414 AJR:189, August 2007

AJR 2007; 189:414–419

0361–803X/07/1892–414

© American Roentgen Ray Society

Mueller et al.Cardiac CTA After Bypass Surgery

C a rd i a c I m ag i n g • O r i g i n a l R e s e a rc h

Cardiac CT Angiography After Coronary Bypass Surgery: Prevalence of Incidental Findings

Jeffrey Mueller1,2

Jean Jeudy1

Robert Poston3

Charles S. White1

Mueller J, Jeudy J, Poston R, White CS

Keywords: bypass, cardiac imaging, CT coronary arteriography, lung diseases

DOI:10.2214/AJR.06.0736

Received June 1, 2006; accepted after revision March 19, 2007.

1Department of Diagnostic Radiology, University of Maryland School of Medicine, 22 S Greene St., Baltimore, MD 21201. Address correspondence to C. S. White.

2Present address: Department of Radiology, Allegheny General Hospital, Pittsburgh, PA.

3Division of Cardiac Surgery, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD.

OBJECTIVE. Cardiac CT angiography (CTA) is commonly performed after coronary ar-tery bypass grafting surgery (CABG) to assess graft patency, but the images also include partsof the lungs, abdomen, and mediastinum. The purpose of our study was to retrospectively as-sess the prevalence of unsuspected disease identified on cardiac CTA examinations after CABGand to determine their potential clinical significance.

MATERIALS AND METHODS. CTA was performed postoperatively in 259 patients(mean, 5.2 days), and 40 patients underwent a follow-up CT scan (mean, 12.7 months). CardiacCTA was acquired using a 16-MDCT scanner with ECG-gating and bolus timing with a smallfield of view centered on the heart. Two thoracic radiologists assessed each examination in con-sensus. The prevalence of graft disease and incidental findings (cardiac and noncardiac) wasestablished. The electronic medical record was reviewed. A finding was judged potentially sig-nificant if a therapeutic intervention or radiologic follow-up was deemed advisable on the basisof the cardiac CTA. Bypass graft occlusions were analyzed separately.

RESULTS. In the immediate postoperative period, 51 patients (19.7%) had at least one un-suspected, potentially significant finding. Twenty-four patients (9.3%) had a cardiac findingsuch as a ventricular pseudoaneurysm, ventricular perfusion deficit, or intracardiac thrombus,and 34 patients (13.1%) had a noncardiac finding including pulmonary embolism, lung cancer,or pneumonia. At least one bypass graft was occluded in 17 patients (6.6%) in the immediatepostoperative period. In the later postoperative period, seven patients (17.5%) had a potentiallysignificant unsuspected finding. Four patients (10.0%) had at least one graft occlusion.

CONCLUSION. Cardiac CTA after CABG revealed a high prevalence of unsuspectedcardiac and noncardiac findings with potential clinical significance. Interpreters of these stud-ies should be familiar with the spectrum of these abnormalities.

CG-gated cardiac CT, initiallywith electron beam CT (EBCT)and more recently with MDCT, isincreasingly being used to evaluate

the coronary arteries and to provide an assess-ment of noncoronary cardiac disease. CardiacCT angiography (CTA) examinations are typi-cally acquired with a small field of view fo-cused on the heart, but portions of the lungs,pleura, chest wall, mediastinum, thoracic skel-eton, and upper abdomen are often included aspart of the examination. Although a wider fieldof view may be reconstructed from the rawdata to assess for additional thoracic findings,these images are not typically used to evaluatethe coronary arteries and bypass grafts.

A substantial rate of incidental findingsnecessitating therapeutic intervention orfurther radiologic evaluation has been foundin patients undergoing coronary artery cal-

cium scoring examinations without IV con-trast with EBCT [1–3]. However, limited in-formation exists regarding the prevalence ofclinically significant incidental unsuspectedfindings in patients undergoing CTA [3–7].The rate of incidental findings with MDCTmay be higher because thinner reconstruc-tions are used and IV contrast material is ad-ministered. In addition, previous incidentalMDCT cardiac CTA studies have focusedon patients suspected of having coronary ar-tery disease. To our knowledge, no informa-tion currently exists on the rate of incidentalfindings in patients with known ischemicheart disease or following cardiac surgery.We retrospectively evaluated the frequencyof unsuspected cardiac and noncardiac dis-ease in patients who underwent cardiac CTAfor routine assessment of coronary arterybypass graft (CABG) patency.

