ORIGINAL

Annals of Nuclear Medicine Vol. 6, No. 1, 43-49, 1992

Circulating myosin light chain I levels after coronary reperfusion:a comparison with myocardial necrosis evaluated from singlephoton emission computed tomography with pyrophosphate

Hiroshi YOSHIDA,* Mamoru MocHIZUKI,** Kazuyuki SAKATA,* Mitsuru TAKEZAWA,**Yasunori MATSUMOTO, ** Masami YOSHIMURA, ** Noriko MORI, * Shoichi YOKOYAMA, *

Tsuneo HOSHINO ** and Tsuneo KABURAGI *

*Department of Cardiology and **Department of Nuclear Medicine,Shizuoka General Hospital, Shizuoka, Japan

This study was performed to assess the influence of coronary reperfusion on the serial serummyosin light chain (LC)I levels and to evaluate the relationship between the peak LCI leveland the infarct size calculated from single photon emission computed tomography (SPECT)with technetium-99m pyrophosphate (Tc-99m PYP) in 11 patients who underwent coronaryreperfusion. Blood was drawn before reperfusion, immediately after reperfusion, and oncea day for 14 days, to estimate the time course of serum LCI release. The infarct size estimatedby Tc-99m PYP ranged from 7.3 to 62.4 ml. The LCI levels obtained before reperfusionwere less than 2.5 ng/ml but those obtained immediately after reperfusion were much higher.The value ranged from 2.7 to 9.7 ng/ml and that expressed as a percentage of peak LCI (peak LCI) ranged from 19 to 83 %. Collateral circulation, reperfusion arrhythmia and thedegree of residual stenosis had no influence upon the Y. peak LCI. The correlation betweenpeak LCI levels and SPECT-determined infarct size was good, with a correlation of 0.76(p<0.01, regression line by least squares method y=-3.31+1.53x). Early serum LCImight be influenced by coronary reperfusion but the peak LCI value reflected acute myo-cardial necrosis in patients who underwent coronary reperfusion.

Key words: myosin light chain I, coronary reperfusion, myocardial necrosis, 99 mTc-PYP/201T1 dual SPECT

INTRODUCTION

ESTIMATING INFARCT SIZE in acute myocardial infarc-tion is very important, because morbidity and mor

-tality are related to the extent of myocardial damage.To limit the infarct size and to improve patients'survival, intracoronary thrombolysis, emergent per-cutaneous transluminal coronary angioplasty, andintravenous infusion of tissue plasminogen activatorhave been proposed. Several methods have beendeveloped to evaluate infarct size in man. The 12-

Received August 16, 1991, revision accepted November27, 1991.

For reprints contact: Hiroshi Yoshida M.D., Depart-ment of Cardiology, Shizuoka General Hospital, Kita

-andou 4-27-1 Shizuoka 420, JAPAN.

lead electrocardiogram (ECG), cumulative or peakcreatine phosphokinase-MB (CPK-MB), ejectionfraction of the left ventricle, and several radionuclidemethods have been used. Myosin light chains arestructural protein that are specific to cardiac mus

-cle.1,2 During myocardial infarction, persisting intra-cellular acidosis or activation of proteolytic enzymes,or both, finally leads to the release of structurallybound myosin light chains. This results in the con-tinuous appearance of myosin light chains in serumwell beyond the first week after the onset of myo-cardial infarction.3 The purposes of this study wereto assess the influence of coronary recanalization onthe serial serum myosin light chain (LC) I levels andto evaluate the relationship between the serum peakLCI level and the infarct size calculated from thesingle photon emission computed tomography

Vol. 6, No. 1, 1992 Original 43

Table 1 Characteristics of study patients

Patient Infarct Interven- Residual Interval Reperfusion CollateralLCI (ng/ml)

