Conventionally, left-sided accessory
pathways (AP) are ablated using radiofrequency
energy either with retrograde or transseptal approaches
(1,2). In a considerable proportion of patients
peripheral thromboembolic complications including
transient ischemic attacks were reported (3.4).
Cryothermal energy has potential advantages including
less thrombogenity.
Furthermore, unique options such
as ice mapping allow significantly fewer applications.
Cryothermy was reported feasible for various types
of right-sided ablations (5-7), however, until
recently the value of cryothermy in ablations
of left-sided accessory pathway was not evaluated.
The aim of the present report is
to demonstrate how cryothermy can be effectively
used for ablation of left-sided accessory pathways
supported by advanced 3D-imaging/navigation techniques.
A 39-year-old man presented with regular narrow
complex tachycardia for electrophysiology study
and transvenous cryoablation. The 12-lead ECG
of the tachycardia suggested the presence of orthodromic
AV reentry tachycardia using a concealed accessory
pathway. Resting 12-lead ECG of the patient was
normal. Under local anesthesia a decapolar diagnostic
catheter was inserted to the coronary sinus via
a subclavian vein. A quadripolar catheter was
positioned across the tricuspid valve to record
stable His potential. A conventional bipolar pacing
electrode was then inserted via a femoral vein
to the right ventricular apex.
The antegrade activation sequence was normal during
sinus rhythm and atrial pacing at CL 400, 500
and 600 ms. The retrograde activation sequence
during ventricular pacing showed that the earliest
retrograde activation was seen in the distal part
(CS electrode pairs 3 and 4) of the decapolar
catheter placed in the coronary sinus. Orthodromic
atrio-ventricular re-entrant tachycardia was easily
inducible with atrial stimulation and the activation
sequence was identical to the observed sequence
during ventricular pacing (Figure 1). The AP had
a retrograde refractory period of 250 ms, and
the shortest retrograde 1:1 conduction was 270
ms. Induction atrial fibrillation occurred, which
required DC shock for termination. Cryothermal
catheter ablation was undertaken with transseptal
left heart catheterization. Intracardiac echocardiography
was used to guide the puncture of the interatrial
septum using the technique described
elsewhere (8,9).
Shortly, the left femoral vein was punctured and
an intracardiac ultrasound transducer catheter
(model 9900, EP Technologies, Boston Scientific)
was introduced to the right atrium via a multipurpose
introducing sheath (EP Technologies, Boston Scientific).
The transseptal sheath (SL2, DAIG) was introduced
to the SVC. The sheath was loaded with a Brockenbrough
needle (DAIG), which was advanced to within 1
cm of the dilator tip. The position was checked
in three fluoroscopy views (AP, LAO, RAO). The
entire sheath was then withdrawn from the SVC
to the right atrium. The intracardiac ultrasound
was reactivated.
The characteristic downward “jump”
of the sheath was detected simultaneously by fluoroscopy
and intracardiac echocardiography. When the septum
was approached by the sheath, the ultrasound demonstrated
the characteristic tenting of the fossa. Sudden
collapse of the tented fossa indicated a successful
puncture. Finally, echo contrast material was
injected into the left atrium and detected by
the echocardiography.
The cryocatheter is a 7F steerable
catheter with four electrodes at its distal end,
a distal cooling 4-
Fig. 4. The cryothermy temperature
curve. At 30 seconds VA prolongation was observed,
and further freezing was decided achieving the
-75-degree Celsius effective ablation temperature.
After offset of cryothermy the temperature immediately
rose to normal level.
mm-tip electrode, and three proximal
ring electrodes. The catheter has a hollow shaft
with a closed tip into which the refrigerant fluid,
nitrous oxide, is delivered under pressure from
a control console. Within the tip, a phase change
occurs (liquid to gas), and the resultant gas
is removed under vacuum. This transformation causes
cooling of the tip to temperatures as low as -70
degree Celsius. The gas is conducted away from
the tip through the vacuum return lumen and is
collected in the console.
A Cryothermy ablation catheter (type
I) was then used to map the mitral annulus and
to deliver cryothermy through the transseptal
sheath. Initially ice mapping was performed by
cooling to -30 degree Celsius for a maximum of
80 seconds. Because of catheter adherence at this
level of cooling, ventricular extrastimulus testing
could be
Fig.5. LocaLisa images showing
the ice maps and the corresponding electrograms
on the sites where cryothermy was applied.
sed, to show loss of VA conduction,
respectively. If mapping was performed during
orthodromic tachycardia, the termination of the
tachycardia or a progressive increase of VA time
was considered to be a promising site (Figure
2). When these signs were observed, cryoablation
was performed by cooling to -75° C for a 4-minute
period, to create a permanent lesion (Figures
3 and 4).
