Evolution of ablation techniques: from WPW to complex arrhythmias
1 First Department of Medicine-Cardiology, University Hospital Mannheim, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany
2 Department of Cardiology, Kerckhoff Klinik Bad Nauheim, Bad Nauheim, Germany
* Corresponding author. Tel: +49 621 383 2204; fax: +49 621 383 3061. E-mail address: martin.borggrefe{at}med.ma.uni-heidelberg.de
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Abstract |
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 Top Abstract IntroductionEnergy sourcesMapping techniquesIntegration of cardiac imagingSteering and navigationAblation targetsConclusionReferences |
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Radiofrequency ablation of cardiac arrhythmias has come to widespread use since it was first performed in the mid-1980s. Together with an increasing understanding of arrhythmia mechanisms both at the atrial and ventricular levels, technology has made tremendous progress. With improvements in catheter materials and function, development of different energy sources, and the advance of mapping techniques, catheter ablation can nowadays be used to cure all types of arrhythmia including focally induced atrial and ventricular fibrillation. With the most recent innovations in the integration of mapping and cardiac imaging, robotic and magnetic navigation, success rates and safety of catheter ablation have greatly increased. Catheter ablation has become not only an alternative to drug therapy in the treatment of supraventricular arrhythmias, but is nowadays in many cases the first therapeutic choice. In the future, the reduction of radiation exposure by using non-fluoroscopic imaging and robotic navigation will further advance this curative approach.
Key Words: Radiofrequency • Catheter ablation • Arrhythmias • Cardiac imaging • Transvenous
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Introduction |
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TopAbstractIntroductionEnergy sourcesMapping techniquesIntegration of cardiac imagingSteering and navigationAblation targetsConclusionReferences |
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Since the early days of the first use of radiofrequency (RF) ablation in Wolff–Parkinson–White (WPW) syndrome by Borggrefe et al.,1 Kuck et al.,2 and Jackmann et al.,3 catheter ablation of arrhythmias has evolved massively not only in terms of efficacy, but also by being extended to complex arrhythmias such as atrial fibrillation, arrhythmias in congenital heart disease, and arrhythmias after surgical repair of congenital heart disease.
The introduction of temperature-controlled ablation by Wittkampf4 and Hindricks et al.5 and irrigated tip ablation by Calkins et al.6 as well as cryoenergy have further increased the safety of transvenous cathether ablation and limited complications related to the energy delivery itself.
A fundamental innovation in this field, which is still evolving, has been the integration of electroanatomical mapping, non-contact mapping, and the fusion of these additional tools with cardiac imaging. Its sophistication has finally been achieved by new steering modes such as remote magnetic navigation and robotic advancement of catheters.
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Energy sources |
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TopAbstractIntroductionEnergy sourcesMapping techniquesIntegration of cardiac imagingSteering and navigationAblation targetsConclusionReferences |
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The most frequently used energy mode for catheter ablation is still RF current. The first to use this energy in humans have been Borggrefe et al., who disconnected a right-sided accessory pathway. Their pioneering work, which had then subsequently been followed by many, opened the door to transvenous ablation at a significantly lower risk compared with direct current (DC) ablation and rendered RF ablation a widely applicable therapy for patients with supraventricular and ventricular arrhythmias. The major drawback of RF current ablation at this time was the fact that there was no limit on energy delivery or temperature control, which at least in theory still left a residual potential for undetected carbonization, impedance rise, and finally the risk of perforation. However, the very low complication rates were remarkable and it does not seem retrospectively that there were great limitations.
This type of energy was and is still sufficient for focal ablation and small targets in thin tissue such as focal atrial tachycardia, accessory pathway, and ablation in the region of the atrioventricular (AV) node. However, when it comes to the ablation of larger areas in thicker tissues and when ablation is performed on the left side, the efficacy of RF ablation is limited and the risk of charring and thrombus formation becomes an issue, especially, when high-power settings and high target temperatures are used. Therefore, it was time to think about alternatives. The use of cryoenergy was one potential alternative, but the efficacy at least until recently, especially, when ablating in the left ventricle, was limited. Then, after a long series of animal experiments mainly performed by Wittkampf,4 irrigated tip RF ablation using closed or open irrigation were introduced and this gave a major advance especially on the left side of the heart. In prospective studies, Calkins et al.6 demonstrated that in ablation of ventricular tachycardia (VT), the long-term success rates were significantly higher using irrigated tip energy compared with non-irrigated RF ablation. Its major role evolved then with the introduction of catheter ablation of atrial fibrillation, where extensive energy on the arterial side meant a significant risk of thrombus formation, and, although there has been no comparative study yet, it can be assumed that when using the same number of lesions, the risk of thromboembolism would be significantly higher with non-irrigated tip ablation in AF ablation.
