- Email: [email protected]
CPK-MB isoenzyme: Use in diagnosis of acute myocardial infarction in the early postoperative period
CPK-MB isoenzyme: Use in diagnosis of acute myocardial infarction in the early postoperative period The diagnosis of acute myocardial infarction (A Ml) in the early postoperative period may be quite difficult in certain patients. Electrocardiograms fail to be diagnostic of A Ml in as many as one third of patients with myocardial injury found at autopsy. Enzyme patterns commonly used to diagnose AMI in patients admitted to coronary care units are obscured by muscle injury, medications, cardioversion, surgical manipulation, and blood transfusion. The MB isoenzyme of creatinine phosphokinase (CPK) has been described as a specific indicator of myocardial injury. Therefore the CPK-MB isoenzyme level was evaluated as a potential aid in the diagnosis of AMI in the early postoperative period. Thirty patients undergoing cardiac surgery and 7 patients undergoing thoracic surgery not involving the heart were studied. CPK-MB isoenzyme was present in the serum in 10 of 30 patients after cardiac surgery but in none of 7 patients after thoracic surgery. The presence of CPK-MB isoenzyme was found to be a valuable adjunctive indicator in the diagnosis of A Ml in the early postoperative period.
R. Bradford Pyle, M.D., David J. Blomberg, M.D., M. Desmond Burke, M.D., William G. Lindsay, M.D., and Demetre M. Nicoloff, M.D., Ph.D., Minneapolis, Minn.
J. he diagnosis of acute myocardial infarction (AMI) in the early postoperative period is at times quite difficult. The patient is often unable to describe the typical symptom of substernal chest pain because of anesthesia or analgesia. As many as 44 per cent of patients undergoing abdominal surgery have postoperative changes in their electrocardiograms.1 Electrocardiographic changes of infarction are difficult to distinguish in patients with abnormal preoperative cardiograms and, unfortunately, these patients are at greatest risk of having AMI during the operation. Electrocardiograms have been reported to have established the diagnosis of AMI in 65 per cent of patients who were found to have myocardial injury at postmortem examination.2 Thus, relying solely on the electrocardiogram for the diagnosis of AMI will result in missed diagnoses in as many as one third of the patients with AMI. From the University of Minnesota Hospitals, Minneapolis, Minn. 55455. Supported by funds from Minnesota Medical Foundation and a Grant-in-Aid from the Minnesota Heart Association. Received for publication Jan. 13, 1975. Accepted for publication Nov. 21, 1975.
884
Patterns of changes in serum enzyme levels have been established to be of value in the diagnosis of AMI in nonsurgical patients. Levels of serum glutamic oxaloacetic transaminase (SGOT), lactic dehydrogenase (LDH), the heat-stable fraction of lactic dehydrogenase (LDH-HS), and creatinine phosphokinase (CPK) have been described which are diagnostic of AMI.3, 4 However, trauma to tissues during the operation has resulted in variable elevations of these enzymes, so that their reliability as indicators of AMI in the early postoperative period is reduced. Various patterns of enzyme changes stated to be diagnostic of AMI in the early postoperative period have been published. However, all too frequently the clinician is unable to distinguish a diagnostic enzyme pattern. Use of the MB isoenzyme of CPK is currently being investigated as a more sensitive and specific indicator of AMI in patients admitted to coronary care units.5' 6 This report describes the use of the CPK-MB isoenzyme as an indicator of myocardial injury in the early postoperative period. Methods In order to evaluate CPK-MB elevations as an aid in the detection of significant myocardial damage and/or
Volume 71 Number 6 June, 1976
necrosis in the early postoperative period, we studied consecutive patients over the age of 12 years who were undergoing cardiac and thoracic surgery. The study included 30 patients who underwent cardiac surgery with the support of cardiopulmonary bypass and 7 patients who underwent thoracotomy. These patients were studied with serial analysis of SGOT, LDH, and LDH-HS preoperatively, postoperatively in the recovery room, and then daily for 5 days. CPK and isoenzymes of CPK were evaluated preoperatively, postoperatively in the recovery room, at 6 hour intervals for 36 hours, and then at daily intervals thereafter through the fifth postoperative day. Electrocardiograms were obtained preoperatively, postoperatively in the recovery room, and on postoperative days 1,3, and 5. The clinical course was monitored closely for any evidence of myocardial infarction. Blood was collected from either an arterial line or a peripheral vein. Samples were allowed to clot and were then centrifuged twice for 10 minutes at 1,000 r.p.m. Serum for SGOT and CPK determinations was frozen at —15° C. if not immediately analyzed. All analyses were completed within 7 to 10 days; experiments in this laboratory have shown no significant sample deterioration over this limited time period. Serum for study of LDH activity was stored at 25° C. if not analyzed immediately. All LDH analyses were completed within 48 hours. Serum CPK was determined by the method of Oliver.7 LDH activity was determined by a modification of Wagner's8 small methods. These analyses utilized reagent substrates supplied by BoehringerMannheim and were performed kinetically with a Gilford 2400 spectrophotometer (Gilford Instrument Laboratories, Oberlin, Ohio). LDH and CPK activities were determined at 32° C , and the LDH activities were then remeasured after heat inactivation in phosphate buffer for 45 minutes at 63° C. to determine the heat-stable fraction. SGOT activity was determined by the method of Morgenstern9 by use of the SMA 12/60 AutoAnalyzer (Technicon Corporation, Tarrytown, N.Y.) at 45° C. The normal values for these methods are as follows: CPK less than 60 ml.U. per milliliter, LDH 44 to 88 ml.U. per milliliter, heat-stable LDH less than 24 per cent of total activity, and SGOT 7 to 40 ml.U. per milliliter. CPK isoenzymes were determined by vertical acrylamide slab electrophoresis by means of the method of Blomberg and Burke.10 Seven patients undergoing thoracic surgery not involving the heart and 30 patients undergoing cardiac surgery with the use of cardiopulmonary bypass were studied. Patients undergoing thoracic surgery had a
CPK-MB isoenzyme
885
standard thoracotomy with removal of a single rib. Two underwent wedge resections of coin lesions, 2 had pleural abrasions, one had excision of a portion of the chest wall involved with tumor, one had an associated rib biopsy, and one underwent pneumonectomy. In all patients undergoing cardiac surgery, the heart was exposed through a midline sternotomy incision. The operations performed included valve replacement, coronary artery bypass, correction of an acquired ventricular septal defect, and closure of an atrial septal defect. Cardiopulmonary bypass was used uneventfully in all patients. The Bentley bubble oxygenator was primed with lactated Ringer's solution, mannitol, and fresh blood. The hemodilution volume was 16 c.c. per kilogram, and flow rates were maintained above 60 ml. per kilogram per minute in all patients. Moderate hypothermia was employed in all patients, minimal esophageal temperatures varying from 28° to 30° C. In all patients undergoing aortic valve replacement, coronary artery perfusion was carried out to at least the left coronary artery with a flow of 100 to 150 c.c. per minute. Fibrillation of the heart was instituted electrically in all patients except those undergoing aortic valve replacement. Defibrillation was effected by countershock of 50 to 200 watt-seconds when necessary after rewarming to 35 to 37° C. Results Postoperatively, the presence of CPK-MB isoenzyme was demonstrated in the serum of 10 of the 37 patients studied. One patient who developed a ventricular septal defect after a preoperative AMI was found to have the CPK-MB fraction in the serum drawn preoperatively as well as postoperatively. This was the only patient who died. The presence or absence of CPK-MB isoenzyme was correlated with the clinical course, electrocardiograms, and the pattern of other serum enzymes (total CPK, SGOT, and LDH). The operative events were correlated with the CPK-MB analysis, considering specifically the total duration of cardiopulmonary bypass, the duration of aortic crossclamping, and the total time period during which the aorta was cross-clamped but the coronary arteries were not perfused. The single patient with preoperative CPK-MB was excluded from considerations of the correlation of operative procedures with the finding of CPK-MB in postoperative serum. Factors in the clinical evaluation which were used as indicators of myocardial injury were: (1) low cardiac output state manifested by difficulty in being weaned from cardiopulmonary bypass; (2) hypotension lasting 50 to 60 minutes or requiring support with vasopressors
The Journal of Thoracic and Cardiovascular Surgery
8 8 6 Pyle et al.