In order to visualize anatomically
and electrophysiologically important structures,
a novel 3D navigation system (LocaLisa, Medtronic)
was used. The LocaLisa system is based on the
principle that when electrical current is externally
applied through the thorax, a voltage drop occurs
across internal organs like the heart, which can
be recorded via standard catheter electrodes and
potentially can be used to determine electrode
position.’
Using a combination of the above mentioned systems,
a total of three applications were applied to
the atrial side of the mitral annulus with continuous
VA signals during orthodromic tachycardia (Figure
2). The first ablation resulted in a termination
of the tachycardia and consequent VA block during
ventricular pacing 47 seconds after the onset
of cryothermy energy.
The conduction of the accessory pathway
returned 20 minutes after this application. Using
the LocaLisa system, an adjacent but more ventricular
site was searched for, and confirmed by the local
electrograms (Figure 5). The second application
was unsuccessful. The last pulse – delivered to
an adjacent site to the distal CS catheter – which
was temporary, was displayed on the screen of
the LocaLisa system and resulted in an abrupt
(2,7-sec) termination of the tachycardia (Figure
4). The retrograde activation sequence showed
a loss of accessory pathway conduction. Thirty
minutes after ablation, ventricular pacing showed
VA block. Post ablation, there were no signs of
recurrence of accessory pathway conduction. Intravenous
administration of adenosine (12 mg) resulted in
a short lasting VA block during ventricular pacing
confirming successful ablation of the left-sided
accessory pathway.
Radiofrequency catheter
ablation of accessory pathways, including the
ones located in the left side of the heart, is
first-line therapy with high acute success rate.
Although ablations of accessory pathways guided
by fluoroscopic landmarks and electrograms have
a success rate of around 94%, thromboembolic complications
are reported in a considerable proportion of the
patients (3,4).
Alternative energy sources are on
trial to increase efficacy and to decrease procedure-related
complications. Cryothermy has some potential advantages.
The lesion created by cryothermy seems more homogenous
and the underlying tissue structure remains intact
(12). Theoretically it is less thrombogenic and
less proarrhythmic. Furthermore,
the unique option of ice mapping, which is tissue
cooling to less negative values to demonstrate
reversible loss of function, enables us to predict
the effect of permanent lesion formation (5-7,12).
This approach may result in a significant
reduction of the number of permanent lesions.
The cryoadherence is an additional benefit, which
prevents the catheter tip from dislodgment during
cryoenergy application (5,6). This can reduce
fluoroscopy time, since continuous monitoring
of the catheter position is not necessary. These
advantages stimulate the further development of
cryothermy.
The feasibility of cryothermal ablation
in right sided procedures were demonstrated recently
(5,7-12). The His bundle and the slow pathway
can be reliably and effectively ablated using
this method (5,6). Right-sided accessory pathways,
including right anteroseptal accessory pathways,
are also successfully and safely ablated by cryothermy
(7).
However, the role of cryothermy in the
treatment of left-sided accessory pathways has
not been clarified. It was demonstrated that cryothermy
is very sensitive to blood pool warming while
delivering cryoablation lesions (5).This warming
effect can be disadvantageous in high-flow areas,
especially in the left side of the heart. This
potential pitfall can be counteracted by more
accurate mapping during the ablation procedure.
Mapping that is purely based on electrogram analysis
has certain limitations. Filter setting, noise,
and artifacts can influence the objective judgment
of the signals, and previous energy applications
can modify the arrhythmia substrate which can
influence the results. Accurate three-dimensional
localization of the mapping catheters can facilitate
the ablation procedure as it was demonstrated
in the present case. Using the LocaLisa system,
the position of important anatomical landmarks
could be easily identified.
Furthermore, all of the previous
mapping and ablation sites can be indicated, stored,
and consequently retrieved by using the system.
The growing experience
with this novel 3D-navigation system and cryothermy
technique, these methods are becoming valuable
tools for increasing the efficacy of transcatheter
ablation, including the treatment of left-sided
accessory pathways.
Theoretically, the risk for thromboembolic
complications can be minimized during ablation
procedures by using this setup. Furthermore, with
more experience the radiation exposure of the
procedure could be decreased significantly (13).®
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