A sensitivity analysis of enzymatic estimation of infarct size

Cardiac troponin elevation pattern in patients undergoing a primary percutaneous coronary intervention for ST-segment elevation myocardial infarction: characterization and relationship with cardiovascular events during hospitalization

HYPOTHESIS

We aimed to describe the kinetics and associated prognostic implications of the cardiac troponin release curve after a primary percutaneous coronary intervention (PPCI) in patients presenting with ST-segment elevation myocardial infarction (STEMI).

PATIENTS AND METHODS

We prospectively determined, in a prespecified timely manner, serial cardiac troponin I levels and obtained clinical, ECG, and echocardiographic data from 175 consecutive patients hospitalized with STEMI who underwent PPCI. The median peak troponin levels and time until troponin peaking were determined.

RESULTS

The troponin elevation curve following PPCI was single peaked, with a median value measuring 715 times the upper normal limit and a median peaking time of 8 h. Later-peaking troponin levels were associated with a TIMI flow grade of 0/1 at the initiation of angiography and with lack of at least 70% regression in the ST-elevation on the first post-PPCI ECG. Higher peak values were similarly associated with these two parameters as well as with a lower blush score and with distal embolization during PPCI. Both higher peak values and later peaking of troponin were associated independently with higher occurrence of the combined adverse cardiovascular event outcomes consisting of death, congestive heart failure, and recurrent infarction.

CONCLUSION

The cardiac troponin elevation curve following PPCI for STEMI shows a single peak and is affected by the adequacy of myocardial reperfusion. This method can serve as a simple surrogate for risk stratification of patients with STEMI who undergo PPCI.

Enzyme estimates of infarct size correlate with functional and clinical outcomes in the setting of ST-segment elevation myocardial infarction

Background

Cardiac biomarkers are routinely obtained in the setting of suspected myocardial ischemia and infarction. Evidence suggests these markers may correlate with functional and clinical outcomes, but the strength of this correlation is unclear. The relationship between enzyme measures of myocardial necrosis and left ventricular performance and adverse clinical outcomes were explored.

Methods

Creatine kinase (CK) and CK-MB data were analyzed, as were left ventricular ejection fraction (LVEF) by angiogram, and infarct size by single-photon emission computed tomography (SPECT) imaging in patients in 2 trials: Prompt Reperfusion In Myocardial-infarction Evolution (PRIME), and Efegatran and Streptokinase to Canalize Arteries Like Accelerated Tissue plasminogen activator (ESCALAT). Both trials evaluated efegatran combined with thrombolysis for treating acute ST-segment elevation myocardial infarction (STEMI).

Results

Peak CK and CK area-under-the-curve (AUC) correlated significantly with SPECT-determined infarct size 5 to 10 days after enrollment. Peak CK had a statistically significant correlation with LVEF, but CK-AUC and LVEF correlation were less robust. Statistically significant correlations exist between SPECT-determined infarct size and peak CK-MB and CK-MB AUC. However, there was no correlation with LVEF for peak CK-MB and CK-MB AUC. The combined outcome of congestive heart failure and death were significantly associated with CK AUC, CK-MB AUC, peak CK, and peak CK-MB measurements.

Conclusion

Peak CK and CK-MB values and AUC calculations have significant correlation with functional outcomes (LVEF- and SPECT-determined infarct size) and death or CHF outcomes in the setting of STEMI. Cardiac biomarkers provide prognostic information and may serve as valid endpoint measurements for phase II clinical trials.

Relation of temporal creatine kinase-MB release and outcome after thrombolytic therapy for acute myocardial infarction. TAMI Study Group

Measuring biochemical marker release after acute myocardial infarction helps in estimating infarct size and prognosis. We sought to relate in-hospital outcomes and curve-fitted creatine kinase (CK)-MB variables after thrombolysis. We measured CK-MB mass initially and at 30 and 90 minutes, and at 3, 8, and 20 hours after thrombolysis in 130 patients also undergoing cardiac catheterization at 90 minutes and at 5 to 7 days. Data were fitted, and maximums and curve areas calculated. CK-MB maximums related to infarct location (p = 0.014) and time to therapy (p = 0.002); curve area did not. Neither maximums nor curve area related to Thrombolysis in Myocardial Infarction trial flow grade at 90 minutes. Maximums related to ejection fraction at 90 minutes (p = 0.0004) and at 5 to 7 days (p = 0.0014), as did curve area (p = 0.0076 and 0.030, respectively). Maximums related to infarct zone function at 90 minutes (p = 0.024) and at 5 to 7 days (p = 0.042); curve area related only at 90 minutes (p = 0.027). Both maximums and curve area predicted congestive heart failure (p = 0.008 and p = 0.042, respectively) and a composite of congestive heart failure or death (p = 0.004 and p = 0.047, respectively); however, after adjusting for maximums, curve area no longer predicted congestive heart failure (p = 0.92). Maximums predicted the composite outcome after adjustment for curve area, and showed a trend toward predicting congestive heart failure (p = 0.089). We conclude that CK-MB maximums relate to infarct zone function, left ventricular function, and in-hospital outcomes after thrombolysis for acute myocardial infarction.