Table I. Detection of CPK-MB isoenzyme after cardiac and thoracic surgery, compared with other indicators of myocardial injury in the early postoperative period CPK-MB isoenzyme No. of cardiac surgery cases Criteria
Result
Total
Positive
ECG
Positive Equivocal Negative
6 13 11
4 4 2
Total enzyme pattern
Positive Equivocal Negative
4 10 16
Clinical course
Positive Equivocal Negative
4 7 19
No of thoracic surgery cases Total
Positive
Negative
2 9 9
0 3 4
0 0 0
0 3 4
3 1 6
1 9 10
0 5 2
0 0 0
0 5 2
3 3 4
1 4 15
0 1 5
0 0 0
0 1 5
Negative
Legend: CPK, Creatinine phosphokinase.
for longer than 4 hours; (3) sudden onset of pulmonary edema; (4) oliguria persisting over 3 hours and peripheral cyanosis in the absence of hypovolemia, sepsis, or respiratory distress; and (5) premature ventricular beats of two or more foci or of a frequency greater than 6 to 10 per minute which persisted for more than 4 hours (or required treatment with antiarrhythmic agents for more than 4 hours) in the absence of hypokalemia and alkalosis. Electrocardiograms were interpreted as showing no evidence of infarction if there was no change from the preoperative to the postoperative tracings. The Minnesota code was used to define the presence of myocardial infarction.11 Basically, infarction was indicated by the appearance of Q waves or of definite ischemic changes in the ST-T segment postoperatively which had not been apparent in the preoperative tracings. The enzymatic definition of AMI is somewhat more difficult. Person and Judge3 described the pattern of enzyme elevation (total CPK, SGOT, and LDH) postoperatively as that of an initial rise and gradual decline to normal levels after 5 to 8 days in patients without AMI. Hobson and associates12 described an elevation above two to five times normal levels of SGOT and LDH in the absence of liver or biliary tract trauma as an indicator of AMI. When liver or biliary tract surgery was performed, they viewed elevations greater than six times normal as an indication of myocardial injury. Person and Judge3 stated that factors which caused elevation of SGOT and LDH, besides liver and biliary tract operations, were massive necrosis such as that seen in the presence of an abscess or
massive tissue trauma which occurs with a thoracotomy incision. Killen13 stated that an elevation in SGOT and LDH above normal for greater than 3 to 5 days after an operation is an indication of AMI. Dixon and associates14 stated that CPK values should be expected to return to normal by 3 to 5 days postoperatively in the absence of AMI or other massive tissue trauma. Einzig's group15 stated that a secondary elevation after initial peak and decline in enzyme levels was diagnostic of AMI. Each of these criteria was used in the present study as an indicator of AMI. Since 25 of 30 patients who underwent operations requiring cardiopulmonary bypass and all 7 patients who underwent thoracotomy had elevations of total CPK greater than five times normal, the elevation of total CPK was not used as a criterion of myocardial damage. Heat-stable LDH was considered to be an indicator of AMI if it was detected in the serum. Table I presents the results obtained from the evaluation of these 37 patients. Data from patients with and without CPK-MB isoenzyme are compared with the other criteria used to indicate AMI: electrocardiogram, total enzyme pattern, and clinical course. It was found that 10 of the 30 patients who had cardiac surgery had definite evidence of CPK-MB enzyme in the serum, a finding considered diagnostic of myocardial injury. In 2 of these patients, evaluation of other enzymes, electrocardiograms, and the postoperative clinical course gave no evidence of AMI. In one of these 2 patients, the CPK-MB enzyme appeared in only one sample obtained in the recovery room after the operation, and there was no further evidence of MB isoenzyme afterward. This patient underwent aortic
Volume 71 Number 6 June, 1976
CPK-MB isoenzyme
Table II. Presence of CPK-MB isoenzyme after cardiac surgery correlated with each of the other enzymes commonly employed to diagnose myocardial damage Enzyme test
Table III. Correlation of CPK-MB isoenzyme in the postoperative period with various cardiac surgical procedures Operative procedure
Negative
Result
Total
SGOT
Positive Negative
6 20
3 3
3 17
LDH
Positive Negative
0 27
0 10
0 17
Heatstable LDH
Positive
21
Negative
6
1
5
Pattern of total CPK
Positive
13
3
10
Negative
17
7
10
Maximum value of total CPK
Positive
25
10
15
Negative
Positive
88 7
12
5
Legend: SGOT, Serum glutamic oxaloacetic transaminase. LDH, Lactic dehydrogenase.
valve replacement and was supported by cardiopulmonary bypass for 1 hour, 27 minutes. The aorta was cross-clamped for 1 hour, 17 minutes, and the coronary arteries were perfused for a total of 1 hour of this time. The second patient underwent aortic and mitral valve replacement, having a pump time of 2 hours, 22 minutes. The total cross-clamp time in this patient was 2 hours, 7 minutes with perfusion of the coronary arteries for only 1 hour, 25 minutes. CPK-MB was absent from the serum in 3 of 10 patients who were diagnosed as having AMI by evaluation of enzymes, electrocardiograms, or clinical course. Two of these patients with AMI who lacked CPK-MB had definite evidence of AMI on postoperative electrocardiograms, although one had a completely uncomplicated postoperative course. The third patient required the temporary use of isoproterenol to be weaned from cardiopulmonary bypass because of persistent low output syndrome following double valve replacement. The electrocardiogram of this patient was nondiagnostic of AMI although changes had occurred since the preoperative tracings. Eleven patients who underwent cardiac surgery had findings in the clinical course or electrocardiogram which were suggestive of AMI. In 3 of these patients, CPK-MB isoenzyme was identified in the sera. All patients in the thoracotomy group failed to show evidence of CPK-MB isoenzyme.
