Linear catheter ablation by DC-shock

Catheter ablation is a standard treatment for atrial fibrillation. For this
method of ablation, 2 catheters are necessary in the left atrium: 1 diagnostic
spiral *Lasso* catheter with which electrograms in the pulmonary veins can be
measured and 1 ablation catheter with which radiofrequent energy (RF) can
create sequential circular heating lesions in the left atrium. With these
lesions the pulmonary veins are electrically isolated from the rest of the left
atrium. Cardiac arrhythmia*s, which often originate from the pulmonary veins,
can no longer reach the left atrium.
This method works reasonably to well in patients with paroxysmal atrial
fibrillation. But, in patients with persistent atrial fibrillation this method
works poorly. Almost all patients need at least a second ablation procedure.
Scientific research has shown that creating extra linear lesions in the left
atrium gives a better treatment result. With the current RF-technique these
linear lesions are difficult to create. The borders of application of the
current techniques are within sight. Oftentimes the linear lesions are not
complete and there remain electrical conduction *gaps* in the linear lesion,
through which other atrial arrhythmia*s can easily be created. This is why
physicians oftentimes do not create the linear lesions, because an incomplete
linear lesion is pro-arrhythmogenic (e.g. atrial tachycardia).
Before the RF-ablation era direct current (DC) ablation was administered. With
this technique a high-energy shock (350-500 Joule) was applied through the
distal electrode of an endocardial catheter. Subsequently a relatively large
(>2 cm diameter) lesion was created, Nowadays it is known that this mechanism
of ablation is based on a high current density which destroys the ion channels
in the cell membranes. Myocardial cells die due to electroporation and are
being replaced by fibrous tissue. During this high-energy shock a spark was
formed, which causes a small explosion. The explosion caused a pressure wave
and in the past incidentally serious complications have been reported. When
RF-ablation was being developed around 1990, the development and the use of
DC-ablation was stopped. The use of current shocks through catheters however
remained in use as a method for electrocardioversion of atrial fibrillation.
Recently we have restarted the research for this method of ablation and at this
moment we can create relatively large lesions without the adverse side effects.
Due to increasement of the large electrode surface with a factor 10 and
decreasement of the energy to 200 Joule, we can stay below the threshold where
sparks can be created. The lesions are about 1 cm deep and there has never
happened any complication of adverse event during one of the approximately 260
ablations which we have conducted in 30 pigs until now. The reaction of the
body on an ablation like this is similar to the reaction of an endocardial
electrocardioversion.
The new method is being used in animal experiment for circular as well as
straight linear lesions, both in the left atrium. For the linear DC-ablations
we want to use an existing catheter which is designed for endocardial
electrocardioversions. We have come to the conclusion that this catheter is
also eligible for performing DC-ablations (off-label use). With the department
of Medical Techniques & Clinical Physics we have agreed on a method to use
these catheters for this human pilot study. The required DC-generator is
currently being developed by the department of Medical Techniques & Clinical
Physics.

The purpose of this study is to investigate the applicability of this method of
ablation in human patients.
The investigation will be conducted in patients with persistent atrial
fibrillation who, with use of the current method (RF-ablation), can only be
treated very difficultly. With the current technique this group of patients
almost always requires several lengthy treatments and even then the success
rate is lower than in other groups of patients with atrial fibrillation.
Scientific research has shown that the treatment result can be improved by
creating 2 linear lesions in the left atrium. These linear lesions are very
difficult to create with the current RF-ablation technique.

The investigation consists of 2 parts:
Firstly, the linear catheter must be positioned well of the area where we want
to perform the linear lesion. We anticipate that we will be able to do this in
the majority of patients.
Secondly, the linear catheter must be able to creat a linear leasion. In test
animals (pigs) this worked really well and 1 shock was sufficient to create an
approximately 3 cm long and transmural lesion in the left atrium.

