Computed tomography coronary angiography for imaging in children with Kawasaki disease: An update

Kawasaki disease (KD) is an acute febrile illness that usually affects children below 5. KD has a predilection for involvement of medium-sized arteries and the development of coronary artery abnormalities (CAAs) is an important complication.1 If untreated or diagnosed late, CAAs can occur in up to 25% of KD patients, but with prompt treatment, this can be reduced to <5%.1 CAAs of KD need long-term surveillance as these are prone to the development of complications such as thrombosis, coronary artery calcification, and steno-occlusive lesions. Two-dimensional echocardiography (2DE) has been the imaging modality of choice in patients with KD both in the acute phase and during long-term follow-up. However, there are several inherent limitations of 2DE. Other modalities for coronary artery assessment in KD include invasive catheter coronary angiography (CCA), CT coronary angiography (CTCA), and magnetic resonance coronary angiography (MRCA).2 Recently, CTCA has become a feasible imaging modality that is being increasingly used in clinical practice for comprehensive assessment of CAAs in patients with KD.3 In this review, we have discussed the evolution and role of CTCA in KD. Coronary artery abnormalities require prompt and accurate diagnosis as timely intervention prevents progression and complications.1 CAAs in the acute phase of illness include coronary artery dilatation and aneurysms. These may either undergo remodeling or show resolution, especially if the size is small. Larger CAAs may persist and may develop thrombosis or stenoses.2, 4, 5 Precise and accurate imaging is required to evaluate these complications. Two-dimensional echocardiography is the current standard for KD care, offering the advantages of noninvasiveness, cost-effectiveness, and convenience.2, 6 However, it has several limitations like operator dependency, inability to assess the left circumflex artery, and distal segments of coronary arteries. Additionally, poor acoustic windows in older children hinder coronary artery assessment. Several complications (e.g., coronary thrombosis, calcifications, and stenosis) are liable to be missed on 2DE.1, 2 Coronary artery abnormalitie is the gold standard for detecting CAAs in patients with KD. However, it is invasive, has high radiation exposure, and cannot be frequently repeated. Also, it fails to demonstrate mural abnormalities.2 Cardiac MR is time-intensive, often needs general anesthesia (especially in infants and young children who cannot do breath holding), and demands special expertise. MRCA is especially useful for the evaluation of coronary thromboses.7 Considering the limitations of 2DE, CCA, and MRCA, there is a requirement for an imaging technique that can address these issues. CT coronary angiography has now emerged as an important modality for imaging coronary arteries in KD. It is noninvasive and can be performed as a daycare procedure without the requirement for anesthesia or heavy sedation.2, 3, 5 CTCA provides precise details of lumen and mural abnormalities along the entire length of coronary arteries. Carbone et al. demonstrated the accuracy of CTCA in characterizing and measuring CAAs, suggesting it could reduce the need for invasive CCA.8 CT coronary angiography is a noninvasive imaging modality for assessment of coronary arteries. This modality emerged after the advent of 64-multidetector CT. However, its use in the assessment of CAAs of KD was restricted due to high radiation exposure (5–7 mSv) and poor image quality due to low temporal resolution.9 With the emergence of higher detector and dual-source CT scanner (DSCT) technology, there is advancement in temporal resolution and spatial resolution (image quality), which, along with radiation optimization techniques, has facilitated scanning of young children who inherently have high heart rates.2, 3 Moreover, CTCA can be done with only light sedation in infants. In our experience, children less than 5 years of age require no sedation.3 Newer generation CT scanners can provide precise information on size and location of CAAs with high spatial resolution and improved image quality.2, 10 Consequently, CTCA is increasingly becoming the preferred imaging modality for detailed coronary artery assessment in KD (Table 1). The problem of high radiation exposure has been largely addressed by higher detector and DSCT scanners that have high grades of temporal resolution and fast gantry rotation. As a result, patients can now be assessed with sub-millisievert radiation exposure.2, 10, 11 Van Stijn et al. have recently published their work on coronary artery evaluation in 70 KD patients using a 3rd generation DSCT platform (2 × 192-Slice CT scanner). The authors reported a radiation exposure of 0.3–9.4 mSv.12 Mean effective radiation exposure in our own experience is 0.83 mSv.13 Gellis et al. have shown good inter- and intra-observer agreement for measurements of coronary arteries on CTCA. Furthermore, there was good agreement between CTCA and 2DE readings for most coronary artery segments. For the proximal coronary segments, there was a high degree of agreement in the absolute measures between CTCA and 2DE; however, the circumflex and distal segments showed more