Single artery bypass Double coronary artery bypass Coronary artery bypass and other procedure Aortic valve replacement Mitral valve replacement Double valve replacement Other procedures
Total
Positive
Negative
2 4 2 9 5 5 3
Three of 4 patients whose total enzyme patterns indicated AMI had detectable CPK-MB. Six of 16 patients undergoing cardiac surgery whose total enzyme pattern was not diagnostic of AMI had detectable CPK-MB isoenzyme. If the CPK-MB enzyme is indicative of myocardial damage or necrosis, then reliance upon the total enzyme pattern alone as an indicator of myocardial damage would have left undetected the myocardial injury in these 6 patients. If each of the cardiac enzymes evaluated in patients after cardiac surgery is considered separately, we find that SGOT was the most reliable indicator of myocardial damage as defined by the presence of CPK-MB isoenzyme (Table II). Apparently, the hemolysis associated with multiple transfusion and cardiopulmonary bypass invalidates the results of LDH and heat-stable LDH. The extensive tissue injury associated with the sternotomy incision, which was employed in all 30 patients who underwent cardiac surgery, obscures the diagnosis of AMI in the early postoperative period if the diagnosis is being based on the pattern of total CPK disappearance or the maximum total CPK level. In patients who underwent cardiac surgery, other factors associated with the presence of myocardial injury were evaluated by using the presence of CPK-MB isoenzyme as an indicator of myocardial damage (Table III). Only one patient of 8 who underwent direct coronary artery revascularization and only one of 5 patients who underwent mitral valve replacement had detectable CPK-MB in the serum after the operation. However, 5 of 9 patients who underwent aortic valve replacement and 2 of 5 patients who
The Journal of Thoracic and Cardiovascular Surgery
8 8 8 Pyle et al.
Table IV. Correlation of postoperative detection of CPK-MB isoenzyme with duration of cardiopulmonary bypass (CPB) Duration of CPB
Total
Positive
Table V. Correlation of postoperative detection of CPK-MB isoenzyme with total duration of aortic cross-clamping during cardiopulmonary bypass
Negative
< 30 min. 30 min. to 1 hr. 1 to \Hi hr. Vh t o 2 h r . 2 to 2 'A hr. > 2hr.
underwent double valve replacement sustained myocardial injury as indicated by the presence of CPK-MB isoenzymes. Technical factors associated with the operations are listed in Tables III to V. No patient had detectable CPK-MB whose total time on cardiopulmonary support was less than 1 hour (8 patients). Only 3 of 7 patients with greater than 60 minutes' but less than 90 minutes' pump time had detectable CPK-MB. Seven of 15 patients with a pump time greater than 90 minutes had CPK-MB isoenzyme detected in their postoperative serum. One of 14 patients whose total aortic crossclamp time was less than 30 minutes had detectable CPK-MB. Six of 10 patients with a total aortic cross-clamp time greater than 1 hour, 15 minutes had detectable CPK-MB. As an indication of the duration of ischemia, the period of coronary artery perfusion was subtracted from the total aortic cross-clamp time. In 22 patients, this period without coronary artery perfusion for greater than 30 minutes caused detectable CPK-MB isoenzymes to develop. Discussion Enzyme patterns have been evaluated by numerous investigators to determine if any particular pattern can be correlated with AMI in the early postoperative period. However, no clear consensus has been established in the literature. At best, the enzyme patterns currently used substantiate infarction only 3 to 5 days after the surgical procedure. The criteria established in the literature, although offering several guidelines, may be applied only with difficulty to any specific situation. The MB isoenzyme of CPK is currently being studied as a more specific and sensitive indicator of myocardial injury in patients admitted to coronary care units. 5,18 " 20 The structure of CPK has been defined as a dimer, as opposed to LDH which is a tetramer. The subunits of the CPK dimer have been designated M and B. The MM dimer is readily detected in skeletal muscle, the BB dimer in brain tissue, and the MB
Duration of aortic cross-clamping
Negative
No cross-clamping 1 to 15 min. 15 to 30 min. 30 to 45 min. 45 min. to 1 hr. 1 to l'/4 hr. 1 Vi to I '/2 hr. l'/2 to 2 hr. > 2 hours
hybrid in cardiac muscle.19 These three isoenzymes can be separated electrophoretically. Roe and associates19 have described the specificity of the MB isoenzyme of CPK for detecting myocardial necrosis to be virtually 100 per cent in medically treated patients admitted to their coronary care unit with chest pain. CPK-MB is detectable 2 to 6 hours after AMI and has cleared by 36 hours in patients not treated surgically, with the maximum level at 12 to 18 hours.18 This offers the physician the advantage of having to wait only 6 to 12 hours for diagnosis rather than 3 to 5 days when applying the parameters of electrocardiography or other enzyme patterns. Oldham and associates22 have applied the detection of CPK-MB as an indication of myocardial injury in 39 patients undergoing coronary artery surgery. They found that patients in whom the diagnosis of AMI was made in the postoperative period demonstrated CPK-MB in serum drawn during the surgical period. They described a group of patients whose serum demonstrated CPK-MB for a prolonged interval after the operation (36 hours) and in whom there was a diagnosis of AMI. In a second group whose serum demonstrated CPK-MB isoenzyme only transiently (6 hours), the correlation with electrocardiographic findings was not as good. They reported that 7 of 9 patients who underwent coronary artery surgery with the use of cardiopulmonary bypass demonstrated transient or persistent CPK-MB in the absence of significant changes in postoperative electrocardiograms other than pericarditis. Blomberg and associates20 examined the value of the method of analysis used in the present study in evaluating a series of 212 admissions to coronary care units. They found no instance of false-positive CPK-MB activity and only a 6 per cent incidence of false-negative results. They concluded that detectable
