(Circulation. 1998;98:2168-2179.)
© 1998 American Heart Association, Inc.
Clinical Investigation and Reports |
Endocardial Activation Mapping of Ventricular Tachycardia in Patients
First Application of a 32-Site Bipolar Mapping Electrode Catheter
From the Department of Cardiology, Leiden University Medical Center, Netherlands.
Correspondence to Martin J. Schalij, Department of Cardiology, Leiden University Medical Center, PO Box 9600, 2300RC Leiden, Netherlands.
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Abstract |
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Background—Localization of early activated endocardial areas during ventricular tachycardia (VT) is mandatory for performance of surgical or radiofrequency catheter interventions. The use of a multielectrode catheter may shorten the procedure time and increase the accuracy of the procedure compared with single-electrode mapping techniques. This study was performed to evaluate the safety and efficacy of a 32-bipolar-electrode mapping catheter in patients.
Methods and Results—The basket-shaped mapping catheter (BMC), integrated with a computerized mapping system, allowed on-line reconstruction of endocardial activation maps. Twenty patients with VT were studied before surgery (n=4) or radiofrequency catheter ablation (n=16). End-diastolic left ventricular (LV) volume was 280±120 mL, with an LV ejection fraction of 33±14%. The volume encompassed by the BMC was 164±27 mL (130 to 200 mL); the deployment time was 46±11 minutes. Endocardial activation time during sinus rhythm was 105±34 ms; 14±5 electrodes could be used to stimulate the heart. Cycle length of VT was 325±83 ms. Earliest endocardial activation was recorded 58±42 ms before the onset of the surface ECG. Complications were pericardial effusion (n=2) and transient cerebral disorientation (n=1).
Conclusions—Percutaneous multielectrode endocardial mapping in patients with VT is feasible and relatively safe. The use of this technique shortens the time patients have to endure VT.
Key Words: reentry • tachycardia • mapping • ischemia • heart diseases
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Reentry is the underlying mechanism of most ventricular arrhythmias in patients with ischemic heart disease. Surviving cell layers within the infarcted myocardium play a key role in the induction and perpetuation of reentry.1 2 3 4 5 These cell layers are often localized within the subendocardium of the left ventricle (LV) or intramurally within the interventricular septum.1 2 6 7 Drug therapy, still the first-choice treatment modality in most patients, is associated with high recurrence rates.8 9 If arrhythmias recur, surgical resection or radiofrequency catheter ablation may serve as alternative treatment modalities.10 11 12 13 Before treatment, endocardial activation mapping to localize the arrhythmogenic site13 14 15 16 17 is mandatory. Current mapping techniques are limited. Single-electrode mapping or the use of multiple catheters, during which the patients have to endure ventricular tachycardia (VT) for prolonged periods,13 14 are uncomfortable for the patients, and reconstruction of the geometrical localization is difficult. A new, high-resolution mapping technique18 that uses a magnetic technology for localization purposes and a single electrode that is "dragged" over the endocardial surface may overcome some of the disadvantages of the other techniques but is still a time-consuming procedure.
A multielectrode catheter inserted percutaneously may allow detailed and reproducible endocardial mapping of VT within a short period of time. This study was performed to evaluate the safety and efficacy of the use of a novel multielectrode mapping catheter in patients with VT.
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Methods |
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Twenty patients were studied between December 1995 and November 1997. This study was approved by the institutional ethics committee. Informed consent was obtained from all patients. Before the mapping procedure, patients underwent neurological and cardiac examinations, including 24-hour Holter monitoring, echocardiography (either transthoracic or transesophageal) to rule out the presence of LV pedunculated thrombi, and coronary plus biplane LV angiography. Patients underwent an electrophysiological study before the procedure. During the mapping procedure, heparin (activated coagulation time of 2.5 to 3 times the baseline value) was given intravenously. Systemic blood pressure and heart rate were monitored continuously.