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Materials and MethodsPatients

Patients who receive CABG at the Universityof Maryland Medical Center often undergo car-diac CTA to assess for graft patency as part of theirroutine postoperative care. From our radiology in-formation system, we identified all individualswho underwent CTA after CABG surgery betweenOctober 2002 and March 2006. In the immediatepostoperative period, 259 patients (mean age, 63.7years; age range, 37–89 years; 73.4% men, 26.6%women) underwent a routine contrast-enhancedcardiac CTA examination. Surgical techniques in-cluded both off-pump (178 patients, 68.7%) andon-pump (69 patients, 26.6%) cardiac bypass andminimally invasive (six patients, 2.3%) or hybrid cor-onary bypass grafting (six patients, 2.3%). On aver-age, examinations were performed on postoperativeday 5.2 (range, 1–38). Of the original group, a subsetof 40 patients underwent a routine follow-up cardiacCTA an average of 12.7 months (range, 2–22 months)after CABG as part of a research protocol for bypassgraft patency. Patients who underwent scanning fornonroutine cardiopulmonary disease were excluded.An institutional review board exemption was grantedfor this study, and the study was performed incompliance with Health Insurance Portability andAccountability Act (HIPAA) regulations.

Image AcquisitionCT angiography was acquired using a 16-

MDCT scanner (MX8000 IDT, Philips MedicalSystems). For each patient, retrospective ECG-gated images were obtained through the entirechest during a single breath-hold beginning at theinferior margin of the heart and extending to the topof the lung apices (Fig. 1). Patients were advised toexhale slowly if they could not maintain breath-holding throughout the examination. The scanningprotocol included collimation of 0.75 mm × 16with section thickness of 1 mm. The scanning tech-nique was 140 kVp and 350–500 mAs. The typicalfield of view was 250 mm with a matrix of512 × 512. A pitch of 0.2–0.3 was used with a scan-ner rotation time of 0.42 second. Iodinated contrastmaterial (120–150 mL) was injected through an 18-to 20-gauge angiocatheter into an antecubital veinat 3–4 mL/s. Automated bolus timing was per-formed using a threshold value of 150 H and a re-gion of interest was placed over the ascendingaorta. Beta blockade was typically provided as partof routine postoperative care. For accurate imageacquisition, sinus rhythm was required, with amean heart rate less than 100 beats per minute.

Average scanning time was 30–40 seconds. Allimages were reconstructed with a small field ofview centered on the heart. In each patient, a phaseobtained at 75% of the R-R interval was recon-

structed and used for primary analysis. Otherphases were reconstructed in some patients butwere not used for this analysis. The primary datawere also reconstructed using curved planar recon-structions along the long axis of the bypass grafts.Wider field of view images (x, y direction) were notreconstructed from the raw data.

Image Interpretation and ReviewEach examination was interpreted at the time of

scanning by a thoracic radiologist. Axial CT im-ages at 75% of the R-R interval and curved planarpostprocessed images were predominantly used forimage interpretation. Additional images retrospec-tively reconstructed at 10 phases of the cardiac cy-cle were also available if needed. The reviewer pro-vided a qualitative assessment of the overall qualityof the scan and reviewed all images on soft-tissue,mediastinal, lung, and bone windows. The patencyof each graft was assessed. The grafts were gradedas occluded or nonoccluded. When radial graftswere used, spasm was defined as a patent graft withdiffuse narrowing. Relevant cardiac and noncardiacfindings were described in the final report.

