Preoperative and postoperative technetium-99m pyrophosphate myocardial scintigraphy in the assessment of operative infarction in coronary artery surgery

Preoperative and postoperative technetium-99m pyrophosphate myocardial scintigraphy in the assessment of operative infarction in coronary artery surgery The incidence of operative myocardial infarction was assessed by electrocardiogram (ECG) and technetium-vvm pyrophosphate (9!J/IITc_PyP) myocardial scintigrams in 89 consecutive patients undergoing coronary artery bJ1JaSS grafting (CARG), Myocardial scintigrams were performed 011 the day before operation and repeated 2 to 3 days postoperativelv. All pari ellis survived operation, with three in-hospital deaths not related 10 myocardial infarction (mortality rate 3 percent]. Operative infarction was assessed to have occurred in four (~r 89 pari ellis (4 percent}. Two had nell' Q 11'£11'1'.1' and positive scintigrams: one, major ST-T It'{l\'e changes and a positive scintigram; and the fourth, new Q Wl/l'es without a positive scintigram. Threefurther pari ellis (3 percent) had Q Wl/l'es and positive scintigrams postoperativelv, but myocardial infarction was evolving be/fire anesthesia and operation. Twenty-seven of 89 pari ellis (30 percent) were found to have abnormal scintigrams preoperatively, In two patients, both operated upon with evolving myocardial infarction, the scintigram was worse postoperatively, In 13 patients the scintigram was improved after operation. In 12 patients (13 percent) the abnormal preoperative scintigram was unchanged after operation. Preoperative and postoperative myocardial scintigrams and ECG's must be compared to assess the incidence of operative myocardial infarction in pari ellis undergoing CARG.

J. Hung, M.B., F.R.A.C.P.,* D. T. Kelly, M.B., F.R.A.C.P., F.A.C.C.,** A. F. McLaughlin, M.B., F.R.A.C.P.,*** R. F. Uren, M.B., F.R.A.C.P.,*** and D. K. Baird, B.Sc.(Med), M.B., B.S., F.R.A.C.S., F.A.C.S.,****

Camperdown, N.S.

w.. Australia

T

he reported incidence of myocardial infarction after coronary artery surgery varies from five to forty percent. 1 The incidence from different surgical centers may vary because of case selection, technical expertise, or according to the methods of assessing myocardial damage. New Q waves on the electrocardiogram (ECG) usually indicate infarction, but there are noted

From the Hallstrom Institute of Cardiology and the Departments of Cardiothoracic Surgery and Nuclear Medicine, Royal Prince Alfred Hospital, Camperdown. New South Wales, Australia, Supported in part by the Postgraduate Medical Foundation. University of Sydney. Received for publication Oct, 25, 1978, Accepted for publication Feb, 5, 1979. Address for reprints: D. T. Kelly, Scandrett Professor of Cardiology. Hallstrom Institute of Cardiology. Royal Prince Alfred Hospital, Camperdown, N, S. W, 2050, Australia. *Research Fellow, Hallstrom Institute of Cardiology. **Scandrett Professor of Cardiology, University of Sydney, ***Physician, Nuclear Medicine, Royal Prince Alfred Hospital. ****Surgeon. Cardiothoracic Surgery, Royal Prince Alfred Hospital.

68

exceptions." Postoperative ST-T wave changes are common and may be due to pericarditis, electrolyte disturbance, or digitalis therapy. Cardiac enzymes, including the myocardium-specific creatine phosphokinase isoenzyme, MB-CPK, are commonly found to be elevated after cardiac operations without myocardial infarction.": 4 Scintigraphy with technetium-99m pyrophosphate (99mTc_pyp) has been used to assess myocardial damage independently following cardiac surgery":" and usually reveals a higher incidence than that indicated by ECG. 5 • 6 Some patients with myocardial ischemia will have an abnormal scintigram preoperatively," and comparison of the preoperative and postoperative scintigrams is necessary before operative infarction can be diagnosed. In order to assess the incidence of operative infarction, we obtained ECG's and 99mTc_pyp myocardial scintigrams before and after operation in 89 consecutive patients undergoing coronary artery bypass grafting (CABG).

