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Table of Contents
ORIGINAL ARTICLE
Year : 2019  |  Volume : 9  |  Issue : 3  |  Page : 154-164

Diagnostic accuracy of 256 slices computed tomography coronary angiography in post coronary artery bypass graft Egyptian patients


1 Departement of Cardiovascular, Faculty of Human Medicine, Zagazig University, Zagazig, Egypt
2 Ain Shams University, Resident of Cardiology in Kobry Elkobba Military Hospital, Cairo, Egypt

Date of Web Publication3-Dec-2019

Correspondence Address:
Prof. Hanan Radwan
Faculty of Medicine, Zagazig University, Zagazig, Sharkia Governorate
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JICC.JICC_18_19

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  Abstract 


Objective: Evaluate the diagnostic accuracy of 256 slices computed tomography (CT) coronary angiography (CA) (multidetector CT [MDCT]) in the assessment of native coronary arteries and grafts in post-coronary artery bypass graft (CABG) surgery Egyptian patients. Patients and Methods: It included 70 patients with a history of isolated CABG with recurrent chest pain. We excluded patients with a history of redo CABG or other open-heart surgeries, renal impairment, severe claustrophobia, chronic liver disease, dye allergy, tachycardia with contraindication to beta blockers (BB), pregnancy. All patients were subjected MDCT and CA. Both examinations were done within 3 months. Results: In our study, 161 grafts evaluated (63 left internal mammary artery [LIMA] in situ grafts, 5 right internal mammary artery (RIMA) and 2 radial grafts, and 91 venous grafts). CA failed to detect 3 LIMA and 7 venous grafts. All were seen only by MDCT. For grafts CT compared to CA has sensitivity (91.5%, 84.8%), specificity (98%, 100%), accuracy (95.65%, 96.9%), positive predictive value (PPV) (96.43%, 100%), and negative predictive value (NPV) (95.24%, 96.2%) in the assessment of significant stenosis and total occlusion of grafts, respectively. For grafted vessels CT has sensitivity (94%, 100%), specificity (98%, 100%), accuracy (96.94%, 100%), PPV (95.92%, 100%), and NPV (97%, 100%) in the assessment of significant stenosis and total occlusion of grafted vessel, respectively. For native vessels CT has sensitivity (100%, 97.7%), specificity (84.2%, 98.4%), accuracy (97.14%, 98.1%), PPV (96.6%, 97.7%), and NPV (100%, 98.37%) in the assessment of significant stenosis and total occlusion of native vessels, respectively. Conclusion: Our study demonstrated a high diagnostic accuracy of MDCT for the assessment of bypass grafts and grafted or native coronary arteries compared with CA. Detection of grafts or native vessels occlusion was better than detection of substantial stenosis. MDCT is a good negative test for native vessels as it has a high sensitivity since it tends to overestimate stenosis degree, so patients with negative MDCT angiographic results mostly have patent vessels.

Keywords: Coronary artery bypass grafts, multidetector computed tomography, noninvasive coronary angiography


How to cite this article:
Radwan H, Kandil N, Elshaer M, Abd-Elkader A. Diagnostic accuracy of 256 slices computed tomography coronary angiography in post coronary artery bypass graft Egyptian patients. J Indian coll cardiol 2019;9:154-64

How to cite this URL:
Radwan H, Kandil N, Elshaer M, Abd-Elkader A. Diagnostic accuracy of 256 slices computed tomography coronary angiography in post coronary artery bypass graft Egyptian patients. J Indian coll cardiol [serial online] 2019 [cited 2019 Dec 13];9:154-64. Available from: http://www.joicc.org/text.asp?2019/9/3/154/272167




  Introduction Top


Coronary artery bypass graft surgery (CABG) with use of either venous or internal mammary artery (IMA) grafts has become an established treatment for symptomatic multi-vessel coronary artery disease.[1] One of the most important variables that determine the successful clinical outcome of coronary artery bypass graft placement is the short- and long-term patency rate of the grafts.[2] Up to 10% of grafts become occluded during the perioperative period. After 10 years, occlusion rates of 59% and 17% have been reported for venous and arterial grafts, respectively.[3] Frazier et al.[4] found that angina recurred within 1 year post-CABG in 24% of patients and within 6 years in more than 40%. A total of 25% of grafts are found to be occluded within 5 years after surgery. Conventional coronary angiography (CA) has been considered the standard reference for evaluation of the patency and luminal stenosis of coronary artery and grafts post CABG.[5] However, the main drawbacks of conventional CA include invasiveness, patient discomfort, and risk of complications. A less invasive imaging modality is desirable for evaluation of patients suspected of having luminal stenosis or occlusion.[6] The major improvements of the recently developed 128-section or higher and dual-source computed tomography (CT) machines compared with the old four-section scanners, include improved temporal resolution due to shorter gantry rotation time, better spatial resolution owing to sub-millimeter collimation, and considerably reduced scan acquisition times.[7] Despite the recent technical advances, the 256-detector row CT CA is still sensitive to arrhythmia. Persistent irregular cardiac rhythm such as atrial fibrillation and frequent extra-systoles preclude MDCT CA. However, motion artifacts owing to mild arrhythmia (e.g., single ventricular extra-systole) can be diminished by manual repositioning the reconstruction windows.[8]