Creatine kinase in the dog: a review

In the dog, creatine kinase (CK) is mostly present in the skeletal muscles, myocardium, brain and intestine. The MM isoenzyme predominates in muscles and myocardium. In plasma, reference values depend on the technique used and CK-MB accounts for about 30-45% of total CK activity. Sex has no influence on plasma CK activity, which is higher in young dogs than in adults. Plasma CK is elevated after physical exercise. After its release from the cells, CK reaches the plasma mostly via the lymphatic route and then remains in the plasma compartment. It is rapidly cleared with a half-life of about 2 hours. Muscle diseases are the main source of plasma CK elevations: inherited myopathies, malignant hyperthermia, hypothyroidism, vitamin E-selenium deficiency, prolonged decubitus, intramuscular injections, surgery, etc. Plasma CK is also increased in experimental myocardial infarction, for which the dog is an interesting model, allowing quantification of the damage by measuring the total CK activity released.

Use of medical care for chest pain: differences between blacks and whites

Data from a 1980, community-based survey of adult residents of Edgecombe County, North Carolina were analyzed to examine differences between Blacks and Whites in the reported use of medical care after experiencing chest pain. Of all adults (N = 302) with chest pain in the year prior to interview, 49 percent of Blacks and 27 percent of Whites did not see a physician following the chest pain (difference = 22%, 95% CI = 12, 33). A multivariable analysis found that although the association between race and utilization was reduced at poverty levels of income, it was not explained by differences in demographic characteristics, health status or other dimensions of access to care.

Rapid enzyme release from acutely infarcted myocardium after early thrombolytic therapy: washout or reperfusion damage?

In a randomized study on early intracoronary thrombolytic therapy in patients with acute myocardial infarction (AMI), serial plasma enzyme activities were measured to analyze the rate of enzyme appearance in plasma with reference to treatment allocation, area at risk, and infarct size. Cumulative activities of alpha-hydroxybutyrate dehydrogenase (HBDH) appearing in plasma in the first 24 hours (Q24), 48 hours (Q48), and 72 hours (Q72) were calculated to obtain infarct size (= Q72) and rate of HBDH appearance in plasma (= Q24/Q72). Analyzed on the basis of "intention to treat" in 448 patients with AMI, the mean Q24/Q72 value (+/- SEM) was 0.653 +/- 0.011 in 230 patients receiving thrombolytic therapy; this value was significantly (p less than 0.001) higher than that observed in 218 patients receiving conventional therapy (0.504 +/- 0.012). In the thrombolysis group Q24/Q72 was independent of infarct size, whereas in the control group Q24/Q72 was negatively correlated with infarct size (r = -0.26; p less than 0.001). Plotted against the sum of ST segment elevations at admission (sigma ST) mean Q24 values were similar in both treatment groups, but mean Q48 and especially Q72 values were larger in the control group than in the thrombolysis group. We conclude that: (1) in reperfused infarctions the time course for development of infarct is accelerated in comparison to unreperfused infarcts; (2) this accelerated process of necrosis lasts about 40 to 50 hours, a duration that is hardly influenced by infarct size; and (3) the reperfusion-induced acceleration of enzyme release resembles the reoxygenation-induced enzyme release from anoxic hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of the size of isolated right ventricular infarction with the changes of ST segment in dogs

Vectorcardiographic, electrocardiographic, and hemodynamic changes in isolated infarction (infarct confined to the right ventricular free wall) were studied in 19 mongrel dogs. An isolated right ventricular infarction was produced by embolizing the right coronary artery with Spongel under closed chest conditions. The size of the infarct, identified by TTC staining, accounted for 6-65% (35.9 +/- 22.0%, mean +/- SD) of the right ventricular free wall. The STx, STy, STz, and the spatial magnitude of the ST segment (STM) were continuously recorded with an automated, real-time vectorcardiographic ST-segment analyzer (ST-monitor) using the Frank lead system. The cardiac index (CI) ratio (CI after embolization/CI before embolization) of all dogs with larger infarcts (infarct greater than 35% of the right ventricle) was below 1.0. In dogs with smaller infarcts (% RVI less than or equal to 35%), there were no differences in the hemodynamic data before and 4 h after embolization. In dogs with larger infarcts, however, pulmonary arterial pressure and heart rate 4 h after embolization were significantly decreased compared with those before embolization. In addition, right atrial pressure 4 h after embolization in the larger infarct group was significantly elevated compared with that in the smaller infarct group. In dogs with larger infarcts, STx, STy, and STM were significantly larger than in those with smaller infarcts both 15 min and 4 h after embolization. There were no significant correlations between infarct size and change in vectorcardiographic ST segments in the smaller infarct group.(ABSTRACT TRUNCATED AT 250 WORDS)