There have been some experimental studies and also in vivo use of ultrasound energy, which proved to be very effective, but also to carry some risk of complications in its present form. This has, to date, been the reason that this type of energy is not frequently used. Further studies are necessary to assess, whether there is a role for ultrasound energy in catheter ablation.
Last but not least, cryoenergy, which had already been successfully used for a long time by cardiac surgeons for ablation during cardiac surgery, has been implemented into transvenous catheters and is currently used with increasing frequency not only in paediatric electrophysiology, but also for ablation close to the AV node, right-sided pathways and here especially paraseptal and paraHisian pathways, and for pulmonary vein ablation. Its great merits are painless application and the reduced risk of thrombus formation and charring, which especially on the left side is an important advantage. Comparative studies of the success rates of cryoenergy vs. RF are still lacking and some ongoing large-scale studies in ablation of atrial flutter and AV-nodal-reentrant tachycardia (AVNRT) are awaited. However, it can be stated that cryoenergy is an excellent tool for ablation in children and neonates using the so-called cryomapping mode, which allows for transient testing of ablation sites with reversible lesions.
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Mapping techniques |
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TopAbstractIntroductionEnergy sourcesMapping techniquesIntegration of cardiac imagingSteering and navigationAblation targetsConclusionReferences |
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Although in the early days of ablation, tedious point-by-point mapping of local electrical signals with serial replacement of the mapping and ablation catheters was necessary to describe activation patterns, in the early to mid-1990s multipolar conventional catheters were developed that allowed simultaneous recordings of larger areas in the heart, especially in the coronary sinus and along the right atrial wall, thereby facilitating fast comprehension of larger reentrant circuits and localization, for example, of retrograde activation in accessory pathways.
More importantly, in different types of atrial flutter and macro-reentrant atrial tachycardias both on the left and the right sides, this new technology rendered diagnosis much easier and less time consuming. Entrainment became feasible by pacing from different areas in the heart without moving the catheter each time.
When in the early 1990s, the pioneering work of Cosio et al.7–9 was able to identify the anatomical barriers together with the area of slow conduction that predispose to the occurrence of typical atrial flutter; the new multipolar catheters helped greatly both to record the entire reentrant circuit and to monitor activation simultaneously after ablation using differential pacing to test lines of block. The same is true for the basic studies on the electrical properties of the crista terminalis, which would have hardly been feasible in humans using only bi- or quadripolar catheters.
However, the story of mapping did not stop with this first great achievement, but went on to more complex systems, which were designed to ablate non-sustained arrhythmias, reentrant circuits in the left atrium and the left ventricle, and incorporate the information of not only the timing of local activation, but also the electrical properties in terms of signal amplitude and scarring in a comprehensive fashion.
This was the time of non-contact mapping and electroanatomical mapping. A great amount of engineering had preceded the introduction of these systems into clinical practice and the mathematical complexity of, for example, the non-contact mapping was new to therapy. Already the first versions of these systems yielded excellent capture of arrhythmias and helped to identify phenomena such as shifting of activation in focal atrial tachycardias, which until then were the great ‘enemy’ of the physician and very difficult to follow. The local resolution of this new technology was very high, with an extremely small spatial error for both systems, so that the recordings obtained from mapping were very reliable.
For the electrophysiologist trained in the era of fluoroscopy-guided conventional mapping, now propagation maps have unveiled bystander regions and areas of slow conduction on-line thereby, placing more pieces in the puzzle.
A major advantage of these systems was also the fact that by colour-coded visualization of local electrogram amplitudes, the delineation of areas of low amplitude, scar, and fully viable myocardium became possible and helped, together with conventional techniques including entrainment mapping and pace mapping, to identify reentrant circuits. Ablation became feasible even in non-tolerated VT or non-sustained arrhythmias during sinus rhythm, the so-called anatomical approach.10 A number of investigators could demonstrate, for example, in both idiopathic dilated cardiomyopathy and in patients with post-myocardial infarction, that ablation during sinus rhythm is a reasonable approach with a high success rate.
Finally, with the introduction of the theory of focally triggered atrial fibrillation by Haissaguerre et al.11 and the development of ablation strategies to cure the patients with atrial fibrillation, a number of issues came up that had to be resolved, and as we now know, would not have been accomplished without the integration of these advanced mapping systems.
