Imaging
Published on September 20, 2023 Reading 14 min
Théo PEZEL, Departments of Cardiology and Radiology, CHU Lariboisière, APHP, Paris Core Laboratory MIRACL.ai (INSERM UMRS 942)
Due to its potential diagnostic utility, cardiac CT has become an increasingly used imaging modality in cardiology. In this article, we examine the value of coronary CT in the diagnosis of ischemic heart disease based on the latest European recommendations.
The value of coronary CT in the diagnosis of ischemic heart disease: an approach based on the latest European recommendations. Location of Coronary CT Scan Recent European recommendations have established clear guidelines for the use of coronary CT in the diagnosis of ischemic heart disease. These recommendations suggest that coronary CT can be used as a first-line tool in patients with symptoms of atypical chest pain or an intermediate probability of coronary artery disease, allowing the diagnosis of single or multiple significant stenosis (Figure 1) or even chronic coronary occlusion (Figure 2). It is also recommended to rule out significant coronary artery disease in low-risk patients and to assess the extent of coronary artery disease and guide treatment decision-making in high-risk patients. In addition, coronary CT can also provide information about the composition of atheromatous plaques by identifying vulnerable coronary plaques, which can help predict the risk of cardiovascular (CV) complications and facilitate the choice of treatment. Figure 1. Clinical case of a 69-year-old patient with non-ST elevation ACS showing bituncle lesions at the proximal IVA and middle CD. (Courtesy of the Cardiology and Radiology team, CHU Lariboisière, APHP, Paris) Figure 2. Clinical case of a 71-year-old patient with atypical chest pain for months, revealing a chronic occlusion of the 1st diagonal. (Courtesy of the Cardiology and Radiology Team, CHU Lariboisière, APHP, Paris) Limitations of Coronary CT Although coronary CT has many advantages, it also has certain limitations. First, this technique exposes patients to ionizing radiation. However, the development of machines makes it possible to significantly reduce the radiation exposure of patients with the latest models. In addition, coronary CT may be limited in evaluating calcified stenoses or in patients with cardiac arrhythmias and increased heart rate despite the use of beta-blockers. In fact, the image quality is then worse and therefore the performance of the coronary analysis decreases and the risk of false positive results increases. For coronary artery disease with numerous non-obstructive calcifications, it is common to complete the confirmatory examination with another non-invasive imaging modality such as stress MRI, stress echo, or scintigraphy. Special training is also essential to correctly interpret images and optimize results. How are asymptomatic patients treated during screening? While the management of symptomatic patients with chest pain is now relatively clearly outlined in the latest European ESC 2019 recommendations (Table 1)(1), screening for coronary artery disease in asymptomatic patients at high cardiovascular risk is more complex and requires accurate stratification of cardiovascular risk of our patients. To address this problem, multimodal CV imaging has emerged as an indispensable weapon for the clinician. In fact, the range of options for screening our patients is very wide, from Coroscan to cardiac stress MRI, including stress ultrasound or scintigraphy. The recommendations state that the choice of imaging examination should be tailored to the conduct of the test, patient preference, site experience and availability of the examination. Therefore, our role as clinicians is to know the advantages and limitations of each of these techniques in order to best orchestrate the screening and examination strategy for our patients in daily practice. However, it is important to emphasize that CT scan is the only examination of the range proposed in the recommendations that makes it possible to identify patients with non-stenosing atheroma, indicating the prescription of statin treatment with more specific goals. stricter than current primary prevention. The everyday tool in outpatient cardiology: the coronary calcium score. Principle of coronary calcium score. The coronary calcium score is a simple measurement performed in less than a minute using a cardiac scanner and without the need for contrast injection (Figure 3). )(4). The principle is simple: it detects coronary calcifications, which are defined in a very standardized way by Agatston as: “at least 4 contiguous pixels with > 130 Hounsfield units in a recording without injection”. It is important to remember that the coronary calcium score validated in the American MESA(5) cohort can predict the rate of cardiovascular events at 10 years (Table 2). Due