Isosorbide dinitrate sublingual therapy for inferior myocardial infarction: randomized trial to assess infarct size limitation

To assess the potential of isosorbide dinitrate sublingual therapy for limiting myocardial infarct size, 41 patients with inferior acute myocardial infarction (AMI) were studied. Twenty patients were randomly assigned to the control group and 21 to the treatment group. Patients in the treatment group received 10 mg of isosorbide dinitrate every 2 hours for 72 hours. To estimate infarct size, QRS scoring, peak creatine kinase (CK) serum levels and CK curves were used. There were no significant differences between the 2 groups in maximal or cumulative activity of CK or QRS score (percent of left ventricle infarcted: 16% in the control group, 17% in the treatment group). In both groups the QRS score increased significantly by 13 hours after AMI, and the increase was highly significant by 19 to 23 hours. Thus, sublingual isosorbide dinitrate at the dosage given did not reduce infarct size in patients with inferior AMI.

Size estimation of acute myocardial infarction from serial serum myoglobin observations with due consideration of individual differences in basic kinetics

Thirty-three consecutive patients suffering from acute myocardial infarction were studied. Serial serum myoglobin and CK-MB measurements were made, and in seven patients individual kinetic constants for myoglobin were available from previous single injection studies. A two-compartment model for myoglobin kinetics was used for infarct size estimation. Given values for the basic kinetic constants (elimination rate constant, exchange rate constants, and distribution volume), the adjustment of a flexible, parameterized 'blood-appearance rate-function', phi AMI (mg X h-1), allowed estimation of start-time (t0), peak-time (tpeak) and end-time (tend) of myoglobin inflow into blood from the infarct area, in addition to the total cumulative release (A), which was used as a measure of infarct size. Use of patient-mean values for the kinetic constants caused a mean difference in estimated 'infarct size' of 34% (n = 7). Individual estimation of the elimination rate constant from the 'final slope' of the serum myoglobin curve could neither be recommended from a theoretical point of view nor from the practical outcome of numerical calculations; the 'true' elimination rate constant is underestimated by a factor of about 10 on average. Good correlation was found between our myoglobin estimates of 'infarct size' (using patient-mean kinetic constants), and independent estimates from serial serum CK-MB data, as calculated by the use of the method by Sobel et al.. Large inter-individual variations were found in the estimated infarct parameters, a circumstance which is of special interest in evaluation of therapeutic intervention studies on AMI-patients, and in infarct size prediction calculations.

Limitation of enzymatic models for predicting myocardial infarct size

The possibility of predicting myocardial infarct size from early enzyme measurements was studied using a physiological two compartment distribution model. Based on this the time dependent appearance function in plasma was calculated for creatine kinase, aspartate aminotransferase, and lactate dehydrogenase in 29 patients suffering from acute myocardial infarction. On average, the appearance function of the three enzymes started four hours after the onset of symptoms, and the maximum was reached after 12 hours for creatine kinase, 13 hours for aspartate aminotransferase, and 22 hours for lactate dehydrogenase. The cumulated appearance function was used as an acceptable estimate of infarct size. The prediction of infarct size from defined points of the appearance function curve for each of the three enzymes was attempted according to a set schedule during the first 25 hours after the onset of myocardial infarction. The prediction using creatine kinase was superior to the other enzymes. Even so, a reliable prediction could only be established at the very earliest from nine hours and this is too late, as irreversible loss of myocardium occurs rapidly after the onset of symptoms. This, together with the fact that other models have unacceptable variability of the prediction, lead to the conclusion that enzymatic predictive models are of no practical value in clinical intervention studies to reduce infarct size.