Symptomatic patients post-CABG often pose a challenging diagnostic problem to the angiographer. The calcified, tortuous, and diffusely diseased coronary arteries complicate precise delineation of the lesions.[9] Performing this angiographic evaluation in a noninvasive fashion is even more challenging.[10] High-quality angiographic images and thorough knowledge of the coronary anatomy are required in order to adequately determine revascularization options.[11]

Objective

Evaluate the diagnostic accuracy of 256 slices CT CA in the assessment of the native coronary arteries and bypass grafts in post CABG Egyptian patients.


  Patients and Methods Top


Patients

The study was carried out in cardiology department, Zagazig University and Kobri El Koba Hospitals from 2016 to 2017.

It included 70 patients with a history of isolated CABG with or without cardiopulmonary bypass presenting with recurrent chest pain and in need to assess the patency of grafts and progression of the disease in the native arteries. The exclusion criteria were patients with history of redo CABG or other open heart surgeries, need for concomitant valve replacement or aneurysmal resection, renal impairment with creatinine >1.6 mg/dl, severe claustrophobia, chronic liver disease, history of dye allergy, active gastrointestinal bleeding, tachycardia with contraindication to rate control medications, pregnancy, clinically unfit patients (unable to stop breathing during the examination).

Methods

All patients were subjected to the following: (a) Complete history taking with special emphasis to cardiovascular disease (CAD) risk factors likes hypertension, diabetes mellitus, dyslipidemia, smoking and family history of ischemic heart disease. Also presence of chest pain or dyspnea. (b) Electrocardiography (ECG) to detect ischemic changes (c) Laboratory investigations: with special emphasis to cardiac markers (troponin, creatine kinase-MB) creatinine, CBC, lipid profile. Multi-detector row CT angiography (CTA) and invasive coronaryl angiography. Both examinations were done within 3 months provided no intervention or change in the clinical condition of the patients occurred between the examination.

Computed tomography coronary angiography

Patient preparation

Serum creatinine level was checked just before the examination and a patient's consent is obtained. Patients were asked to fast 4–6 h prior to the examination. Medications are not to be discontinued apart from the oral hypoglycemic drugs should be stopped. The heart rate was evaluated before the examination. The examination was done if the heart rate is below 65 beats/min. Patients with heart rates above 70 beats/min were given cardio-selective beta-blocker; 100 mg of metoprolol or atenolol orally 1 h before the study to obtain a stable low heart rate, provided that no contra-indications to β-blockers. Nitroglycerine was not administrated prior to the study because, in spite of its coronary-dilator effect that enhances visualization; the drug has the potentiality to increase the heart rate and also falsely increases the estimated diameter reduction of the stenotic lesions. The steps of the study were explained in details for each patient. To evaluate patients ability of breath-withholding; they were required to perform a deep inspiration and to continue to hold their breath without pushing (i.e., Valsalva maneuver). During this trial, the patient was observed for compliance.[12]

Contrast material

A bolus of 70–80 ml of water-soluble non-ionic contrast (Ultravist370 mg Schering, Berlin, Germany) was injected through 18 gauge canula into an upper limb vein (right antecubital vein in all our cases to reduce left sided artifacts) with a flow rate of 5 to 5.5 ml/s. This injection was automatically followed by injection of about 40–50 cc of saline at a flow rate of 4 ml/s using a programmed dual-head power injector pump (MedRad; USA) to maintain good opacification of the coronary vessels with washout of contrast material from the SVC and right side of the heart that may cause artifacts.[13]

