Key Teaching Points
•
Hemodynamic support by the Impella continuous-flow mechanical circulatory support
device (Abiomed Inc, Danvers, MA) seems to be compatible with remote magnetic navigation–guided
ablation and did not result in electromagnetic interference.
•
To prevent electromagnetic interference of the Impella with the strong magnetic fields
used in remote magnetic navigation–guided ablation, we advise careful positioning
of materials as well as starting the Impella before activating the magnets.
•
Precautionary use of the manual mode on the Impella instead of the automatic mode
is recommended during remote magnetic navigation–guided ablation.
Introduction
Catheter ablation (CA) is an important treatment option for patients with ischemic
heart disease presenting with ventricular tachycardia (VT).1, 2 Various CA techniques
are currently available, including remote magnetic navigation (RMN)–guided ablation.
2
Most published studies reported superiority of RMN-guided VT ablation over manual
ablation, with respect to acute success, recurrence, procedure time, fluoroscopy time,
and complications.3, 4, 5 The RMN system (Niobe Epoch, Stereotaxis Inc, St. Louis,
MO) uses 2 permanent magnets mounted on pivoting arms, 1 magnet on either side of
the patient, which creates a computer-controlled steerable magnetic field to remotely
guide the movement of a magnetically enabled ablation catheter.
6
Unfortunately, many VTs are not suitable for mapping during VT ablation, mostly because
of their hemodynamic instability.
7
It is well known that hemodynamically unstable VT might be successfully ablated with
the aid of mechanical circulatory support (MCS), using a variety of devices.8, 9,
10 However, most of the currently available continuous-flow MCS devices operate using
a metal pump as core of the technology, which limits their use in a magnetic environment.
The risk of electromagnetic interference has resulted in restraint in the use of percutaneous
continuous-flow MCS during RMN-guided VT ablation.11, 12 This would be a major limitation,
especially in centers with a preference for RMN-guided VT ablation. For the first
time, we report a case in which, with careful planning, RMN-guided VT ablation was
successfully combined with hemodynamic support using the Impella continuous-flow MCS
(Abiomed Inc, Danvers, MA).
Case report
A 67-year-old man with a past medical history of coronary artery disease causing ischemic
cardiomyopathy was admitted to our hospital because of recurrent VTs. In 2006, the
patient had undergone a successful resuscitation after ventricular fibrillation caused
by an acute anterior myocardial infarction. Rescue percutaneous intervention of the
left anterior descending coronary artery was performed. Chronic total occlusion of
the mid right coronary artery was noted. The distal right coronary system was supplied
by collateral circulation from the left anterior descending coronary artery. In 2008,
the patient was readmitted with myocardial infarction due to stent occlusion. Left
ventricular (LV) function was poor (LV ejection fraction 16%). Magnetic resonance
imaging showed a transmural anterior infarction. A VVI implantable cardioverter–defibrillator
(ICD) was inserted for secondary prevention. The ICD was upgraded to a cardiac resynchronization
therapy-ICD in 2018 because of progressive heart failure.
In 2016, the patient developed slow VTs, which had a cycle length under the programmed
detection zone of the ICD. These VTs caused rapid hemodynamic deterioration requiring
immediate basic life support. Medical treatment with amiodarone was started. The patient
did not experience recurrences until 2018, when he was admitted again with slow VTs
causing rapid hemodynamic deterioration. A manually guided VT ablation (NaviStar SmartTouch
D-curve catheter, Biosense Webster, Diamond Bar, CA) was undertaken. The ablation
procedure could not be completed because of difficulty in maneuvering in the extremely
dilated LV and frequent spontaneous induction of unstable VTs during mapping that
caused severe hemodynamic deterioration. A repeat procedure with hemodynamic support
was proposed. However, because of the difficulties encountered during the first ablation
attempt, the operator could not prioritize between RMN-guided ablation to facilitate
maneuvering and hemodynamic support by continuous-flow MCS. The patient provided written
informed consent for the procedure as well as presentation of his medical history.