Comparison of radionuclide and enzymatic estimate of infarct size in patients with acute myocardial infarction

A comparison was made of the estimated size of the myocardial infarction occurring in 26 patients with a first infarction using creatine kinase (CK) enzyme release between radionuclide gated blood pool measurement of total and regional ventricular function and thallium-201 scintigraphic measurement of myocardial perfusion defects. Creatine kinase estimates of infarct size (enzymatic infarct size) correlated closely with the percent of abnormal contracting regions, left ventricular ejection fraction and thallium-201 estimates of percent of abnormal perfusion area (r = 0.78, 0.69 and 0.74, respectively, p less than 0.01). A close correlation also existed between percent abnormal perfusion area and percent of abnormal contracting regions (r = 0.81, p less than 0.01) and left ventricular ejection fraction (r = 0.69, p less than 0.01). Enzymatic infarct size was larger in anterior (116 +/- 37 CK-g-Eq) than inferior (52 +/- 29 CK-g-Eq) myocardial infarction (p less than 0.01) and was associated with significantly more left ventricular functional impairment as determined by left ventricular ejection fraction (33 +/- 7 versus 60 +/- 10%) (p less than 0.01) and percent abnormal perfusion area (58 +/- 14 versus 13 +/- 12) (p less than 0.01). No significant correlation was observed between enzymatic infarct size and right ventricular ejection fraction. These different methods of estimating infarct size correlated closely with each other in these patients with a first uncomplicated myocardial infarction.

Late prognostic value of scintigraphic parameters of acute myocardial infarction size in complicated myocardial infarction without heart failure

Perfusion scintigraphy with thallium-201, infarct scintigraphy with technetium-99m pyrophosphate (TcPYP), and equilibrium blood pool scintigraphy were performed during the initial hospitalization for acute myocardial infarction (MI) in 25 patients without evidence of heart failure who presented with advanced electrocardiographic rhythm and conduction disturbances requiring treatment. Scintigraphic findings during short-term hospitalization were related to the late clinical follow-up performed an average of 14 months later, where patients were grouped as asymptomatic, 8 patients; symptomatic, 9 patients; and deceased, 8 patients. Quantitation of perfusion abnormalities, TcPYP image abnormalities, and left ventricular ejection fraction (EF) revealed that the deceased group had significantly larger TcPYP abnormalities (36 +/- 20 cm2), absolute perfusion abnormalities (32 +/- 16 cm2), and perfusion abnormalities expressed as a percentage of the projected left ventricular area (42 +/- 8%) than the asymptomatic group (13 +/- 8 cm2, 14 +/- 6 cm2, and 20 +/- 9%; p less than 0.05, p greater than 0.05, and p less than 0.01, respectively). The percent perfusion abnormality was significantly larger in the deceased group (42 +/- 8%, p less than 0.01) than in either the symptomatic group (35 +/- 13%, p less than 0.01) or the asymptomatic group (20 +/- 9%), and this parameter in the symptomatic group also differed from that in the asymptomatic group (p less than 0.01). The study indicates that patients with rhythm and conduction disturbances and without congestive heart failure during acute MI may follow an uncomplicated or a complicated late clinical course. Early scintigraphic measurements of MI and perfusion correlate well with this outcome; however, EF could not differentiate among prognostic subgroups.

The effects of cyanide and iodoacetate intoxication and ischaemia on enzyme release from the perfused rat heart

Isolated rat hearts perfused in the presence of iodoacetate show inhibition of glycolysis and release enzymes into the perfusate. Hearts perfused with cyanide, a mitochondrial inhibitor, show acceleration of glycolysis and no enzyme release. The adenine nucleotide content of the iodoacetate, but not the cyanide-perfused hearts was reduced. These results indicate that the membranes were permeable in the former treatment group. The adenylate energy charge and the ATP content of both the cyanide and iodoacetate treatment groups were similar but, as the extent of enzyme release was quite different, it appears that the energy state of the cell was not the prime factor controlling membrane integrity. Isolated perfused hearts were rendered ischaemic by placing a one-way ball valve in the aortic outflow tract. ATP concentration declined, as did ADP after an initial rise of short duration. AMP concentrations rose as the time of ischaemia increased. At the time at which enzyme release was first determined, the intracellular total adenine nucleotide content began to decline, suggesting that the membrane had become permeable to both small and large molecules. Glycolysis was stimulated by the hypoxia induced in the preparation and then this increase became inhibited. The point at which this inhibition was observed was also the point at which membrane permeability was evident. Taken together, the data from these experiments suggest that the energy derived from the activity of the glycolytic pathway may be important to the heart for maintenance of membrane function, particularly in ischaemia.

