Catheterization and Cardiovascular Diagnosis 2:329-336 (1976)

DETERMINATION OF THE ORIGIN OF ELEVATED PLASMA CPK AFTER CARDIAC CATH ETERlZATlON

Robert Roberts, M.D., Burton E. Sobel, M.D., and Philip A. Ludbrook, M.D.

Episodes of chest pain are not uncommon in patients undergoing cardiac catheteriza- tion. The diagnostic implications of this symptom may be complicated by the occa- sional appearance of electrocardiographic changes mimicking those seen in acute myocardial infarction, and by the frequent elevation of conventionally measured serum enzymes. Exclusion of infarction is particularly important when coronary revasculariza- tion is contemplated. Since the MB CPK isoenzyme is relatively specific to myocardium, we assayed CPK isoenzymes in plasma samples from 184 patients undergoing cardiac catheterization to determine whether CPK elevations accompanying catheterization can be distinguished from those associated with myocardial infarction. Samples were obtained every 2 hr for 24 hr, and CPK isoenzymes quantified by a kinetic fluorometric method. Total plasma CPK increased in all patients (mean peak 0.238 k0.042 (SD) IU/ml) but MB CPK remained normal in 181 patients (<0.005 IUlml). In the three remaining patients, MB CPK was elevated and myocardial infarction was confirmed by $$mTc (SN) pyrophosphate scan. Twelve patients after catheterization, in whom no intramuscular premedication was given, exhibited only minimal elevation of total plasma CPK. In contrast, 100 control patients with acute myocardial infarction exhibited peak total CPK activity averaging 0.833 ? 0.037 (SD), and MB CPK was elevated in all cases (0.078 * 0.027 (SD) IUlml). Thus, CPK elevations after catheterization reflect release of enzyme from noncardiac sources rather than from injured myocardium. Furthermore, increased plasma MB CPK activity may be considered a reliable index of myocardial infarction in patients undergoing cardiac catheterization.

Key words: Cardiac catheterization, CPK isoenzymes, myocardial infarction, intramuscular injec- tions

The number of patients requiring cardiac catheterization and coronary arteriog- raphy has markedly increased in recent years, in part because of increasing enthusi- asm for coronary bypass procedures for patients with angina pectoris. However, this operation may not be beneficial when undertaken in patients with evolving

From Barnes Hospital and Washington University School of Medicine, St. Louis, Mlssouri

This work was supported in part by NHLI SCOR in Ischemic Heart Disease 1 P17 HL 17646 (Washington University, St. Louis, Mo.).

Reprint requests to: Philip A. Ludbrook, M.D., Medical Director, Cardiac Catheterization Laboratory, Washington University School of Medicine and Mallinckrodt Institute of Radiology, 660 South Euclid Avenue, St. Louis, MO 63110

Received December 15, 1975; revision accepted February 24, 1976

329 0 1 9 7 6 Alan R. Liss, Inc., 150 F i f th Avenue, New York, NY 10011

330 Roberts. Sobel, and Ludbrook

acute myocardial infarction (1). In fact, under these circumstances, surgery may actually be deleterious due to extension of infarction (2). Sustained chest pain or electrocardiographic changes compatible with ischemic injury may occasionally occur during catheterization (3), particularly in patients with coronary insufficiency due to severe proximal coronary artery obstruction (4), or those with advanced left ventricular dysfunction (5). However, severe or unstable angina pectoris is, in many centers, an indication for invasive diagnostic evaluation because of the possibility of imminent infarction for which prophylactic revascularization is con- templated (6). Accordingly, sensitive and specific techniques are needed for detec- tion of myocardial damage which may occur prior to, during, or following cardiac catheterization and coronary arteriography . Electrocardiography may be mislead- ing because of nonspecific changes, previous infarction, conduction defects, ven- tricular hypertrophy, or arrhythmias. Therefore, detection of myocardial necrosis is conventionally based on elevated activity of plasma enzymes, such as SGOT, LDH, or total CPK. However, activity of these enzymes is frequently elevated after cardiac catheterization (7-9) even in the absence of apparent myocardial damage, presumably as a result of soft tissue injury (10, 11).

The recent availability of a fluorometric kinetic procedure (12) permits quantifi- cation of activity of individual CPK isoenzymes in plasma (13). Elevated plasma activity of MB CPK, an isoenzyme found primarily in myocardium is both a sensitive and a specific index of myocardial injury (14-16). In a preliminary report we observed an absence of MB CPK elevation after uncomplicated cardiac catheterization (17). In the present study we evaluated a large group of patients requiring diagnostic cardiac catheterization for multiple cardiac disorders to char- acterize the frequency of elevated plasma CPK in this patient population, to identify the organ source of the elevated CPK, and to ascertain whether increased MB CPK is a reliable diagnostic index of myocardial injury in this setting.

METHODS AND MATERIALS

The 184 patients undergoing cardiac catheterization comprised 118 males and 66 females, ranging in age from 17 to 76 years (mean 48.4). Written informed consent was obtained from each patient. One hundred and ten patients were investigated because of chest pain, 53 because of apparent valvular disease, and 10 because of suspected congenital cardiac defects. Eleven patients with the “preinfarction syn- drome” were studied on an emergency basis because of consideration of urgent coronary revascularization (18).