Scan protocol

CT angiographic examinations were performed by CT scanner namely: Definition 256-Dual source MDCT (Siemens Medical Systems, Germany) in Kobri El Koba hospital. Patients were positioned supine on the CT table. ECG leads were fixed on the chest wall. All reconstructions are performed using the retrospective ECG gating. For this technique; an ECG must be recorded simultaneously throughout the duration of the scanning. A scanogram was taken that presented an AP and lateral views of the examined region. It was used to position the imaging volume of the coronary arteries that extends from the level of tracheal bifurcation down to about 1 cm below diaphragm. In cases of post CABG status the imaging volume should extend from the level of the root of the neck down to about 1 cm below diaphragm to include the entire course of the arterial or venous grafts.[14] The center of the field of view is 2 cm to the left of the dorsal spine on the AP scout and at the level of the hilum on the lateral scout.[14] No calcium scoring was done for our patients due to the presence of radiopaque coronary stents or surgical clips in patients after CABG that would lead to false high scores. Then, automated determination of the starting time using the Bolus-tracing technique” was done. It entails injection of the whole volume of the utilized contrast material as a one bolus at the pre-determined rate. After a delay of about 10 s from the start of injection (time estimated for the contrast to reach the great vessels of the chest, being variable according to the site of the cannula, rate of injection, body built and heart rate); series of axial images at the level of the origin of the left main coronary artery is acquired. The density within the descending aorta is monitored in each axial image on a real-time base while the region of interest carefully monitored.[14] Time-attenuation curves were generated. When the density within the descending aorta exceeds 120 HU (i.e., the contrast started to arrive), the scanning is triggered with a delay of further 3 s (time needed for the table movement to the cranial start position while the patient is instructed to hold breathing). This time delay also allows for increase in the contrast concentration at the ascending aorta and coronary arteries. It is to be noted that the axial images taken at the “Bolus-tracing technique” are of low radiation dose with a 120 KV and 40 mAs (not of diagnostic value). This is to reduce the radiation exposure. And then the volume data set was taken in a spiral mode with simultaneous acquisition. During the helical scan; the ECG signal was recorded digitally. Patients were automatically instructed to maintain an inspiratory breath hold while the CT data and the ECG trace were acquired.[15] No adverse reactions were noted due to contrast material.

Image reconstruction

For most patients, the grafts and the native arteries were best visualized at 75% and 40% of the cardiac cycle. If these images were not satisfying, further phases of the cardiac cycle were used to visualize the different coronary segments.[15] In patient with some motion artifacts; 4 data sets were created during different time instants of the cardiac cycle (50%, 60%, 70% and 80% of the R-R interval); the data set containing the fewest motion artifacts (on the bases of cross-sectional images) was used for further creation of the reconstructed images and evaluation of the coronary artery. The average time of the study was 10 min. Another 60 min were spent for result evaluation at the workstation.[15]