RMN-guided VT ablation with hemodynamic support
In July 2018, VT ablation was scheduled with hemodynamic support using a continuous-flow
MCS device in combination with RMN. The procedure was performed with the patient under
local anesthesia. The left and right femoral arteries and veins were punctured. A
5F sheath was introduced in the left femoral artery for hemodynamic monitoring. The
Impella CP percutaneous continuous-flow MCS was inserted via a 14F sheath in the right
femoral artery, crossing the aortic valve. A quadripolar catheter and intracardiac
echocardiographic transducer were inserted in the right ventricular apex and right
atrium, respectively. After the MCS was activated, programmed ventricular stimulation
resulted in fast VTs that were not mappable. Mean arterial pressure (MAP) remained
adequate with help of the MCS. Next, intracardiac echocardiography-guided transseptal
puncture was performed using an 8.5F SL1 sheath. After transseptal puncture, a bipolar
voltage map of the LV was created using the CARTO 3-dimensional electroanatomic mapping
system (Biosense Webster) together with the RMN system and the NaviStar RMT ThermoCool
ablation catheter (Biosense Webster). After a very dense voltage map was completed,
scar homogenization was performed using the following radiofrequency settings: continuous
ablation with 50 W, 43°C, flow 20 mL/min. Because of MCS, it was hemodynamically well
tolerated to ablate during VT for >35 minutes in total (Figure 1). The mapping and
ablation were performed using a NaviStar RMT ThermoCool catheter. The very extensive
anterior scar became unexcitable, as proven by pacing maneuvers. Only (nonclinical)
fast VTs and ventricular fibrillation were inducible after ablation and were well
tolerated because of the continuous-flow MCS. Total procedure time was 354 minutes,
total fluoroscopy time 27 minutes, and total ablation time 2971 seconds. Continuous
rhythm observation during 48 hours postprocedure showed no VT recurrences. Kidney
function remained stable (CKD-EPI [Chronic Kidney Disease Epidemiology Collaboration]
estimated glomerular filtration rate 51 mL/min preprocedure, 45 mL/min postprocedure).
The patient was discharged home the second day after the procedure.
Figure 1
Several procedural recordings from the remote magnetic navigation–guided ventricular
tachycardia (VT) ablation procedure. A: Fluoroscopic image of the Impella (Abiomed
Inc, Danvers, MA) and catheters in the right anterior oblique (RAO) view. B: Intracardiac
electrogram of a VT with a cycle length of 300 ms recorded during ablation. C: Surface
electrocardiogram (ECG) and mean arterial pressure (MAP) curve showing induction of
VT. The pulsatile MAP curve changes into a flat curve around 60 mm Hg because of the
hemodynamic support provided by the Impella. D: Surface ECG and MAP recorded a few
minutes later. MAP remains constant around 60 mm Hg during sustained VT. E: Image
of the CARTO map (Biosense Webster, Diamond Bar, CA). All ablation points on the anterior
wall of the left ventricle are visualized. ICD = implantable cardioverter–defibrillator;
RA = right atrium; RF = radiofrequency; RV = right ventricle.
Procedural precautionary measures
Preprocedure, several precautionary measures were taken to safely combine the Impella
continuous-flow MCS with RMN-guided ablation. Preprocedure, a step-by-step procedural
approach was designed by the electrophysiologist, interventional cardiologist, and
operating team, along with technical support from engineers from Abiomed and Stereotaxis.
At the start of the procedure, CARTO patches (Biosense Webster) were positioned carefully
on the chest and back of the patient, with the Impella motor lying as far out of their
field as possible to prevent EMI (Figure 2). Subsequently, the Automated Impella Controller
(AIC) module, the Impella user control interface, was positioned carefully outside
the magnetic field (5-Gauss zone). The continuous-flow MCS was positioned and activated
before the RMN magnets were put in navigate position to prevent eventual motor stop.
The flow rate of the Impella can be adjusted by performance levels (P-levels), corresponding
to a fixed rate of motor rotations per minute. Instead of using the automatic flow
mode, the Impella was switched to manual P-control mode during this procedure. Level
P8 was chosen as the start level, which corresponds to a high flow of ±3.5 L/min.