variation. The authors reported that 2DE readings tended to be higher than CTCA when the coronary diameters were large.14 Distal stenosis, missed by 2DE, can be clearly delineated on CTCA.14, 15 Magnetic resonance coronary angiography is also being evaluated for assessment of CAAs. Compared with CTCA, MRCA has lower spatial and temporal resolutions.2, 16 Additionally, typically requires longer scanning times, ranging between 45 and 60 minutes, and requires general anesthesia in infants and young children. CTCA, in contrast, provides superior assessment of steno-occlusive lesions.16 MRCA is superior, nevertheless, when evaluating coronary arteries with significant intramural calcifications (which can cause a blooming artifact on CT), determining the viability and myocardial perfusion, and periodically monitoring thrombotic aneurysms.2, 13 CT coronary angiography can explicitly delineate the entire length of all coronary arteries both during the acute and convalescent phases of KD and during the long-term follow-up where 2DE becomes increasingly challenging due to poor acoustic window (Table 1). It precisely evaluates the (i) distal segments of coronary arteries along with their branches, (ii) left circumflex coronary artery, and (iii) intramural thrombi (Figure 1A–C). CTCA scores over CCA for follow-up studies as it is noninvasive, has much less radiation exposure, demonstrates temporal changes in CAAs (e.g., resolution, persistence, or remodeling), mural (e.g., calcifications), and luminal (e.g., stenosis, occlusion) abnormalities as well (Figure 1D–F).3, 15 Additionally, calcium scoring, integrated into follow-up imaging, enhances its utility.17 It is possible to do calcium scoring on follow-up in KD, using low radiation CT procedure without intravenous contrast.17, 18 It has been shown that coronary calcification was usually absent in KD patients who did not develop CAAs during the acute phase. There was a higher risk of coronary calcification in patients who had developed CAAs in the acute phase. In individuals with a remote history of KD, calcium scoring by CT is another helpful method for identifying undiagnosed CAAs.17 Mural calcifications in KD are usually restricted to CAAs and are very dense as compared to the calcifications associated with coronary artery disease. It is currently unknown whether the level of calcification in KD patients has any prognostic significance. If the test is carried out several years after the acute episode of KD, a zero-calcium score suggests that coronary involvement was probably not significant.13 CT coronary angiography data can be used to generate patient-specific hemodynamic models with specialized software. Rebuilding the coronary tree with realistic details is made possible by high-resolution pictures obtained from new image capture sequences19, 20 Application of computational modeling to KD patients may eventually result in individualized treatment plans based on numerical hemodynamic characteristics unique to each patient. Sengupta and colleagues pioneered patient-specific hemodynamic simulations in KD patients, demonstrating that proximal CAAs led to increased shear stress gradients at the neck of the aneurysm. In a follow-up study involving 5 KD patients with CAAs, they showed that hemodynamic measures could better stratify patient risk than diameter alone, with a higher thrombosis risk observed in fusiform aneurysms compared with saccular aneurysms.21 Ischemic areas of the myocardium can now be accurately demonstrated with cardiac single-photon emission computed tomography (SPECT) and CT hybrid imaging.13 Abe et al. have shown that SPECT/CT can assess myocardial hypoperfusion in patients with KD.22 Cinematic rendering (CR) is a new 3D visualization methodology that has recently become available and is being studied in KD patients. It helps in the identification of distal and small-caliber CAAs.20 Primary concern with the use of CTCA in children is the radiation risk. However, present-day CT scanners with radiation optimization techniques have largely addressed this concern and it is now possible to do CTCA with radiation exposures <1 mS.2, 13 Singhal et al. suggested that in children with CAAs on 2DE, CTCA should be considered as a supplemental imaging modality. Treatment planning necessitates a follow-up CTCA when distal CAAs are present on the initial CTCA. Children may be monitored by 2DE if distal CAAs are not seen on CTCA, but CTCA may still be necessary to identify complications such as thrombus, stenosis, and mural calcifications.15 With the emergence of DSCT platform technology, it is now possible to perform CTCA at sub-millisievert radiation exposure. CTCA can detect CAAs along the entire length of the coronary arteries and delineate mural abnormalities that are otherwise very difficult to pick up on 2DE. CTCA can be performed both during the acute and convalescent phases of KD and during follow-up. CTCA is likely to become the preferred imaging modality for evaluating coronary arteries in children with KD. All authors have contributed to the preparation of the manuscript and agreed for the peer review and publication. The authors declare no conflicts of interest. The data underlying this article are available in the manuscript and in our records. These data can be shared upon request.