB CK more frequently presented with ST segment depression (23 versus 11%, p less than 0.01), with anterior location of ischemia or infarction (71 versus 52%, p less than 0.01) and with a lower mean left ventricular ejection fraction (41.4 versus 47.4%, p less than 0.01). Despite more extensive left ventricular dysfunction at initial presentation, patients with an early peak MB CK had a smaller mean MB CK infarct size index (12.6 versus 18.9 g-Eq/m2, p less than 0.01), with no difference in the incidence of in-hospital complications, including death. The early left ventricular dysfunction improved in the patients with an early peak MB CK, evidenced by a 4.5% increase in ejection fraction from admission to 10 days after infarction, whereas the ejection fraction did not improve in patients with a late peak MB CK. However, the patients with an early peaking MB CK had myocardium in jeopardy as reflected by a higher incidence of ST segment depression and a decrement in the global left ventricular ejection fraction with exercise. The 4 year life table estimate for the rate of recurrent myocardial infarction after hospital discharge was higher in patients with an early peak MB CK (33 versus 22%, p less than 0.05), with an even more striking difference in the 4 year estimate for the rate of fatal recurrent infarction (20 versus 8%, p less than 0.001). The 4 year mortality estimate was markedly higher in hospital survivors with an early peak MB CK than in those with a late peak (47 versus 19%, p less than 0.0001) and, even after adjustment for differences in baseline characteristics, the residual excess mortality in those with an early peak was still significant (p less than 0.02).(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiac myonecrosis in hypertensive crisis associated with monoamine oxidase inhibitor therapy

A young woman taking tranylcypromine for depression was hospitalized with severe chest pain and hypertension after eating cheese. Electrocardiography initially showed arrhythmias and precordial ST segment depression. Myocardial creatine kinase values were elevated, and echocardiography showed regional ventricular dysfunction, suggestive of focal cardiac myonecrosis. The cardiovascular pathophysiology of tyramine hypertensive crisis and related catecholamine excess states, including pheochromocytoma and clonidine withdrawal, is reviewed. Cardiac myonecrosis is a potential adverse effect of the hypertensive crisis associated with monoamine oxidase inhibitor use. Psychiatric indications for monoamine oxidase inhibitors may be expanding, but clinicians should continue to exercise caution in the use of these agents.

Comparison of enzymatic and anatomic estimates of myocardial infarct size in man

Enzymatic estimates of myocardial infarct size based on plasma levels of MB creatine kinase (MB-CK) were compared with anatomic infarct size in 49 human hearts obtained at autopsy. The patients studied had been enrolled in the Multicenter Investigation of Limitation of Infarct Size (MILIS) study program within 18 hr of the onset of acute infarction and were treated at one of five participating hospitals. Infarct size was estimated from serial measurements of plasma MB-CK made at the core laboratory for CK analysis. Hearts obtained at autopsy were studied independently by the core pathology laboratory without knowledge of the MB-CK levels or clinical results. Data from the two laboratories were compared at the data coordinating center. Of 49 hearts, 12 were excluded either because anatomic infarct size could not be established or because the infarct occurring at the time of enrollment in the MILIS study could not be distinguished with certainty from other infarcts. Of the remaining 37 hearts, peak MB-CK level was available in 36, but samples sufficient for estimation of infarct size were available in only 25. The overall correlation coefficient (Spearman) was .87 for these 25 hearts, indicating that enzymatic estimates of infarct size correlate closely with anatomic measurements. The results indicate that CK estimates of myocardial infarct size represent a valid clinical end point for assessing myocardial infarct size, and the effect of therapy thereon, in groups of treated and control patients.

