Triple coronary artery bypass grafts and stents

A 46-year-old male patient, complaining of atypical chest pain, presented himself to the hospital. He had an elevated cardiovascular risk including a history of smoking and hypertension. Five years ago, he had suffered a Non-ST-Elevation Myocardial Infarction (NSTEMI) and had undergone triple coronary artery bypass grafting (CABG) of the left coronary arteries, as well as coronary stenting with three drug-eluting stents (DES) of the right coronary artery (RCA). Grafting was not considered suitable for the RCA at the time. The patient had been on a pharmacotherapy regimen including aspirin, Clopidogrel and beta-blocker. A CT follow-up scan was requested to evaluate the patency of the grafts, the anastomoses and the stents. An ultra-high resolution (UHR) coronary CT angiography (CCTA) was therefore performed on a dual-source photon- counting detector CT (PCD-CT), NAEOTOM Alpha®. The patient received oral Metoprolol (50 mg) and sublingual spray of Nitrate (0.8 mg) prior to the CT scan.

CCTA images revealed triple bypass grafts with three coronary anastomoses. A left internal mammary artery (LIMA) graft, originating off the left subclavian artery (LSA), was anastomosed end-to-side to the distal LAD. Two right saphenous vein grafts (SVGs), originating from the anterior wall of the ascending aorta, had been laid over the main pulmonary artery and were anastomosed end-to-side to the first (D1) and the intermediate (IM) diagonal branches of the LAD. All grafts and anastomoses remained patent, with no evidence of stenosis or occlusion. Three interconnected stents (3 mm in diameter, 71 mm in length), from the origin through the middle segment of the RCA, were seen free of in-stent restenosis.

Extensive calcifications were visualized in the original coronary arteries, causing moderate stenosis (50–69%) in the left main coronary artery (LM) and the posterior descending artery (PDA), severe stenosis (70–99%) in the proximal LAD, occlusions in the mid-LAD, proximal and mid-Cx. The coronary system was right dominant. The gracile Cx was not considered suitable for intervention. There was no evidence of any cardiac structural abnormalities.

Based on the CCTA findings, no further invasive examination was considered and the patient was recommended to begin with intensified statin treatment.

Fig. 2: Curved MPR images show the patency of the anastomoses (arrows): LIMA-distal LAD (Fig. 2a–2b), SVG-D1 (Fig. 2c) and the SVG-IM (Fig. 2d).

CABG and coronary stenting are performed in patients with obstructive coronary artery disease to improve myocardial blood flow and alleviate symptoms. The long-term clinical outcome depends upon the patency of the grafts, the anastomoses and the stents. Traditionally, graft patency is assessed using invasive coronary angiography (ICA); however, the procedure carries an associated risk of complications and encounters technical difficulties. Over the past decade, 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 with a short acquisition time. [1] CCTA assessment for the patency of coronary stents, using conventional CT, has been limited to a borderline of 3 mm stent diameter in the American Heart Association guidelines for patients who experience symptomatic changes despite guideline-directed management and therapy. [2]

A recent study using the UHR mode of PCD-CT achieved a 100% negative predictive value for coronary stent patency evaluation against invasive angiography as the reference standard. [3] This result showed the potential improvement of PCD-CT in the stent imaging. The combination of high temporal resolution (66 ms) from the dual source principle and the increased spatial resolution provided by PCD-CT improves optimal image quality, effectively overcoming the blooming artifact caused by stent struts or calcifications. [4] The photon-counting detectors do not require optical crosstalk to be prevented by separating layers between the individual detector elements. The individual detector pixels are defined by a strong electric field. Therefore, they can be more finely structured than scintillation detectors, [5] resulting in small subpixels without loss of radiation dose efficiency.

In this case, the patency of the triple CABG and the stents, as well as the original coronary arteries, are successfully evaluated by the clinician using the UHR images. No additional invasive workup was required, as no target lesions were observed, which spared the associated risks and costs of invasive coronary angiography for this patient.