Volume 71 Number 6 June, 1976
CPK-MB isoenzyme activity by acrylamide slab electrophoresis had a predictive value for the diagnosis of AMI comparable to that of positive evidence on the electrocardiogram. They further decided that the absence of CPK-MB isoenzyme activity in the 24 hour period following onset of symptoms excludes the diagnosis of AMI with a probability equivalent to that provided by normal standard cardiac enzyme results. Summary Because of the reported specificity of CPK-MB for myocardial necrosis and the difficulty in establishing the diagnosis of AMI in patients treated surgically, the value of determining CPK-MB levels in postoperative patients was studied. A group of patients undergoing cardiac surgery with the assistance of cardiopulmonary bypass who could be expected to have a high frequency of myocardial injury was evaluated. A comparable, smaller group of patients who underwent thoracotomy but who did not undergo manipulation of the heart was also studied. The utilization of CPK-MB isoenzyme in this series of 37 patients was valuable in that the presence of CPK-MB isoenzyme could be used as a further indication that AMI had occurred. The presence of MB isoenzyme was demonstrated in 2 of these patients who had no other evidence of AMI. It should be stated that Roe and associates 19 have reported on a patient with detectable CPK-MB whose electrocardiogram was nondiagnostic but who had anatomic evidence of AMI. When the detection of CPK-MB was correlated with other factors in patients undergoing cardiac surgery, it was found that patients who had aortic or double valve replacement had a significantly higher incidence of detection of CPK-MB isoenzyme in the postoperative period. When the presence of CPK-MB was correlated with technical factors associated with cardiac surgery, it was found that the presence of CPK-MB was significantly more common in patients (1) who were supported by cardiopulmonary bypass longer than 90 minutes, (2) whose aortic cross-clamp time was greater than 1 hour, 15 minutes, or (3) whose coronary artery flow was interrupted for a period of 30 minutes or more. The determination of the level of CPK-MB isoenzyme in the blood of patients after an operation offers another parameter which can be used with the electrocardiogram and the clinical course to establish the diagnosis of myocardial injury. The advantage of the rapidity with which CPK-MB appears in the serum following myocardial injury offers a method for the early diagnosis of AMI postoperatively in patients.
CPK-MB isoenzyme
889
REFERENCES 1 Chamberlain, D. A., and Seal, J. E.: Effects of Surgery Under General Anesthesia on the Electrocardiogram in Ischemic Heart Disease and Hypertension, Br. Med. J. 542: 784, 1964. 2 Johnson, W. J., Achor, R. W. P., Burchell, H. B., and Edwards, J. E.: Unrecognized Myocardial Infarction: A Clinicopathological Syndrome, Arch. Intern. Med. 103: 253, 1959. 3 Person, D. A., and Judge, R. D.: Effect of Operation on Serum Transaminase Levels, Arch. Surg. 77: 892, 1958. 4 Cohen, L., and Morgan, J.: The Enzymatic and Immunologic Detection of Myocardial Injury, Med. Clin. North Am. 57: 105, 1973. 5 Wagner, G. S., Roe, C. R., Limbird, L. E., Rosati, R. A., and Wallace, A. G.: The Importance of Identification of the Myocardial Specific Isoenzyme of Creatine Phosphokinase (MB form) in the Diagnosis of Acute Myocardial Infarction, Circulation 47: 263, 1973. 6 Crowley, L. V.: Creatine Phosphokinase Activity in Myocardial Infarction, Heart Failure, and Following Various Diagnostic and Therapeutic Procedures, Clin. Chem. 14: 1185, 1968. 7 Oliver, I. T.: A Spectrophotometric Method for the Determination of Creatinine-Phosphokinase and Myokinase, Biochem. J. 61: 116, 1955. 8 Wagner, W. E. B., Ulmer, D. D., and Vallee, B. L.: Metalloenzymes and Myocardial Infarction. II. Malic and Lactic Dehydrogenase Activities and Zinc Concentrations in Serum, N. Engl. J. Med. 255: 449, 1956. 9 Morgenstern, S., Oklander, M., Auerbach, J., Kaufman, J., and Klein, B.: Automated Determination of Serum Glutamic-Oxaloacetic Transaminase, Clin. Chem. 12: 95, 1966. 10 Blomberg, D. J., and Burke, M.D.: Isoenzymes of Creatinekinase, Separation by Acrylamide Gel Electrophoresis, Ann. Clin. Lab. Sci. 4: 456, 1974. 11 Coronary Drug Project, Circulation 47, 48: 1, 1973. 12 Hobson, R. W., Ill, Fleaning, A., Conaut, C , Mahoney, W. D., and Baugh, J. H.: Postoperative Serum Enzyme Patterns, Mil. Med 136: 624, 1971. 13 Killen, D. A.: Serum Enzyme Elevations: A Diagnostic Test for Acute Myocardial Infarction During the Early Postoperative Period, Arch. Surg. 96: 200, 1968. 14 Dixon, S. H., Jr., Fuchs, J. C. A., and Ebert, P. A.: Changes in Serum Creatinine Phosphokinase Activity Following Thoracic, Cardiac, and Abdominal Operations, Arch. Surg. 103: 66, 1972. 15 Einzig, S., Lindsay, W. G., Todd, E. P., Lucas, R. V., Castaneda, A. R., and Nicoloff, D. M.: The Value of Creatinine Phosphokinase in Determining Intraoperative Myocardial Ischemia, Minn. Med. 57: 683, 1974. 16 Kelly, J. L., Cambell, D. A., and Bradt, R. C : The Recognition of Myocardial Infarction in the Early Postoperative Period, Arch. Surg. 94: 673, 1967. 17 Coodley, E. L.: Evaluation of Enzyme Diagnosis in Myocardial Infarction, Am. J. Med. Sci. 256: 300, 1968.
8 90
Pyle et al.
18 Kontineu, A., and Hannu, S.: Determination of Serum Creatinekinase Isoenzyme in Myocardial Infarction, Am. J. Cardiol. 29: 817, 1972. 19 Roe, C. R., Limbird, L. E., Wagner, G. S., and Nerenberg, S. T.: Combined Isoenzyme Analysis in the Diagnosis of Myocardial Injury: Application of Electrophoretic Methods for the Detection and Quantification of the Creatinine Phosphokinase MB isoenzyme, J. Lab. Clin. Med. 80: 577, 1972. 20 Blomberg, D. J., Kimber, W. D., and Burke, M. D.: Creatinekinase Isoenzymes: Predictive Value in the Early Diagnosis of Acute Myocardial Infarction, Am. J. Med. 59: 464, 1975.