0022-5223/79/070068+06$00,60/0 © 1979 The C. V. Mosby Co,

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Operative infarction in coronary bypass

Number 1 July, 1979

NORMAL

POSITIVE

69

2 +DIFFUSE

Fig. I. ""I11Tc-PyP scintigrams in the left anterior oblique (LAO) projection. A normal, a positive, and an equivocal (2+ diffuse) scintigram are illustrated.

Methodology fl9mTc_pyp myocardial scintigraphy was performed by a technique previously described. t Imaging was commenced 90 minutes after intravenous injection of 20 mCi of 9f1mTc_pyp (Skeltec II AAEC) with an Ohio Nuclear mobile gamma camera fitted with a highresolution collimator wheeled to the patient's bedside. A total of 400,000 counts was obtained in the anterior, left anterior oblique, and left lateral positions and recorded on Polaroid film. The scintigram was performed within I day before operation and was repeated 2 to 3 days after operation. Two independent observers reported on the scintigrams without prior knowledge of the patient's clinical history. If disagreement occurred (6 percent of scintigrams), a third independent observer arbitrated. The myocardial 99mTc_pyp uptake was graded on standard criteria in which 0 and 1+ represented zero and equivocal uptake and 2+,3+, and 4+ represented definite uptake less than, equal to, and greater than bone, respectively. H In addition, the uptake was reported as either focal (localized) or diffuse (nonlocalized). Myocardial scintigrams with zero or I + uptake were considered negative for myocardial infarction. Scintigrams showing a 2+ diffuse pattern were considered equivocal, as the nonlocalized uptake of fl9mTc_Pyp was difficult to separate from residual blood pool activity.": 9 All other scintigrams showing a 2+ to 4+ uptake (focal or diffuse) were considered positive for myocardial infarction. Fig. I illustrates a normal, a positive, and an equivocal scintigram in the left anterior oblique view. ECG. A standard twelve-lead ECG was performed preoperatively, daily postoperatively for 3 days, and thereafter weekly. Myocardial infarction was diagnosed if new pathological Q waves appeared in the postoperative ECG, but major persistent ST-T wave

changes and conduction block developing postoperatively were also noted. Patient population. Eighty-nine consecutive patients, 82 men and seven women, mean age 52 years (range 37 to 70 years), underwent CABG between June and November, 1977. This group consisted of 45 patients (51 percent) with unstable angina pectoris and 44 whose angina was stable. Previous myocardial infarction was documented in 51 patients (57 percent). Three patients (3 percent) had uncontrolled chest pain with evolving myocardial infarction at the time of operation. Eleven patients (12 percent) had congestive heart failure (CHF). At coronary arteriography, single-vessel disease (2::70 percent diameter stenosis) was present in 12 patlents, double-vessel disease in 23, triple-vessel disease in 45, and left main coronary artery disease (2::50 percent diameter stenosis) with accompanying other major vessel disease in nine. The number of aorta-coronary bypass grafts inserted ranged from one to six, averaging 3.3 per patient. In addition, a left ventricular aneurysm was resected in two patients. Cardiopulmonary bypass was established with a bubble oxygenator, hemodilution to 30 percent, and hypothermia to 28° C. Cardiac fibrillation was induced electrically and allowed to continue while all the distal anastomoses were performed. The aorta was not cross-clamped and total cardiopulmonary bypass was maintained at a mean arterial pressure of 40 to 50 mm. Hg. As the proximal anastomoses were performed, the patient was rewarmed and the heart defibrillated. Results Preoperative. Before operation an abnormal myocardial scintigram was found in 27 of 89 patients (30 percent). Eleven patients (Nos. 1 to 11) had positive scintigrams and 16 patients (Nos. 12 to 27) had

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Hung et al.

Table I. Coronary artery graft surgery: Abnormal preoperative or postoperative 99I11TC_PyP scintigrams ECG Patient No.*

Age (yr.)