Effect of propranolol on myocardial-infarct size in a randomized blinded multicenter trial

A multicenter randomized single-blind study was performed to evaluate the effects of propranolol administered during the evolution of myocardial infarction. Five centers enrolled a total of 269 patients, with 134 receiving propranolol and 135 placebo. Propranolol or placebo was given intravenously upon randomization (0.1 mg per kilogram of body weight) and then orally for nine days to keep the heart rate between 45 and 60 beats per minute. Less than 2 per cent of patients were treated within 4 hours after the onset of symptoms, but 50 per cent received therapy within 8 hours of onset of chest pain, and the remainder between 8 and 18 hours. The heart rates in the propranolol-treated group were significantly lower than those in the placebo group (P less than 0.001). Base-line characteristics, including the mean heart rate (79.6 vs. 81.3) and the left ventricular ejection fraction (49.0 vs. 49.5), were similar in the two groups. The primary end point evaluated--infarct size as estimated from plasma MB creatine kinase activity--was virtually identical in the two groups, averaging 13.3 and 13.6 gram-equivalents of MB creatine kinase per square meter of body-surface area. Peak plasma levels of the enzyme were also similar in the two groups. No significant difference was observed between the propranolol and placebo groups in the change in left ventricular ejection fraction, extent of area involved in pyrophosphate uptake, R-wave loss on electrocardiograms, or mortality (after three years). These results do not support the use of propranolol administered four or more hours after the onset of symptoms to limit infarct size.

Significance of early two-dimensional echocardiography after acute myocardial infarction

We performed serial two-dimensional echocardiography (2D echo) in 35 patients with a first transmural myocardial infarction, to correlate initial left ventricular wall motion abnormalities with subsequent in-hospital cardiac complications, peak total creatine kinase level, and haemodynamic alterations, and to observe serial changes in the left ventricular wall motion. A wall motion score was derived by analysing endocardial motion in 15 left ventricular segments. Left ventricular wall motion could be analysed in 30 patients, 14 without (Group 1) and 16 with complications (Group 2). The initial wall motion score in Group 1 patients was 5.2 +/- 0.7 (+/- SEM) compared to 14.2 +/- 1.2 in Group 2 patients (P less than 0.001). A wall motion score of greater than or equal to 10 correlated with the occurrence of complications in 15 of 16 patients (sensitivity 93%, specificity 92%). Initial wall motion score did not correlate significantly with peak total serum creatine kinase and did not change significantly during the first 72 hr in both the groups. In 12 patients who underwent right heart catheterization together with 2D echo, the average wall motion score was 16.4 +/- 2.0 and cardiac index 2.4 +/- 0.3. Wall motion score correlated inversely with the cardiac index in these patients (r = -0.78; P less than 0.01). Thus, 2D echo performed in first transmural myocardial infarction patients soon after admission can identify those likely to have in-hospital complications. 2D echo wall motion score correlated significantly with the cardiac output in this study.

Electrocardiographic and clinical criteria for recognition of acute myocardial infarction based on analysis of 3,697 patients

Over a 34.5-month period, all admissions to 5 university hospital coronary care units were screened for eligibility for the Multicenter Investigation of the Limitation of Infarct Size (MILIS), an ongoing study of the effects of hyaluronidase, propranolol and placebo on myocardial infarct (MI) size. Of 3,697 patients with greater than or equal to 30 minutes of discomfort that was thought to reflect myocardial ischemia who were assessed for the presence or absence of certain electrocardiographic abnormalities at the time of hospital admission, the electrocardiogram was considered predictive of acute MI if greater than or equal to 1 of the following abnormalities was present: new or presumably new Q waves (greater than or equal to 30 ms wide and 0.20 mV deep) in at least 2 of the 3 diaphragmatic leads (II, III, aVF), or in at least 2 of the 6 precordial leads (V1 to V6), or in I and aVL; new or presumably new ST-segment elevation or depression of greater than or equal to 0.10 mV in 1 of the same lead combinations; or complete left bundle branch block. In the screened population, the diagnostic sensitivity of the electrocardiographic criteria was 81%, whereas the overall infarct rate in the total population screened was 49%. The diagnostic specificity of these entry criteria was 69% and the predictive value 72%.(ABSTRACT TRUNCATED AT 250 WORDS)