Data evaluation

The reconstructed axial images at different points of the cardiac cycles are sent to an off-line workstation where detailed reconstruction was made to each data set to get the data by 2 observers different from the observer of the of the invasive CA. Visibility of the vessel was considered “good” when there is sharp delineation from the surrounding structures and sufficient contrast detected between the vessel lumen and wall, with less blurring artifacts. Visualization was considered “adequate” in presence of image-degrading artifact that didn't interfere with evaluation with moderate confidence and “poor” in the presence of image-degrading artifacts when the evaluation is possible yet only with low confidence. The examined graft was considered “nonassessable” when the image-degrading artifacts were severe enough to prevent differentiation between the significant stenosis and occlusion on one hand and the normal segment or mildly stenotic lesions on the other hand. so these grafts were excluded from the study.[16] In case one vessel was uninterpretable, an intention to diagnose strategy was applied using different data sets or axis. However, if more than one vessel was uninterpretable, the entire examinations were considered to be of non-diagnostic image quality and were excluded. Each bypass graft was considered as a separate segment. The arterial and venous conduits were evaluated as evaluable or unevaluable by visual estimation as before. Evaluable conduits were classified as patent or occluded. In patent grafts, presence or absence of a significant stenosis (≥50% reduction in diameter) was identified and located.[17] Stenosis were classified on the basis of their location in the body of the graft and at the proximal or distal anastomotic sites. Thin-slab maximum intensity projection (MIP) allowed assessment of extended lengths of the grafts at once. In the presence of calcium or metal, the use of MIP resulted in assessment-limiting artifacts, in which case multi-planner (specially the curved planes) reconstructions were then more suitable. Volume-rendered reconstructions were used to obtain general information regarding the status and anatomy of grafts and native coronary arteries.[18] To summarize: The grafts were classified as evaluable or nonevaluable depending on the image quality (being mainly assessed at the sequential axial images). The non-evaluable grafts are discarded from the statistical analysis. The evaluable grafts are categorized as being either: (0) Normal (smooth parallel or tapering arterial walls), (1) Showing either coronary artery wall irregularities or non-significant stenotic lesion(s) (with less than 50% diameter reduction),(2) Showing significant stenotic lesion(s) (defined as equal to or more than 50% diameter reduction; (3) Occluded. Grafts were numbered for each patient starting from G1 which is usually the arterial graft then G2, 3,… to the number of maximum number of grafts for patient. For each patient all the grafts (G1, 2,…) are assessed by both multislice computed tomography (MSCT) and invasive coronary angiography (ICA) and compared together and results are shown for each graft separately. The axial as well as the reconstructed images including the multi-planer reformatted (MPR), thin slab MIP and the volume rendered images are all used in combination to evaluate the coronary artery disease. MIP was the modality that used to identify the coronary lesions while the degree of stenosis was evaluated primary on the axial scans and MPR (specially the curved reformatted images) using the software and scale calibration, automatic determination of the degree of stenosis was available with possible manual editing when necessary. Identification of coronary artery segments was based on the model suggested by the American Heart Association, where the right coronary artery (RCA) shows proximal (1), middle (2) and distal (3) segments and the posterior descending artery (PDA) branch.[12],[19] The left coronary system [Figure 1] is formed by the left main trunk (LMT) (5) that bifurcates to left anterior descending (LAD) and left circumflex (LCX). The LAD has proximal (6), middle (7) and distal (8) segments. It gives off at least two sizable diagonal branches (9) and (10). The LCX artery has proximal segment (11) before it gives off the first obtuse marginal artery (12). The distal segment (13) turns on the inferior surface of the heart. LCX may give additional obtuse marginal branches (14) and (15) that are not included in statistics owing to their small size.[12],[19] The coronary artery segments are further classified into proximal (RCA 1, LMT 5, LAD 6), middle (RCA 2, LAD 7, LCX 11), distal (RCA 3, LAD 8, LCX 13) and branches (including the diagonals of LAD [9 and 10], obtuse marginal of the LCX [12] and PDA [4].[12],[19] Grafted vessels are considered separate vessels starting from the site of anastomosis. Segment of grafted vessel before the anastomosis is evaluated as a part of native vessel. Of nongrafted vessels, the LAD coronary artery, LCX coronary artery and the RCA were assessed as separate vessels. The left main and diagonal vessels were considered to be part of the LAD. The intermediate branch and obtuse marginal branch were considered part of the LCX, branches of RCA as (right ventricle), or sometimes (PDA or posterolateral) were considered part of it. Evaluation of native and grafted vessels for stenosis was categorized as before. All results were compared to the conventional coronary artery angiography (CA) results as shown through 3 sets of comparisons. Comparison one: is to compare performance of CT to differentiate between significant and nonsignificant lesions so 0 and 1 group were considered nonsignificant whereas group 2 and 3 were considered significant. Comparison two: is to compare performance of CT to differentiate between significant lesions and total occlusions so comparison was done between group 2 and 3. Comparison three: is to detect the deficiency or inability of CA to evaluate some grafts in certain conditions regardless the cause. In comparison one and two results of each vessel assessed by CT and ICA was obtained separately followed by the results of comparison of the vessel group as a whole (grafts, native vessels or grafted vessels).
Figure 1: Segmental anatomy of right coronary artery (lateral view) and left coronary artery (right anterior oblique view) with the left main trunk, left anterior descending, and left circumflex according to American Heart Association

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Invasive coronary angiography

ICA was performed according to a standard procedure using a femoral approach. Angiograms were assessed by an independent experienced observer blinded to CTA data. All grafts, recipient vessels and non-grafted vessels were visually classified as normal (no atherosclerosis or minor wall irregularities with ≤20% luminal narrowing) or abnormal (>20% luminal narrowing). All vessels were evaluated for the presence of significant (≥50%) stenosis in the angiographic view with most severe luminal narrowing.[16]

Ethics

Human rights statements and informed consent: All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1964 and later revisions. Informed consent was obtained from all patients for being included in the study

Statistical analysis

The collected data was revised, coded, tabulated and introduced to a PC using Statistical Package for Social Science (SPSS 15.0.1 for windows; SPSS Inc., Chicago, IL, 2001). The comparison between two paired groups regarding qualitative data was done by using McNemar test. Inter-rater weighted Kappa agreement was used to assess the percentage of agreement between CT and CA. Receiver operating characteristic was used to assess the sensitivity, specificity, A P < 0.05 was considered significant and P < 0.001 was considered highly significant.


  Results Top


This study included 70 patients who had history of CABG. The mean age of the included patients was 60 years, 67 patients (95.7%) were males. Out of them; 50 (71.4%) had hypertension, 45 (64.3%) had diabetes mellitus, 54 (77.1%) had dyslipidemia, 51 (72.9%) were smokers, 9 (12.9%) had positive family history, 16 (22.9%) had previous PCI. Left ventricular ejection fraction 47.90% ± 8.90%. Median (interquartile tange) time from CABG was 3 years and mean 4.5 years with a range between 1 and 23 years.

