a new option for challenging left atrial tachycardias?
Thomas Rostock, MD1, Alexander P. Benz, MD,
MSc1,2 and Raphael Spittler, MD,
MSc1
1 University Hospital Mainz, Center for Cardiology,
Department of Cardiology II / Electrophysiology, Mainz, Germany
2 Population Health Research Institute, McMaster
University, Hamilton, Ontario, Canada
Running title: PFA for left atrial tachycardia
Word count: 1,369
Corresponding author:
Thomas Rostock, MD
University Hospital Mainz
Center for Cardiology
Cardiology II / Electrophysiology
Langenbeckstr. 1
55131 Mainz, Germany
Email:
throstock@gmail.com
Disclosures: None declared.
Funding: None.
Keywords: Pulsed field ablation, atrial tachycardia, left posterior wall
isolation, atrial fibrillation, catheter ablation
Catheter ablation is a highly effective treatment for most cardiac
arrhythmias. It has therefore received high-degree recommendations,
including as first-line therapy, in current international guidelines.
Introduced into clinical practice more than 30 years ago, radiofrequency
(RF) ablation carries several important advantages and remains the
cornerstone of catheter ablation. Application of RF current results in
discrete lesions due to careful titration of ablation energy. Besides
its well-established efficacy, there is a detailed understanding of the
biophysiological processes in lesion development with RF ablation. On
the other hand, application of RF current may also affect tissues other
than the target area and may induce pro-inflammatory processes in and
adjacent to the ablated tissue.
It is with this background that the potential detrimental consequences
of RF ablation prompted the search for alternative ablation energy
sources. Mainly developed for catheter ablation of atrial fibrillation
(AF) with a single-shot balloon device, cryo-ablation, laser energy and
high-intensity focused ultrasound (HIFU) were introduced into clinical
practice over the last 20 years. However, all of these techniques may
cause serious collateral damage, especially to the phrenic nerve and the
esophagus. The high incidence of fatal complications with the HIFA
balloon has led to its withdrawal from the market (1).
An ablation technique specifically targeted at the myocardium, without
affecting adjacent extracardiac structures represents the ideal tool for
the interventional treatment of cardiac arrhythmias. Recently introduced
into clinical practice, pulsed field ablation (PFA) seems to provide
these properties. PFA is a non-thermal ablation modality that creates an
electrical field via ultra-rapid electrical pulses, ultimately resulting
in cardiomyocyte cell death. The only PFA catheter that has received
regulatory approval in selected regions is the multielectrode
pentaspline catheter (Farawave, Farapulse Inc. / Boston Scientific).
However, this catheter is only approved for catheter ablation of AF by
means of pulmonary vein isolation. Therefore, data on the use of PFA
applied to substrates other than the pulmonary veins are limited (2,3).
In this issue of the journal, Gunawardene and co-workers present
their early experience with PFA for the treatment of patients with
post-AF ablation atrial tachycardia (AT) (4). Their analysis includes 15
patients with a history of multiple AF/AT ablation procedures. In these
patients, a total of 19 left atrial (LA) tachycardias were explored
using ultra-high-density mapping. Eighteen of the 19 LATs represented
macro-reentry tachycardia. There were 7 anterior, 5 perimitral, and 4
roof-dependent ATs, as well as 1 AT originating from each the LA
appendage and the posterior LA wall, respectively. Using the pentaspline
catheter that was inserted into the LA via a deflectable sheath (13 Fr),
the authors performed anterior “line” ablation in 11, LA posterior
wall isolation in 10, and roof “line” ablation in 3 patients, and
mitral isthmus ablation in 1 patient. Acute success of AT ablation was
achieved in all cases. Twelve of the 19 ATs terminated with the first
PFA impulse. Of note, a considerable mean number of 38±17 PFA
applications was required to achieve bidirectional conduction block
along the ablated areas. The mean procedure time was two hours and 20
minutes, and the mean fluoroscopy time was 18 minutes. There were no
procedural complications. Done in almost all patients in whom posterior
LA isolation had been performed, endoscopy demonstrated the absence of
any mucosal lesions in the esophagus. During a limited median follow-up
duration of 7.7 months, one of the 15 patients experienced AT recurrence
following a 90-day blanking period. Two patients were treated with an
antiarrhythmic drug at the end of follow-up.