The primary author, a fellow in thoracic radiol-ogy with 6 months of cardiac CTA experience, ret-rospectively assessed each finalized report and re-viewed the electronic medical record of eachpatient to determine the clinical relevance of eachfinding. A data sheet was generated that includedthe patient’s age, sex, postoperative day, status ofthe bypass grafts, and cardiac and noncardiac find-ings. A finding was defined as potentially signifi-cant if a therapeutic intervention was required or iffurther radiologic evaluation was deemed neces-sary by the interpreting radiologist. Cardiac diseasewas documented if the abnormality was paracar-diac, pericardial, or within the heart itself. Noncar-diac was classified as pulmonary, mediastinal,pleural, or involving the upper abdomen. Commonand expected postsurgical findings (e.g., smallpleural or pericardial effusions, pneumomediasti-num, mild pulmonary edema, etc.) were not in-cluded. Findings of minimal clinical significance(e.g., goiter, hiatal hernia, etc.) and known disease(e.g., cardiomegaly, emphysema, etc.) based on in-formation in the electronic medical record (historyand physical, operative note, discharge summary,echocardiogram, clinic notes, previous radiologystudies, etc.) were noted, but not included in the fi-nal analysis. Repeat findings on the immediate andlate postoperative examinations were excludedfrom consideration on the second CT scan.

Some significant findings were defined accordingto following guidelines. A native coronary artery an-eurysm was defined as a lumen diameter at least 1.5times the size (> 6 mm) of a normal adjacent coro-nary artery segment (usually 2–4 mm). Pulmonary

hypertension was designated if the main pulmonaryartery diameter was greater than 3.1 cm. A smallpericardial effusion was judged to be present if peri-cardial fluid did not completely encircle the heart. Amoderate or large pericardial effusion was denotedby fluid completely encircling the heart.

Graft abnormalities were analyzed separately.All incidental findings and graft abnormalities werereviewed independently by two radiologists (theprimary author and a second thoracic radiologist) tosubstantiate their presence and a final decision wasbased on consensus.

Statistical AnalysisSignificant findings were divided into cardiac

and noncardiac disease. The prevalence of eachfinding was calculated. The prevalence of bypassgraft occlusion was determined.

ResultsFifty-one patients (19.7%) were found to

have at least one potentially significant findingrequiring therapeutic intervention or further ra-diologic evaluation. Among these, 24 patients(9.3%) had at least one cardiac finding and 34patients (13.1%) had at least one noncardiacfinding. Seven patients (2.3%) had both a car-diac and noncardiac finding. Five patients hadtwo noncardiac findings (1.9%). Three patientshad two cardiac findings (1.2%).

The most common cardiac findings were amoderate or large pericardial effusion (Fig. 2)(eight patients, 3.1%), intracardiac thrombus(Figs. 3 and 4) (six patients, 2.3%), and sub-stantial paracardiac or mediastinal hemorrhage(six patients, 2.3%). Among noncardiac abnor-malities, pulmonary nodule (nine patients,3.5%), pneumonia (six patients, 2.3%), tra-cheal or lobar mucous plugging (six patients,2.3%), and pulmonary embolism (Fig. 5) (fivepatients, 1.9%) were most frequent (Table 1).

On the basis of the CT interpretation, 15 pa-tients (5.8%) had a documented clinical inter-vention and 12 patients (4.6%) had a radiologicfollow-up. Two patients had both a clinical in-tervention and a radiologic follow-up. The re-maining 26 patients (10.0%) were lost to fol-low-up or did not have further intervention toour best knowledge. Further interventions in-cluded repeat cardiac surgery (three patients,1.2%), hospital readmission (one patient,0.4%), insertion of a pericardial drainage cath-eter (one patient, 0.4%), lung carcinoma (onepatient, 0.4%), anticoagulation (five patients,1.9%), bronchoscopy for a large mucous plug(one patient, 0.4%), blood transfusion (two pa-tients, 0.8%), and antibiotic treatment forpneumonia (three patients, 1.2%).

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416 AJR:189, August 2007

Of the nine pulmonary nodules that werefound, one patient underwent pulmonaryconsultation, PET, and lung biopsy with ahistologic diagnosis of lung carcinoma(Fig. 6). Three patients received follow-upchest CT revealing nodule stability. A fourthpatient is scheduled for CT follow-up. Of thetwo adrenal masses, both patients receivedfollow-up abdominal CT. One mass was di-agnosed as a lipid-rich adrenal adenoma.The second adrenal mass remained indeter-minate on follow-up abdominal CT. The pa-tient has not undergone additional workup or

therapy. The decision to transfuse two pa-tients was based on the combination of theCT interpretations and the low hemoglobinlevels. One of the patients who had large mu-cous plug underwent bronchoscopy for aspi-ration of the plug. We presume the remain-ing patients with mucous plugging receivedpulmonary toilet, but clinical documentationis not available for confirmation.

