History
A 59-year-old male patient, who had undergone triple coronary artery bypass grafting (CABG) three months ago, came to the hospital with nonspecific symptoms. He had a history of coronary stenting five years ago and had been under anticoagulation therapy. A prospectively ECG-triggered sequential CT scan with a dual source photon-counting detector CT, NAEOTOM Alpha®, was performed to evaluate the patency of the grafts, the anastomoses and the stent.
Diagnosis
CCTA images revealed triple bypass grafts with three coronary anastomoses. A left internal mammary artery (LIMA) graft, originating off the proximal left subclavian artery (LSA), was anastomosed end-to-side to the distal left anterior descending artery (LAD). Two right saphenous vein grafts (SVGs), originating from the anterior wall of the ascending aorta, were present – the upper one, laid over the main pulmonary artery, was anastomosed end-to-side to the first diagonal branch (D1) of the LAD; the lower one, with an external support of a VEST device, was anastomosed end-to-side to the posterior descending artery (PDA). The middle segment of this SVG appeared thin. Two severe stenoses were visualized in the distal segment. The anastomosis was patent, however, narrowed. The LIMA graft and the upper SVG along with their anastomoses remained patent, with no evidence of stenosis or occlusion. A hypoattenuating area in the stent implemented in the mid LAD was seen suggesting an in-stent re-stenosis. Evaluation of the native coronary arteries showed extensive calcifications. Mixed plaques were seen in the left main coronary artery (LM), the proximal LAD, and the left marginal branch of the circumflex (Cx), causing moderate stenoses (50–69%). Calcified plaques, causing severe stenoses (>70%) in the proximal D1 and the distal right coronary artery (RCA), as well as moderate stenoses in the LM, the PDA and the first proximal marginal branch of the RCA (RMA1) were also seen. The coronary system was right dominant. There was no evidence of any cardiac structural abnormalities.
Based on CCTA findings, a selective coronary angiography was considered, however, not performed immediately, as the patient had no specific symptoms.
Fig. 1: A cinematic VRT image (Fig. 1a) and a curved MPR image (Fig. 1b) show the SVG with a VEST device anastomosed to the PDA. The middle segment appears thin. Two severe stenoses (arrows) are visualized in the distal segment. An oblique MPR image shows the anastomosis of the SVG to the PDA, which is patent, but narrowed (Fig. 1c, arrow).
Fig. 2: A cinematic VRT image (Fig. 2a) and curved MPR images (Fig. 2b & 2c) show a patent anastomosis of the LIMA graft to the distal LAD (Fig. 2a & 2b, arrows) and the SVG to the D1 (Fig. 2a & 2c, dotted arrows).
Fig. 3: A cinematic VRT image (Fig. 3a) and curved MPR images of the LAD (Fig. 3b) and the left marginal branch of the Cx (Fig. 3c) show extensive calcification. Moderate stenoses caused by mixed plaques (arrows) in the LM, the proximal LAD, and the left marginal branch of the Cx are also seen.
Comments
SVGs are the most frequently used conduits in CABG. The main limitation to their use is a higher rate of occlusion compared to arterial conduits. Previous studies have shown that SVG failure is mainly driven by intimal hyperplasia, an adaptative response to higher pressures of the arterial circulation. The VEST device, an external support for SVGs, has been proposed as a mechanical approach to minimize the post-implantation dilatation of the SVGs and to improve the graft flow patterns and the subsequent development of intimal hyperplasia. [1] As a SVG failure may have significant adverse clinical effects in patients, follow-ups on its patency are important. CCTA has been increasingly performed in post-CABG assessment, as it is non-invasive and can reliably depict the entire course of the grafts with a single bolus of contrast media at a short acquisition time. The challenge, in this case, is to visualize the graft lumen without the interference of the blooming and/or metal artifacts caused by the metal struts of the VEST device.
PCD-CT provides energy-resolved CT data at increased spatial resolution, with inherent spectral information, without electronic noise. [2] Virtual monoenergetic images (VMIs) can be reconstructed and displayed at a low energy level (55 keV in this case) to achieve an increased contrast enhancement and an improved visualization of the vessel lumen. ZeeFree, a novel reconstruction technique, using a non-rigid registration in the reconstruction process between the transitions of adjacent cardiac cycle acquisitions, is implemented in standard image reconstruction to correct and reduce potential misalignment caused by insufficient patient breathhold, movement or irregular heart rate during the acquisition. [3] Furthermore, a combination of a high temporal resolution of 66 ms from the dual source CT principle also in spectral reconstructions such as VMIs, a refined Quantum Iterative Reconstruction algorithm (QIR), an optimized image reconstruction kernel (Bv56) and an increased spatial resolution contributes to a clear visualization of the two severe stenoses of the SVG inside the VEST device, without interference of blooming or metal artifacts. The assessment of the LIMA grafts, the SVG without the VEST device, the anastomoses, the stent and the native coronary arteries is also successful.
Examination Protocol