The patient will be catheterized in the standard manner. A 4-polar catheter
will be introduced in the right atrium, a thin screw-catheter will be placed in
the atrial septum, and an 8-polar catheter will be placed in the coronary sinus.
Specially for the new treatment an intracardiac ultrasound catheter (ICE) with
be placed in the right atrium. With this ICE-catheter the interior of both
atria and the contact between the catheter and the myocardium can be
visualized. In many hospitals, both nationally and internationally, this
ICE-catheter is used in a standard fashion when performing ablation procedures
in the left atrium.
Then 1 or 2 transseptal punctures will be performed in order to place catheters
in the left atrium. Subsequently, a spiral Lasso catheter will be introduced
through a transseptal sheath and an RF-catheter will be introduced either
adjacent to a single transseptal sheath or through a second transseptal sheath.
For the new treatment we will use a steerable transseptal sheath. The spiral
catheter is a circular catheter with which electrograms in the pulmonary veins
can be recorded. The RF-ablation catheter has a slightly larger distal
electrode with irrigation holes through which a saline irrigation solution is
being sprayed during the ablations. With this RF-ablation catheter the regular
pulmonary vein isolation will be conducted. This happens by means of sequential
RF-applications around the ipsilateral ostia of the pulmonary veins. After
complete pulmonary vein isolation the linear lesions will be applied with
DC-ablation:
The RF-ablation catheter will be replaced by a linear DC-ablation catheter,
which will be placed in the left atrium through the steerable transseptal
sheath. With help of the ICE-catheter the DC-ablation catheter will be directed
to the region between the left inferior pulmonary vein and the mitral valve
annulus. Only when on the images by the ICE-catheter and according to the
electrical signals from the electrodes of the DC-ablation catheter there is
good contact between the DC-ablation catheter and the myocardium 1 or several
200 Joule DC-shock(s) will be applied. These shocks will be delivered after
sedation with propofol or etomidate, as is customary with any
electrocardioversion. If no good contact between the DC-ablation catheter and
the myocardium can be achieved no DC-shock will be applied. After each DC-shock
the (bidirectional) completeness of the linear lesion will be checked with
differential pacing between the spiral catheter placed in the left appendix and
the catheter in the coronary sinus.
After that the linear ablation catheter will be placed against the roof of the
left atrium. Also here 1 or several DC-shocks will be applied. Also, if no good
contact between the DC-ablation catheter and the myocardium can be achieved no
DC-shock will be applied. After each DC-shock the (bidirectional) completeness
of the linear lesion will be checked with differential pacing between the
spiral catheter and the catheter in the coronary sinus.

The following extra actions are required for linear DC-ablations:
1. Instead of a non-steerable sheath through the interatrial septum we will use
a steerable sheath. The steerable sheath is registered for transseptal
procedures and is nationally and internationally routinely used in ablation
procedures in the left atrium.
2. For extra visualization an ICE-catheter will be placed in the right atrium.
This is a routine procedure in many national and international centres in
ablation procedures in the left atrium.
3. The conventional RF-catheter will be replaced by the linear DC-ablation
catheter.
4. The patient will be sedated with propofol or etomidate for a short time.
This will take place under continuous observation of heart rhythm, blood
pressure and oxygen saturation. Propofol or etomidate are routinely being used
for electocardioversions.
5. One of several 200 Joule shock(s) with be applied by the linear DC-ablation
catheter.

The strain on the patient is in our opinion similar or less compared to the
current ablation method.
The total time of the extra actions is estimated to be 1 to 1,5 hours. This is
shorter than the time which it currently takes to create linear lesions with
sequential RF-ablations. Also, RF-ablation lesions oftentimes seem to be
incomplete. This significantly increases the risk of occurence of other cardiac
arrhythmia*s.

Possible risks for the patients.
In the mean while we have performed more than 250 DC-ablations in 30 test
animals (pigs), no complication has occured. Possible complications could be:
1. Cardiac perforation, this can happen with any diagnostic or therapeutic
catheter. Perforation could lead to cardiac tamponade.
2. The ablation shock causes contraction of the myocardium, similar to an
electrocardioversion. When there are blood clots present in the left appendix
(due to atrial fibrillation), these blood clots could embolize due to the
contraction and cause a stroke. This is a risk that every patient has during
any treatment with RF-ablation also, because during ablation of persistent
atrial fibrillation almost always 1 or more electrocardioversion(s) is/are
needed. To minimize this risk all patients who are being treated with ablation
for atrial fibrillation currently have to undergo a transesophageal ultrasound,
also patients who participate in the study.
3. In none of the approximately 250 animal experimental DC-shocks a
complication has occurred. However, we can not exclude the occurrence of any
yet unknown complication due to 200 Joule DC-ablation shocks. The current
intensity of these DC-shocks is 2 times higher than the customary 50 Joule
endocardial electrocardioversion.
4. In animal experiments the coronary arteries seem to remain undamaged after a
waiting time of 3 weeks after application of DC-ablations in very close
proximity of the coronary arteries. However, we can not exclude the possibility
that, on the long run, the coronary arteries will sustain any damage. With
RF-ablation, the current standard technique to perform linear ablations, acute
and chronic complications have repeatedly been reported. We expect therefore
that the DC-ablation method is safer for the coronary arteries than the present
RF-ablation method.
5. It is possible that we will not succeed in positioning the linear ablation
catheter well against the myocardium. When we will not perform any DC-ablation
and all extra actions taken have been in vain.