"Basket" Mapping Catheter
The 8.5F mapping catheter (Cardiac Pathways) consists of an
open-lumen catheter shaft with a collapsible, basket-shaped,
32-bipolar-electrode array on the distal end (Figure 1A
). The catheter is constructed of 8
equidistant metallic arms, each containing 4 electrode pairs with an
interelectrode spacing of 1 to 1.5 cm. Three arms contain radiopaque
markers for localization (Figure 1B). The catheter (50, 130, 170, or
200 mL) was inserted into the LV through an 11F guiding catheter, which
was introduced percutaneously into the right femoral
artery and positioned in the LV. The size of the basket catheter was
chosen on the basis of the LV end-diastolic volume and the
length of the LV (calculated from the LV angiogram). The central lumen
of the catheter was flushed (4 U heparin/mL saline) with an infusion
pump (during insertion, 100 mL/h; after deployment, 50 mL/h). A
transthoracic echocardiogram was made to study the
deployment of the basket and to rule out aortic
regurgitation caused by the catheter.
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Mapping System
The mapping system (Cardiac Pathways) consists of an acquisition
module connected to a SPARC 20 computer (Sun Computers). The system is
capable of simultaneously processing (1) 32 bipolar
electrograms from the basket catheter, (2) 16 bipolar/unipolar
electrogram signals, (3) a 12-lead ECG, and (4) a pressure signal.
Color-coded activation maps are reconstructed on-line. Signals are
sampled at 3 kHz/channel with a resolution of 14 bits. The high-pass
filters are set at 30 Hz and the low-pass filters at 500 Hz.
Electrograms and activation maps are displayed on a computer monitor
and printed in color. The signals are stored on optical disk for
off-line analysis. Activation marks are generated automatically
with either a peak or slope algorithm. The peak algorithm places
activation marks on the maximum amplitude; the slope algorithm places
the activation marks on the maximum absolute slope (dV/dt). The
activation times can be adjusted manually.
Programmed Electrical Stimulation
The hearts were stimulated with a pulse width of 2 ms by use of
a constant-current stimulator (Medtronic). The output of the stimulator
could be directed to any of the electrode pairs of the basket catheter
or to any of the 16 bipolar electrode leads.
To test the contact between the electrodes and the endocardium, the heart was stimulated through each of the basket electrode pairs at an output of 2.0 mA, at a rate of 20% above the intrinsic sinus rate, and checked for ventricular capture. Next, the output was set at 5.0 mA, and the pacing protocol was repeated. Programmed electrical stimulation applying up to 3 extrastimuli at 2 times diastolic threshold was used to induce VT.
Radiofrequency Ablation Procedure
In 16 patients, a radiofrequency ablation procedure was
performed immediately after removal of the basket catheter. A standard
ablation catheter (Steerocath, EP Technology) was used. Detailed
localization included the reconstruction of pace maps during
stimulation from the tip of the ablation catheter, stimulation during
tachycardia to reveal concealed entrainment, and the
characterization of locally recorded electrograms. Radiofrequency
current was delivered for 60 seconds and repeated until the target
tachycardia was no longer inducible.
After the Procedure
The arterial sheath was removed 4 to 6 hours after
the procedure. The patients then received heparin for at least 24
hours. Neurological examination, an echocardiogram, and a chest
radiograph were obtained within 24 hours after the procedure.
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Results |
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Patient Characteristics
Twenty patients (all male, 64±7 years old, Table 1
) with drug-refractory VT were
studied before surgical resection (n=4) or radiofrequency catheter
ablation (n=16).
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Introduction and Deployment of the Mapping Catheter
The mapping catheter was inserted successfully in all patients. No
significant changes were observed in heart rate or blood pressure
during the procedures. No sustained arrhythmias were elicited
by the insertion of the catheters. Insertion and deployment of the
catheters took 9 to 16 minutes (11±2.6 minutes). Although it was
difficult to manipulate the basket within the LV, it was possible to
rotate the catheters slightly and adjust the deployment in most
patients. A satisfactory fit within the LV was obtained in each
patient. However, in all patients, the arms of the mapping catheter
were unevenly distributed over the endocardial surface.