Assessment of grafts

161 grafts in 70 patients were evaluated by MSCT CA and conventional CA.10 of which were seen only by MSCT so 151 grafts' evaluated data were compared for both modalities. MSCT evaluation – Grafts were classified as follow: 70 arterial grafts (63 of them were left IMA (LIMA) in situ arterial grafts and 7 other arterial (5 right IMA [RIMA] and 2 radial) grafts and 91 venous grafts. Fifty-three of the arterial grafts were seen patent, 1 narrowed with mild lesion, 16 showed significant lesions (9 of which were totally occluded. Fourty-seven of LIMA grafts were patent, one grafts was narrowed with mild lesion, 15 showed significant lesions (9 of which were totally occluded). One RIMA graft showed significant stenosis at anastomotic site while other 4 were patent. The 2 radial grafts were patent. As for venous grafts 47 grafts were patent, 4 grafts were narrowed with mild lesion, 40 grafts showed significant lesions (19 of which were totally occluded). Two studies showed sequential venous grafts, one of them was patent and the other was totally occluded. CA finding – Ten grafts (6%) were not seen by ICA (3 arterial and 7 venous grafts). They were excluded from comparisons between results of significant and total occlusion lesions (all were totally occluded by MSCT). Other 151 grafts were classified as follow: 67 arterial grafts (60 of them were LIMA in situ arterial grafts and 7 other arterial [5 RIMA and 2 radial grafts]) and 84 venous grafts. Fifty of the arterial grafts were seen patent, 1 narrowed with mild lesion, 16 showed significant lesions (9 of which were totally occluded). Forty-four of LIMA grafts were patent, one grafts was narrowed with mild lesion, 15 showed significant lesions (9 of which were totally occluded). One RIMA graft showed significant stenosis at anastomotic site while other 4 were patent. The 2 radial grafts were patent. As for venous grafts 48 grafts were patent, 3 grafts were narrowed with mild lesion, 33 grafts showed significant lesions (14 of which were totally occluded). Two studies showed sequential venous grafts one of them was patent and the other was totally occluded. There was no significant difference between the two modalities in the detection of significant stenosis and total occlusion of the grafts. With overall sensitivity (91.5% and 84.8%), specificity (98% and 100%), positive predictive value (PPV) (96.43%, and 100%), negative predictive value (NPV) (95.24% and 96.2%) and accuracy (95.65% and 96.9%) respectively [Table 1], [Table 2] and [Figure 2], [Figure 3].
Table 1: Comparison of severity of graft lesion and graft total occlusion between computed tomographic angiography and invasive coronary angiography

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Table 2: Diagnostic performance of multislice spiral computed tomography angiography to detect total occlusion and significant lesions of native, grafted vessels and grafts

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Figure 2: To the left: Curved multi-planer reformatted image of the left internal mammary artery graft showing that it is patent along it whole course down to the distal anastomotic site to the mid left anterior descending. Left anterior descending then continues with good distal run off. To the right: Curved multi-planer reformatted image of the saphenous vein graft to diagonal showing a proximal significant lesion with free body and distal anastomotic site, diagonal then continues with no significant lesions

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Figure 3: Left anterior oblique cranial view showing proximal significant lesion of saphenous vein graft to diagonal

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Comparison of computed tomography angiography and invasive coronary angiography for evaluation of grafts not accessible by invasive coronary angiography

Ten grafts out of 161 (6%) were not seen by ICA (3 were arterial LIMA grafts and 7 were venous free grafts). Sixty-one patients had at least 2 grafts with significant difference for the unseen grafts, 24 patients had at least 3 grafts, 5 patients have at least 4 grafts, and one patient had 5 grafts with no significant difference for unseen grafts for 3rd, 4th and 5th grafts so multiplicity of grafts is most probably not the main obstacle [Table 3].
Table 3: Comparison of computed tomographic angiography and invasive coronary angiography: For evaluation of unseen grafts by invasive coronary angiography

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Evaluation of grafted vessels