Of the 40 patients who underwent a routinefollow-up cardiac CTA in the late postopera-tive period (mean, 12.7 months), seven pa-tients (17.5%) had an incidental and unsus-pected finding. Among these, three patients(7.5%) had a cardiac finding and four patients(10%) had a noncardiac finding. These find-ings included a new left subclavian arterythrombus, pulmonary edema, apical left ven-tricular perfusion defect, moderate pericar-dial effusion, new central venous obstruction,and moderate-sized pleural effusion. Allseven patients were treated conservatively.

With respect to bypass graft assessment,one or more bypass grafts were occluded in17 patients (6.6%) in the immediate postoper-ative period and in four patients (10.0%) inthe late postoperative period. All of the oc-cluded grafts (Fig. 7) were saphenous veingrafts. One patient had two saphenous veingrafts occlude in the immediate period. Noneof the internal mammary artery grafts oc-cluded. Spasm was a frequent finding with ra-dial artery grafts, although none of thesegrafts were occluded. Graft patency was notconfirmed with catheter angiography.

DiscussionOur study of a rather large cohort of pa-

tients suggests a frequency of unsuspectedand potentially significant findings of approx-imately 20% in patients who undergo cardiacCTA both immediately and remotely afterCABG. Several studies have assessed the fre-quency of incidental findings in the context ofvarious types of cardiac-focused CT exami-nations [1–7].

A modest body of literature has been pub-lished concerning incidental findings on un-enhanced EBCT scans obtained for coronarycalcium scoring [1–3]. Horton et al. [1] re-

Fig. 1—Scout topogram shows typical field of view used for each examination. To include entire course of internal mammary arteries, craniocaudad (z-axis) field of view is more cephalad than typical cardiac CT angiography.

Fig. 2—45-year-old man who underwent cardiac CT angiography 6 days after coronary bypass grafting surgery. Axial CT image shows anterior ventricular pseudoaneurysm (white arrow) and large hemopericardium (open arrow). Patient had good recovery after surgery.

Fig. 3—73-year-old man who underwent routine cardiac CT angiography 7 days after coronary bypass grafting surgery. Axial CT image shows thrombus in left atrial appendage (arrow). Intraoperative transesophageal echocardiogram showed no intracardiac thrombus (not shown).

Fig. 4—67-year-old man who underwent coronary artery bypass grafting surgery after inferior myocardial infarction. Axial CT image from routine cardiac CT angiography 7 days after surgery shows unsuspected left ventricular thrombus (arrowhead).

Fig. 5—63-year-old symptomatic man who underwent routine cardiac CT angiography 2 days after coronary artery bypass grafting surgery. Axial CT image shows saddle pulmonary embolism (arrow).

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ported that 7.8% of patients undergoing coro-nary calcium scoring required additionalworkup for noncardiac disease. In a laterstudy, Schragin et al. [2] found 4.2% of pa-tients required CT follow-up and 20.5% ofexaminations had at least one noncardiacfinding, including one patient where the inci-dental finding was the cause of death. Thesestudies differ from the current study in thatthey were performed with relatively thick sec-tions (3 mm) and without the use of IV con-trast material, precluding evaluation of car-diovascular and mediastinal structures. Inaddition, we studied postoperative patientsafter cardiovascular surgery, whereas many ofthe patients studied with EBCT were outpa-tients. This may explain the lower rate of ab-normalities with potential clinical impact de-tected in the EBCT studies.

The prevalence of incidental findings wasfound to be higher with the use of IV contrast.Hunold et al. [3] examined patients who under-went a cardiac EBCT examination for calciumscoring or coronary angiography. Combining

both incidental cardiac and noncardiac disease,they determined that 9.3% of patients requiredfurther radiologic investigation, and specifictherapy was initiated in 22 patients (1.2%). Ma-lignant disease was detected in three patients.