After it was widely accepted that ablation within the pulmonary veins using RF current carries a high risk of pulmonary vein stenosis, the so-called antral approach was favoured to limit the risk of stenosis by RF ablation. However, to ensure that the pulmonary veins are not entered during ablation, the use of non-contact mapping or electroanatomical mapping is, even if not absolutely necessary, extremely helpful. Further, to prove that there is an abatement of local activity or elimination of atrial activity inside the encircled area within seconds, it is necessary to use tools such as these. They are even more important, when other approaches such as compartmentalization of the left atrium are used or block across linear lesions in the left atrium has to be tested.
It can be summarized that the widespread use of catheter ablation has become reality, because fortunately, the development of new mapping techniques has kept pace with the increasing knowledge on arrhythmia mechanisms both from human and experimental studies in the past 21 years, since the first RF ablation.
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Integration of cardiac imaging |
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TopAbstractIntroductionEnergy sourcesMapping techniquesIntegration of cardiac imagingSteering and navigationAblation targetsConclusionReferences |
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In the first 20 years of ablation, physicians were effectively working in the dark, relying on the limited visibility of the boundaries of the heart, given by grey shadows. Guidance for steering of catheters was provided more by electrical signals and landmark catheters placed in the RV apex, the high right atrium, and the coronary sinus. On the left side, placement of catheters or wires within the pulmonary veins helped orientation within the heart. This has been sufficient for ablation of many types of arrhythmia except for atrial fibrillation, where important extracardiac tissues and organs are in close proximity and need to be protected from energy effects. With these new reasons for caution, imaging and image integration became mandatory, and currently most of the groups performing ablation of atrial fibrillation use the information provided by preintervention CT or MRI scans. These images give exact information of the number of pulmonary veins, branching patterns, and help to correlate electrical signals with anatomical areas, e.g. differentiation of far-field signals from local signals. They further give insight into the variable course of the oesophagus related to the posterior left atrium to avoid creating collateral damage to the oesophagus and creating atrio-oesophageal fistula. Moreover, the dimension and extension of the left atrial appendage and its course along the left upper pulmonary vein with the connecting ridge can be visualized, and this can be used to guide ablation. With the most recent devices superimposition and alignment of the MRI and CT scans with the electrical information from electroanatomical mapping or non-contact mapping facilitate both creating a concept for ablation as well as orientation and steering of the ablation catheter.
Finally, intracardiac ultrasound has been further developed for two important issues: first imaging of the left atrial chamber and the pulmonary veins, and second monitoring possible thrombus formation and adjusting energy while applying RF current to the different delicate areas of the left atrium. Three-dimensional reconstruction of chamber anatomy by intracardiac ultrasound is far advanced and can nowadays be performed almost instantaneously.
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Steering and navigation |
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TopAbstractIntroductionEnergy sourcesMapping techniquesIntegration of cardiac imagingSteering and navigationAblation targetsConclusionReferences |
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The first ablations were performed with bipolar catheters together with non-steerable bi- or quadripolar exploration catheters, which required frequent relocation. It is hard to imagine for young electrophysiologists that these limited leads could be used to describe correctly macro-reentrant tachycardias. However, maybe also because of the limitations of the equipment available in the early stages of cardiac electrophysiology, fundamental manoeuvres such as entrainment mapping were developed and success rates were extremely high in the early days comparable with today.
When transvenous catheter ablation began, the catheter structure was rather stiff and the electrodes were subject to carbonization. When considering an ablation of VT in a dilated left ventricle with an aneurysm, perhaps complicated by a kinked aorta, it is hard to imagine that creation of a number of lesions was then feasible (Figures 1 and 2). With this in mind, it must be stated that the pioneers of ablation showed great skill and stamina in performing these procedures with such high success and low complication rates.
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It must have been a great gift to all of those pioneers to acquire the first steerable ablation catheter, which they did not have to preshape and which did not lose its shape while advancing up the abdominal aorta.
From single deflecting catheters, other catheters were developed with dual and asymmetrical deflection to reach better the most technically challenging areas of the heart.
In recent times, another major step forward has been made with the introduction of robotic guidance of the catheter and magnetic navigation, performed remotely from the patient. The accuracy and the local stability of the ablation catheter are dramatically improved, and it is astonishing how fast this new technique can be learned. This technology does not only facilitate ablation, but also dramatically reduces radiation exposure to the physician, which has always been and is still a major issue in interventional electrophysiology.
With the most recent devices, automatic anatomical mapping and automatic deployment of serial lesions after creation of design lines have become reality.