149 grafted vessels were classified as follow: (69 grafted LAD [gLAD], 27 grafted diagonal [gDiag], 27 grafted OM [gOM], 26 grafted RCA [gRCA]). Note: grafted PDA, PL were considered apart of gRCA or gOM according to origin from RCA or LCX. Two LAD vessels were grafted twice after total occlusion of LIMA graft. Findings of MSCT – Out of the 149 evaluated grafted vessels 87 vessels were patent, 13 vessels narrowed with mild lesions, 49 vessels showing significant lesions 4 of which were totally occluded. For gLAD out of 69 grafted vessels 36 vessels were patent, 8 vessels narrowed with mild lesions, 25 vessel showing significant lesions 3 of which were totally occluded. For gDiag out of 27 grafted vessels 17 vessels were patent, one vessel narrowed with mild lesion and 9 vessels showing significant lesions none of which were totally occluded. For gOM out of 27 grafted vessels 22 vessels were patent. One vessel was narrowed with mild lesions and 4 vessels showing significant lesions none of which were totally occluded. For gRCA out of 26 grafted vessels 12 vessels were patent. 3 vessels were narrowed with mild lesion, and 11 vessels showing significant lesions one of which was totally occluded. Findings of ICA – Out of the 149 evaluated grafted vessels 90 vessel were patent, 9 vessels narrowed with mild lesions, 50 vessels showing significant lesions 4 of which were totally occluded. For gLAD out of 69 grafted vessels 39 vessels were patent, 6 vessels narrowed with mild lesions, 24 vessel showing significant lesions 3 of which were totally occluded. For gDiag out of 27 grafted vessels 18 vessels were patent, 9 vessels showing significant lesions none of which were totally occluded. For gOM out of 27 grafted vessels 21 vessels were patent. 2 vessels were narrowed with mild lesions and 4 vessels showing significant lesions none of which were totally occluded. For gRCA out of 26 grafted vessels 12 vessels were patent. One vessel was narrowed with mild lesion, and 13 vessels showing significant lesions one of which was totally occluded. There was no significant difference between the two modalities in the detection of significant stenosis and total occlusion of grafted vessels with overall sensitivity (94% and 100%), specificity (98% and 100%), PPV (95.92% and 100%), NPV (97% and 100%) and accuracy (96.64 and 100%) respectively [Table 2], [Table 4] and [Figure 4], [Figure 5].
Table 4: Comparison of grafted vessels lesions severity and total occlusion between computed tomographic angiography and invasive coronary angiography

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Figure 4: To the left: Virtual reality image of the saphenous vein graft to left anterior descending showing that it is patent along it whole course down to the distal anastomotic site. To the right: Virtual reality image of left anterior descending showing significant lesion with fair filling distally

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Figure 5: To the left: Left anterior oblique cranial view showing patent saphenous vein graft to left anterior descending. To the right: Showing significant left anterior descending lesion distal to anastomosis then left anterior descending continues with no significant lesions

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Evaluation of native vessels

210 native vessels were classified as follow: 70 LAD, 70 LCX, 70 RCA. Note: PDA, PL were considered apart of RCA or LCX according to origin from RCA or LCX. The proximal segment of grafted vessel proximal to anastomotic site was assessed as a part of native vessels. 12 of those proximal LAD segments of grafted vessels showed heavily calcification resulting in difficult assessment by CT. Findings of MSCT – Out of 210 native vessels 18 vessels were patent, 14 vessel were narrowed with mild lesions, and 178 vessels showed significant lesions 87 of which were totally occluded. For native LAD; only one vessel was patent, one vessels were narrowed with mild lesions and 68 vessels showed significant lesions 44 of which were totally occluded. For native LCX; 9 vessels were patent, 6 vessels were narrowed with mild lesions and 55 vessels showed significant lesions 12 of which were totally occluded. For native RCA; 8 vessels were patent, 7 vessels were narrowed with mild lesions and 55 vessels showed significant lesions 31 of which were totally occluded. Findings of ICA – Out of 210 native vessels 21 vessels were patent, 17 vessel were narrowed with mild lesions, and 172 vessels showed significant lesions 87 of which were totally occluded. For native LAD; only one vessel was patent, 2 vessels were narrowed with mild lesions and 67 vessels showed significant lesions 46 of which were totally occluded. For native LCX; 12 vessels were patent, 6 vessels were narrowed with mild lesions and 52 vessels showed significant lesions 11 of which were totally occluded. For native RCA; 8 vessels were patent, 9 vessels were narrowed with mild lesions and 53 vessels showed significant lesions 30 of which were totally occluded. There was no significant difference between the two modalities in the detection of significant stenosis and total occlusion of native vessels with overall sensitivity (100% and 97.7%), specificity (84.2% and 98.4%), PPV (96.6% and 97.7%), NPV (100% and 98.37%) and accuracy (97.14% and 98.1%) respectively [Table 2], [Table 5] and [Figure 6].
Table 5: Comparison of native vessels lesions severity and total occlusion between computed tomographic angiography and invasive coronary angiography

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Figure 6: To the Left: curved multiplanar reformatted image showing multiple right coronary artery lesions. To the right: curved multiplanar reformatted image showing a significant obuse marginal artery proximal lesion

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  Discussion Top


Coronary artery bypass graft surgery has become an established treatment for symptomatic multi-vessel coronary artery disease.[1]