Transthoracic ultrasound examinations during the procedures
did not reveal aortic regurgitation in any of the
patients.
Endocardial Electrical Activity
The noise level was <50 to 75 µV. An example of the electrical
activation recorded during sinus rhythm (SR) (A) and during VT (B)
is given in Figure 2. Except for 2 leads
showing no electrical activity (E2,
E4), the signals were of acceptable quality with
a noise level of <75 µV. Although movement of the electrodes may
occur during contraction of the heart, movement artifacts did not
hamper analysis of the recordings. The signal-to-noise
ratio was acceptable even in case of low-amplitude fragmented
activation.
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Recording During SR
During SR, electrical activation could be recorded from 31±1
of the 32 available electrode pairs (Figure 3, Table 2).
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Stimulation
Stimulation via the basket electrodes was performed in all
patients but one. Patient 16 developed VT during pacing from the right
ventricular apex. After cardioversion, the catheter had
moved back into the aorta and had to be removed. Fourteen (±5)
electrode pairs (43%) could be used to stimulate the heart, with an
output of 5 mA (Table 2
, Figure 4).
Stimulation was not always possible when the electrode pairs were
localized within infarcted regions or when the electrodes were located
near the base of the heart.
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Induction of VT
The initiation of VT is shown in Figure 5. In the lower panel, 3 ECG tracings and
4 intracardiac electrograms are shown. VT (cycle length [CL], 410 ms)
was initiated after the second premature stimulus (S3). During pacing
(S1; CL, 600 ms) from the right ventricular apex, a zone of
late activation can be detected around electrode rows D and E
(posterobasal part of the LV). The corresponding intracardiac tracings
from this region (lower panel) show progressive delay of activation of
this part of the ventricle during the consecutive premature beats (S2,
S3) and become increasingly fragmented. Ultimately,
tachycardia was initiated by an impulse propagating slowly
through this area (electrode D1-2). The same pattern of induction of
tachycardia could be reconstructed in 12 of 20 patients.
Because of the limited resolution of the electrode, an exact
reconstruction of the reentrant pathway was not possible. In the
remaining patients, it was not possible to reconstruct the initiation
of tachycardia either because of the limited resolution of
the catheter or because the tachycardia originated from the
right side of the intraventricular septum.
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Mapping of VT
VT (CL, 325±83 ms) was induced in all patients (Table 2, Figure 6). Earliest endocardial activation was
recorded 58±42 ms (0 to 176 ms) before the onset of the surface
ECG. In 17 of 20 patients, VT was terminated by burst pacing within 60
seconds after induction. Cardioversion was necessary in 3 patients
because of hemodynamic deterioration. In patients
studied before surgery, a reasonable correlation was found between the
earliest endocardial activated area during
percutaneous mapping, and the area was removed during
surgery. In 2 patients, the findings were confirmed by endocardial
mapping during surgery (using a multielectrode balloon); in the other 2
patients, VT was not inducible during surgery. In these 2 patients, the
location of the endocardial resection was based on the findings
obtained during the percutaneous mapping procedure
(although a larger part of the endocardium was removed). Radiofrequency
catheter ablation was successful in 14 of 16 patients (88%). In 3 of
16 patients (19%), the site of successful RF application was located
on the right side of the intraventricular septum.
In 11 of 13 patients (85%), the localization of the site of
arrhythmia initiation by catheter mapping was
consistent with the results obtained by the basket catheter
(both between the fluoroscopic position and between the locally
recorded electrical activity). Ablation was not successful in 2
patients with hemodynamically unstable VT.
