We enrolled 40 patients with prior CABG assessed using CCTA and ICA to detect graft patency and native vessel disease progression.

In the study group, most patients were older than 60 years (55%) with a male predominance (80%). Among the population under study, 27 patients had DM (67.5%), 36 patients had hypertension (90%), and 12 patients were smokers (30%). In this study, the mean BMI was 28.89 ± 5.17 kg/m2. Regarding the lipid profile results of the study group, the mean LDL level was 84.28 ± 27.34 mg/dL, and the mean triglyceride (TG) level was 142.40 ± 66.95 mg/dl. In total, 67.5% of the study patients were on statin therapy. The mean left ventricular ejection fraction (LVEF) in this study was 57.23% ± 8.25% (range 36%–71%). The mean duration since CABG was 5.25 ± 4.04 years (range 2–21 years) (Table 1).

In total, 124 native vessels were assessed using both CCTA and ICA and classified as 40 LADs, 40 left circumflex arteries (LCXs), 40 right coronary arteries (RCAs), and 4 ramus intermedius arteries. The posterior descending artery was assessed as part of the RCA or LCX according to origin. The main findings of CCTA for native LADs were as follows: one vessel showed an insignificant lesion, 15 vessels showed significant lesions, and 24 vessels were occluded. The same results were found on ICA indicating a good agreement between CCTA and ICA (kappa value = 1.0).

For native LCXs, CCTA revealed one normal vessel, one vessel with an insignificant lesion, 22 vessels with significant lesions, 12 totally occluded vessels, three vessels with diffuse atherosclerosis, and one non-evaluable vessel due to severe calcification, whereas ICA revealed two normal vessels, one vessel with an insignificant lesion, 23 vessel with significant lesions, 12 occluded vessels, and two vessels with diffuse atherosclerosis; therefore, agreement between CCTA and ICA was good (kappa value = 0.8).

CCTA findings for native RCAs revealed five normal vessels, one narrowed vessel with an insignificant lesion, 16 vessels with significant lesions, 15 totally occluded vessels, one vessel with diffuse atherosclerosis, and two non-evaluable vessels due to severe calcifications, whereas ICA revealed six normal vessels, one vessel with an insignificant lesion, 12 vessels with significant lesions,16 totally occluded vessels, three vessels with diffuse atherosclerosis, and two vessels that failed to be cannulated or visualized (abnormal posterior origin); therefore, the agreement between CCTA and ICA was accepted (kappa value = 0.67).

For the ramus intermedius, CCTA revealed two vessels with significant lesions and two totally occluded vessels, which were findings consistent with the results of ICA, indicating that the agreement between CCTA and ICA was good (kappa value = 1.0).

In our study, there were 97 evaluable grafts. The most frequently evaluated grafts were venous (59 SVGs) and arterial (38 LIMA grafts) grafts.

We evaluated 38 LIMA grafts; CCTA detected 29 patent grafts, seven non-patent grafts, and two non-evaluable grafts due to artifacts caused by metallic clips, whereas ICA detected 28 patent grafts, four non-patent grafts, and six grafts that failed to be cannulated (Fig. 1).

a ICA of a male patient post-CABG showing LIMA graft cannulation. b CCTA of the same post-CABG (curved MPR technique) showing a patent LIMA along its length with good anastomotic site and good distal opacification of LAD. c CCTA of the same patient post-CABG (volume-rendering images) showing patent LIMA to LAD, patent SVG to ramus intermedius, and patent SVG to RCA

In terms of venous grafts, 59 venous grafts were evaluated. CCTA revealed 20 patent grafts and 39 non-patent grafts, whereas ICA revealed only 12 patent grafts, 39 non-patent grafts, and eight grafts that failed to be cannulated.

In this study, we calculated the radiation dose in both CCTA and ICA as dose area product (DAP) (mGy cm2) and found a significantly lower radiation dose in CCTA than in ICA (1165.77 ± 123.54 vs. 47589.78 ± 6967.53, p < 0.001).

We compared the different factors affecting LIMA graft patency and our findings that variable cardiovascular risk factors such as age, sex, DM, hypertension, and smoking, have no significant influence on LIMA graft patency. Dyslipidemia, as evaluated by LDL and TG levels, had no significant association with LIMA graft patency. Moreover, no correlation was observed between LVEF and LIMA graft patency. Furthermore, no correlation was found between the mean duration since CABG and LIMA graft patency.

The severity of native vessel stenosis (LAD) has been evaluated, and all LIMA grafts were anastomosed to either significant stenosis or total occlusion, so we could not assess the relation between LAD stenosis severity and graft patency (Tables 2, 3).

Regarding SVG patency, we examined the same determinants of graft patency and found no association between graft patency and different risk factors, including age, sex, DM, hypertension, obesity, and smoking, and SVG patency and the severity of native vessel lesion, but we found a significant association between SVG patency and LDL and TG levels (LDL level: 68.02 ± 29.73 mg/dL vs. 104.45 ± 15.24 mg/dL; p = 0.002) (TG level: 109.78 ± 22.97 mg/dL vs. 127.00 ± 22.03 mg/dL; p = 0.05). Furthermore, lower LVEF values have been associated with lower SVG patency (62.83% ± 6.11% (range, 55.0%–70.0%) vs. 55.4% ± 7.45% (range 40.0%–67.0%; p = 0.04)) (Tables 4, 5, 6, 7).

In this study, six LIMA grafts failed to be cannulated by ICA and were evaluated using CCTA, two grafts were patent, three grafts were non-patent, and one graft was non-evaluable due to metallic clips. Furthermore, eight venous grafts failed to be cannulated by ICA and were evaluated using CCTA. We found two patent grafts, two grafts with significant stenosis, and four totally occluded grafts.