Aritmologia in Campania

Elettrofisiologia Cardiaca

L’ablazione transcatetere per il trattamento della tachicardia ventricolare ischemica e della tachicardia ventricolare idiopatica

Application of the Intellanav Stablepoint™ Ablation Catheter featuring contact force and local impedance information to treat ventricular ischemic substrate

Francesco Solimene, MD Electrophysiology Unit, Clinica Montevergine, Mercogliano, Italy and Francesco Maddaluno Boston Scientific, Italy

Introduction

Many scientific publications have discussed the utility
of using contact force (CF) information and lesion
indices in the context of atrial fibrillation ablation, but
few have addressed the same topic in the context
of ventricular tachycardia (VT) ablation. For the first
time, the novel INTELLANAV STABLEPOINT™ Ablation
Catheter (Boston Scientific) allows clinicians to study
the interaction of CF and local impedance in lesion
creation. This knowledge could potentially open new
scenarios in treating diseased tissue. Thus, we present
a case illustrating a strategy to create optimal ablation
lesions in the context of VT ablation by leveraging the
unique information provided by the INTELLANAV
STABLEPOINT™ Ablation Catheter featuring DIRECTSENSE™
Technology.

Patient history
A 63-year-old male with a history of hypertension and
inferior myocardial infarction with a left ventricular ejection
fraction (LVEF) of 27 %, received several shocks from his
dual-chamber defibrillator despite optimized medical
therapy. We decided to ablate the ischemic substrate using
both CF and local impedance information derived from
the INTELLANAV STABLEPOINT™ Ablation Catheter.

Procedure
The procedure was performed under conscious sedation.
A Dynamic XT™ decapolar catheter (Boston Scientific) was
used to cannulate the coronary sinus (CS). Both aortic
retrograde and transseptal approaches were performed
and were used interchangeably to obtain the best contact
in different regions. The INTELLAMAP ORION™ Mapping
Catheter was used with the RHYTHMIA HDx™ Mapping
System to create a LV map during atrial pacing rhythm.
APPLICATION OF THE INTELLANAV STABLEPOINT™ ABLATION
CATHETER FEATURING CONTACT FORCE AND LOCAL IMPEDANCE
INFORMATION TO TREAT VENTRICULAR ISCHEMIC SUBSTRATE
A total of 10,805 points was obtained in 22 minutes,
while pacing from the CS at a cycle length of
500 to 600 ms. A steerable sheath was used with both
the INTELLAMAP ORION™ and INTELLANAV STABLEPOINT™
catheters. LUMIPOINT™ software (Boston Scientific) was
used to highlight all late potentials recorded by the
INTELLAMAP ORION™ catheter. The illuminated area was
localized in the infero-posterior wall.

AutoTag pre-set feature
For this procedure, we benefited from features available
in the latest update to the RHYTHMIA HDx™ software. The
AutoTag feature available in SW4.0 allowed us to drop
ablation tags automatically according to user-defined
criteria. In our experience, we usually selected the following
settings:

  • Stability: 3 mm for 3 seconds
  • Local impedance: DIRECTSENSE™ Technology drop of 10 ohms
  • CF: 5 grams for 50% of the stability time

Regarding the stability setting, we used just 3 seconds
because radiofrequency (RF) can create a good lesion
very quickly, especially if a higher power is used. Thus,
provided that contact is good and the local impedance
drop is adequate, there is no need to maintain stability for
a longer period of time.
In our opinion, the local impedance drop is the main
indicator of lesion formation so we required a minimum
drop of at least 10 ohms.
Finally, the CF criteria was required to ensure that the
local impedance drop we achieved during RF application
was due to tissue damage and not due to the catheter
shifting into the blood pool.
The criteria we used for tag coloring was based entirely
on the local impedance drop: thresholds of 15 ohms and
25 ohms (Figure 1).

