Summary
Cardiac catheterization has contributed to the progress made in the management of patients with congenital heart disease (CHD). First, it allowed clarification of the diagnostic assessment of CHD, by offering a better understanding of normal cardiac physiology and the pathophysiology and anatomy of complex malformations. Then, it became an alternative to surgery and a major component of the therapeutic approach for some CHD lesions. Nowadays, techniques have evolved and cardiac catheterization is widely used to percutaneously close intracardiac shunts, to relieve obstructive valvar or vessel lesions, and for transcatheter valve replacement. Accurate imaging is mandatory to guide these procedures. Cardiac imaging during catheterization of CHD must provide accurate images of lesions, surrounding cardiac structures, medical devices and tools used to deliver them. Cardiac imaging has to be ‘real-time’ with an excellent temporal resolution to ensure ‘eyes–hands’ synchronization and ‘device–target area’ accurate positioning. In this comprehensive review, we provide an overview of conventional cardiac imaging tools used in the catheterization laboratory in daily practice, as well as the effect of recent evolution and future imaging modalities.
Résumé
Le cathétérisme cardiaque a contribué aux progrès réalisés dans la prise en charge des cardiopathies congénitales. Il a tout d’abord permis de mieux appréhender l’anatomie et la physiologie des malformations complexes. Le cathétérisme est de nos jours de plus en plus interventionnel, suppléant ou complétant la chirurgie cardiaque. Il permet entre autres l’occlusion de shunt, la dilatation de valves, vaisseaux ou conduits sténosés et le remplacement valvulaire percutané. Une imagerie de précision est nécessaire en salle de cathétérisme pour guider ces interventions. Cette imagerie doit permettre de bien visualiser les lésions à traiter, les structures avoisinantes, les dispositifs médicaux et les systèmes permettant de les acheminer. Cette imagerie doit être temps-réel pour permettre à l’opérateur une bonne coordination « main–œil » et « prothèse–zone cible ». Dans cette revue générale, nous abordons les avantages et les inconvénients des outils d’imagerie actuellement utilisés en salle de cathétérisme, l’impact des évolutions récentes ainsi que les perspectives futures.
Introduction
Cardiac catheterization has contributed to the progress made in the management of patients with congenital heart disease (CHD). It is widely used to percutaneously close intracardiac shunts , to relieve obstructive valvar or vessel lesions, and for transcatheter valve replacement . Cardiac imaging has always been closely related to the development of cardiac catheterization. Catheterization became feasible under fluoroscopy . It remains the cornerstone of cardiac imaging, but two-dimensional (2D) and three-dimensional (3D) echocardiography has become a complementary useful tool in the catheterization laboratory . Fusion imaging between fluoroscopy and echocardiography or tomography further assist complex percutaneous procedures . Multi-modalities imaging in the catheterization laboratory is thus nowadays available. In this comprehensive review, we provide an overview of conventional cardiac imaging tools used in catheterization laboratories in daily practice, as well as the effect of the recent evolution of and future imaging modalities. First, conventional fluoroscopy and its improvement are described. Then, the effect of multimodal echocardiography is discussed with regards to CHD current practice in the catheterization laboratory. Other 3D imaging techniques are further described, with their potential application in CHD. The focus is on the strengths and weaknesses of each imaging modality.
How the feasibility of cardiac catheterization was demonstrated
The first cardiac catheterization in man was demonstrated by X-ray imaging in 1929 . At age 25, while receiving clinical instruction in surgery, Werner Forssmann (1904–1979) passed a urethral catheter through one of his left antecubital veins until its tip entered the right atrium. He then walked to the radiology department where an X-ray was taken . Together with Cournand and Richards, he obtained the Nobel Prize in 1956. During his Nobel lecture, Cournand stated elegantly that cardiac catheterization was the ‘key in the lock’ to summarize its effect on the diagnosis and treatment of heart diseases. In the 1950s, dynamic images of heart cavities were feasible through the development of cineangiograms on roll films and image intensifiers. Percutaneous treatments, such as pulmonary valvar stenosis dilation (1953) and balloon atrial septostomy (1966) then became feasible under fluoroscopy guidance .
Fluoroscopy: the cornerstone of interventional catheterization
Temporal resolution and image cadence with fluoroscopy are very high. The frame rate in routine practice is adjusted between 10 and 30 images per second to limit irradiation. Fluoroscopy allows a user-friendly real-time cardiac imaging. The radio-opacity of medical devices, wires and delivery sheaths is high, facilitating interventional procedures. Excellent temporal resolution ensures ‘eyes–hands’ synchronization and ‘device–target area’ accurate positioning. Since the very beginning of cardiac catheterization, and still today, almost all diagnostic and interventional catheterization procedures are performed under fluoroscopy. Thus, according to most operators, fluoroscopy is the cornerstone of catheterization and no other cardiac imaging technique is absolutely necessary ( Table 1 ).