Angina pectoris

I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

68 66 51 43 43 53 52 56

Chronic Unstable Chronic Chronic Unstable Unstable Unstable Unstable Unstable Chronic Unstable Unstable Chronic Unstable Chronic Unstable Unstable Unstable Chronic Unstable Chronic Unstable Unstable Chronic Chronic Unstable Unstable Unstable Chronic Unstable Unstable Chronic

64 46 51

64 56 62 58 49 59 58 45 47 41 64 46 52 44 53 49 40 38 54 53 50

I

CHF

CAD

Preop.

CHF

4 4 3 2 3 2 3 3 4 2 3 3 3 3 3 3 3 3 2 3 2 2 4

Old ant. infarction Recent info infarction Old ant. infarction Minor T Old ant. infarction Normal Recent ant. infarction Recent info infarction Old ant. infarction Old ant. infarction Normal Recent inf. infarction Old ant. infarction Old info infarction Minor T Recent ant. infarction Recent inf. infarction Minor T Old ant. infarction Recent info infarction Normal Old info infarction Recent ant. infarction Old ant. infarction Normal Major T (CPK elevated) Major T (CPK elevated) Major T (CPK elevated) Old ant. infarction Recent ant. infarction Normal Old ant. infarction

CHF CHF CHF

CHF

CHF CHF

I

2 2 3 4 3 2 3 3

Scintigram

Postop.

CABG

Preop.

No change Minor T Minor T No change Minor T Minor T Minor T Major T No change Minor T Minor T Minor T No change Minor T No change No change Major T Major T No change Minor T Minor T No change Minor T No change Minor T Acute inf. infarction Acute inf. infarction Acute inf. infarction Acute inf', infarction Acute ant. infarction Major T Acute ant. infarction

XI x3 x2 x3 x4 x3 x4 x5 x4 xz + LVA x4 x3 x4 x4 x3 x5 x3 x4 x I + LVA x6 x3 x2 x4 x I x3 xl x4 x5 x3 x2 x3 x3

2+ F 2+ F 3+ F 2+ F 3+ F 2+F 3+ F 3+ F 2+ F 3+ F 2+ F 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 2+ D 1+ 0 1+ 1+ 1+

I

Postop. 2+ F 2+ F HF 2+ F 2+ F 2+ F 2+ F 2+ F 1+ 0 0 2+ D 2+ D 2+ D 2+ D 1+ 1+ 1+ 1+ 1+ 0 0 0 0 0 HF 3+ F 4+ F 3+ F 4+ F HF 1+

Legend: CHF, Congestivehean failure. CAD, Coronaryartery disease: I to 3 represents numberof vesselswith «70 percentdiameterstenosis;4 represents in addition «50 percent stenosis of left main coronaryartery. ECG, Electrocardiogram. CABG, Coronaryartery bypassgrafts x numberdone. Recent, Less than 3 months.Old, Greater than 3 months. Ant.. Anterior. Inf., Inferior. LVA, Left ventricularaneurysmectomy. T, ST-T wave abnormalities. D, Diffuse. F, Focal. *Patienlli are numbered by scintigram results and not by order in consecutive series.

equivocal scintigrams (2+ diffuse pattern), Data on the patients are given in Table I, Myocardial infarction was previously documented in 18 of these 27 patients. In eight the myocardial infarction was within 3 months prior to operation, and in seven it was a large infarction associated with CHF, In the patients (Nos, I to I I) with preoperative focal abnormality on the scintigram, the site of scintigraphic uptake corresponded to the infarction site (Q waves) on the ECG, except in one patient in whom there was disagreement in site and in two in whom Q waves were not present on the ECG, Angina pectoris was unstable in 17 of the 27 patients with positive or equivocal preoperative scintigrams. Of four patients with stable angina pectoris but without a previous myocardial infarction, one had a positive scintigram and the other three had equivocal scintigrams.