One of the most important variables that determine the successful clinical outcome of coronary artery bypass graft placement is the short-and long-term patency rate of the grafts.[2] Venous grafts are still the most widely used type of grafts due to their availability.[20] In our study also, venous grafts were the most common type of grafts. It represented 57% of the grafts (91 of the 161 grafts). Yet, there is high rate of complications with venous grafts due to their high rate of occlusion and narrowing.[1],[21],[22] Knowing that the mean time after operation was about 4.5 years, our study showed that about 44% of the venous grafts (40/91) were significantly narrowed and about 21% (19/91) were totally occluded (i.e., 47% of those significantly narrowed). The diagonal and obtuse marginal (OM) branches were the commonest site for grafted vessels about 33% (27 Diagonal, 27 OM out of 80 grafted vessels with venous grafts) followed by the RCA (with gRCA vessels 32.5% [26/80 [32.5%]). Yet 11% (10 grafts) of the venous grafts were occluded with no knowledge of their supposed landing site as they were only seen as a dimple at their origin site from the ascending aorta and due to lack of operative details. In our study, the in situ arterial grafts were used more common than the free arterial grafts, 97% (68/70) of arterial grafts were in situ (90% [3/70] were in situ LIMA grafts, 7% [5/70] were in situ RIMA grafts) and 3% (2/70) of the arterial grafts were free radial arterial grafts. This is due to their high patency rates after a long time for in situ grafts and more complication rates for free arterial grafts. This finding is concordant with Nwasokwa and Nishida et al.[23],[24] The radial artery is the most commonly used free arterial graft due to its easy harvesting, yet it is highly susceptible to spasm.[25] In our study, all of the free arterial grafts were radial artery grafts. The LIMA is the most widely used in situ arterial graft (90% of the in situ arterial grafts in our study). Due to its arterial nature, it has less incidence rate complications.[26] The LIMA grafts showed about 75% rate of patency in our study (47 out of 63) compared to 90% rate of patency after 10 years according to Loop.[27] There was a 24% (15 out of 63) rate of significant narrowing, out of them a 14% (9 out of 63) total occlusion in our study. The LAD is the most common site for landing of the LIMA graft, as it is the most important coronary artery branch supplying the left ventricle and due to other anatomical considerations as they are both anteriorly located in the chest.[28] This is concordant with our finding that 100% of LIMA grafts ended at the LAD. The grafts are usually closely related to a lot of surrounding surgical clips that may make them nonevalubale, In our study 6 out of 191 (3%) of grafts anastomotic site. We found that the sensitivity and specificity of 256-slice CT were 92%, 98% for assessment graft stenosis which were comparable to the results reported by de Graaf et al.[16] but better than results reported by Ropers et al.[29] (sensitivity, 75%; specificity, 92%). Ropers et al.[29] used ECG-gated a four detector row CTA with (sensitivity, 75%; specificity, 92%) for graft stenosis. de Graaf et al.[16] evaluated the diagnostic performance of 320-slice multidetector CT CA in patients post CABG. Their results demonstrate that the sensitivity, specificity and diagnostic accuracy in the evaluation of significant graft stenosis were 96%, 92%, and 93% respectively which were comparable to our study finding (92%, 98% and 96%) respectively. For arterial grafts the sensitivity, specificity and accuracy were 100%, 91% and 93% and for venous grafts were 95%, 93% and 93% respectively. In comparison to our study results that showed sensitivity, specificity, and accuracy for arterial grafts were 84%, 100% and 96%, while 95%, 96% and 96% for venous grafts respectively. Our study showed that the sensitivity, specificity, and accuracy for graft total occlusion were 84%, 100% and 97% respectively (for the arterial grafts were 75%, 100% and 96% and for the venous grafts were 90%, 100% and 98% respectively). For the grafted vessels occlusion were 100%, 100%, and 100% respectively For the native non-grafted vessels occlusion were 98%, 98%, and 98% respectively. Theses finding was comparable to the findings of Ropers et al.[29] and de Graaf et al.,[16] Ropers et al.[29] study, showed that the sensitivity and specificity of CT for graft total occlusion were 97% and 98%. de Graaf et al.,[16] showed that the sensitivity, specificity and accuracy for graft total occlusion were, 100%, 94% and 96% respectively (for the arterial grafts were 100%, 91%, and 93% and for the venous grafts were 100%, 95%, and 97% respectively). For the grafted vessels occlusion were 100%, 91%, and 92% respectively. For the native non-grafted vessels were 100%, 100% and 100% respectively Hamon et al.[30] performed a meta-analysis to evaluate the accuracy of 16-and 64-section spiral CT to assess bypass grafts. The results of their meta-analysis demonstrate that obstructive bypass graft disease can be detected by using at least a 16-section CT with a high diagnostic accuracy with a sensitivity of 98%, a specificity of 97%, with only 92.4% of scanned grafts being fully assessable. This performance is better than for nongraft coronary arteries as shown in a meta-analysis by Hamon et al.,[31] on a per-vessel basis where the sensitivity was90% and specificity was 93%, for the diagnosis of significant coronary artery stenosis. Compared to the results of native arteries in our study where the sensitivity was 100% and specificity was 84%. This improvement in performance may be explained by a number of differences between bypass grafts and native coronary arteries. Graft conduits often have a larger diameter, are less frequently calcified and are relatively immobile, making CT imaging less challenging. Moreover, they are more often occluded than stenosed, which may make the diagnosis of obstruction more clear cut. Indeed, in the studies where information about occlusion rate was given in addition to the overall rate of substantial stenosis, there was much better detection of occlusion than for substantial stenosis. We found that the sensitivity, specificity and diagnostic accuracy of 256 CT were 94%, 98%, and 97% for the grafted vessels stenosis and 100%, 84%, and 97%, respectively, for native non-grafted vessels stenosis which were better than results of Leta et al.,[19] de Graaf et al.[16] and Makaryus et al.[32] and were comparable to Chao et al.[33] and Chua et al.,[34] Leta et al.,[19] found that the sensitivity and specificity for the detection of significant coronary lesions using 16 multidetector-row spiral CT were 75% and 91%, respectively. de Graaf et al.[16] found that the sensitivity, specificity and diagnostic accuracy for assessment of grafted vessels stenosis were 88%, 89%, and 89% and for the native nongrafted vessels were 83%, 77%, and 80%, respectively. Makaryus et al.,[32] found that the sensitivity and specificity for the detection of significant coronary lesions using 64-detector-CT to conventional CA were 86%, 84% respectively. Chao et al.[33] used 256 CT compared with that of ICA. They concluded that 256-row CTA is a highly sensitive test of CAD and has a high predictive value. The diagnostic accuracy rates of 256-slice CTCA were comparable to invasive CA. The sensitivity and specificity for detecting significant stenosis >50% were (based on patient analysis [98.8%, 50%], vessel analysis [94.3%, 87.3%], and segment analysis [93.5%, 95%]). Chua et al.,[34] used the 256-slice CTCA was compared to 64-slice CTCA using quantitative ICA as a reference using a validated quantitative CA (QCA) computerized software. The diagnostic accuracy rates of 256-slice CTCA were significantly superior to those of 64-slice CTCA (based on patient analysis [97% vs. 83%, P < 0.05], vessel analysis [95% vs. 85%], and segment analysis [94% vs. 88%]) However, the performance of 256-slide CTCA is affected in those segments that are severely calcified and/or stented. According to Leber et al.[35] using Dual-source CT (DSCT) angiography without using negative chronotropic medication, The accuracy to detect patients with coronary stenosis >50% (sensitivity 92 vs. 100%; specificity 88 vs. 91%) was not significantly different among patients with HR >65 b.p.m. and <65 b.p.m. Budoff et al.[36] compared the diagnostic performance of CTA versus CA for the detection of lesion-specific ischemia using fractional flow reserve as the gold standard. they found CTA and ICA exhibited similar diagnostic performance (diagnostic accuracy, sensitivity, specificity, were 69%, 79%, 63%, for coronary CTA) for the detection of lesion-specific ischemia. to determine appropriate revascularization targets.


