Assessment of coronary artery bypass graft patency by multidetector computedtomography and electron-beam tomography

L.H. Piers1, J. Dorgelo2, R.A. Tio1, G.A.J. Jessurun1, M. Oudkerk2 & F. Zijlstra11Department of Cardiology, University Hospital Groningen, The Netherlands; 2Department of Radiology,University Hospital Groningen, The Netherlands

Received 28 June 2004; accepted in revised form 4 November 2004

Key words: angiography, bypass, computed tomography, imaging

Abstract

This case report describes the use of retrospectively ECG-gated 16-slice multidetector computed tomog-raphy (MDCT) and electron-beam tomography (EBT) for assessing bypass graft patency in two patientswith recurrent angina after coronary artery bypass graft surgery. The results of each tomographic modalitywere compared to the findings of traditional coronary angiography. In the first patient MDCT showedocclusion of the left internal mammary artery (LIMA) and saphenous vein graft after the second anas-tomosis. Coronary angiography confirmed these findings. In the second patient EBT showed patency of theLIMA and saphenous vein graft. After the first anastomosis of the saphenous vein graft, the connectedvessel filled poorly. Coronary angiography confirmed both grafts to be patent, and detected an occlusiondistal to the first anastomosis. These findings support the evidence that both MDCT and EBT are suitabletechniques for establishing bypass graft patency by non-invasive means.

Abbreviations: CABG – coronary artery bypass graft surgery; EBT – electron-beam tomography; LAD – left

anterior descending coronary artery; LIMA – left internal mammary artery; MDCT – multidetector computed

tomography

Introduction

Many new diagnostic and treatment modalitiesaim to provide minimally invasive hardware toenhance operator and patient convenience. Non-invasive imaging techniques such as electron-beamtomography (EBT) and multidetector computedtomography (MDCT) have gained considerableinterest for the visualization of the coronary arterytree [1]. Albeit, traditional coronary angiographyis yet the ‘golden standard’, the aforementioneddiagnostic tools may add value to the overall ap-proach of subjects with coronary artery disease.We will present two cases to illustrate the clinicalimplementation in daily cardiovascular care.

Case report

Case 1

A 55-year-old-man was evaluated because of pro-gressive angina despite optimal drug therapy(Figure 1). An exercise testing suggested myocar-dial ischemia. He had undergone uncomplicatedcoronary artery bypass graft (CABG) surgery15 years before. The left internal mammary artery(LIMA) was anastomosed to the left anteriordescending coronary artery (LAD), and a saphe-nous vein graft to the second diagonal, anterolat-eral, left posterolateral branches and the posteriordescending coronary artery.

The International Journal of Cardiovascular Imaging (2005) 21: 447–451 � Springer 2005DOI 10.1007/s10554-004-6136-x

The patient was scheduled for a diagnosticcatheterization. One-day prior to coronary angi-ography, he underwent contrast enhanced 16-sliceMDCT to assess patency of the grafts. MDCT wasperformed using a 16-slice scanner (‘Sensation 16’,Siemens Medical Solutions, Forchheim, Ger-many). After bolustiming, 140 ml contrast agent(Iodixanol 270 mg/ml) was injected into the cu-bital vein at 4 ml/s which was followed by a 50 mlsaline chaser with a similar flow rate. Next, avolume data set was acquired (collimation12 · 0.75 mm, table feed per gantry rotation2.8 mm, tube voltage and current 370 mA and120 kV, respectively). Using ECG-synchronizationthe data were reconstructed at a point in the

RR-interval with the least motion, using a slicethickness of 1.0 mm. The mean heart rate was57.6 bpm (range: 56–60 bpm) during scanning.Two observers evaluated the reconstructed dataseton an off-line workstation (Vitrea 3.1; Vital Ima-ges, Plymouth, MN).