Noninvasive markers of intravenous streptokinase coronary thrombolysis

Early creatine kinase (CK) enzyme peaking, rapid electrocardiographic (EKG) changes toward normal, reperfusion arrhythmias, pain disappearance, and 201thallium myocardial scintigraphy appear useful to identify the success or failure of intravenous (i.v.) thrombolytic therapy in patients with acute myocardial infarction (AMI). Most patients with AMI are treated currently in community hospitals which do not possess coronary angiographic capabilities. Recent evidence indicates that early intravenous streptokinase results in coronary thrombolysis in the majority of patients treated. A composite of noninvasive markers of coronary reperfusion was assessed in two similar patients with transmural AMI. One received intravenous streptokinase (STK) 750,000 U 90 min after AMI onset; the other received intracoronary (i.c.) STK 4000 U/min 140 min after onset. Within one hour each showed a sudden change in elevated EKG ST segments toward normal, followed by frequent premature ventricular beats and pain disappearance. Posttreatment angiograms documented recanalization of each infarct-related artery. Early CK peaking occurred at 10 hours after the onset of chest pain in the first patient and at 12 hours in the second. This contrasts with delayed CK peaking at 26.4 hours among 384 patients reviewed with untreated AMI. Early CK peaking appears the most accurate indirect marker of successful coronary thrombolysis.

The prognostic value of serum acetylcholinesterase in myocardial infarction. Theoretical and clinical considerations

The aim of the present work was to determine experimentally the prognostic value of reduced activity of serum acetylcholinesterase (ACE) in cases of acute myocardial infarction (AMI). In the first part of the research we studied the mechanism of this reduction by comparing the serum results with the levels of the enzyme in cardiac tissue in such cases. It was found that ACE activity is reduced in serum and also in cardiac tissue in AMI, in contrast to creatine kinase (CK) that is augmented in serum but reduced in cardiac tissue. This fact was interpreted as a "reduced cardiac flow of ACE," in contrast to the "augmented cardiac clearance of CK" in similar cases. In the second part of our research, 50 patients, admitted in our hospital for AMI, were examined and their blood analysed mainly for ACE and CK at brief intervals (every 2-3 days), during hospitalization, and thereafter every 1-2 weeks for 1-4 months. From the results of ACE activity it was possible to classify these variations into four groups, each of them having a defined prognostic value for the evolution of the AMI, a persistent reduced serum activity being interpreted as a bad, severe prognosis, with high morbidity or mortality (groups II and III). We suggest, therefore, that the determination of ACE in serum in cases of AMI, especially before discharge home of such patients, may be an additional useful laboratory test in such cases.

Immediate detection of early high-risk patients with acute myocardial infarction using two-dimensional echocardiographic evaluation of left ventricular regional wall motion abnormalities

Forty-three patients with acute myocardial infarction (AMI) were studied with serial two-dimensional echocardiography (2DE) to define a high-risk subset for in-hospital cardiovascular complications including pump failure, life-threatening arrhythmias, or death. A 2DE segment score was developed representing the extent of left ventricular (LV) regional wall motion abnormality (WMA) which was correlated with peak total creatine kinase (CK) release. Patients with transmural AMI had a segment score of 7.2 +/- 3.8, whereas those with nontransmural AMI had a segment score of 4.7 +/- 3.4 (p less than 0.025). Peak total serum CK enzyme level correlated statistically with segment score but with a low correlation coefficient. Thirteen (30%) of the 43 patients had an in-hospital complication and their segment score was 10.0 +/- 3.4 compared to 4.6 +/- 2.7 in those patients without a complication (p less than 0.005). A segment score greater than or equal to 8 was found in 11 of 13 (85%) of those who suffered a cardiac complication and in only five (16%) of the 30 patients without complication (p less than 0.05; sensitivity 85%, specificity 83%). Patient's initial clinical Killip classification was specific but very insensitive in predicting an early complicated course. Thus, 2DE study of LV regional wall motion can predict in the immediate post-AMI stage the in-hospital likelihood of such patients developing a cardiovascular complication during acute myocardial infarction.

Creatine kinase

Creatine kinase is present in significant concentrations in skeletal muscle and cardiac muscle and to a lesser extent in gastrointestinal tract and brain tissue. The enzyme has been purified from a variety of tissues and an examination of its kinetic and physical properties reveal that the enzyme consists of two subunits and can exist as three isoenzymes containing essential cysteine residues. These properties are important in understanding its stability, the assay conditions, and the techniques used to identify the different isoenzymes. The relationship between the properties and the determination of the enzyme in biological fluids will be a main thrust of the review. Creatine kinase activity in serum rises rapidly in conditions such as acute myocardial infarction and trauma to skeletal muscle. However, the interpretation of such increases is dependent upon a sound knowledge of the factors which influence both the total and isoenzyme activities. The nature of these factors will be discussed in detail.