No. Age/Sex relatedartery tion stenosis

(/) toreflow arrhythmia flow before immediately

° reflow after reflow

1 61/M Seg. 1 ICT 50 1H AIVR poor <2.5 6.52 49/M Seg. 1 ICT 50 6H (—) good <2.5 5.43 77/M Seg. 1 ICT 90 2H (—) good <2.5 6.34 72/M Seg. 1 PTCA 25 3H VT poor <2.5 9.65 67/F Seg. 2 PTCA 25 3.5H (—) good <2.5 3.96 65/M Seg. 15 ICT 90 4H (—) poor <2.5 5.57 71/M Seg. 6 ICT 90 3H AIVR good <2.5 5.88 76/M Seg. 6 ICT 90 2H (—) poor <2.5 7.09 53/M Seg. 6 ICT 0 5H (—) poor <2.5 2.7

10 38/M Seg. 7 ICT 0 3.5H AIVR poor <2.5 9.711 61/M Seg. 9 ICT 90 4H VT poor <2.5 4.0

M=male; F=female; Seg.=the segment of the coronary artery as defined by the AHA committee report; ICT=PTCA=percutaneous transluminal coronary angioplasty; H=hour; AIVR=accelerated idioventricular rhythm;CPK-MB=creatine phosphokinase-MB; PYP-uptake= value of uptake`of technetium-99m pyrophosphate calculatedcomputed tomography. LCI=myosin light chain I; % peak LCI=LCI obtained immediately after reperfusion ex-

(SPECT) with technetium-99m pyrophosphate (Tc-99m PYP).

MATERIALS AND METHODS

Study patientsThe study population comprised 11 patients withacute myocardial infarction. The diagnosis of acutemyocardial infarction was determined on the basisof a history of precordial chest oppressive sensationdue to cardiac ischemia lasting more than 30 minutesand an electrocardiographic ST elevation of at least2 mm in 2 or more adjacent leads. All patients weretransferred to the catheter laboratory immediatelyafter arrival and emergency coronary angiographywas performed. All the infarction-related arteries hadbeen totally or subtotally occluded. Six patients hadgood collateral flow from the contralateral coronaryartery. Urokinase was infused into the infarct-relatedarteries at the rate of 24,000 U/min, to a dose of960,000 U, in every patient. Angiography wasrepeated every 10 minutes to determine the precisetiming of reperfusion. Nine of 11 patients had rapiddistal opacification of the coronary artery involved.The remaining 2 patients did not achieve successfulreperfusion by intracoronary thrombolysis, so per-cutaneous transluminal coronary angioplasty wasattempted, and good antegrade coronary flow wasobtained. Accelerated idioventricular rhythm orventricular tachycardia was followed by reperfusionin 5 of 11 patients. The interval from the onset ofacute myocardial infarction to recanalization waswithin 6 hours in all patients. The site of infarctionwas inferior in 6 of 11 patients and anterior in theremaining 5 patients (Table 1). After successful

reperfusion, all patients were transferred to the coro-nary care unit. Hemodynamics were stable and nofatal arrhythmias were noted in any of the patients.A standard 12-lead ECG was recorded every 4 hours.

Measurements of serum CPK-MBBlood samples for CPK-MB assay were obtainedbefore and immediately after the reperfusion, every2 hours within 24 hours from the onset of infarction,and every 4 hours during the next 24 hours. TotalCPK activity was determined by the modified Rosalkimethod. 4 CPK-MB was measured by cellulose ace-tate membrane electrophoresis.

Measurement of serum myosin light chain IBlood was drawn before and immediately after thereperfusion, and once a day for 14 days, to estimatethe influence of reperfusion on serum LCI levels andto obtain the peak LCI level. The LCI value obtainedimmediately after reperfusion was expressed as thepercent of the peak LCI value (% peak LCI). Weuse a sensitive immunoradiometric assay kit (MyosinLI Assay Kit "Yamasa") for cardiac myosin lightchain I by using anti-myosin light chain I mono-clonal antibodies. This kit measures circulating LCIin the range of 2.5 to 100 ng/ml and shows littleintra- or inter-assay variation. 5

Radionuclide studiesWithin 7 days from the onset of acute myocardialinfarction (range 2-7 days), scintigraphy of Tc-99mPYP and thallium-201 (T1-201) was simultaneouslyimaged at the nuclear medicine laboratory. Threehours after the injection of 740 MBq Tc-99m PYP,111 MBq T1-201 was injected. Five minutes later,