In three patients (Nos. 26 to 28) operated upon for uncontrolled chest pain, evidence of evolving myocardial infarction was present at the time of operation. All three had major inferior and anterior ST-T wave changes on the ECG and elevated CPK within 6 hours prior to operation, The preoperative myocardial scintigram was negative in one and equivocal in the other two. Postoperative. Four patients (Nos. 29 to 32) had a myocardial infarction after CABG. In three the scintigram changed from negative preoperatively to positive postoperatively, Two of these patients showed new Q waves and the other, major ST-T wave changes consistent with subendocardial infarction, One patient (No, 32) with a negative scintigram postoperatively had new Q waves on ECG suggesting myocardial infarction. In each patient myocardial infarction occurred in the terri-

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Operative infarction in coronary bypass

Number 1 July, 1979

PRE-OP.

ECG

POSf-OP.

ECG

11

11--.

V2

J\

-i

'--

IA

II--il..- V2

III

PRE-OP.

12+DIFFUSEJ

7 I

POST-OP.

......... r' '-...

W..J('-

13+FOCALJ

Fig. 2. Patient 27: Preoperative and postoperative electrocardiograms (ECC' s) and 99mTc_Pyp scintigrams in the left anterior oblique (LAO) projection. Preoperative ECG shows evolving inferior infarction and anterior ischemia. The scintigram is equivocal with 2+ diffuse uptake. The postoperative ECG shows inferior infarction and resolution of anterior ischemia. The scintigram is positive with 3+ focal uptake. tory of a stenosed vessel that had been grafted. Q waves developed postoperatively in the three patients (Nos. 26 to 28) with evolving infarction at the time of operation. Scintigrams which preoperatively were negative in one and equivocal in the other two became positive postoperatively in all three. Fig. 2 shows the preoperative and postoperative ECG's and scintigrams in Patient 27. The preoperative ECG shows an evolving inferior myocardial infarction and anterior ischemia. The preoperative scintigram is equivocal with a 2+ diffuse uptake. The postoperative ECG shows an inferior transmural infarction and resolution of anterior ischemia. The scintigram is now positive with a 3 + focal uptake corresponding to the site of infarction. In the 27 patients with an abnormal preoperative scintigram, the study became negative after operation in 13, including three (Nos. 9 to II) with a positive preoperative scintigram and 10 (Nos. 16 to 25) with an equivocal preoperative scintigram. The study was still abnormal but unchanged after operation in 12 patients, including eight (Nos. I to 8) with a positive preoperative scintigram and four (Nos. 12 to 15) with an equivocal preoperative scintigram.

In the remaining two patients (Nos. 26 and 27) with an abnormal preoperative scintigram, the study worsened from equivocal preoperatively to positive postoperatively. In both, myocardial infarction was evolving prior to operation. Major persistent ST-T wave changes occurred after operation in six patients, associated with development of a positive postoperative scintigram in one patient only. In no case did a major conduction block develop postoperatively. Hospital deaths. Three patients (3 percent) who did not have ECG or scintigraphic evidence of operative infarction died during in-hospital convalescence. One patient, who had serious ventricular tachyarrhythmias preoperatively, died from sudden ventricular fibrillation on the third postoperative day. Another patient with CHF preoperatively died from CHF and renal failure 20 days after operation. The third patient died 15 days after operation of late pericardial tamponade while receiving anticoagulants. Discussion The incidence of myocardial infarction after CABG is difficult to assess, because the ECG 2 and cardiac

72

Hung et al.