to recent technological advances, the radiation dose for performing a Cal-ic score is now very low and close to that of a chest x-ray. Figure 3. Example of Agatston calcium score measurement in an asymptomatic patient with high cardiovascular risk. Measurement of calcium score based on semi-automated selection of coronary calcifications represented in color at the level of the common trunk (green), anterior interventricular area (yellow) and circumflex (sky blue). Thus, the calcium score can be assessed artery by artery, but the studies and recommendations only refer to the overall coronary calcium score, as described by Agatston(4). LAD: left anterior descending coronary artery (IVA); CX: circumflex coronary artery; RCA: right coronary artery; LM: common core In addition, when interpreting the calcium score, it is important to take into account the age, gender and ethnicity of each patient in order to correctly analyze the result; To do this, you can use the MESA calculator, which is easily available online (Figure 4). Figure 4. Example of a normalized coronary calcium score using the MESA cohort website (https://www.mesa-nhlbi.org/Calcium/input.aspx)(5). 48-year-old Caucasian patient with a calcium score reading of 90, which corresponds to the 91st percentile and therefore reflects significant calcified atheromatous burden and therefore a very high cardiovascular risk. Indications for performing a coronary calcium score? The indications for performing the coronary calcium score are currently relatively clear in the recommendations that propose the use of the coronary calcium score as a stand-alone true cardiovascular risk factor (ESC class IIb recommendations)(1,2). Therefore, the calcium score can be prescribed to any patient who has at least an intermediate or low cardiovascular risk, but has a family history of coronary artery disease. In practice, it is easiest to remember that you are looking at a symptomatic patient who has already been identified as being at high cardiovascular risk, or a coronary patient who is already known to be in secondary prevention Under no circumstances should you prescribe a calcium score. In fact, the calcium score does not provide additional information for patient care in these situations (Table 3). But how then should the value of a coronary calcium score be interpreted? For the analysis of the coronary calcium score, standardized categories with scores were developed to facilitate its interpretation: – Calcium score = 0: no calcified plaque (very low CV risk); – Calcium score 1 to 10: little calcified plaque (low CV risk); – Calcium score 10 to 100: mild calcified atheromatous burden (intermediate CV risk); – Calcium score 100 to 400: moderate calcified atheromatous burden (high CV risk); – Calcium score > 400: significant calcified atheromatous burden (very high CV risk). In addition, the American AHA/ACC recommendations suggest the use of the calcium score as a tool to indicate the prescription of statins with (3.7): – Calcium score = 0: no statin (unless the patient is a smoker, diabetic or has a serious family history). ); – Calcium score 1 to 99: Statins should be considered if the patient is over 55 years old; – Calcium score ≥ 100 (or at the 75th percentile according to the MESA calculator): Statins are recommended. Finally, very recent data presented at the last European EACVI Congress in Barcelona in 2023 showed that a coronary calcium score > 300 or > 85th percentile is equivalent to secondary prevention in terms of long-term prognosis for patients (data currently being published in). JACC CV imaging). The revolution of photon-counting cardiac scanners The world of cardiac scanners is undoubtedly experiencing an unprecedented technological revolution: the arrival of photon-counting scanners! These scanners, currently being developed in very few French centers (Bordeaux IHU, Paris Gustave Roussy, Monaco, Lille, etc.), represent a real technological masterpiece in terms of spatial and temporal resolution, with a cost of around 3.5 million Euros per device. The aim of this part is to introduce the basic principles of this scanner of the future for our practice! Basic principle The technology used by photon counting scanners is completely different from current scanners in terms of image capture (8,9). The detectors commonly used in conventional scanners are solid-state scintillation detectors, which acquire images in two steps: 1) the absorption of X-rays, which are converted into visible light in the scintillation crystal, and 2) the conversion of the obtained light into an electrical one Signal a photodiode attached to the back of each detection cell. In photon counting scanners, fixed scintillation detectors are replaced by a semiconductor that can convert X-ray photons directly into electrical signals (Figure 5)(8). Thus, these new detectors make it