The Journal of Thoracic and Cardiovascular Surgery
21 Goto, I., Nagamine, M., and Katsuki, S.: Creatinine Phosphokinase Isoenzymes in Muscles, Arch. Neurol. 20: 422, 1969. 22 Oldham, H. N., Jr., Roe, C. R., Young, W. G., Jr., and Dixon, S. H.: Intraoperative Detection of Myocardial Damage During Coronary Artery Surgery by Plasma Creatine Phosphokinase Isoenzyme Analysis, Surgery, 74: 917, 1973. 23 Klein, M. S., Shell, W. E., and Sobel, B. E.: Serum Creatine Phosphokinase (CPK) Isoenzyme After Intramuscular Injections, Surgery, and Myocardial Infarction, Cardiovascu. Res. 7: 412, 1973.
R. Bradford Pyle, M.D., David J. Blomberg, M.D., M. Desmond Burke, M.D., William G. Lindsay, M.D., and Demetre M. Nicoloff, M.D., Ph.D., Minneapolis, Minn.
J. he diagnosis of acute myocardial infarction (AMI) in the early postoperative period is at times quite difficult. The patient is often unable to describe the typical symptom of substernal chest pain because of anesthesia or analgesia. As many as 44 per cent of patients undergoing abdominal surgery have postoperative changes in their electrocardiograms.1 Electrocardiographic changes of infarction are difficult to distinguish in patients with abnormal preoperative cardiograms and, unfortunately, these patients are at greatest risk of having AMI during the operation. Electrocardiograms have been reported to have established the diagnosis of AMI in 65 per cent of patients who were found to have myocardial injury at postmortem examination.2 Thus, relying solely on the electrocardiogram for the diagnosis of AMI will result in missed diagnoses in as many as one third of the patients with AMI. From the University of Minnesota Hospitals, Minneapolis, Minn. 55455. Supported by funds from Minnesota Medical Foundation and a Grant-in-Aid from the Minnesota Heart Association. Received for publication Jan. 13, 1975. Accepted for publication Nov. 21, 1975.
884
Patterns of changes in serum enzyme levels have been established to be of value in the diagnosis of AMI in nonsurgical patients. Levels of serum glutamic oxaloacetic transaminase (SGOT), lactic dehydrogenase (LDH), the heat-stable fraction of lactic dehydrogenase (LDH-HS), and creatinine phosphokinase (CPK) have been described which are diagnostic of AMI.3, 4 However, trauma to tissues during the operation has resulted in variable elevations of these enzymes, so that their reliability as indicators of AMI in the early postoperative period is reduced. Various patterns of enzyme changes stated to be diagnostic of AMI in the early postoperative period have been published. However, all too frequently the clinician is unable to distinguish a diagnostic enzyme pattern. Use of the MB isoenzyme of CPK is currently being investigated as a more sensitive and specific indicator of AMI in patients admitted to coronary care units.5' 6 This report describes the use of the CPK-MB isoenzyme as an indicator of myocardial injury in the early postoperative period. Methods In order to evaluate CPK-MB elevations as an aid in the detection of significant myocardial damage and/or
Volume 71 Number 6 June, 1976
necrosis in the early postoperative period, we studied consecutive patients over the age of 12 years who were undergoing cardiac and thoracic surgery. The study included 30 patients who underwent cardiac surgery with the support of cardiopulmonary bypass and 7 patients who underwent thoracotomy. These patients were studied with serial analysis of SGOT, LDH, and LDH-HS preoperatively, postoperatively in the recovery room, and then daily for 5 days. CPK and isoenzymes of CPK were evaluated preoperatively, postoperatively in the recovery room, at 6 hour intervals for 36 hours, and then at daily intervals thereafter through the fifth postoperative day. Electrocardiograms were obtained preoperatively, postoperatively in the recovery room, and on postoperative days 1,3, and 5. The clinical course was monitored closely for any evidence of myocardial infarction. Blood was collected from either an arterial line or a peripheral vein. Samples were allowed to clot and were then centrifuged twice for 10 minutes at 1,000 r.p.m. Serum for SGOT and CPK determinations was frozen at —15° C. if not immediately analyzed. All analyses were completed within 7 to 10 days; experiments in this laboratory have shown no significant sample deterioration over this limited time period. Serum for study of LDH activity was stored at 25° C. if not analyzed immediately. All LDH analyses were completed within 48 hours. Serum CPK was determined by the method of Oliver.7 LDH activity was determined by a modification of Wagner's8 small methods. These analyses utilized reagent substrates supplied by BoehringerMannheim and were performed kinetically with a Gilford 2400 spectrophotometer (Gilford Instrument Laboratories, Oberlin, Ohio). LDH and CPK activities were determined at 32° C , and the LDH activities were then remeasured after heat inactivation in phosphate buffer for 45 minutes at 63° C. to determine the heat-stable fraction. SGOT activity was determined by the method of Morgenstern9 by use of the SMA 12/60 AutoAnalyzer (Technicon Corporation, Tarrytown, N.Y.) at 45° C. The normal values for these methods are as follows: CPK less than 60 ml.U. per milliliter, LDH 44 to 88 ml.U. per milliliter, heat-stable LDH less than 24 per cent of total activity, and SGOT 7 to 40 ml.U. per milliliter. CPK isoenzymes were determined by vertical acrylamide slab electrophoresis by means of the method of Blomberg and Burke.10 Seven patients undergoing thoracic surgery not involving the heart and 30 patients undergoing cardiac surgery with the use of cardiopulmonary bypass were studied. Patients undergoing thoracic surgery had a
CPK-MB isoenzyme
885
standard thoracotomy with removal of a single rib. Two underwent wedge resections of coin lesions, 2 had pleural abrasions, one had excision of a portion of the chest wall involved with tumor, one had an associated rib biopsy, and one underwent pneumonectomy. In all patients undergoing cardiac surgery, the heart was exposed through a midline sternotomy incision. The operations performed included valve replacement, coronary artery bypass, correction of an acquired ventricular septal defect, and closure of an atrial septal defect. Cardiopulmonary bypass was used uneventfully in all patients. The Bentley bubble oxygenator was primed with lactated Ringer's solution, mannitol, and fresh blood. The hemodilution volume was 16 c.c. per kilogram, and flow rates were maintained above 60 ml. per kilogram per minute in all patients. Moderate hypothermia was employed in all patients, minimal esophageal temperatures varying from 28° to 30° C. In all patients undergoing aortic valve replacement, coronary artery perfusion was carried out to at least the left coronary artery with a flow of 100 to 150 c.c. per minute. Fibrillation of the heart was instituted electrically in all patients except those undergoing aortic valve replacement. Defibrillation was effected by countershock of 50 to 200 watt-seconds when necessary after rewarming to 35 to 37° C. Results Postoperatively, the presence of CPK-MB isoenzyme was demonstrated in the serum of 10 of the 37 patients studied. One patient who developed a ventricular septal defect after a preoperative AMI was found to have the CPK-MB fraction in the serum drawn preoperatively as well as postoperatively. This was the only patient who died. The presence or absence of CPK-MB isoenzyme was correlated with the clinical course, electrocardiograms, and the pattern of other serum enzymes (total CPK, SGOT, and LDH). The operative events were correlated with the CPK-MB analysis, considering specifically the total duration of cardiopulmonary bypass, the duration of aortic crossclamping, and the total time period during which the aorta was cross-clamped but the coronary arteries were not perfused. The single patient with preoperative CPK-MB was excluded from considerations of the correlation of operative procedures with the finding of CPK-MB in postoperative serum. Factors in the clinical evaluation which were used as indicators of myocardial injury were: (1) low cardiac output state manifested by difficulty in being weaned from cardiopulmonary bypass; (2) hypotension lasting 50 to 60 minutes or requiring support with vasopressors
The Journal of Thoracic and Cardiovascular Surgery
8 8 6 Pyle et al.