Baseline impedance and zero for CF
After creating the substrate map and highlighting the
targeted electrograms with the LUMIPOINT™ Module, the
baseline local impedance value (blood pool) and the zero
value for the CF must be set. We set zero for CF in the left
atrium via the transseptal access, since it could be quite
difficult to avoid intermittent contact in the LV. In this
patient, the baseline local impedance in the blood pool
was approximately 130 ohms.

Use of CF for catheter positioning
prior to ablation

CF information is very useful in ventricular substrate
ablation as it helps ensure that the physician does not
press the catheter too hard against the tissue. It also
provides certainty about catheter contact in the scar region.
With the INTELLANAV STABLEPOINT™ Catheter, we never
deliver radiofrequency if contact force is less than 5 grams
(Figure 2).
Provided that force was above a minimum of 5 grams, we
did not find much value in increasing the CF in order to
achieve greater local impedance drops for the patient in
this case (Figure 3).

Use of the local impedance to predict and
assess lesion formation

As with the INTELLANAV MiFi™ OI Ablation Catheter
(Boston Scientific), we found that with the INTELLANAV
STABLEPOINT™ Ablation Catheter, electrical coupling with
tissue prior to RF application was predictive of the
subsequent local impedance drop: the higher the
baseline local impedance of the tissue, the higher the
drop. After a minimum force greater than 5 grams was
obtained, we tried to optimize catheter positioning
to achieve a higher baseline local impedance. If we
were able to get a local impedance value of at least
10 – 15 ohms greater than blood pool local impedance in
diseased tissue, we started RF delivery regardless of the
force value provided as we were above 5 grams (Figure 4).

Combining information from the local
impedance and contact force graphs to
explain unexpected findings

In addition to the force and local impedance information
displayed as numerical values in the widgets, we found
that we could sort out counterintuitive findings by
examining the graphs. For example, consider the situation
in which the average force was very high (30 grams)
implying very good contact, but with a local impedance
value very similar to the blood pool (133 ohms). This could
be explained by looking at the force graph. We found
that the CF was extremely variable and that the catheter
probably was not in contact with the tissue most of the
time. This explains the low baseline local impedance
value. The interpretation was also confirmed by the very
low local impedance drop obtained after RF delivery
(Figure 5, top panel).
In a second example, consider a similar finding but with a
different interpretation (Figure 6). In this case, the CF graph
displayed fast oscillation but the local impedance graph
was stable and achieved a higher value than the blood pool
impedance (142 ohms) (top panel). This finding indicated
that the catheter was in good contact with the diseased
tissue during most of the excursion time, explaining the
higher and stable local impedance value. This was also
confirmed by the very good local impedance drop obtained
after RF delivery (bottom panel).

These examples clearly explain why electrical coupling can
be more predictive of local impedance drops compared to
force alone, and why it is extremely important to look at the
interplay between these two variables.

Discussion
In this case, we performed ischemic substrate ablation
using the INTELLANAV STABLEPOINT™ Ablation Catheter
in combination with the INTELLAMAP ORION™ Mapping
Catheter and the RHYTHMIA HDx™ Mapping System. The
unique combination of CF and local impedance information
available with the INTELLANAV STABLEPOINT™ catheter
proved very useful and enabled the precise assessment
of catheter electrical coupling with the scar, mechanical
contact and tip stability.
The main findings of this case highlight the
complementary information provided by CF and local
impedance. While information about CF is crucial to
ensuring catheter contact with diseased tissue, stable and
good quality electrical coupling seems to better predict
optimal lesion creation in this type of tissue. Provided a
minimal CF of approximately 5 grams was obtained, the
proportional relationship between an increase in CF force
and a drop in local impedance typically seen in healthy
tissue, was not observed in this case. This confirms the
complex biophysics involved in lesion creation in low
voltage tissue and underscores the utility of the combined
information about CF and local impedance when ablating
this kind of tissue.

Conclusion
This case demonstrates the use of the INTELLANAV
STABLEPOINT™ Ablation Catheter technology for VT
substrate ablation and confirms that the combination
of contact force and local impedance information
available with this technology is extremely useful for
assessing safety, catheter contact and lesion formation in
diseased tissues.