possible to expand the limits of current scanner detectors by providing tomodidensitometric data with very high spatial resolution (about three times better than with a traditional scanner) without electronic noise and are characterized by an improved contrast ratio and also a lower noise Radiation dose. In fact, these new scanners, with better image quality and much greater spatial resolution, enable a dose reduction of an estimated 40%(8,10). Figure 5. Principle of the photon counting scanner (8). Differences between the classic solid state scintillation detector and the new photon counting detector. (Courtesy of Siemens Healthineers) Advantages This new tool offers many advantages over traditional cardiac imaging techniques. Firstly, it allows you to get high quality images in a much shorter time. While traditional scanners often require tens of seconds to capture cardiac images, the photon counting scanner can do this in just a few seconds. This significantly reduces X-ray exposure time and improves patient comfort. In addition, the photon counter cardiac scanner provides excellent spatial and temporal resolution, allowing smaller coronary lesions to be detected and cardiac function to be accurately assessed. In certain cases, it also offers the possibility of carrying out examinations without injecting contrast agents, thanks to its ability to detect photons naturally emitted by the body. This is particularly advantageous for patients with impaired kidney function or allergies to contrast media containing iodine. Interpretation in everyday clinical practice When creating the coronary scan, increasing the spatial resolution is crucial in order to further improve the diagnostic performance at the coronal level (11). In fact, several advantages are highlighted with these new scanners: – Improvement of in-stent analysis in a patient already wearing a coronary stent to assess in-stent retenosis (Figure 6); – Possibility of using algorithms to subtract coronary calcification (Figure 7); – possible analysis of the smallest coronary arteries and coronary branches (septal, diagonal, marginal, etc.); – Improve identification of plaques at risk through better visualization of coronary plaque and its composition; – Improve morphological analysis of valve prostheses such as TAVI to detect thrombi during TAVI (Figure 8). Figure 6. Optimization of coronary in-stent analysis through improved spatial resolution of the photon counting scanner. (Courtesy of Siemens Healthineers) Clinical case of a 77-year-old patient with known coronary artery disease who was treated for anterior ST+ ACS and revascularized at the proximal IVA 3 years ago. The patient has been suffering from atypical angina pectoris pain again for 10 days. A Coroscan is performed using a NAEOTOM Alpha® photon counting scanner (Siemens Healthineers). The very high spatial resolution of the examination allows visualization of an intra-stent space without intra-stent restenosis with a perfectly permeable stent. Figure 7. Principle of the coronary calcification subtraction algorithm on a photon counting scanner. (Courtesy of Siemens Healthineers) Clinical case of a 52-year-old diabetic patient with calcified stenosis of the trunk performed with a NAEOTOM Alpha® photon counting scanner (Siemens Healthineers). On the left image (native) we can see the presence of a calcified coronary stenosis at the level of the common trunk. Then, on the image to the right, we apply a coronary calcification subtraction algorithm (Pure Lumen, Siemens Healthineers), which completely removes the image of calcifications. This reduces the impact of artifacts in contact with calcifications and thus improves the interpretation of this Koroscan. Figure 8. Searching for a thrombus on a TAVI aortic prosthesis using a photon counting scanner. Reconstructions with high spatial resolution made it possible to evaluate the thickening of the hypodense leaflets for valve prostheses. (According to Van der Bie J et al.(12)) Future perspectives FFR-CT: an innovative technique for the diagnosis of coronary artery disease Fractional flow reserve (FFR) is a key parameter for determining the severity of coronary stenosis and for supporting clinical decision-making. FFR-CT (fractional flow reserve from coronary CT angiography) is a non-invasive technique that allows assessment of FFR with a coronary scanner, thus representing a promising alternative to invasive angiography (13,14). This part of the article presents the technical principle, the main publications, the advantages, disadvantages and limitations of this technique, as well as its interest in clinical routine and future prospects. Technical principle FFR-CT combines coronary imaging using CT with a computer simulation of blood flow in the coronary arteries. This technique uses complex algorithms to calculate blood pressure in the coronary