Table I. Detection of CPK-MB isoenzyme after cardiac and thoracic surgery, compared with other indicators of myocardial injury in the early postoperative period CPK-MB isoenzyme No. of cardiac surgery cases Criteria
Result
Total
Positive
ECG
Positive Equivocal Negative
6 13 11
4 4 2
Total enzyme pattern
Positive Equivocal Negative
4 10 16
Clinical course
Positive Equivocal Negative
4 7 19
No of thoracic surgery cases Total
Positive
Negative
2 9 9
0 3 4
0 0 0
0 3 4
3 1 6
1 9 10
0 5 2
0 0 0
0 5 2
3 3 4
1 4 15
0 1 5
0 0 0
0 1 5
Negative
Legend: CPK, Creatinine phosphokinase.
for longer than 4 hours; (3) sudden onset of pulmonary edema; (4) oliguria persisting over 3 hours and peripheral cyanosis in the absence of hypovolemia, sepsis, or respiratory distress; and (5) premature ventricular beats of two or more foci or of a frequency greater than 6 to 10 per minute which persisted for more than 4 hours (or required treatment with antiarrhythmic agents for more than 4 hours) in the absence of hypokalemia and alkalosis. Electrocardiograms were interpreted as showing no evidence of infarction if there was no change from the preoperative to the postoperative tracings. The Minnesota code was used to define the presence of myocardial infarction.11 Basically, infarction was indicated by the appearance of Q waves or of definite ischemic changes in the ST-T segment postoperatively which had not been apparent in the preoperative tracings. The enzymatic definition of AMI is somewhat more difficult. Person and Judge3 described the pattern of enzyme elevation (total CPK, SGOT, and LDH) postoperatively as that of an initial rise and gradual decline to normal levels after 5 to 8 days in patients without AMI. Hobson and associates12 described an elevation above two to five times normal levels of SGOT and LDH in the absence of liver or biliary tract trauma as an indicator of AMI. When liver or biliary tract surgery was performed, they viewed elevations greater than six times normal as an indication of myocardial injury. Person and Judge3 stated that factors which caused elevation of SGOT and LDH, besides liver and biliary tract operations, were massive necrosis such as that seen in the presence of an abscess or
massive tissue trauma which occurs with a thoracotomy incision. Killen13 stated that an elevation in SGOT and LDH above normal for greater than 3 to 5 days after an operation is an indication of AMI. Dixon and associates14 stated that CPK values should be expected to return to normal by 3 to 5 days postoperatively in the absence of AMI or other massive tissue trauma. Einzig's group15 stated that a secondary elevation after initial peak and decline in enzyme levels was diagnostic of AMI. Each of these criteria was used in the present study as an indicator of AMI. Since 25 of 30 patients who underwent operations requiring cardiopulmonary bypass and all 7 patients who underwent thoracotomy had elevations of total CPK greater than five times normal, the elevation of total CPK was not used as a criterion of myocardial damage. Heat-stable LDH was considered to be an indicator of AMI if it was detected in the serum. Table I presents the results obtained from the evaluation of these 37 patients. Data from patients with and without CPK-MB isoenzyme are compared with the other criteria used to indicate AMI: electrocardiogram, total enzyme pattern, and clinical course. It was found that 10 of the 30 patients who had cardiac surgery had definite evidence of CPK-MB enzyme in the serum, a finding considered diagnostic of myocardial injury. In 2 of these patients, evaluation of other enzymes, electrocardiograms, and the postoperative clinical course gave no evidence of AMI. In one of these 2 patients, the CPK-MB enzyme appeared in only one sample obtained in the recovery room after the operation, and there was no further evidence of MB isoenzyme afterward. This patient underwent aortic
Volume 71 Number 6 June, 1976
CPK-MB isoenzyme
Table II. Presence of CPK-MB isoenzyme after cardiac surgery correlated with each of the other enzymes commonly employed to diagnose myocardial damage Enzyme test
Table III. Correlation of CPK-MB isoenzyme in the postoperative period with various cardiac surgical procedures Operative procedure
Negative
Result
Total
SGOT
Positive Negative
6 20
3 3
3 17
LDH
Positive Negative
0 27
0 10
0 17
Heatstable LDH
Positive
21
Negative
6
1
5
Pattern of total CPK
Positive
13
3
10
Negative
17
7
10
Maximum value of total CPK
Positive
25
10
15
Negative
Positive
88 7
12
5
Legend: SGOT, Serum glutamic oxaloacetic transaminase. LDH, Lactic dehydrogenase.
valve replacement and was supported by cardiopulmonary bypass for 1 hour, 27 minutes. The aorta was cross-clamped for 1 hour, 17 minutes, and the coronary arteries were perfused for a total of 1 hour of this time. The second patient underwent aortic and mitral valve replacement, having a pump time of 2 hours, 22 minutes. The total cross-clamp time in this patient was 2 hours, 7 minutes with perfusion of the coronary arteries for only 1 hour, 25 minutes. CPK-MB was absent from the serum in 3 of 10 patients who were diagnosed as having AMI by evaluation of enzymes, electrocardiograms, or clinical course. Two of these patients with AMI who lacked CPK-MB had definite evidence of AMI on postoperative electrocardiograms, although one had a completely uncomplicated postoperative course. The third patient required the temporary use of isoproterenol to be weaned from cardiopulmonary bypass because of persistent low output syndrome following double valve replacement. The electrocardiogram of this patient was nondiagnostic of AMI although changes had occurred since the preoperative tracings. Eleven patients who underwent cardiac surgery had findings in the clinical course or electrocardiogram which were suggestive of AMI. In 3 of these patients, CPK-MB isoenzyme was identified in the sera. All patients in the thoracotomy group failed to show evidence of CPK-MB isoenzyme.