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An example of a fast VT is shown in Figures 7 and 8
(patient 15). In this case, a 130-mL basket (end-diastolic
volume, 260 mL) was deployed within the infarcted area. During SR
(Figure 7A), a zone of late activation can be detected in the
inferoposterior area of the LV (rows A, G, and H). Although the map
suggests an even distribution of the electrode arms, rows A, B, and C
were near each other. During VT1 (CL, 215 ms; panel B), activation
started 42 ms before the onset of the surface ECG, with early
activation recorded from electrodes C1-2, B1-2, and A1-2. During
VT2 (CL, 252 ms; panel C), activation started 67 ms before the onset of
the surface ECG, with early activation recorded from electrodes
A7-8 and B7-8. In the lower panels (D, E, and F), the electrograms
recorded from electrodes A1-2 to B7-8 are displayed. During SR,
fragmented activation was recorded in all electrodes. Purkinje
deflections were recorded in B5-6 and B7-8. During VT1, the areas
around electrodes A1-2 and B1-2 were activated relatively early
in the cycle, with a gradual spread of activation to electrodes A7-8
and B7-8. During VT2, the areas around electrodes A7-8 and B7-8 were
now activated relatively early, whereas the areas around A1-2
and B1-2 were activated relatively late.
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The activation map recorded during tachycardia
before ablation is shown in Figure 9A.
Early activation is recorded around electrode H5-6.
Middiastolic potentials preceding myocardial activation can
be detected 170 ms before onset of the surface ECG (panel B). During
the ablation procedure (panel C), middiastolic potentials
preceding the myocardial activation can be detected. During ablation at
this site, tachycardia stopped within 2 seconds and was no
longer inducible.
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Adverse Events
The catheters were deployed for 46±11 minutes (20 to 65
minutes). No thrombus formation could be detected on any of the
catheters. No embolic complications were observed. Ultrasound studies
did not reveal mitral valve or aortic valve damage in any patient. In 2
patients, pericardial effusion developed. In patient 1, 4 hours after
the procedure, 
500 mL of fluid was removed by pericardiocentesis. At
surgery for endocardial resection (10 days later), no perforation site
could be identified. In patient 14, 1 week after stent implantation,
when the patient was still receiving aspirin and ticlopidine,
pericardial effusion developed during the procedure. At emergency
surgery, a small perforation was detected in the lateral wall of the
LV; the patient's recovery was uneventful. In patient 7, cerebral
disorientation was observed the first 12 hours after the procedure; the
patient's recovery was uneventful. No vascular complications were
observed.
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Discussion |
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This study reports the safety and efficacy of percutaneous endocardial mapping with a multielectrode basket-shaped catheter in patients with VT.
Mapping of VT
Reentry is an important mechanism of VT in patients with
ischemic heart disease.1 2 6 Because of
limitations of single-catheter mapping techniques, it has been
difficult to elicit the mechanisms of tachyarrhythmias
in patients during percutaneous
mapping.14 The mapping catheter used in this
study may be useful to unravel some of the mechanisms of VT in
patients. Local electrophysiological
characteristics contributing to induction or perpetuation of reentry
may now be studied in detail.
We demonstrated areas of fragmented early endocardial activation in almost all patients. These areas play an important role in the induction and perpetuation of reentry, as demonstrated either by concealed entrainment during pacing4 13 or by the fact that the tachycardias were terminated during radiofrequency application at those sites. Although because of the limited resolution of the mapping catheter used in this study, a high-resolution reconstruction of reentrant circuits was not possible, in the majority of patients reentry seems to be the underlying mechanism of the VT. The fast reconstruction of endocardial activation maps resulted in a reduction of the time patients must endure tachycardia compared with single-point mapping techniques or the insertion of multiple electrodes into the LV.13 14 In this study, the duration of tachycardia totalled maximally 60 seconds.
The spatial resolution of the basket catheter is still limited
(1 cm along the arms of the catheter and 
1 cm between the arms).