44 Hiroshi Yoshida, Mamoru Mochizuki, Kazuyuki Sakata, et al Annals of Nuclear Medicine

peak CPK-MB Infarctpeak LCI (IU/Z) size (ml)

(%) peak (PYP-uptake)

24.8 26 507 62.421.2 26 331 17.313.1 29 45 8.432.1 30 648 52.311.1 35 126 9.76.6 83 132 15.7

30.5 19 574 27.910.9 64 220 12.25.6 48 135 11.1

14.4 67 502 17.611.4 35 388 7.3

intracoronary thrombolysis;VT=ventricular tachycardia;on single photon emissionpressed as the percentage of peak LCI.

imaging was performed with a rotating single-headeddigital gamma camera (SHIMADZU SNC-500R)equipped with a low-energy, high resolution, parallel-hole collimator. This gamma camera was interfacedto a dedicated computer (SHIMADZU Scintipac700). A 15 % window was centered over the 140 keVphotopeaks characteristic of Tc-99m PYP, and a20% window was centered over the 75 keV photo-peaks characteristic of T1-201. Data were obtainedwith the gamma camera from 32 equally spacedstops over a 180 degree arc, from 45 degrees rightanterior oblique to 45 degrees left posterior oblique.All projection data were acquired for 30 sec andyield 120,000 to 180,000 counts of T1-201 and120,000 to 160,000 of Tc-99m PYP. On the average,7% of these respective counts were within the myo-cardial region with thallium and technetium activity.Tomographic data were acquired in a 64 x 64 matrixwith a 1.3 >< hardware zoom factor. The image dis-plays of SPECT were a vertical long axis, a hori-zontal long axis, and a short axis. To eliminate boneactivity, reconstructions were masked by drawing aregion of interest around the heart. The weight ofthe myocardial infarction was measured by auto-matically drawing a region of interest around themyocardial Tc-99m PYP uptake for each short axialslice. Thresholds were determined from phantomstudies. A 2 ml capsule phantom was enclosed in acone shaped myocardial phantom which was sus-pended eccentrically in a 20 cm diameter cylinder.The capsule phantom was mounted with 1.85 MBqof technetium-99m and the remainder of the coneshaped myocardial phantom was mounted with18.5 MBq of thallium-201. Both 18.5 MBq of tech-netium-99m and thallium-201 were enclosed in the

cylinder simulated back ground, then dual nuclideSPECT was performed with photopeaks and win-dows identical to those in the vivo study. A 70cutoff method yielded the SPECT-estimated volumethat was closest to the actual volume of the uptake.Therefore, we used the 70 % cutoff level in thepresent study. In short axial slices, all pixels withinthe region of interest that were equal to or greaterthan 70 percent of the maximal count rate wereincorporated into the infarct weight. The total num-ber of pixels in all slices demonstrating increasedtracer uptake were then added together and mul-tiplied by the voxel volume (0.05758 ml). The voxelvolume was calculated from the pixel size.

Statistical analysisComparison of peak LCI levels, peak CPK-MBsand infarct size determined by Tc-99m PYP uptakewas performed by regression equations calculated byleast squares methods. The correlation coefficientsreported are Pearson r values calculated by regres-sion analysis. The difference in the % peak LCI wascompared by two sample Wilcoxon test.

RESULTS

In all 11 patients, Tc-99m PYP accurately accumu-lated in the infarcted area on SPECT images cor-responding with the territory of the infarct-relatedartery and the serial ECG (Fig. 1). The Tc-99m PYPestimates of infarct size ranged from 7.3 to 62.4 inl(Table 1).

The LCI levels obtained before reperfusion wereless than 2.5 ng/ml in all 11 patients. But the LCIlevels obtained immediately after reperfusion wereconsiderably increased, even within 6 hours from theonset of acute myocardial infarction. The valuesranged from 2.7 to 9.7 ng/ml. The % peak LCIranged from 19 to 83 % (Fig. 2). Good collateralcirculation, reperfusion arrhythmia and residualstenosis less than 90 % were noted in 4, 5 and 6 of11 patients, respectively. There was no difference inthe % peak LCI between cases with and withoutcollateral circulation. Reperfusion arrhythmia andthe degree of residual stenosis had no significantinfluence upon the % peak LCI. (Fig. 3). The peakLCI levels ranged from 5.6 to 30.5 ng/ml and peakCPK-MBs ranged from 45 to 648 IU//(Table 1).