The scan showed that the LIMA was not patent.Surgical clips identified the position where theLIMA should be located, however, no contrastfilling was seen, which indicated a proximalocclusion. From the LAD a small distal portion ofthe LIMA was visible by retrograde filling. At theanterior side of the aorta the venous bypass graftwas located with its anastomoses to the seconddiagonal and anterolateral branches. The graft

Figure 1. This patient received a left internal mammary artery bypass graft, which was anastomosed to the left anterior descending

coronary artery, and a saphenous vein graft to the second diagonal, anterolateral, left posterolateral branches and the posterior

descending coronary artery. (A) Volume rendering image of the heart, coronary arteries and bypass grafts acquired by contrast

enhanced multidetector computed tomography in which the LIMA showed to be occluded. Surgical clips (open arrow) were visible,

indicating the course of the occluded graft. The venous graft was visible up to and including the second anastomosis; second diagonal

(closed arrow) and anterolateral branches (closed arrowhead) were clearly visible. An occlusion was located after the second anas-

tomosis (open arrowhead). (B) Coronary angiography displayed surgical clips of the LIMA (open arrow). However, no filling of the

graft was visible. (C) The LAD (open arrow) was filled retrogradely by the second diagonal branch (closed arrow). After the second

anastomosis a thrombus (open arrowhead) was visible on the coronary angiogram. Both the second diagonal and the anterolateral

(closed arrowhead) branches were visible.

448

appeared to be occluded after the second anasto-mosis. Diffuse calcification was visible in the nativeright coronary artery, resulting in a significantstenosis of the mid-segment.

Similar to the scan, coronary angiographyshowed an occlusion of the LIMA. Furthermore, athrombus was visible in the saphenous vein graftafter the anastomosis to the anterolateral branch.The LAD was filled retrogradely by the seconddiagonal branch. A type C lesion was present inthe right coronary artery.

Hereafter, a second CABG was performed. Theright internal mammary artery was connected to

the LAD and anterolateral branch, and the leftradial artery was anastomosed to the right coro-nary artery. The patient was discharged on day 7after an uneventful recovery.

Case 2

A 60-year-old man was referred to our hospitalbecause of typical anginal complaints (Figure 2).Echocardiographic evaluation had demonstrateda moderate left ventricular function. CABG hadbeen performed three-and-a-half years earlierbecause of ischaemic heartfailure. A LIMA was

Figure 2. Patient with a left internal mammary artery bypass graft to the left anterior descending artery and a saphenous vein graft

anastomosed to the diagonal, anterolateral and obtuse margonal branches. (A) Three-dimensional reconstruction of the heart obtained

with electron-beam tomography showed patency of the LIMA (closed arrows). Due to presence of surgical clips (closed arrowhead),

the anastomosis to the LAD could not be evaluated. (B) Three-dimensional cardiac reconstruction obtained with electron-beam

computed tomography. The saphenous vein graft was clearly visible (open arrows), as well as the anterolateral and obtuse marginal

branches (open and closed arrowhead, respectively). The course of the diagonal branch was not visualized (closed arrow). (C)

Coronary angiography confirmed the patency of the LIMA (closed arrow) anastomosed to the LAD (closed arrowhead). (D) Coronary

angiography showed patency of the saphenous vein graft (open arrow). The proximal part of the diagonal branch filled retrogradely

with contrast (open arrowhead), implying an occlusion distal to the anastomosis.

449

connected to the LAD and a saphenous vein graftto the diagonal, anterolateral and obtuse mar-ginal branches. The electrocardiogram showedcharacteristic abnormalities, compatible withischemia. A diagnostic coronary angiography wasscheduled.

One day prior to the coronary angiography, anEBT with contrast was performed, using a dualslice scanner (E-speed, Imatron, San Francisco,CA). First the contrast agent transition time wasdetermined. Second 100 ml contrast agent (Iodix-anol 270 mg/ml) was injected in the cubital vein at4 ml/s. After the assessed transition time, the dataset was acquired with a slice thickness of2 · 1.5 mm. The prospectively ECG-triggeredscan was performed at 54% of the RR-interval ofeach heartbeat in end-inspiratory breathhold. Themean heart rate was 77.9 bpm (range: 75–82 bpm)during scanning. The data were transferred to aworkstation (Vitrea 3.1; Vital Images, Plymouth,MN) and reviewed by two observers.