Flow of 1.5 L/min was chosen as the lower limit to prevent aortic regurgitation. In
manual P-control mode, the P-levels have to be downregulated manually when suction
alarms appear. During this procedure, no suction alarms occurred. No dislocation or
interference due to the magnetic field was noted. However, the motor power and flow
rate displayed on the AIC monitor seemed to be falsely elevated when the magnets were
in navigation mode (average false elevation of flow of 0.5 L/min). Because MAP remained
constant, a technical origin was suspected. Motor power and flow rate returned to
baseline values when the magnets were moved to the stowed position.
Figure 2
Schematic posteroanterior overview of positioning of the Impella CP continuous-flow
mechanical circulatory support device (Abiomed Inc, Danvers, MA) and the CARTO patches
(Biosense Webster, Diamond Bar, CA). The CARTO patches were positioned anterior and
posterior on the chest and back of the patient so that the Impella CP motor was lying
as far out of their field as possible. A = anterior; P = posterior.
Discussion
To the best of our knowledge, this is the first reported case in which hemodynamic
support by the Impella continuous-flow MCS was used during RMN-guided VT ablation.
Despite the magnetic field, the Impella functioned normally during the procedure.
There are different approaches for VT ablation. An ablation approach based on substrate
modification does not require routine use of MCS. However, in patients with structural
heart disease undergoing VT ablation, the numerous comorbidities, the complexity of
underlying substrates, and procedural factors such as fluid overload and use of anesthesia
might lead to acute hemodynamic decompensation.13, 14 Moreover, only an average of
30% of patients can hemodynamically tolerate VT.
7
In the context of manually guided VT ablation, many studies reported on the safe use
of continuous-flow MCS for periprocedural hemodynamic support.8, 9, 10, 13 Furthermore,
emergent rescue MCS insertion during VT ablation because of hemodynamic collapse is
associated with a high 30-day mortality compared to pre-emptive MCS insertion.
15
Therefore, it is important to identify high-risk patients undergoing CA of scar-related
VT for prophylactic MCS.
14
Many studies compared RMN-guided with manual VT ablation3, 4, 5 and reported superiority
of RMN with respect to acute success, recurrence, procedure time, fluoroscopy time,
and complications. Compatibility of hemodynamic support devices with the preferential
VT ablation technique is desirable. This case illustrates that it is possible to safely
combine the Impella CP continuous-flow MCS with RMN-guided VT ablation. However, several
hazards must be overcome when combining MCS with the strong magnetic fields used in
RMN-guided ablation. The primary concern is the risk of EMI.
11
Theoretically, interference will be particularly seen when ablating in the LV outflow
tract, right ventricular outflow tract, and septal wall because of proximity to the
MCS motor. Based on early clinical experiences,
12
we advise careful positioning of the CARTO patches, AIC monitor, and catheters to
reduce EMI as much as possible. In case of EMI, a possible resolution is lowering
the P-level of the Impella until EMI resolves, as proposed by Vaidya and colleagues
11
(eg, from P8 to P6). Fortunately, this was not necessary in our case. When the magnets
are in the navigation position before the MCS is activated, there is a theoretical
hazard of motor stop because of its alignment with the magnetic field. Therefore,
it is recommended to position and start the MCS before activating the magnets. In
automatic Impella motor control mode, measurements of the rotational speed of the
motor could become inaccurate because of the magnetic field, and the flow rates could
become uncontrollable. We observed that in navigation mode, Impella motor power and
flow rate displayed on the AIC were falsely elevated and should be interpreted with
care. Consequently, it is recommended to monitor MAP and use the manual P-control
mode instead of the automatic mode. Our experience is based on a single case, and
further research is warranted to establish the safety of combining the Impella CP
continuous-flow MCS with magnetic-guided ablation. However, the 2 techniques seem
to be compatible, which extends treatment options for patients experiencing hemodynamic
unstable VTs.
Conclusion
The Impella CP continuous-flow MCS can be used to provide hemodynamic support during
RMN-guided VT ablation.