The correlation between peak LCI levels andSPECT-determined infarct size was good, with acorrelation of 0.76 (p<0.01, regression line by leastsquares method y=-3.31+1.53x). Peak CPK-MBscorrelated less satisfactorily with SPECT-determinedinfarct size, with a correlation of 0.71 (p<0.05,regression line by least squares method y=1.39+0.06x) (Fig. 4). The correlation between peak LCI

Vol. 6, No. 1, 1992 Original 45

Fig. 1 Short axial reconstructions from simultaneous thallium-201 chrolide (top) andtechnetium-99m pyrophosphate (bottom) SPECT acquisitions from patient 11. The thresholdlevel of thallium-201 (T1-201) was 30 % and that of technetium-99m pyrophosphate (Tc-99m PYP) was 70%. The uptake of T1-201 was reduced in the anterior and anterolateralwalls, and the uptake of Tc-99m PYP was observed in the same region. The infarct sizeobtained from Tc-99m PYP was 7.3 ml.

Fig. 2 Time course of serum myocardial light chain I (LCI) following acute myocardialinfarction in two patients. Serum LCI increased significantly after reperfusion and a prolongedincrease in LCI was noted. Upper panel, Case 7; lower panel, Case 6.

46 Hiroshi Yoshida, Mamoru Mochizuki, Kazuyuki Sakata, et al Annals of Nuclear Medicine

collateral flow reperfusion arrhythmia residual stenosis100

it 50Ca

ogood poor (+) (—) >_90% <90%

* not significant

Fig. 3 Comparison of the % peak LCI in the cases with and without collateral circulation,with and without reperfusion arrhythmia, and in the degree of residual stenosis. The % peakLCI was not affected by the presence of good collateral circulation, the presence of reperfu-sion arrhythmia or the degree of residual stenosis.

E

Ui

0.0.áá

5 10 15 20 25 30

peak myosin light chain (ng/ml)

ÉSi

0áá

1.39+0.06x

0.71 p<0.05

PEAK-CPKMB (IU /L)

Fig. 4 Correlation of infarct size calculated from tech-netium-99m pyrophosphate uptake on SPECT withpeak myosin light chain (upper) and peak CPK-MB(bottom). The correlation between the peak myosin lightchain level and SPECT-determined infarct size was good,with a correlation of 0.76 (p<0.01, regression line byleast squares method y= — 3.31-{-1.53x). Peak CPK-MBcorrelated less satisfactorily with SPECT-determined in-farct size, with a correlation of 0.71 (p<0.05, regressionline by least squares method y=1.39+0.06x).

levels and peak CPK-MBs was also good, with acorrelation of 0.83 (p<0.01).

DISCUSSION

Our data demonstrated that early serum LCI levelsunderwent reperfusion influence, but that the peakLCI levels obtained 3 to 7 days after the onset ofacute myocardial infarction reflected infarct size inpatients with successful reperfusion.

The size and location of infarcted tissue has animportant influence on patient mortality and mor-bidity. Several methods have been developed toestimate acute infarct size. The ECG is useful forthe diagnosis of acute myocardial infarction, but itis not quantitative. Serial and peak CPK-MB isdirectly related to infarct size, 6 but early contact withthe patient and serial blood samples are required forthis assay. Furthermore, the CPK-MB release ratewas accelerated and the recovery rate of CPK-MBinto the serum was increased in the presence ofcomplete reperfusion in dogs. 7 The estimation ofinfarct size by serial CPK-MB should therefore bedone with caution in a patient who has undergonecoronary reperfusion. Ejection fraction is an indirectmeasure of infarct size and a useful parameter indetermining post infarction prognosis.$ Howeverfactors other than the extent of myocardial necrosis,including the function of the nonischemic myocar-dium, the size of the ventricle, preload and afterloadof the left ventricle, heart rate, and drugs affect theejection fraction. In addition, previous myocardialscarring also influences the degree of depression of