The EBT scan showed patency of the LIMA.The anastomosis to the LAD was difficult to assessdue to interference by surgical clips. After the firstanastomosis of the saphenous vein graft, contrastfilling of the diagonal branch was poor. The an-terolateral and marginal obtuse branches wereadequately filled and the anastomoses to thesecoronary vessels were patent.

Coronary angiography showed a functionalLIMA and saphenous vein graft. However, onlyretrograde filling of the diagonal branch was visi-ble. This implicates that the anastomosis to thediagonal branch was patent and the occlusion waslocated distal to the anastomosis.

Discussion

We exemplified the clinical implementation ofEBT and MDCT with two cases. Both non-invasive visualization techniques correctly as-sessed venous as well as arterial bypass graftpatency. Diagnostic benefit of coronary angiog-raphy and MDCT or EBT in both patients wasidentical.

Both figures show comparable imaging quality,even though there are several differences between

both CT techniques [2]. A first difference betweenMDCT and EBT is that MDCT scans in a helicalway and EBT in a sequential way. Consequentlyimages made by MDCT are smoother than madeby EBT. Second, the partial resolution of the 16-slice MDCT is much higher than that of the EBT.On the contrary, the temporal resolution of theEBT is much higher compared to that of MDCT.Fourth, MDCT and EBT differ in radiationburden. The radiation dose of an EBT scan(approximately 1 mSv) is much lower than of aMDCT scan (approximately 10 mSv in case of 4-slice scanning technique).

The implementation of computed tomography todetect patency of coronary bypass grafts, has firstbeen reported in the early 1980s [3]. In the last dec-ade, several studies showing the usefulness of 4-sliceMDCT to assess bypass graft patency, demon-strated a sensitivity and specificity of 67–100% and96–100%, respectively [4–8]. Studies evaluatingEBT angiography showed similar results, with asensitivity of 98–100% and specificity of 92–100%[9–11]. Recently, two studies reported on thepractical utility of 16-slice MDCT angiography forevaluation of bypass grafts [12, 13].

Overall, 4-slice MDCT assessment of venousgrafts was superior than arterial grafts, becauseimage quality is reduced by smaller vessel sizeand the presence of foreign bodies, such as sur-gical clips [8]. These findings correspond with theuse of EBT [10, 14]. With these techniques, clin-ical assessment of coronary arteries was limited tolarger vessels with a diameter ‡2.0 mm. Thislimitation of its scope of use has been overcomewith the new generation MDCT scanners, as aresult of higher spatial resolution [15]. Optimalevaluation of the coronary circulation is yet re-stricted by artifacts caused by motion artifacts,extreme calcifications and surgical clips [13, 15].Also, the competition of flow between bypassgraft and native coronary arteries cannot beassessed.

One major opportunity for cardiologists to usethese non-invasive diagnostic tools in subjects withbypass grafts arises from the technical inability toengage the grafts percutaneously. Extremelyangulated, calcified and obstructive cardiovasculardisease is susceptible to trauma, despite meticulous

450

manipulation of intravascular catheters. This mayresult in subclinical cerebrovascular accidentscaused by embolic particles [16].

Both MDCT and EBT are feasible techniquesfor assessment of coronary bypass graft patency.Competition between both modalities may resultin further improvements of spatial and temporalresolutions. This evolution will enhance theability of CT scanners to produce betterdiagnostic imaging of the beating heart, and thusencourage its use for the diagnosis of cardiovas-cular disease. Computed tomography couldespecially be a useful technique for visualizationof bypass grafts in patients with a less typicalpresentation of an acute closure, no typical an-gina or ECG changes suggestive of ischaemia, oreven for follow up of the bypass graft. Futurestudies may clarify the exact clinical role of non-invasive techniques in addition to quantitativecoronary angiography to assess graft patency insymptomatic patients.

References

1. Budoff MJ, Achenbach S, Duerinckx A. Clinical utility of

computed tomography and magnetic resonance techniques

for noninvasive coronary angiography. J Am Coll Cardiol

2003; 42(11): 1867–1878.