This resolution will be sufficient to locate the earliest
activated endocardial site before surgical resection, because a
larger part of the endocardium will be resected during this procedure.
In case of a catheter ablation procedure, in which only a small area is
treated, the spatial resolution is not always sufficient. The outcome
of this study is in accordance with this perception. The results of the
mapping procedure guided the operator toward the earliest
activated endocardial regions, but detailed localization, using
pace mapping and entrainment studies,12 13 16 was
necessary to localize precisely the regions of interest. Asymmetric
mapping devices with a locally enhanced spatial density of electrodes
may be required to study these regions of interest precisely.
Mapping System
The mapping system allows simultaneous
recording of electrical activation from multiple sites and fast
reconstruction of endocardial activation maps. The algorithms used to
construct activation maps did result in an accurate detection of 75%
of the activation times. Manual adjustment was necessary when
low-amplitude fragmented signals or noisy signals were
recorded.
At this time, only limited 2-dimensional graphic features are available. To enhance the graphic representation, 3-dimensional (3D) reconstruction of activation would be advantageous.
Mapping Techniques
The main objective of endocardial mapping is to reveal sites
activated early (with respect to the surface ECG) during
tachycardia, to reveal middiastolic potentials,
and to identify sites demonstrating concealed
entrainment.13 These sites are targets for either
surgical or catheter interventions.13 Current
methods for mapping include single-point mapping, the insertion of
multiple catheters, and the use of endocardial multielectrode balloons
during surgery.1 10 Single-point mapping,
although a reliable technique, is inherently less accurate,
time-consuming, and not suitable for the mapping of fast
tachycardia. The insertion of multiple catheters yields an
increased spatial resolution but entails a lengthy procedure, and
activation maps are difficult to reconstruct.14
The use of multielectrode balloons is restricted to surgery. A recently
developed technique18 combines a magnetic 3D
localization system with a single roving electrode that allows the
reconstruction of high-density (<1 cm) endocardial activation maps.
The combination of 3D geometry with electrical activation may guide the
operator toward a target site for RF ablation. However, this is also a
long procedure.
Limitations of the Technique
Although almost all patients suffered from large myocardial
infarctions and most ventricles were seriously deformed, all catheters
were deployed successfully. However, the limited torque capabilities of
the mapping catheter hampered the correct placement of the catheter.
These problems may be improved by adding steerability to the catheter
shaft, but the manipulation of the catheter will continue to require
extensive training. Furthermore, because of deformation of the
ventricles, not all electrodes were in close contact with the
endocardial surface (only 44% of the electrodes could be used to
stimulate the heart). Electrodes located near the posterobasal part of
the LV were often not suitable for pacing; however, local electrical
activity could be recorded from most of these sites. These
limitations may be resolved by designing specially shaped catheters for
different LV shapes. Another limitation of LV endocardial mapping may
be that reentrant circuits located either on the right side of the
intraventricular septum or intramurally cannot be
reconstructed in detail.
Limitations of This Study
By virtue of its capability to reduce the procedure time and
duration of tachycardia, the basket catheter allows mapping
of hemodynamically unstable tachycardia.
However, this study was (with a few exceptions) limited to patients who
tolerated tachycardia for a prolonged period. It is another
limitation that the protocol of this safety and feasibility study did
not allow simultaneous insertion of a radiofrequency
ablation catheter, which hampered the correlation between the
activation maps and the site of successful ablation. Furthermore,
entrainment of tachycardia using the mapping catheter
electrodes to stimulate the heart was not studied systematically.
Conclusions
Percutaneous endocardial mapping with the
basket catheter is feasible and relatively safe. The technique
facilitates endocardial mapping during tachycardia and
considerably shortens the time patients have to endure VT. Potentially,
the simultaneous deployment of a basket catheter and an
ablation catheter will allow the treatment of fast and
hemodynamically unstable VT.
Received February 18, 1998; revision received July 7, 1998; accepted July 11, 1998.
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