Premedication with intramuscular diazepam (Valium) and/or pentobarbital (Nembutal) was utilized in 168 patients. Sixteen patients received no intramuscular premedication so that the contribution of intramuscular injections to total serum CPK activity could be evaluated (19). In all patients, percutaneous puncture and brachial artery cutdown sites were anesthetized by infiltration of 2% lidocaine (Xylocaine). All patients were systemically anticoagulated by administration of Heparin (100 U/kg body weight). Combined right and left heart catheterization was performed in 92 patients; in the remaining 92, left heart catheterization alone was performed. Selective coronary arteriography was performed in 149 patients, using the brachial artery approach in 82 (20) and the percutaneous femoral artery tech- nique in 57 (21). Adjunctive procedures performed in some but not all patients

Cardiac Catheterization and ME CPK lsoenzymes 331

included cardiac output measured by Fick, indicator dilution, or thermodilution techniques; hydrogen studies; bicycle ergometry; His bundle electrography, and atrial and ventricular endocardial pacing studies. Timed power injections of 75% Hypaque (sodium diatrizoate) were utilized for chamber angiography, and selective coronary arteriograms were performed with the use of manual injections of 6-12 ml of Renografin 76 (meglumine diatrizoate and sodium diatrizoate). Blood samples for determination of total CPK and CPK isoenzyme activities were obtained immedi- ately before catheterization and every 2 hr thereafter for 24 hr in all patients undergoing cardiac catheterization. The results of the CPK isoenzyme determina- tions in patients undergoing cardiac catheterization were compared to those ob- tained from 100 patients admitted to the Cardiac Care Unit who sustained elec- trocardiographically documented transmural infarction, and from 50 hospitalized control patients without known cardiovascular disease.

Total CPK and CPK lsoenzyme Determinations

Blood samples were collected in 0.005 M neutralized EGTA, centrifuged at 2,000 x g for 10 min, decanted, and protected with 0.010 M mercaptoethanol. Total CPK activity was determined spectrophotometrically according to the method of Rosalki (22).

CPK isoenzyme activity was determined qualitatively after separation by cel- lulose acetate electrophoresis (24). The procedure entails separation of CPK isoen- zymes by electrophoresis at a constant voltage of 250 V for 60 min at 4°C in 0.05 M Tris barbital, pH 8.8, containing 0.001 M EGTA. Isoenzyme bands are visualized after incubation of sample strips juxtaposed to strips previously soaked in NADPH-generating mediums. Isoenzyme activity exceeding 0.010 IU/ml is readily detectable. Since plasma samples from normal subjects contain less than 0.005 IU/ml (12), no MB CPK activity is detected by this qualitative technique.

Quantitative determinations of activity of individual CPK isoenzymes were performed by a kinetic fluorometric technique (12), results of which are linear with respect to time and enzyme activity and are reproducible within 3%. Activity exceeding 0.002 IU/ml is readily detectable. Samples from normal subjects assayed under these conditions consistently exhibit less than 0.005 IU/ml of MB CPK activity (12).

RESULTS

Total CPK Activity

Peak plasma total CPK activity was elevated above control levels in all patients (n = 184) after cardiac catheterization (ranging from 0.028 to 0.675 IU/ml [mean peak 0.238 & 0.042 (SD)] (Fig. 1) ). Peak total CPK activity exceeded the upper limits of normal in 175 of these patients.

In nine patients without intramuscular premedication, the only injection during the procedure was infiltration of the femoral artery puncture site with lidocaine. In these nine patients, mean total plasma CPK activity before and after catheterization averaged 0.024 and 0.037 IU/ml, respectively, i.e. total CPK activity was only minimally elevated above control, in no instance exceeding the upper limits of normal. Hence, it appears that soft tissue injury resulting from skeletal muscle

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Fig. 1 Total plasma CPK activity in patients following myocardial infarction, cardiac catheteriza- tion, and hospitalized controls, as Indicated. The vertical line represents one standard deviation of the mean.

Fig. 2 Plasma MB CPK activity in patients following myocardial infarction, cardiac catheteriza- tion, and hospitalized controls, as indicated. The vertical line represents one standard deviation of the mean.

Cardiac Catheterization and MB CPK lsoenzymes 333

trauma incurred by intramuscular injection or cutdown procedures accounts for the elevated total plasma CPK activity.

MB CPK Activity

Despite marked increases in total plasma CPK activity after cardiac catheteriza- tion, MB CPK activity determined quantitatively remained within the normal range in 181 patients (less than 0.005 IU/ml) (Fig. 2 ) . Myocardial damage was not suggested by clinical or electrocardiographic criteria in any of the 181 patients with normal MB CPK activity after catheterization.