Single artery bypass Double coronary artery bypass Coronary artery bypass and other procedure Aortic valve replacement Mitral valve replacement Double valve replacement Other procedures
Total
Positive
Negative
2 4 2 9 5 5 3
Three of 4 patients whose total enzyme patterns indicated AMI had detectable CPK-MB. Six of 16 patients undergoing cardiac surgery whose total enzyme pattern was not diagnostic of AMI had detectable CPK-MB isoenzyme. If the CPK-MB enzyme is indicative of myocardial damage or necrosis, then reliance upon the total enzyme pattern alone as an indicator of myocardial damage would have left undetected the myocardial injury in these 6 patients. If each of the cardiac enzymes evaluated in patients after cardiac surgery is considered separately, we find that SGOT was the most reliable indicator of myocardial damage as defined by the presence of CPK-MB isoenzyme (Table II). Apparently, the hemolysis associated with multiple transfusion and cardiopulmonary bypass invalidates the results of LDH and heat-stable LDH. The extensive tissue injury associated with the sternotomy incision, which was employed in all 30 patients who underwent cardiac surgery, obscures the diagnosis of AMI in the early postoperative period if the diagnosis is being based on the pattern of total CPK disappearance or the maximum total CPK level. In patients who underwent cardiac surgery, other factors associated with the presence of myocardial injury were evaluated by using the presence of CPK-MB isoenzyme as an indicator of myocardial damage (Table III). Only one patient of 8 who underwent direct coronary artery revascularization and only one of 5 patients who underwent mitral valve replacement had detectable CPK-MB in the serum after the operation. However, 5 of 9 patients who underwent aortic valve replacement and 2 of 5 patients who
The Journal of Thoracic and Cardiovascular Surgery
8 8 8 Pyle et al.
Table IV. Correlation of postoperative detection of CPK-MB isoenzyme with duration of cardiopulmonary bypass (CPB) Duration of CPB
Total
Positive
Table V. Correlation of postoperative detection of CPK-MB isoenzyme with total duration of aortic cross-clamping during cardiopulmonary bypass
Negative
< 30 min. 30 min. to 1 hr. 1 to \Hi hr. Vh t o 2 h r . 2 to 2 'A hr. > 2hr.
underwent double valve replacement sustained myocardial injury as indicated by the presence of CPK-MB isoenzymes. Technical factors associated with the operations are listed in Tables III to V. No patient had detectable CPK-MB whose total time on cardiopulmonary support was less than 1 hour (8 patients). Only 3 of 7 patients with greater than 60 minutes' but less than 90 minutes' pump time had detectable CPK-MB. Seven of 15 patients with a pump time greater than 90 minutes had CPK-MB isoenzyme detected in their postoperative serum. One of 14 patients whose total aortic crossclamp time was less than 30 minutes had detectable CPK-MB. Six of 10 patients with a total aortic cross-clamp time greater than 1 hour, 15 minutes had detectable CPK-MB. As an indication of the duration of ischemia, the period of coronary artery perfusion was subtracted from the total aortic cross-clamp time. In 22 patients, this period without coronary artery perfusion for greater than 30 minutes caused detectable CPK-MB isoenzymes to develop. Discussion Enzyme patterns have been evaluated by numerous investigators to determine if any particular pattern can be correlated with AMI in the early postoperative period. However, no clear consensus has been established in the literature. At best, the enzyme patterns currently used substantiate infarction only 3 to 5 days after the surgical procedure. The criteria established in the literature, although offering several guidelines, may be applied only with difficulty to any specific situation. The MB isoenzyme of CPK is currently being studied as a more specific and sensitive indicator of myocardial injury in patients admitted to coronary care units. 5,18 " 20 The structure of CPK has been defined as a dimer, as opposed to LDH which is a tetramer. The subunits of the CPK dimer have been designated M and B. The MM dimer is readily detected in skeletal muscle, the BB dimer in brain tissue, and the MB
Duration of aortic cross-clamping
Negative
No cross-clamping 1 to 15 min. 15 to 30 min. 30 to 45 min. 45 min. to 1 hr. 1 to l'/4 hr. 1 Vi to I '/2 hr. l'/2 to 2 hr. > 2 hours
hybrid in cardiac muscle.19 These three isoenzymes can be separated electrophoretically. Roe and associates19 have described the specificity of the MB isoenzyme of CPK for detecting myocardial necrosis to be virtually 100 per cent in medically treated patients admitted to their coronary care unit with chest pain. CPK-MB is detectable 2 to 6 hours after AMI and has cleared by 36 hours in patients not treated surgically, with the maximum level at 12 to 18 hours.18 This offers the physician the advantage of having to wait only 6 to 12 hours for diagnosis rather than 3 to 5 days when applying the parameters of electrocardiography or other enzyme patterns. Oldham and associates22 have applied the detection of CPK-MB as an indication of myocardial injury in 39 patients undergoing coronary artery surgery. They found that patients in whom the diagnosis of AMI was made in the postoperative period demonstrated CPK-MB in serum drawn during the surgical period. They described a group of patients whose serum demonstrated CPK-MB for a prolonged interval after the operation (36 hours) and in whom there was a diagnosis of AMI. In a second group whose serum demonstrated CPK-MB isoenzyme only transiently (6 hours), the correlation with electrocardiographic findings was not as good. They reported that 7 of 9 patients who underwent coronary artery surgery with the use of cardiopulmonary bypass demonstrated transient or persistent CPK-MB in the absence of significant changes in postoperative electrocardiograms other than pericarditis. Blomberg and associates20 examined the value of the method of analysis used in the present study in evaluating a series of 212 admissions to coronary care units. They found no instance of false-positive CPK-MB activity and only a 6 per cent incidence of false-negative results. They concluded that detectable
Volume 71 Number 6 June, 1976
CPK-MB isoenzyme activity by acrylamide slab electrophoresis had a predictive value for the diagnosis of AMI comparable to that of positive evidence on the electrocardiogram. They further decided that the absence of CPK-MB isoenzyme activity in the 24 hour period following onset of symptoms excludes the diagnosis of AMI with a probability equivalent to that provided by normal standard cardiac enzyme results. Summary Because of the reported specificity of CPK-MB for myocardial necrosis and the difficulty in establishing the diagnosis of AMI in patients treated surgically, the value of determining CPK-MB levels in postoperative patients was studied. A group of patients undergoing cardiac surgery with the assistance of cardiopulmonary bypass who could be expected to have a high frequency of myocardial injury was evaluated. A comparable, smaller group of patients who underwent thoracotomy but who did not undergo manipulation of the heart was also studied. The utilization of CPK-MB isoenzyme in this series of 37 patients was valuable in that the presence of CPK-MB isoenzyme could be used as a further indication that AMI had occurred. The presence of MB isoenzyme was demonstrated in 2 of these patients who had no other evidence of AMI. It should be stated that Roe and associates 19 have reported on a patient with detectable CPK-MB whose electrocardiogram was nondiagnostic but who had anatomic evidence of AMI. When the detection of CPK-MB was correlated with other factors in patients undergoing cardiac surgery, it was found that patients who had aortic or double valve replacement had a significantly higher incidence of detection of CPK-MB isoenzyme in the postoperative period. When the presence of CPK-MB was correlated with technical factors associated with cardiac surgery, it was found that the presence of CPK-MB was significantly more common in patients (1) who were supported by cardiopulmonary bypass longer than 90 minutes, (2) whose aortic cross-clamp time was greater than 1 hour, 15 minutes, or (3) whose coronary artery flow was interrupted for a period of 30 minutes or more. The determination of the level of CPK-MB isoenzyme in the blood of patients after an operation offers another parameter which can be used with the electrocardiogram and the clinical course to establish the diagnosis of myocardial injury. The advantage of the rapidity with which CPK-MB appears in the serum following myocardial injury offers a method for the early diagnosis of AMI postoperatively in patients.
