History
A 48-year-old male patient, suffering from a Non-ST-Elevation Myocardial Infarction (NSTEMI), underwent percutaneous coronary intervention (PCI) with multi-vessel coronary stent implantations two years ago. The patient had no traditional risk factors for coronary artery disease (CAD). This unexpected incident had profoundly affected his life, causing substantial stress, and even panic attacks leading to several emergency department visits. The patient also discontinued his statin therapy due to adverse effects. Given the patient's relatively young age and the psychological impact on his symptoms, a non-invasive diagnostic method was preferred over an invasive catheterization procedure for follow-up. Therefore, a coronary CT angiography (CCTA) was performed on a novel dual-source photon-counting detector (PCD) CT scanner, NAEOTOM Alpha®, using an ultra-high resolution (UHR) scan mode (Quantum HD Cardiac) to evaluate the coronary plaque burden and associated risks, as well as the patency of the stents. The patient was prepared with intravenous administration of 10 mg Metoprolol and two sublingual doses of Nitroglycerin prior to the CT scan.
Diagnosis
UHR CCTA images showed five patent stents with different diameters* – one (4 mm) in the proximal right coronary artery (RCA), another small one (2.5 mm) in the posterolateral branch of the distal RCA, two interconnected (3.5 mm) in the distal left anterior descending artery (LAD), and a large one (3 mm) in the distal circumflex (Cx). All the stents were free of in-stent stenosis. A non-calcified plaque in the proximal RCA was seen, causing mild stenosis (25 – 49%). Two other non-calcified plaques with high-risk plaque (HRP) features of spotty calcifications and positive remodeling, were seen in the proximal and mid LAD, causing mild stenosis. CT findings were classified as CAD-RADS 2/P2/HRP/S. Due to absence of acute symptoms, further invasive workup was not necessary.
Fig. 1: Curved MPR images show 5 patent stents with different diameters – one (4 mm) in the proximal RCA, another small one (2.5 mm) in the posterolateral branch of distal RCA (Fig. 1a), two interconnected (3.5 mm) in the distal LAD (Fig. 1b) and a large one (3 mm) in the mid Cx (Fig. 1c). No signs of in-stent re-stenosis were evident in all stents, including the small one in the distal RCA. A non-calcified plaque (Fig. 1a, arrow) in the proximal RCA is seen causing mild stenosis. Two other non-calcified plaques are seen in the proximal and mid LAD causing mild stenoses (Fig. 1b, arrows). Note that the stent struts and the calcified plaque components can be visually well distinguished (Fig. 1c).
Fig. 2: An axial image and a curved MPR image show two non-calcified plaques (arrows) with HRP features of spotty calcifications and positive remodelling in the proximal and mid LAD causing mild stenosis.
Fig. 3: Two cinematic rendering images show an overview of 5 patent stents with different diameters – one (4 mm) in the proximal RCA, another small one (2.5 mm) in the posterolateral branch of the distal RCA, two interconnected (3.5 mm) in the distal LAD and a large one (3 mm) in the mid Cx. Mild stenoses are shown in the proximal RCA, proximal LAD and mid LAD (arrows)
Comments
CCTA is an indispensable diagnostic tool for ruling out obstructive CAD in patients with a low to intermediate risk profile. [1] While its use in patients with pre-existing CAD is generally more restrained, recent guidelines from the American Heart Association have recognized the value of assessing stent patency for patients experiencing symptomatic changes despite guideline-directed management and therapy – if stents with an internal diameter of 3 mm or greater are present. [2]
The diagnostic challenge posed by blooming artifacts, resulting from severely calcified plaques or the stents’ material, has limited the utility of CCTA in this context. [3] The introduction of the novel PCD-CT technology represents a significant advancement in overcoming these challenges: This technology relies on a direct conversion of the incoming x-ray photons in a semiconductor. The individual detector pixels are defined by a strong electric field without the need of septa between them, therefore, small subpixels can be realized without loss of radiation dose efficiency. This enables imaging at an improved spatial resolution of 110 × 110 × 160 μm3. [4] The significance of these technological advancements is underscored by recent studies, which have demonstrated the potential of PCD-CT to reduce artifacts and improve image quality in non-invasive stent assessment, compared to traditional energy-integrating detector (EID) CT. [5] Initial human studies and phantom studies have shown promising results for UHR PCD-CT in stent evaluation, particularly when employing a sharp vascular convolution kernel. [6,7] This approach has facilitated optimal in vivo visualization of stent lumens, with a recent study achieving a 100% negative predictive value for stent patency evaluation against invasive angiography as the reference standard. [8]
The use of Quantum HD Cardiac CT in this case was beneficial for the patient, allowing for a non-invasive assessment of stent patency and coronary artery disease. Furthermore, the detection of the HRPs necessitates a more aggressive preventive pharmacotherapy. Given the patient's adverse reaction to statins, alternative medications such as PCSK9 inhibitors or ezetimibe could be considered, which have been shown to reduce LDL cholesterol effectively. [9] As there were no target lesions observed, no additional invasive workup was required. The unspecific symptoms the patient experienced was considered unlikely derived from progression of his previous CAD.
In summary, PCD-CT's ability to accurately assess patients with stents has confirmed its value in cardiac imaging. This reliable method could expand the use of non-invasive techniques. As clinical availability, experience and scientific evidence with PCD-CT grows, it might start to shape management practices and influence clinical guidelines.
Examination Protocol