| Fluoroscopy | Echocardiography | CT scan Roadmapping | 3D printing | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Conventional | DSA | TTE | TOE | ICE | 2D | 3D | Echonavigator ® | |||
| ASD closure | +++ Feasible without in some teams | – | ++ Sufficient in some teams | ++ | + | ++ Sufficient in most teams | ++ Complementary useful tool but not essential | ++ Interest remains to be demonstrated | – | ? |
| VSD closure | +++ | – | ++ | ++ | – | ++ Sufficient in most teams | + May be a complementary useful tool but not essential | + Interest remains to be demonstrated | – | ? |
| PDA closure | +++ Without in premature | – | + Only used in echo-guided closure in premature | – | – | + | – | – | – | – |
| Pulmonary valvuloplasty | +++ | – | – | – | – | – | – | – | – | – |
| Aortic valvuloplasty | +++ | – | + Useful but not essential | + | – | ++ | + | – | – | ? |
| Foetal aortic valvuloplasty | – | – | +++ | – | – | ++ | – | – | – | – |
| Mitral valvuloplasty | +++ | – | ++ | – | – | ++ | + | – | – | – |
| Aortic (re)coarctation stenting | +++ | – | – | – | – | – | – | – | + | ? |
| Pulmonary artery angioplasty | +++ | + | – | – | – | – | – | – | + | ? |
| Pulmonary valve replacement | +++ | – | – | – | + Used by some teams in complex cases but not essential | + Used by some teams in complex cases but not essential | – | ? | + | + |
| Tricuspid valve replacement | +++ | – | + | + | + | + | ? | + | – | ? |
Improvement in fluoroscopy imaging
Digital subtraction angiography
Digital subtraction angiography is a fluoroscopy technique used to enhance blood vessel visualization. Contrast injection is delayed by around 2 seconds after the beginning of image acquisition. The frame rate is adjusted to 4–6 images per second. Final images are produced by subtracting the pre-contrast image (‘the mask’) from later images. Digital subtraction angiography is useful in CHD catheterization , for example to delineate aorto-pulmonary collaterals in Tetralogy of Fallot with pulmonary atresia, arterio-venous fistula and coronary fistula ( Fig. 1 , Video 1 ).
Mono versus biplane tube
Some CHD catheterization laboratories rely on a single X-ray tube, whereas the value of biplane tube is advocated in other centres and recommendations . Biplane orthogonal imaging is recommended to ensure the accuracy of target lesion description. Nevertheless, all diagnostic and interventional catheterization procedures are feasible using a single mobile tube. Dual tube imaging allows faster biplane imaging during the same contrast injection. Thus, in some long procedures, such as pulmonary valve replacement, it may decrease the amount of injected contrast and help prevent contrast-induced nephropathy. Today, however, with the availability of low-osmolar iodine contrast, this is no longer a critical issue in paediatric cardiology, but it may be more relevant in adult CHD. Dual tube imaging is particularly useful in procedures involving the great vessels. It allows biplane imaging without moving the tubes or the examination table. Reference images are available for the interventionist, with anatomical markers such as bones without position changes, facilitating device or balloon positioning. Dual tube imaging may theoretically increase fluoroscopy time, but attention is taken by the operator to use simultaneous dual tube imaging in selected cases. Furthermore, in single X-ray tube imaging, the fluoroscopy time may be increased by tube position movement and image adjustment when multiple working incidences are necessary. Furthermore, with improvements in tube technology, the results of a recent study demonstrated that biplane imaging with flat-panel detectors produced less irradiation than a conventional system equipped with an image intensifier .
Spatial relationship may also be investigated through rotational angiography . A dynamic angiogram is recorded during a semi-rotation of the X-ray tube ( Video 2 ). However, it remains a 2D-imaging technique with the same limitations. Furthermore, it does not provide easily comprehensive video sequences and irradiation is increased. Thus, it remains little used in clinical practice.
Limits of fluoroscopy
Strength and weaknesses of fluoroscopy are displayed in Table 2 .
| Fluoroscopy | Echocardiography | Echonavigator ® | 3D-CT roadmapping | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Conventional | DSA | TTE | TOE | ICE | 2D | 3D | |||
| Minimum number of operators | 1 | 1 | 1 | 2 | 2 | 2 | 1 | ||
| Ease of use | +++ | ++ | +++ | ++ | + | +++ | + | + | + |
| Imaging cadency | +++ | + | +++ | +++ | +++ | +++ | + | ++ | – |
| Real-time | Yes | Yes | Yes | Yes | Yes | Yes | Yes | Yes | No |
| 3D | No | No | Yes | Yes a | Yes | No | Yes | Yes | Yes |
| Irradiation | +++ | ++ | – | – | – | – | – | +/– b | +/– b |
| Medical device visualization | +++ | + | ++ | ++ | ++ | ++ | ++ | +++ | +++ |
| Wires visualization | +++ | + | + | + | + | + | – | +++ | +++ |
| Target lesion visualization | Requires iodine contrast | +++ For intracardiac shunt, valves and ventricular outflow tracts | +++ For intracardiac shunt and valves | +++ For ventricular outflow tracts and vessels | |||||
| Side effects | Irradiation | Irradiation | None | Oesophageal perforation | Vascular access | None | None | None | None |
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