Plasma enzymes in myocardial infarction. An appraisal of quantitative, clinical and pathophysiological information

In twenty-nine patients suffering from acute myocardial infarction changes of concentrations in plasma of creatine kinase, aspartate aminotransferase and lactate dehydrogenase were monitored 1 week following onset of infarction. The temporal characteristics of enzyme changes described are (i) the time lag from onset of chest pain until increasing enzyme concentrations occur, (ii) the time of maximum concentrations, and (iii) the period during which enzyme is released into blood. Three estimates for the extent of the infarct (i) the peak value of the plasma enzyme curves,(ii the value of the cumulated plasma curves, and (iii) the size of the infarct in grams of necrotic myocardial tissue were, as expected, closely correlated. It is concluded, that the three types of quantification of infarct size are of almost identical value for clinical, prognostic usage, From a pathophysiological point of view they are of limited interest being based on assumptions that are either unlikely to occur or cannot be tested in man.

The creatine kinase curve area and peak creatine kinase after acute myocardial infarction: usefulness and limitations

We determined creatine kinase (CK) curve areas in 112 patients with acute myocardial infarction. Two-hour sampling was performed for the first 24 hours or until peak CK was reached, and a gamma density function was used to calculate curve areas from all available samples. Attempts to predict CK curve area by means of the portion of the curve prior to peak CK proved to be inaccurate; not until values 2 hours or more beyond peak CK were utilized did predicted and actual CK areas agree well. A good correlation (r = 0.93) was found between CK area and peak CK. To establish an approach for detecting peak CK in the clinical setting, a range of sampling intervals (4 to 24 hours) was assessed; 4- and 6-hour sampling intervals for 48 hours produced maximum CK values at or above 85% of true peak CK in 90% and 89% of patients, respectively, and average maximum CK at both sampling intervals exceeded 94% of that obtained with 2-hour samplings. We conclude that this simplified approach can provide a basis for estimating infarct severity in the individual patient.

Serial thallium-201 myocardial perfusion scanning in acute myocardial infarction

Serial myocardial perfusion scanning was performed in 30 patients with acute myocardial infarction. Scanning was commenced less than six hours after onset of symptoms in 12 patients, 6-24 hr in eight and 24-120 hr in ten. All 30 patients showed thallium defects corresponding to the ECG site of infarction. When initial and four-hour scans were compared, constant defects were present in ten patients and changing defects in 20. Of the 169 segments with defects on the initial scan, 117 (69%) remained constant, 41 (24%) improved, and 11 (7%) deteriorated. More defects changed in the patients scanned earlier (less than 6 hr) than in the patients scanned later (more than 6 hr) (42% vs 23% P less than 0.025), and more defects changed in patients with subendocardial compared to transmural infarction (49% vs 26% P less than 0.025). During a mean follow-up period of 18 months, seven patients died, two developed left ventricular failure, seven had angina and 14 remained asymptomatic. The non-survivors had significantly larger thallium defects than the survivors (55 +/- 15% vs 37 +/- 14%, P less than 0.005). Serial change on thallium scanning was not related to the clinical course. Perfusion defects on serial thallium scanning are useful in detecting and localising early myocardial infarction and the size of defects is related to the subsequent clinical course. Changing perfusion defects on serial scanning suggesting peri-infarctional ischaemia are common, and make assessment of therapeutic interventions to limit infarct size difficult, but are not related to the clinical course.

Effect of arterial pressure on left ventricular O2 consumption, coronary blood flow, and reserve capacity following coronary occlusion

The effect of mean systemic arterial pressure (SAP) on myocardial O2 consumption (MVO2) coronary blood flow (CBF) and the reduction of left ventricular (LV) reserve capacity resulting from coronary artery occlusion was studied in 25 open-chest pentobarbital anesthetized dogs with fixed cardiac output and controlled heart rate (HR) and SAP. In all animals, baseline MVO2 and CBF were obtained and LV reserve capacity was determined by identifying the HR and SAP level which raised mean left atrial pressure to 12 mm. Hg. After uniform placement of a pericoronary snare, the dogs were randomized to five equal groups, and SAP was set at 40, 70 (two groups), 100, and 130 mm. Hg. MVO2 and CBF were redetermined and the coronary artery was ligated in all except one group (70 mm. Hg) which served as sham control. thirty minutes after coronary occlusion, MVO2, CBF, and LV reserve capacity were determined again. Percent of nonperfused myocardium did not differ among groups (27.6 +/- 1%). MVO2 bore a linear relationship to SAP setting wheras CBF bore a curvilinear relationship. Coronary occlusion did not modify these relationships. Significant, but similar decreases in tolerated HR (23.1 +/- 4.7 min.-1) and SAP (41.9 +/- 6.2 mm. Hg) from control values were observed in all four groups regardless of SAP setting. We concluded that the impact of coronary ligation on MVO2, CBF, the loss of functional reserve capacity, and possibly the extent of ischemic injury of the left ventricle, is not modified by afterload changes. However, optimal O2 supply-to-demand ratio appears at SAP of about 100 mm. Hg.