Despite cautious technique, nonsustained chest pain accompanied by transient nonspecific electrocardiographic changes occurred in several patients with ad- vanced coronary artery disease during coronary angiography. In three patients exhibiting chest pain, MB CPK activity was transiently elevated, returning to normal within 24 hr in each instance. In one of these patients, severe left main coronary ostial disease was documented, and sustained chest pain without evolu- tion of electrocardiographic evidence of transmural infarction occurred after the procedure. Two other patients with transiently elevated MB CPK isoenzyme activity experienced chest pain and exhibited serial electrocardiographic changes compatible with subendocardial infarction following catheterization. In both, a diagnosis of calcific aortic stenosis was confirmed and the possibility of coronary artery microembolization following catheter contact with the aortic valve appeared likely (25).

In each of these three patients with elevated MB CPK activity, myocardial damage was also demonstrated by SSmTc(SN) pyrophosphate scintigraphy per- formed 24 hr after cardiac catheterization (26, 27). Elevated serum MB CPK isoenzyme activity and positive 99mTc(SN) pyrophosphate images both correlate closely with morphologic evidence of myocardial injury in experimental animals (26, 28).

In each of 100 patients with documented acute myocardial infarction, total plasma CPK activity exceeded the upper limits of normal, peak total CPK activity averaging 0.833 k 0.127 (SD) (range 0.180 to 1.620 IU/ml) (Fig. 1) . MB CPK isoenzyme activity was elevated in all cases after infarction, peak MB CPK averag- ing 0.078 2 0.027 (SD) IU/ml (Fig. 2 ) . A comparison of the plasma total CPK and MB CPK activity after myocardial infarction (Fig. 3) and after cardiac catheteriza- tion (Fig. 4) is illustrated by the CPK time-activity curves from two representative patients. Plasma activity of both total CPK and MB CPK isoenzymes was within normal limits in all patients without known cardiovascular disease (Fig. 1 ) .

DISCUSSION

Previously available indices of myocardial injury have frequently been found to be unreliable in patients undergoing diagnostic cardiac catheterization. Symptoms, electrocardiographic and vectorcardiographic changes, as well as conventionally measured plasma enzymes often provide inconclusive or insensitive criteria of an ischemic myocardial insult. Elevation of plasma SGOT, LDH (7, 29), and/or total plasma CPK (9, 30) activity have been reported frequently after catheterization; however, the origin of such elevation has not been definitely established (10, 19, 30).

Toto/ CPK X ME CPK

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Fig. 3 Serial total plasma CPK and MB CPK activity from a representative patient for a duration of 48 hr after myocardial infarction. Both total CPK and MB CPK activity are simultaneously ele- vated, as indicated by the curves.

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TIME ( h r l Fig. 4 Serial total plasma CPK and YB CPK activity from a representative patient for a duration of 24 hr after cardiac catheterization. Although total CPK activity is markedly elevated (peak 480 IU/mi x lo3), MB CPK activity never exceeds the upper limits of normal.

Cardiac Catheterization and MB CPK lsoenzymes 335

Three CPK isoenzymes, designated MM, MB, and BB have been identified in plasma; however, only myocardium contains more than trace amounts of the MB isoenzyme (16). Elevated plasma CPK activity after intramuscular injections is not associated with elevated MB CPK isoenzyme activity (24), nor are various forms of noncardiac surgery (3 1). It is now clear that serum MB CPK isoenzyme activity is significantly and consistently elevated in patients with myocardial infarction docu- mented electrocardiographically (13, 16).

In all patients in the present study receiving intramuscular premedication prior to catheterization, peak total plasma CPK activity was significantly elevated after the procedure, exceeding the upper limits of normal. In contrast, peak total CPK activity was only minimally elevated in nine patients without intramuscular pre- medication or extensive percutaneous or cutdown procedures. Since MB CPK is virtually absent from skeletal muscle (16), these results suggest that the elevated total plasma CPK activity after catheterization is released from skeletal muscle, soft tissues, or both by percutaneous or cutdown procedures. Conversely, MB CPK isoenzyme was not detectable with the qualitative procedure and remained within normal limits when assayed quantitatively in all but three patients after cardiac catheterization. Among these three exceptions, one patient had severe left ostial and left main coronary artery obstruction demonstrable angiographically and probably sustained minor ischemic myocardial damage, although no definitive electrocardiographic evidence of transmural infarction ensued. In the remaining two exceptions severe calcific aortic stenosis was documented, and occult myocar- dial damage may have resulted from calcific micro- or macroembolization to the coronary arteries caused by catheter impingement on the diseased valve (25). In each of these three patients with elevated MB CPK activity myocardial damage was confirmed by clinical, ECG, and scintigraphic evidence.

In all other patients undergoing catheterization, MB CPK isoenzyme activity remained normal, in contrast to the consistent elevation of MB CPK isoenzyme activity seen within 6-8 hr of the onset of chest pain in all patients with electrocar- diographically documented acute myocardial infarction. Accordingly, elevation of MB CPK isoenzyme activity would be anticipated within 8 hr of catheterization in any patient sustaining ischemic myocardial damage shortly before, during, or immediately after the procedure.

For these reasons, analysis of MB CPK activity provides a specific and sensitive index of myocardial injury in patients undergoing cardiac catheterization. Hence, detection of elevated MB CPK provides a means of excluding patients with evolv- ing myocardial infarction in whom bypass surgery may be associated with increased risk.

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