Fiorenzo Gaita, Riccardo
Riccardi, Marco Scaglione, Leonardo Calo, Renzo Antolini*, Filippo Lamberti, Elena
Richiardi, Lucia Garberoglio, Michele Kirckhner*.
Department of Cardiology, Ospedale Civile di Asti,
*Department of Physics, University of Trento, Italy
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Atrial fibrillation (AF) is a frequent
supraventricular arrhythmia, which is present in about 4% of patients older than 60 years,
and it may be related to an increased risk of complications such as thromboembolism or
haemodynamic impairment particularly if an associated cardiopathy is present. The risk of
complications together with the symptoms of palpitations makes a therapy advisable.
Despite the high prevalence of this arrhythmia the current available therapy is still
unsatisfactory due to a high incidence of AF recurrences and complications.
The poor effectiveness of drug therapy may be explained considering the lack of
knowledge of the electrophysiologic features and substrate of this arrhythmia. It is now
generally accepted that the electrophysiologic substrate responsible for the maintenance
of AF is the presence of multiple simultaneous re-entrant depolarization wave fronts that
circulate through the atrial tissue as described first by Moe1
and subsequently demonstrated by others2. Recently
however another hypothesis which considers the presence of a rapid atrial focus
responsible for the AF has been revived and demonstrated possible, in some cases, by
catheter ablation studies3.
However, few are the studies dealing with the atrial activation during AF and these
few data mostly derive from animal studies. The few human data were obtained mainly during
cardiovascular surgery, thus in particular conditions and with only a part of the atrium
explored.
The first non pharmacological attempts proposed were the ablation or subsequently
modulation of the AV node. However, these procedures are not curative for AF since they do
not affect the electrophysiologic substrate and their aim is limited to the reduction of
the ventricular rate during AF. Although the reduction of the heart rate may, to some
extent, reduce the development or worsening of ventricular impairment, the persistence of
AF does not reduce the risk of other complications such as thromboembolism; moreover, in
case of complete ablation of the AV node the patient became pacemaker dependent and a
dysfunction of it may expose the patient to lifethreatening risk. On the other side the
modulation of the AV node avoids this problem but sometimes it does not eliminate either
the symptoms or the haemodynamic impairment due to the persistence of the irregular
rhythm; besides it is associated with a high risk of recurrences or inadvertent complete
AV block.
Considering these problems, attempts to cure AF have been performed first by surgical
procedures such as the Corridor and then the Maze procedure 4. In particular, the latter
one, which consisted in multiple incisions in both the atria in order to prevent the
formation and circulation of the wavelets, has shown a high success rate in the prevention
of the recurrences of AF. The need of a complex surgical procedure has limited the use of
this technique to a small group of patients especially those who need cardiovascular
surgery for an associated cardiac disease and has led the electrophysiologists to develop
a new technique of catheter ablation.
Swartz and Haissaguerre5,6 were the first who
published two case reports showing the effectiveness of an ablation procedure consisting
in the creation of linear lesions in the right atrium or in both the atria. Subsequently,
Haissaguerre7 published the results of a catheter
ablation procedure of AF based on the compartmentalization of the atrial tissue, in a
larger group of patients. The success rate, including patients on antiarrhythmic drugs,
was 33% with a procedure limited to the right atrium and it increased up to 60% with
additional ablation in the left atrium. However the safety of a procedure which includes
an extensive ablation both in the right and in the left atrium is not sufficiently proved;
in fact some severe complications, such as cardiac tamponade due to pericardial effusion,
stroke or severe bleeding due to the necessity of heavy anticoagulation have been
reported. This risk of severe complication, although low, may be kept in mind and it
appears in many cases to overload the spontaneous risk related to the persistence of AF.
Based on these considerations and on the fact that the AF may be present in very
different clinical situations and as a consequence supported by different
electrophysiologic substrates a different approach in the catheter ablation of AF has been
studied by our group8. This consisted in an ablation
limited to the right atrium, in order to avoid the aforementioned risks and in the
evaluation if any electrophysiologic criteria were able to guide the ablation procedure or
to predict its success.
This approach was supported by some recent reports on catheter ablation in animals.
They showed the feasibility of a procedure limited to the right atrium in dogs with normal
heart, while the results in dogs with important left atrial enlargement due to a
surgically created mitral regurgitation were less encouraging. Moreover, Morillo9, in an animal model of chronic AF, was able to interrupt
and prevent reinduction of the arrhythmia with a relatively selective cryoablation in the
sites where the shortest FF intervals were recorded.
Moreover some interesting findings may be observed when the features of atrial mapping
during AF are analysed. In fact, in our experience8
different regions of the atria showed different activation patterns and in particular the
septum generally showed the most irregular and disorganised atrial activity while in the
right lateral wall a relatively organised and regular atrial activity was usually
recorded. These data are in accordance with what has been reported by others10,11 on the spatial distribution of the atrial activity
during AF and with the concept that although the atria as a whole participate in the
process of AF not all the parts of the atria contribute equally to the perpetuation of the
fibrillatory process suggesting that selective ablation of the areas characterised by
abnormal conduction patterns may be effective in the treatment of AF.
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