Comparison of enzymic with cineangiocardiographic estimations of myocardial infarct size

Comparisons were made between enzymic indices of myocardial infarct size (total creatine kinase appearance and peak enzyme activity) measured during the acute state of a first myocardial infarct in 32 male patients, and analysis of contraction abnormalities in biplane left ventricular cineangiocardiograms performed one month later. The cineangiocardiograms were analysed independently by two radiologists, each using two different methods for quantification of subjectively classified abnormalities of left ventricular wall motion. A very strong correlation was found between the two enzymic indices of infarct size and somewhat weaker correlations between assessment of contractility abnormalities made by the two radiologists using the same method, or by the same radiologist using the two different methods. Comparisons between enzymic and angiocardiographic indices for all infarcts showed correlation coefficients (r) within the range of 0.53 to 0.72. With all comparisons of enzymic with radiological indices r values were higher for anterior infarcts than for inferior infarcts, and there was a tendency for higher enzyme levels for a given degree of left ventricular damage in inferior than in anterior infarction. This may be the result of variable degrees of right ventricular damage in inferior infarction.

Radioimmunoassay for dog myoglobin

A radioimmunoassay specific for dog myoglobin (MGB) has been developed. Antibody (Ab) to purified dog heart MGB was prepared in rabbits and the Ab was labelled with 125I using the chloramine-T procedure. The assay is conducted at room temperature with addition of second Ab at 24 hr, the forward reaction being 95% complete at this point and irreversible. The assay is free of matrix affects. The working range is 20 to 360 ng/ml. Coefficients of variation for within run replicates are 10.5% (low) and 4.4% (high), and for between run replicates are 13.8% (low) and 7.6% (high). Serial measurement of serum MGB in dogs undergoing experimental myocardial infarction indicates that appearance time, peak time, and disappearance rate are respectively, 1.1 hr, 7.7 hr and 0.0025 min-1 for MGB and 2.6 hr, 13.35 hr, and 0.0018 min-1 for CK.

Quantification of thallium-201 scintigrams in acute myocardial infarction

A method has been developed for measurement of myocardial infarct size from thallium-201 scintigrams that depends on computer measurement of levels of radioactivity in the myocardium. In 16 dogs, thallium-201 scintigrams were obtained in the left lateral and left anterior oblique projections 48 hours after ligation of the left anterior descending coronary artery. Scintigraphic results were obtained by two independent observers and were compared with tissue measurements of infarct volume calculated from thallium autoradiograms and nitro-blue tetrazolium (NBT)-stained tissue slices. Infarct volumes derived from tissue measurements were used to develop criteria for the computer scintigraphic technique. There was no significant difference in the scintigraphic measurements made by the two observers. Scintigraphic infarct size in the left lateral and left anterior oblique projections correlated with tissue infarct size with r values of 0.88 and 0.75, respectively, for thallium autoradiography and 0.71 and 0.70, respectively, for NBT tissue staining. The range of infarct volume was 3.3 to 14.8 percent of the left ventricular mass. Results of this study suggest that scintigraphic quantitation of infarct size is feasible in this dog model.

Prediction of infarct size from serial CK determinations: evaluation by clinical studies and computer simulation

To assess reduction of infarct size by therapeutic intervention, a high predictive accuracy is mandatory. The CK release in the circulation (CKr) was studied in 12 consecutive patients after uncomplicated myocardial infarction, admitted within 5 h after onset of symptoms. Despite improvement of existing methods, such as a more frequent sampling, CK-MB determination instead of total CK determination and use of a gamma-exponential instead of a log-normal curve-fitting technique, the correlation between CKr predicted from measurements within 7 h after the start of CK rise and CKr calculated after completion of the CK curve remained poor. Computer simulations were done to investigate measurement errors as a cause of this failure. Normally distributed noise, with standard deviations ranging from 0.2% to 8.0% of peak CK-MB, was added to the first points of an ideal gamma-exponential CK-MB curve and predictions were made from these "noisy" points. A small noise already produced a great variation in prediction: 0.8% noise resulted in a deviation of predicted CKr from calculated CKr ranging from --20 to +6%. It is concluded that adequate prediction of infarct size from serial CK determinations in the first 7 h after onset of the CK rise must fail if the precision of the biochemical determination is not less than 0.4%.