The rate of incidental disease was higherwith the use of MDCT for coronary CTA. Arecently published study by Haller et al. [4]showed that 4.8% of patients undergoing car-diac CTA with a small field of view had a ma-jor noncardiac finding and 19.9% of patientshad a minor noncardiac finding. In two recentabstracts by Shafique et al. [5] and Onuma etal. [6], the rate of significant noncardiac find-ings requiring further investigation or treat-ment on contrast enhanced cardiac CTA ex-aminations was 16% in both studies. A thirdabstract also showed a high prevalence (44%)of significant or potentially significant non-coronary disease [7]. The prevalence of non-cardiac findings in those studies is similar tothis evaluation. However, the rate of inciden-tal cardiac findings in this study was muchhigher. Nearly every coronary bypass patient

has known ischemic heart disease. Therefore,the discovery of complicating conditions,such as intracardiac thrombi, myocardial per-fusion deficits, and ventricular aneurysms,from significant coronary artery disease is notsurprising. In addition, large mediastinal orparacardiac hemorrhage was included in thecardiac category, another condition that occa-sionally occurs after coronary bypass.

The results of this investigation suggestthat the rate of incidental disease detected oncardiac CTA examinations after major cardio-vascular surgery in the inpatient or criticalcare setting is higher than in cardiac CTA ex-aminations typically performed in the outpa-tient setting. Several issues may account forthis discrepancy. One consideration is that thepatient cohort in our study is presumably ahigher risk group than the majority of patientswho undergo cardiac CTA as outpatients. Inan effort to evaluate the internal mammary ar-teries, the CABG CTA protocol extends morecephalic than a typical cardiac CTA examina-tion. Including the superior thorax with a

TABLE 1: Significant and Unexpected Immediate Postoperative Findingsa

Patients Percent Imaging Follow-Up Treatment

Incidental noncardiac findings

Pulmonary nodule 9 3.5 Four patients (follow-up chest CT) One patient (lung carcinoma)

Pneumonia 6 2.3 Three patients (antibiotics)

Large mucous plug 6 2.3 One bronchoscopy

Pulmonary embolism 5 1.9 Three patients (anticoagulation)

Aortic ulcer or aneurysm 3 1.2 Three patients (follow-up chest CT)

Adrenal mass 2 0.8 Two patients (follow-up abdominal CT)

Moderate pleural effusion 2 0.8 One patient (follow-up chest CT)

Sternal dehiscence 1 0.4 Reoperation

Mediastinitis 1 0.4 One patient (follow-up chest CT)

Sarcoidosis 1 0.4

Pulmonary hypertension 1 0.4

Moderate-sized pneumothorax 1 0.4

Incidental cardiac findings

Moderate-to-large pericardial effusion 8 3.1 One patient (pericardial drain); one patient (reoperation); one patient (hospital readmission)

Large mediastinal hematoma 6 2.3 One patient (follow-up chest CT) One patient (reoperation); two patients (blood transfusion)

Left ventricular thrombus 4 1.5 One patient (anticoagulation)

Left ventricular perfusion deficit 3 1.2

Left ventricular pseudoaneurysm 2 0.8 One patient (reoperation)

Left atrial thrombus 2 0.8 One patient (anticoagulation)

Right ventricular compression, pectus excavatum 1 0.4

Native coronary artery aneurysm 1 0.4

Apical left ventricular aneurysm 1 0.4aAverage postoperative time, 5.2 days.

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longer z-axis area of coverage allows addi-tional abnormalities to be detected (Fig. 1).One mitigating factor that may have paradox-ically lowered the prevalence of certain ab-normalities is that common postoperative ab-normalities such as atelectasis and effusionsobscured significant abnormalities.

Another consideration is that the definitionof what constitutes a clinically significantfinding varies among different studies. Moststudies, including this one, define “signifi-cant” or “potentially significant” if imagingfollow-up or a therapeutic intervention wasadvised. However, to maintain as much clini-cal relevance as possible in a postoperative

setting, we excluded known disease typicallyfound on preoperative pulmonary functiontesting or echocardiography (i.e., emphysemaor cardiomegaly), abnormalities of minimalsignificance (i.e., goiter and hiatal hernia),and expected postoperative conditions (i.e.,pulmonary edema).

We chose to analyze bypass grafts sepa-rately because their assessment was the indi-cation for the CTA, and thus a graft occlusioncould not truly be called incidental. At leastone failed graft occurred in 6.6% of patientsin the immediate postoperative period and10.0% of patients in the late postoperative pe-riod, indicating a significant attrition rate.