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Ablation targets |
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TopAbstractIntroductionEnergy sourcesMapping techniquesIntegration of cardiac imagingSteering and navigationAblation targetsConclusionReferences |
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Clinical catheter ablation began with the treatment of the more dangerous arrhythmias in patients with severe co-morbidity and not with ablation of supraventricular tachycardias.
The largest series of ablation in the early and mid-1980s were interventions for VT. On the basis of fundamental landmark studies by Josephson et al.12–16,24 on the mechanisms of VT, physicians on both sides of the Atlantic Ocean started using DC ablation. His-Bundle ablation and ablation of accessory pathways followed.17,18
Most of the ablations were of a focal nature, targeting the diastolic pathway or exit site of clinical VT. The duration of an ablation procedure was consistently long, often more than 4–8 h, and the complication rates with DC ablation were significant, which was surely the reason why the sicker patients were targeted first, rather than patients with primarily benign arrhythmias such as AVNRT or atrial tachycardia.16 Also, the mechanisms of AVNRT tachycardia were not understood as well in the early stages, when, at least, VT and AV reentrant tachycardia had been fully investigated. The concept of dual AV-node physiology, the anatomical characterization of the compact AV-node, and the fast and slow inputs with their relation to the coronary sinus orifice within the triangle of Koch then rapidly led to a change from AV-node ablation to selective ablation of either the fast or the slow pathway.19–27 It was around 1993, when selective modulation or ablation of the slow pathway became a common approach and consequently the risk of AV-block dramatically decreased.
Retrospectively, it may look strange that the ablation of isthmus-dependent right atrial flutter was started after ablation of the slow pathway or focal atrial tachycardia, since the intellectual and technical requirements for this type of ablation are presumably not as high as for the other arrhythmias. The reason was that the understanding of this macro-reentrant arrhythmia was not as advanced as that of the AV-node or WPW.
This also becomes obvious by the fact that at the beginning of atrial flutter ablation, it was deemed to be sufficient to terminate the flutter, and no one was aware that bidirectional block through the isthmus was necessary to ensure long-term prevention of atrial flutter. Major progress in the knowledge of the treatment of atrial flutter was then rapidly made and with the introduction of large tip electrodes and irrigated tip ablation, success rate rose as high as to more than 95% in the long term.
For some time the major field of catheter ablation was AVNRT, WPW, and atrial flutter, and only the specialized centres performed a few VT ablations per year, mostly in the setting of incessant VT or frequent ICD discharges.
The next advance was the ablation of frequent premature ventricular contractions (PVCs) or idiopathic VT, predominantly arising from the right ventricular outflow tract. The success rates for this type of arrhythmia increased steadily to 70–90%.
Studies over the last 5 years, however, demonstrated that many of the PVCs, which could not be successfully terminated from the right side, can be found either in the left ventricular outflow tract or in the sinus of valsalva. Such ablations have been shown to be very successful with low complication rates.
The oldest and most widespread arrhythmia problem, atrial fibrillation, has been the last to be approached with a view to cure by Haissaguerre et al., who published their first large series in 1998.11 They were able to demonstrate that there is electrical activity from within the pulmonary veins, which was both able to induce and maintain atrial fibrillation. By elimination of this activity, they could achieve freedom from arrhythmia recurrence in a large number of patients. This concept of focal initiation of a chaotic arrhythmia was later also applied to the initiation of polymorphic VT and ventricular fibrillation (VF) in idiopathic VT/VF, genetic diseases and also ischaemic VF with the initiation coming from the Purkinje fibre system.28
Although ablation of polymorphic VT/VF remains a rare intervention, atrial fibrillation is at present one of the most frequent indications for ablation and will in the future make up the largest part of the ablation workload. By moving away from focal ablation within the veins, the application of antral lesions, and linear lesions within the left atrium, complication rates have decreased greatly and this has led to a worldwide rise in AF ablation numbers.29
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Conclusion |
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TopAbstractIntroductionEnergy sourcesMapping techniquesIntegration of cardiac imagingSteering and navigationAblation targetsConclusionReferences |
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Catheter ablation of cardiac arrhythmias is a real success story and in only few fields of medicine has there been such rapid progress. Technology has made a major contribution and helped to accomplish high efficacy rates and acceptable safety for this therapy. However, the intellectual input, which has come from the pioneers of electrophysiology cannot be estimated highly enough and it should always kept in mind that ‘one has to learn before the burn’.
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Acknowledgments |
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Conflict of interest: none declared.
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References |
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