arteries and determine FFR. FFR-CT thus makes it possible to predict the functional effects of coronary stenosis without having to resort to invasive intervention (Figure 9). It provides precise information about the severity of a stenosis and helps make informed treatment decisions. It is important to emphasize that the latest American AHA/ACC recommendations of 2021 included FFR-CT in the examinations to be performed for chest pain with recommendation level IIa. Figure 9. Example of FFR-CT performed with a conventional scanner. Image of coronary perfusion obtained from a standard coronary CT scan. There is a hemodynamically significant stenosis of the middle IVA with an FFR of 0.69, significantly lower than 0.75. (Courtesy of HeartFlow®) Key Publications The FFR-CT technique has been the subject of several clinical studies and major publications. Among the most important publications we can mention the NXT study (HeartFlowNXT)(15), which demonstrated the superiority of FFR-CT compared to visual assessment alone in predicting invasive FFR. Another important study is the PLATFORM trial(16), which showed that the use of FFR-CT reduced the number of unnecessary invasive angiograms without compromising patient safety. Advantages FFR-CT has many advantages over invasive angiography. Firstly, it is non-invasive and therefore avoids the risks and complications associated with invasive surgery. In addition, it enables a precise functional assessment of coronary stenoses, which is helpful in making treatment decisions. FFR-CT can also reduce the number of unnecessary invasive angiograms, which can result in significant cost savings. Disadvantages and Limitations Despite its many advantages, FFR-CT also has disadvantages and real limitations. First, the technique requires a high-quality coronary scanner and expertise in image interpretation. In addition, FFR-CT may be less reliable in calcified lesions, bifurcation lesions, or in small caliber arteries. Additionally, note that several studies have shown that FFR-CT is less accurate for assessing lesions in the distal branches of the coronary arteries. Finally, access to this tool in everyday clinical practice is still very limited and the cost of an analysis by the company HeartFlow® is between 900 and 1,500 US dollars per patient, which today represents the main obstacle to the dissemination of this innovative technique. Interest in clinical routine FFR-CT is of considerable interest in clinical routine, especially for patients with symptoms of coronary artery disease. It helps avoid unnecessary invasive angiograms by identifying patients who do not require coronary intervention. Additionally, FFR-CT can help optimize treatments by identifying patients who would benefit most from revascularization. However, the standard Koroscanner should not be ignored. In fact, the multicenter CREDENCE study recently demonstrated in 612 patients that Coroscanner anatomical data and plaque analysis (patchy calcification, positive plaque remodeling, napkin ring sign, and the presence of low-attenuation plaque <50UH) were superior to functional imaging including perfusion analysis and FFR-CT to diagnose FFR <0.80 as the gold standard(17). Future perspectives FFR-CT opens up many perspectives for the diagnosis of coronary heart disease. In the future, we can expect technical improvements that will allow better assessment of calcified lesions or small-caliber arteries. In addition, the combination of FFR-CT with other imaging methods, such as cardiac MRI, could provide even more precise information about the functionality of coronary stenoses. Finally, FFR-CT could also be used to monitor the evolution of coronary lesions over time and evaluate the effectiveness of treatments. Conclusion Coronary CT represents a major advance in the diagnosis of ischemic heart disease. Based on the latest European recommendations, this imaging technique offers a non-invasive and precise alternative to assess the extent of coronary disease and to guide the choice of treatment. However, it is important to note that coronary CT has some limitations and should be used cautiously, taking individual patient risk factors into account. In order to correctly interpret images and optimize results, highly qualified specialist training is also essential. When screening for coronary artery disease in asymptomatic patients, it is necessary to emphasize the use of coronary calcium score as a true cardiovascular risk factor in its own right to guide and adjust antilipidemic treatment. Finally, the new photon counting cardiac scanner represents a major advance in the field of cardiac imaging. Thanks to its ability to obtain high quality images in a very short time, it offers a precise and non-invasive alternative for the diagnosis of cardiovascular diseases.
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