PRediction of infarct size by enzymatic techniques: modification of a method and clinical application

In an attempt to develop improved methods of prediction of infarct size by enzymatic methods, Shell's original algorithm has been critically evaluated in an unselected series of patients. Poor performance of the model is partly the result of a systematic source of error associated with its mathematical formulation. A new model devoid of such limitations has therefore been developed. Residual deviations between predicted and observed CK release seem to be related to frequent and unpredictable extensions of infarction which could be verified by independent clinical, electrocardiographic, and enzymatic criteria. The modified model may possibly be applied to the evaluation of agents aimed at limiting the spread of irreversible injury.

Early quantification of experimental myocardial infarction with technetium-99m glucoheptonate: scintigraphic and anatomic studies

Recent advances in understanding of the pathophysiology of myocardial necrosis indicate the need for a noninvasive method that will allow detection and quantification of infarcts in the first few hours after the onset of infarction. Myocardial infarct scintigraphy using technetium-99m glucoheptonate is capable of detecting infarction in dogs and man within 4 to 6 hours of onset. Studies were performed in 45 dogs with acute myocardial infarction: 28 with with an anterior infarct, 5 with an inferior infarct, 6 with an anterior infarct studied after infusion of mannitol and 6 with ligation of the left anterior descending coronary coronary artery and reperfusion of the ischemic area. The dogs were given 20 m Ci of technetium-99m glucoheptonate 1 hour after coronary occlusion, subjected to imaging 5 to 9 hours later and then killed. The experiments revealed that (1) scintigraphic infarct size correlated with infarct weight for anterior (r = 0.85) and inferior (r = 0.88) infarcts; (2) technetium-99m glucoheptonate also concentrated in a rim of myocardium around the infarct that probably represented the ischemic zone; and (3) technetium-99m glucoheptonate uptake by infarcted myocardium could be greatly increased with mannitol and reperfusion.

Effect of therapy with methylprednisolone on the size of myocardial infarcts in man

The use of steroids to decrease the size of the infarct and the mortality in patients with acute myocardial infarction has long been the subject of controversy. In the present study, two large doses of methylprednisolone were administered intravenously to 14 patients with relatively uncomplicated myocardial infarction within 17 hours after the onset of symptoms, whereas a comparable group of 15 patients with myocardial infarction served as controls. The size of the infarct was assessed utilizing serial measurements of serum levels of creatine phosphokinase and its myocardial isoenzyme, the MB form of creatine phosphokinase. There was no significant difference between the two groups of patients with regard to peak cumulative levels of total creatine phosphokinase and the MB form of creatine phosphokinase. Similarly, there was no difference between the two groups in mortality or in the incidence of malignant ventricular arrhythmias, atrioventricular block, congestive heart failure, or extensions of the infarct. We conclude that high intravenous doses of steroids given early in the course of myocardial infarction have neither deleterious nor beneficial effects.

The measurement and control of myocardial infarct size

Direct, chemical, electrocardiographic and radio-isotopic methods are described for the estimation of myocardial infarct size in animals and man. Their relative points and failings are discussed. The effects of interventions, physical, metabolic and pharmacological, upon the size of myocardial infarcts, are examined and work attempting to reduce myocardial infarct size in man reviewed.

Coronary angiography and left ventriculography in survivors of transmural and nontransmural myocardial infarction

Recent studies have suggested a similar prognosis for patients with transmural myocardial infarction and nontransmural myocardial infarction despite a smaller infarct size in the latter patients estimated by creatine phosphokinase (CPK). Thirty-one patients with transmural myocardial infarction and 17 patients with nontransmural myocardial infarction as defined by electrocardiographic criteria underwent coronary angiography and left ventriculography from 10 to 24 days after they had an acute myocardial infarction. Forty-three of these 48 patients were asymptomatic following their myocardial infarction. When compared to patients with nontransmural myocardial infarction, those with transmural myocardial infarction had greater peak CPK levels, 1,090 +/- 210 versus 290 +/- 60 IU (p less than 0.01). There was no difference in prevalence of single, double or triple vessel coronary artery disease, mean number of coronary arteries 50 per cent narrowed (2.0 +/- 0.2 versus 2.0 +/- 0.2), near total or total occlusions, coronary score (Friesinger) (7.9 +/- 0.6 versus 8.2 +/- 0.7), left ventricular ejection fraction (48 +/- 2 versus 53 +/- 4), or per cent of akinetic-dyskinetic myocardial segments (66 of 242 [27 per cent] versus 32 of 132 [24 per cent]) between two groups. The similar extent of coronary artery narrowing and degree of left ventricular dysfunction may explain the similar prognosis for patients with transmural myocardial infarction and those with nontransmural myocardial infarction despite differences in enzymatically estimated acute infarct size.