Imagine ... imaging

This invited editorial refers to ‘Initial experience in ablation of typical atrial flutter using a novel three-dimensional catheter tracking system’ by P. Sommer et al., on page 578 Interventional treatment of cardiac arrhythmias has classically been based on analysis of intracardiac electrograms and imaging through conventional fluoroscopy as well as sophisticated electroanatomic mapping systems.1 The advantage, when training has been intense, is a deep understanding of cardiac arrhythmias mechanisms, triggers and substrates that will be targeted by ablation. On the other hand, the limitations of these techniques are obvious: a long-learning curve, the need for a sophisticated and very expensive equipment, and the potential harm for both the patient and the physician, particularly regarding X-ray exposure.2,3 These disadvantages and the current trend towards a more and more sophisticated technical assistance could eventually limit the use of catheter ablation technique worldwide in the next decade. If one assumes that mechanisms, triggers, and substrates of many common arrhythmias like atrial flutters, atrioventricular nodal reentrant tachycradia, accessory pathways, most of atrial tachycardias, and even atrial fibrillation (particularly paroxysmal) have been elucidated, the ablation therapy is then focused on previously identified anatomical spots such as the cavo-tricuspid isthmus, Koch's triangle, tricuspid and mitral annulus, pulmonary veins, etc. In this setting, ‘sophisticated’ reconstructions are no longer needed, and can even be confusing and can be a source of mistakes. A simple navigation tool is often sufficient in order to reach such anatomical zones and deliver ablation easily and safely. Such a tool has long been available thanks to standard fluoroscopy equipment. Traditional X-ray fluoroscopy is easy to use and affordable, and it can also be used for other procedures such as pacemaker implantation or coronary artery interventions. Its learning curve is short, and there is no need for specially trained medical staff. The main disadvantage lays in the ionizing radiation delivered to the patient and the practitioner. In addition, for some, procedures such as ablation of ventricular or incisional tachycardias, it does not provide sophisticated information on the arrhythmia mechanisms. Presently, it appears that there are two options for the future development of imaging-guided navigation for treatment of arrhythmias. Their goal is similar: they both intend to simplify the procedures and to significantly reduce patient's and practitioner's exposure to ionizing radiation. In contrast, their background and philosophy are highly different. The first one is developed more than 10 years ago and is already in current practice in most of the centres involved in the interventional treatment of arrhythmias: three-dimensional (3D) electroanatomic mapping systems.4 Two consoles are available. Each has provided more than three generations of systems involving many major improvements concerning accuracy of navigation, easiness of performing 3D images of heart cavities (coupled to the possibility of merging with computed tomography scan or magnetic resonance imaging), and analysis of intracardiac potentials. These developments have been of an undeniable value for understanding of complex cardiac arrhythmias such as atrial fibrillation, ventricular tachycardia, and may be even more for incisional tachycardias. Nevertheless, the use of such systems needs a dedicated well-trained staff and the interpretation of maps is sometimes tricky and confusing. In addition, it still requires a significant basic fluoroscopy time, particularly at the beginning of the learning curve. Finally, 3D navigation systems are not ‘direct’ because they need a reconstruction of the target cavity. This means that the ablation catheter is moving inside a ‘virtual’ environment and preliminary mapping is crucially important for carrying out an effective ablation. Treatment can be indeed significantly harmful in case of discrepancy between ‘real’ and ‘virtual’ anatomy, patient movements, etc. A second option emerged a few years ago. We could call it ‘direct’ imaging because it is based on the ‘real’ fluoroscopy images that we are all used to manage. The first significant innovation in this field has been rotational angiography.5–7 It is capable of producing, within several seconds, an accurate 3D ‘real’ fluoroscopy anatomical image facilitating easy navigation of diagnostic and ablation catheters. The disadvantage of this method is that it delivers a significant amount of radiation to the patient. In this issue of the Journal, Sommer et al. report their experience with a new generation of a smart imaging system.8 The guided Medical Positioning System (gMPS, European CE Mark certified), utilizing electromagnetic technology, is based on real-time tracking of ‘sub-millimeter’ size sensors, mounted on diagnostic, or ablation catheters. The 3D position and orientation of sensors can then be calculated in real time and projected graphically on recorded background 2D fluoroscopy (fluoroscopic images recorded only at the beginning of the procedure).8,9 The cardiologist no longer has to take fluoroscopic images of the patient each time the catheter is repositioned. It is smart and revolutionary because it is capable of providing a real time navigation of catheters inside a ‘real’ anatomical 2D fluoroscopy image. There is no need for a preliminarily reconstruction of virtual heart cavities: the technique is quick, easy and allows one to avoid mistakes or lack of accuracy. Therefore, its advantages are clear: the learning curve is expected to be short, the method should be easily implemented in standard fluoroscopy systems, it is supposed to be substantially less expensive than other solutions and above all, it involves a very short radiation time (only several seconds of fluoroscopy). It is obvious that this tool can be further improved: it needs dedicated catheters only with a visible tip (the entire catheters are not yet visualized), as well as some modifications in order to reduce artefacts caused by patient movements, respiration, and heart motion. Finally, the ‘return to tradition’, offered by the gMPS, appears of interest for most of previously discussed issues. In addition to radiation and easy-to-use considerations, the projection may also be performed on a 3D imaging, and can be used for many other procedures such as placement of left ventricular leads for cardiac resynchronization (NCT01519739) or a coronary angiogram.10 This system should also be particularly welcome in the current setting of extensive development of cryotherapy for pulmonary vein isolation, with no need for sophisticated electro-anatomical mapping. In summary, ‘direct’ cardiac navigation based on ‘none or little radiation’ fluoroscopy anatomy can be sufficient to treat a vast majority of cardiac arrhythmias. ‘Indirect’ 3D mapping systems based on a virtual reconstruction still have an undeniable value for treating patients presenting with complex and rare arrhythmias, but also for research purposes in order to better understand arrhythmia mechanisms. We can also assume that both imaging tools will be complementary, used at the same time for difficult procedures that require sophisticated mapping. The innovative system described in this article is the first generation and many improvements are expected. This is promising and allows developing a new ‘clean’, safe, and accurate imaging solution in the near future. Conflict of interest: SB is a consultant for Boston Scientific and Medtronic and none to declare for coauthors.