CPK-MB isoenzyme
889
REFERENCES 1 Chamberlain, D. A., and Seal, J. E.: Effects of Surgery Under General Anesthesia on the Electrocardiogram in Ischemic Heart Disease and Hypertension, Br. Med. J. 542: 784, 1964. 2 Johnson, W. J., Achor, R. W. P., Burchell, H. B., and Edwards, J. E.: Unrecognized Myocardial Infarction: A Clinicopathological Syndrome, Arch. Intern. Med. 103: 253, 1959. 3 Person, D. A., and Judge, R. D.: Effect of Operation on Serum Transaminase Levels, Arch. Surg. 77: 892, 1958. 4 Cohen, L., and Morgan, J.: The Enzymatic and Immunologic Detection of Myocardial Injury, Med. Clin. North Am. 57: 105, 1973. 5 Wagner, G. S., Roe, C. R., Limbird, L. E., Rosati, R. A., and Wallace, A. G.: The Importance of Identification of the Myocardial Specific Isoenzyme of Creatine Phosphokinase (MB form) in the Diagnosis of Acute Myocardial Infarction, Circulation 47: 263, 1973. 6 Crowley, L. V.: Creatine Phosphokinase Activity in Myocardial Infarction, Heart Failure, and Following Various Diagnostic and Therapeutic Procedures, Clin. Chem. 14: 1185, 1968. 7 Oliver, I. T.: A Spectrophotometric Method for the Determination of Creatinine-Phosphokinase and Myokinase, Biochem. J. 61: 116, 1955. 8 Wagner, W. E. B., Ulmer, D. D., and Vallee, B. L.: Metalloenzymes and Myocardial Infarction. II. Malic and Lactic Dehydrogenase Activities and Zinc Concentrations in Serum, N. Engl. J. Med. 255: 449, 1956. 9 Morgenstern, S., Oklander, M., Auerbach, J., Kaufman, J., and Klein, B.: Automated Determination of Serum Glutamic-Oxaloacetic Transaminase, Clin. Chem. 12: 95, 1966. 10 Blomberg, D. J., and Burke, M.D.: Isoenzymes of Creatinekinase, Separation by Acrylamide Gel Electrophoresis, Ann. Clin. Lab. Sci. 4: 456, 1974. 11 Coronary Drug Project, Circulation 47, 48: 1, 1973. 12 Hobson, R. W., Ill, Fleaning, A., Conaut, C , Mahoney, W. D., and Baugh, J. H.: Postoperative Serum Enzyme Patterns, Mil. Med 136: 624, 1971. 13 Killen, D. A.: Serum Enzyme Elevations: A Diagnostic Test for Acute Myocardial Infarction During the Early Postoperative Period, Arch. Surg. 96: 200, 1968. 14 Dixon, S. H., Jr., Fuchs, J. C. A., and Ebert, P. A.: Changes in Serum Creatinine Phosphokinase Activity Following Thoracic, Cardiac, and Abdominal Operations, Arch. Surg. 103: 66, 1972. 15 Einzig, S., Lindsay, W. G., Todd, E. P., Lucas, R. V., Castaneda, A. R., and Nicoloff, D. M.: The Value of Creatinine Phosphokinase in Determining Intraoperative Myocardial Ischemia, Minn. Med. 57: 683, 1974. 16 Kelly, J. L., Cambell, D. A., and Bradt, R. C : The Recognition of Myocardial Infarction in the Early Postoperative Period, Arch. Surg. 94: 673, 1967. 17 Coodley, E. L.: Evaluation of Enzyme Diagnosis in Myocardial Infarction, Am. J. Med. Sci. 256: 300, 1968.
8 90
Pyle et al.
18 Kontineu, A., and Hannu, S.: Determination of Serum Creatinekinase Isoenzyme in Myocardial Infarction, Am. J. Cardiol. 29: 817, 1972. 19 Roe, C. R., Limbird, L. E., Wagner, G. S., and Nerenberg, S. T.: Combined Isoenzyme Analysis in the Diagnosis of Myocardial Injury: Application of Electrophoretic Methods for the Detection and Quantification of the Creatinine Phosphokinase MB isoenzyme, J. Lab. Clin. Med. 80: 577, 1972. 20 Blomberg, D. J., Kimber, W. D., and Burke, M. D.: Creatinekinase Isoenzymes: Predictive Value in the Early Diagnosis of Acute Myocardial Infarction, Am. J. Med. 59: 464, 1975.
The Journal of Thoracic and Cardiovascular Surgery
21 Goto, I., Nagamine, M., and Katsuki, S.: Creatinine Phosphokinase Isoenzymes in Muscles, Arch. Neurol. 20: 422, 1969. 22 Oldham, H. N., Jr., Roe, C. R., Young, W. G., Jr., and Dixon, S. H.: Intraoperative Detection of Myocardial Damage During Coronary Artery Surgery by Plasma Creatine Phosphokinase Isoenzyme Analysis, Surgery, 74: 917, 1973. 23 Klein, M. S., Shell, W. E., and Sobel, B. E.: Serum Creatine Phosphokinase (CPK) Isoenzyme After Intramuscular Injections, Surgery, and Myocardial Infarction, Cardiovascu. Res. 7: 412, 1973.