=-3.31+1.53x

0.76 p<0.01

Vol. 6, No. 1, 1992 Original 47

the ejection fraction. So the ejection fraction has agood correlation with the clinical outcome in patientswho have suffered from myocardial infarction, butit is not suitable for estimating directly the infarctsize. Myocardial scintigraphy with T1-201 hasemerged as a noninvasive technique that aids in thedetection, localization, and quantification of myo-cardial necrosis. 9 Tomographic imaging techniquesovercome the geometric limitations of the planarscintigraphic methods. However, myocardial uptakeof T1-201 is reduced in the acute and previous necroticareas, so the acute infarcted area cannot be meas-ured by the extent of the perfusion defect of T1-201.Furthermore, the larger the infarct size, the moredifficult it is to trace the defect by manual techniquesor computerized planimetry.

Tc-99m PYP accumulates in acute necrotic myo-cytes and the myocardial uptake of pyrophosphatereflects myocardial necrosis. SPECT with Tc-99mPYP has been used to determine the size of myo-cardial necrosis. 10,11 A dual tracer SPECT techniquewith Tc-99m PYP and T1-201 enabled us to recordthallium-201 and technetium-99m pyrophosphateimages simultaneously and to compare both imagesin the same slices, so the localization and quantifica-tion of myocardial necrosis is much easier. Severalstudies have described an overestimation of infarctsize calculated by Tc-99m PYP in preparations oftemporary coronary occlusions followed by reperfu-sion, but Jansen reported that SPECT imaging withadequate threshold makes possible accurate localiza-tion and determination of infarct size when Tc-99mPYP was injected 90 min or more after reflow. 12 SoSPECT with Tc-99m PYP is attractive for the evalua-tion of acute infarct size.

Myosin light chains are bound to insoluble myosinheavy chains, whereas only a minor fraction existsas a cytosolic precursor pool of myosin synthesis.In myocardial infarction, myosin light chains aregradually released from myocytes. Nagai et al. andKatus et al. reported that the serum concentrationchanges in myosin light chains showed a biphasicpattern in acute myocardial infarction. An initialrise found at 6 to 18 h after the onset of pain reflecteda release from the cytosolic light chain, and a con-tinuous delayed increase detected up to the 10th dayafter the onset of pain corresponded to an ongoingbreakdown of the insoluble structural cardiac myosinlight chain. 13,14 Isobe et al. reported that the in-fluence of drastic changes in coronary flow soonafter the onset of acute myocardial infarction wouldbe expected to be minimal on the release of myosinlight chains. 5,15 However our study demonstratedthat before reperfusion the serum concentration ofLCI was within normal limits and immediately afterreperfusion the serum concentration of LCI signifi-

cantly increased, even within 6 hours from the onsetof acute myocardial infarction. The % peak LCIranged from 19 % to 83 %, which was not consider-ably influenced by collateral circulation, reperfusionarrhythmia or the degree of residual stenosis. But asignificant increase in LCI obtained after reperfusionmight reflect not only a release from the pool ofsoluble cytoplasmic myosin light chains but also arelease of structurally bound myosin light chainsfrom myofilament caused by proteolysis. Earlyrestoration of coronary blood flow facilitates thewashing out of both CPK-MB and myosin lightchains from the infarct myocardium. Washing outof myocardial myosin light chains release by effectivereperfusion may affect the early phase of the timecourse of myosin light chains. The amount of myosinlight chains released reflects myocardial necrosisestimated by left ventriculography in patients withsuccessful reperfusion or those treated with conven-tional therapy. 5 We also found a good correlationbetween the peak LCI level and the infarct sizeestimated by Tc-99m PYP accumulation in patientswith successful coronary reperfusion.

In the present study, we demonstrated that theearly serum LCI might be influenced by coronaryreperfusion but the peak LCI level reflected acutemyocardial necrosis in patients who underwent coro-nary reperfusion. An early and prolonged increasein LCI might be valuable for detecting the presenceof good reperfusion and evaluating myocardialnecrosis.

ACKNOWLEDGEMENT

We thank Mrs. Sanae Onoda for her expert secretarialassistance.

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