Fig. 6—A 1.1-cm spiculated left upper lobe pulmonary nodule, (arrows) was discovered in 76-year-old man shortly after coronary bypass. Percutaneous lung biopsy revealed carcinoma.

Fig. 7—56-year-old woman with unsuspected thrombosed aortocoronary saphenous vein graft (arrow) 5 days after coronary artery bypass grafting procedure.

A B

Fig. 8—63-year-old asymptomatic man who underwent cardiac CT angiography 3 days after coronary bypass grafting surgery.A, Axial CT image shows left ventricular aneurysm (arrow).B, Oblique multiplanar reformatted image in vertical long axis projection confirms inferior ventricular pseudoaneurysm (arrow). LA = left atrium, LV = left ventricle.

Nearly all graft failures involved saphenousvein grafts and none occurred with internalmammary grafts. Although bypass graft oc-clusion was not routinely confirmed on cath-eter angiography, the rates of graft failure areconcordant with the published literature [8]. Ithas been proposed that subacute prematuresaphenous vein graft failures (i.e., the addi-tional grafts that occluded after the early post-operative period) are due to neointimal hyper-plasia, which predominately affects venousbut not arterial grafts [9, 10].

This study has important clinical ramifi-cations. Bypass graft patency is a commonindication for cardiac CTA, particularlyamong patients with recurrent symptoms af-ter CABG. To our knowledge, this is the firststudy examining the rate of incidental find-ings on cardiac CTA examinations per-formed primarily on postoperative patientsor those with known ischemic heart disease.Previous incidental studies have focused onoutpatients or individuals with suspectedcoronary artery disease [1–7]. As a result,the rate of incidental cardiac disease washigher (9.3%). This highlights the need toevaluate extracoronary cardiac structures aswell as the noncardiac anatomy on everycardiac CTA examination. In addition, car-diac CTA examinations performed after ma-jor cardiovascular surgery have the potentialto detect treatable cardiac and noncardiaccomplications in a more timely fashion.This was evident from our investigation be-cause we found a number of treatable con-ditions that were not clinically suspected atthe time. Treatable disease included pulmo-nary embolism (Fig. 5), pneumonia, cardiacpseudoaneurysms (Figs. 2 and 8), intracar-diac thrombi (Figs. 3 and 4), and mediasti-nal and pericardial hemorrhage.

This study has several important limita-tions. Bias was introduced because of theretrospective design of the study. We did notreview studies without a reported unsus-pected finding because there would havebeen no opportunity to act on these findingseven if they were significant. In addition,long-term clinical and imaging follow-upwere not available in many patients with asignificant finding. We determined thera-peutic intervention on the basis of clinicalinformation in the electronic medical record,which usually includes the operative note,echocardiogram, cardiac catherization, dis-charge summary, and radiology reports.However, this system does not include everyfollow-up surgical, cardiology or primary

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care clinic note. Therefore, determining if atherapeutic intervention or specialty consultwas ultimately performed or planned on thebasis of the imaging interpretation alone wassometimes difficult. Thus, we chose the term“potentially significant.” Other publishedstudies of incidental findings on cardiac CTalso have incomplete or nonexistent follow-up, possibly for the same reasons.

Although our overall patient cohort wassizeable, the number of patients studied inthe later postoperative period was low(n = 40), and incidental findings included inthe first study were not duplicated in the sec-ond. Because our patient population recentlyhad undergone major cardiovascular surgeryand have known ischemic heart disease, wecannot generalize these findings for outpa-tients or patients with suspected coronary ar-tery disease. Also, the raw data were not re-constructed to create a wider field of view (x,y direction) possibly allowing more inciden-tal findings to be discovered. Finally, our di-agnosis of graft occlusion was not confirmedon coronary angiography. Nevertheless, car-diac CTA has shown greater than 90% sensi-tivity and specificity for detection of graftocclusion using invasive angiography as astandard of reference [11–14].

In summary, cardiac CTA performed afterCABG surgery is valuable to determine graftpatency and also frequently detects clinicallyoccult and potentially life-threatening abnor-malities. All physicians interpreting cardiac

CTA should be cognizant of both cardiac andnoncardiac findings commonly present in pa-tients after CABG surgery.

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