enzymes have limited diagnostic specificity. a. ~ The myocardium-specific creatine phosphokinase isoenzyme, MB-CPK, was not measured in this study, because it commonly is elevated following CABG without myocardial infarction.P- ~. 6 99mTc_pyp myocardial scintigraphy has been used to assess the myocardial It often indidamage independently after CABG.~-6 cates more frequent infarction than new Q waves on ECG.5.6 Platt and associates" found a 31 percent incidence of positive myocardial scintigrams postoperatively as compared to a 12 percent incidence of new Q waves, and Righetti and associates" reported a 24 percent incidence of positive myocardial scintigrams as compared to a 15 percent incidence of new Q waves. In a number of surgically treated patients with apparent scintigraphically documented infarction, the scintigram may have been abnormal preoperatively. 5Thirty percent of our patients had an abnormal preoperative scintigram. The high incidence reflects the frequency of unstable angina pectoris, recent myocardial infarction, and large myocardial infarction with CHF or left ventricular aneurysm in our operative series. Abnormal 99mTc_pyp uptake has been reported to occur in these situations. H Operative myocardial infarction is indicated on scintigraphy if a negative preoperative scintigram changes to positive after operation or if an initial abnormal uptake intensifies or appears at another site postoperativeIy. By these criteria, scintigraphy indicated operative myocardial infarction in only three patients in our series. In 13 percent of our patients, operative infarction could be excluded even though an abnormal myocardial scintigram was present postoperatively, because the scintigram and ECG were not significantly changed from those before operation. Scintigram interpretation. Interobserver difference occurred in 6 percent of cases in this series. This disagreement was found mainly in the diffuse I + to 2 + category, as one observer consistently showed a lower threshold than the other. The arbiter resolved this difference to a 2+ diffuse scintigram, and as this was not regarded as positive evidence for infarction, the results were not affected. Equivocal scintigrams. If the 2+ diffuse pattern after operation is routinely accepted as positive for infarction, it will increase the number of apparent scintigraphically documented infarctions.": 6 This pattern commonly is reported in subendocardial infarction 10 and unstable angina pectoris, 11 but Prasquier and associates 12 found a 13 percent incidence of this pattern in patients with normal hearts. In such a case, this pattern probably reflects activity in the blood pool.

The Journal of Thoracic and Cardiovascular Surgery

This pattern of 99mTc_pyp uptake postoperatively was thus regarded as equivocal, and comparison with the preoperative scintigram and ECG was made before infarction was diagnosed. In the four patients with an equivocal scintigram postoperatively, the study was similar prior to operation and their ECG's were unchanged. Operative infarction was therefore reasonably excluded. Most commonly, an equivocal scintigram preoperatively became negative postoperatively (10 of 16 patients). The significance of this change is not clear. However, since many of these patients were operated upon for unstable angina pectoris, it may represent reversal of myocardial ischemia. In only three of I I patients, one of whom had resection of a left ventricular aneurysm, did a preoperatively positive scintigram become negative after operation. Operative infarction. Comparison of the preoperative and postoperative ECG's and myocardial scintigrams indicated that four of 89 patients (4 percent) had operative myocardial infarction. When it occurred, infarction was confined to the territory of a grafted vessel. Both the distal vessel disease and the technical adequacy of the graft appeared to determine operative infarction. Three patients (3 percent) operated upon for uncontrolled chest pain had evolving infarction confirmed by ECG and enzyme studies within 6 hours prior to operation. Uptake of 99mTc_pyp is usually not seen until 12 hours after acute myocardial infarction, t:l and this delay is thought responsible for the initial negative preoperative scintigram in one of these three patients. The other two patients with an initial equivocal scintigram had major inferior and anterior ST-T changes on ECG, and the 2+ diffuse scintigraphic uptake suggested subendocardial infarction.'? Although myocardial infarction in these three patients may be termed perioperati ve , it was not due to anesthesia or the operative procedure and should not be called an operative complication. Evolving infarction should be excluded by ECG and enzyme studies prior to anesthesia in patients operated upon urgently for unrelieved chest pain, because the duration of infarction may be insufficient for uptake of 99mTc_pyp to occur in the damaged tissue prior to operation. The incidence of operative infarction in our series is lower than that reported by other series utilizing scintigraphy, in which operative infarction rates from 16 to 31 percent have been reported.":" Since the high incidence in these series did not appear to affect their postoperative results adversely, as would be expected, 1 the operative infarction rate may have been overdiagnosed

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Operative infarction in coronary bypass

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July, 1979

by scintigraphy. The recognition of evolving infarction prior to operation and positive or equivocal scintigrams postoperatively that do not appear to be associated with infarction may help to determine the true operative incidence of infarction. The diagnostic specificity of scintigraphy in patients undergoing CABG is improved by preoperative scintigraphy, so that preoperative and postoperative scintigrams can be compared. Patients with an abnormal scintigram which is unchanged after operation can be excluded and the interpretation of the difficult equivocal pattern facilitated. Operative infarction was thereby excluded in 13 percent of patients in our series with abnormal postoperative scintigrams.