  Conclusion Top


Our study demonstrated a high diagnostic accuracy of noninvasive 256-Dual source MDCT for the assessment of bypass grafts as well as grafted or native coronary arteries compared with CA. Detection of graft or coronary vessel occlusion was better than detection of substantial stenosis. MDCT angiography is a good negative test for native coronary vessels as it has a high sensitivity since it tends to overestimate stenosis degree, so patients with negative MDCT angiographic results mostly have patent vessels.

Clinical implication and recommendations

Using 256 multidetector row as well as dual-source CT machines will open new frontiers in the assessment of the heart, coronary arteries and grafts. Faster examinations with much less radiation dose are now possible. The latest MDCT scanners show a potential to become a first-line tool for the noninvasive evaluation and follow up of patients with suspected graft, vessel stenosis or occlusion. So we recommend a protocol for dealing with patients after CABG that include using MDCT angiography as a primary modality for confirming their graft patency. A lot of unnecessary invasive conventional angiography will be avoided using MDCT angiography. Conventional angiography may be spared for patients with equivocal CT angiographic results (which is a rarity using the 64 MDCT or dual source machines) or who needs an intervention e.g., angioplasty or stent placement within a graft or a native coronary artery. CTA will be a guide during conventional angiography to save time and contrast to search for occluded grafts with concentrating on the lesions that may need intervention.

Limitations

The sample size was relatively small, further larger studies are needed to confirm our results and document the expected better imaging quality of these machines during the assessment of native coronary arteries as well as bypass grafts.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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