The authors are to be commended for reporting novel and interesting data
on PFA for the treatment of post AF-ablation LAT. Given its promising
results in ablation of AF, it seems reasonable to explore the
application of PFA to the atrial substrate beyond the pulmonary veins.
ATs following complex ablation procedures for persistent AF may
represent a challenging target for catheter ablation (5). Although
currently used high-density mapping systems provide support in exploring
the anatomical und electrophysiological characteristics of AT
mechanisms, ablation using conventional techniques can still be
difficult. Nayak and co-workers elegantly described the anatomical
circuits of complex ATs following AF-ablation which may involve
epicardial bridging sites, mainly at Bachmann’s and the septopulmonary
bundle (6). In their cohort of patients with multiple prior ablation
procedures, the prevalence of an epicardial bridge contributing to the
AT circuit was as high as 38%. Thus, a combined endo-/epicardial
ablation approach has been proposed for use in selected patients (6, 7).
Nevertheless, even with the use of a percutaneous epicardial access,
ablation at Bachmann’s or the septopulmonary bundle can be challenging
due to the close proximity to the coronary arteries, the esophagus or
epicardial fat. Furthermore, access to the target region may be
prevented by pericardial reflections (8). In this context, PFA
represents a novel option to reach and ablate in these areas, obviating
the need for an epicardial access while potentially overcoming some of
the other limitations of epicardial LA ablation. Although the study byGunawardene et al. is limited by its small sample size of only 15
patients and a relatively short follow-up duration, the reported high
rate of efficacy of PFA in complex ATs following AF-ablation is
encouraging and suggests that PFA may be a promising alternative to RF
ablation in this setting.
However, despite all the (justified) enthusiasm about the use of PFA as
a novel strategy in the ablation of complex ATs, a few words of caution
are warranted.
First, the electrical field that is created by the pentaspline catheter
results in lesions that are markedly larger in terms of lesion width as
compared to those created with conventional RF ablation. While a
conventional ablation line is created by point-by-point application of
RF current with a typical inter-lesion diameter of ~5
mm, a PFA application series induces a significantly larger lesion.
Thus, using PFA aimed at creating a bidirectional conduction block
across a target area creates an ablated field rather than a linear
lesion. In the study by Gunawardene et al. , “linear” ablation
at the anterior wall resulted in ablation of a mean of three-fourths of
the entire LA anterior wall. In this study, PFA for roof line ablation
resulted in complete posterior wall isolation in the majority of
patients; and some patients underwent both anterior ablation and
posterior wall isolation. With this in mind, known potentially
detrimental consequences of the elimination of anterior and posterior LA
wall contractility need to be considered. Impaired LA distensibility may
result in increased atrial pressure, with a consecutive rise in
pulmonary venous pressure and the clinical presentation of “stiff LA
syndrome” characterized by dyspnea and exercise intolerance (9).
Furthermore, a higher burden of LA fibrosis may increase the risk of
thromboembolic events, even in sinus rhythm and with an electrically
activated LA appendage (10).
Second, multiple pre-clinical and clinical studies suggest that PFA may
be able to avoid collateral damage to extracardiac tissue because it
aims to selectively affect myocardial cells. Although esophageal damage
with PFA has never been reported, there is a growing body of evidence on
transient phrenic nerve dysfunction and coronary arterial spasm
associated with PFA (2, 11). It does not seem unlikely that these
observations are a direct result of PFA rather than autonomic responses.
Third, PFA in the LA is often painful and may also cause skeletal muscle
contraction. It is intuitive to assume that these effects may be more
pronounced when PFA is applied to the posterior wall. This suggests that
an intensified sedation protocol with comprehensive monitoring or
general anesthesia may be required to ensure a smooth procedure for both
patients and operators.
Technical advances and innovations in the interventional treatment of
cardiac arrhythmias have moved the field forward, but the search for the
ideal ablation energy is still ongoing. Key requirements for a candidate
modality include myocardial cell specificity, creation of discrete
lesions using titratable energy, proven acute and long-term
effectiveness and an insightful understanding of the biophysiological
processes in lesion formation. Present-day PFA seems to comply with some
of these features, but certainly not all of them. However, further
improvements to PFA can be expected. Novel PFA catheters have undergone
preliminary clinical testing and several large-scale clinical trials are
underway to establish a definitive role for PFA in the treatment of
complex cardiac arrhythmias.