Conclusions I. In 89 patients undergoing CABG the hospital mortality rate was 3 percent and the incidence of operative myocardial infarction was 4 percent as assessed by scintigraphic and ECG criteria. 2. Thirty percent of patients were found to have abnormal 99mTc_pyp myocardial scintigrams preoperatively, and in 13 percent the sci ntigram was sti II abnormal but not worse after operation. 3. Preoperative and postoperative myocardial scintigrams must be compared to assess the incidence of operative infarction, and care must be taken to ensure that infarction has not occurred prior to operation.

5

6

7

8

9

10

II

REFERENCES Mundth ED. Austen WG: Surgical measured for coronary heart disease. N Engl J Med 293:75-80. 1975 2 Bassan MM. Oatfield R. Hoffman I, Matloff J. Swan HJC: New Q waves after aortocoronary bypass surgery. N Engl J Med 290:349-353. 1974 3 Alderman EL, Matloff HJ. Shumway NE, Harrison DC: Evaluation of enzyme testing for the detection of myocardial infarction following direct coronary surgery. Circulation 48:135-140. 1973 4 Klein MS. Coleman RE. Weldon CS. Sobel BE. Roberts R: Concordance of electrocardiographic and scintigraphic

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criteria of myocardial injury after cardiac surgery. J THORAC CARDIOVASC SURG 71 :934-937, 1976 Platt MR. Parkey RW. Willerson JT, Bonte FJ, Shapiro W, Sugg WL: Technetium stannous pyrophosphate myocardial scintigrams in the recognition of myocardial infarction in patients undergoing coronary artery rev ascularization. Ann Thorac Surg 21:311-317. 1976 Righetti A. Crawford MH. O'Rourke RA. Hardarson T, Shelbert H, Daily PO. Deluca M. Ashburn W, Ross J: Detection of perioperative myocardial damage after coronary artery bypass graft surgery. Circu lation 55: 173-178, 1977 Kelly DT. Bautovich G, Crocker E. Mclaughlin A. Morris JG: 'Hot spot' myocardial scanning. Experiences with a mobile nuclear camera in a coronary care unit. Med J Aust 2:519-522, 1977 Marcus ML, Kerber RE: Editorial. Present status of m 99 technetium pyrophosphate infarct scintigram. Circulation 56:335-339, 1977 Berman OS. Amsterdam EA. Hines HH, Salel AF, Bailey GJ. Denardo GL, Mason DT: A new approach to the interpretation of technetium-99m-pyrophosphate scintigraphy in the detection of acute myocardial infarction. Clinical assessment of diagnostic accuracy. Am J Cardiol 39:341-346. 1977 Willerson JT, Parkey RW. Bonte FJ, Meyer Sl., Stokely EM: Acute subendocardial myocardial infarction in patients. Its detection by technetium-99m stannous pyrophosphate myocardial scintigrams. Circulation 51 :436441, 1975 Donsky MS. Curry GC, Parkey RW. Meyer SL, Bonte FJ, Platt MR. Willerson JT: Unstable angina pectoris. Clinical angiographic , and myocardial scintigraphic observations. Br Heart J 38:257-263. 1976 Prasquier R, Taradash MR. Botvinick EH. Shames OM. Parmley WW: The specificity of the diffuse pattern of cardiac uptake in myocardial infarction imaging with technetium-99m stannous pyrophosphate. Circulation 55: 61-66, 1977 Willerson JT. Parkey RW. Bonte FJ, Meyer st., Atkins JM. Stokely EM: Technetium stannous pyrophosphate myocardial scintigrams in patients with chest pain of varying etiology. Circulation 51:1046-1052, 1975