2. Achenbach S, Giesler T, Ropers D, et al. Comparison of

image quality in contrast-enhanced coronary-artery visual-

ization by electron beam tomography and retrospectively

electrocardiogram-gated multislice spiral computed tomog-

raphy. Invest Radiol 2003; 38(2): 119–128.

3. Moncada R, Salinas M, Churchill R, et al. Patency of

saphenous aortocoronary-bypass grafts demonstrated by

computed tomography. N Engl J Med 1980; 303(9): 503–

505.

4. Burgstahler C, Kuettner A, Kopp AF, et al. Non-invasive

evaluation of coronary artery bypass grafts using multi-slice

computed tomography: initial clinical experience. Int J

Cardiol 2003; 90(2–3): 275–280.

5. Nieman K, Oudkerk M, Rensing BJ, et al. Coronary angi-

ography with multi-slice computed tomography. Lancet

2001; 357(9256): 599–603.

6. Yoo KJ, Choi D, Choi BW, Lim SH, Chang BC. The

comparison of the graft patency after coronary artery by-

pass grafting using coronary angiography and multi-slice

computed tomography. Eur J Cardiothorac Surg 2003;

24(1): 86–91.

7. Ropers D, Ulzheimer S, Wenkel E, et al. Investigation of

aortocoronary artery bypass grafts by multislice spiral

computed tomography with electrocardiographic-gated im-

age reconstruction. Am J Cardiol 2001; 88(7): 792–795.

8. Silber S, Finsterer S, Krischke I, Lochow P, Muhling H.

Noninvasive angiography of coronary bypass grafts with

cardio-CT in a cardiology practice. Herz 2003; 28(2): 126–

135.

9. Achenbach S, Moshage W, Ropers D, Nossen J, Bachmann

K. Noninvasive, three-dimensional visualization of coro-

nary artery bypass grafts by electron beam tomography. Am

J Cardiol 1997; 79(7): 856–861.

10. Ha JW, Cho SY, Shim WH, et al. Noninvasive evaluation

of coronary artery bypass graft patency using three-

dimensional angiography obtained with contrast-enhanced

electron beam CT. Am J Roentgenol 1999; 172(4): 1055–

1059.

11. Lu B, Dai RP, Jing BL, et al. Evaluation of coronary artery

bypass graft patency using three-dimensional reconstruction

and flow study on electron beam tomography. J Comput

Assist Tomogr 2000; 24(5): 663–670.

12. Dewey M, Lembcke A, Enzweiler C, Hamm B, Rogalla P.

Isotropic half-millimeter angiography of coronary artery

bypass grafts with 16-slice computed tomography. Ann

Thorac Surg 2004; 77(3): 800–804.

13. Gurevitch J, Gaspar T, Orlov B, et al. Noninvasive evalu-

ation of arterial grafts with newly released multidetector

computed tomography. Ann Thorac Surg 2003; 76(5): 1523–

1527.

14. Rensing BJ, Bongaerts A, van Geuns RJ, van Ooijen P,

Oudkerk M, de Feyter PJ. Intravenous coronary angiogra-

phy by electron beam computed tomography: a clinical

evaluation. Circulation 1998; 98(23): 2509–2512.

15. Ferencik M, Moselewski F, Ropers D, et al. Quantitative

parameters of image quality in multidetector spiral com-

puted tomographic coronary imaging with submillimeter

collimation. Am J Cardiol 2003; 92(11): 1257–1262.

16. Omran H, Schmidt H, Hackenbroch M, et al. Silent and

apparent cerebral embolism after retrograde catheterisation

of the aortic valve in valvular stenosis: a prospective,

randomised study. Lancet 2003; 361(9365): 1241–1246.

Address for correspondence: L.H. Piers, Department of Cardi-

ology, University Hospital Groningen, Hanzeplein 1, 9700 RB

Groningen, The Netherlands

E-mail: l.h.piers@thorax.azg.nl

451