Hiroshi
Tada, M.D.
Division of Cardiology, Gunma
Prefectural Cardiovascular Center, Maebashi, Gunma Japan.
Address for
correspondence: Hiroshi Tada, MD, Division of Cardiology, Gunma
Prefectural Cardiovascular Center, 3-12 Kameizumi, Maebashi, Gunma
371-0004, Japan.
E-mail:
tada.h@cvc.pref.gunma.jp
Abstract
Idiopathic
outflow tract
arrhythmias (ventricular tachycardias or symptomatic premature
ventricular
contractions; OT-VT/PVCs) can originate from the left ventricular (LV) epicardium
(Epi-VT/PVCs), and radiofrequency (RF) energy applications from the
aortic
sinus of Valsalva can eliminate Epi-VT/PVCs in selected patients.
Among the
various ECG findings, the R-wave
duration index
and R/S amplitude index in leads V1 or V2 are useful for identifying
Epi-VT/PVCs,
and the Q-wave ratio of leads aVL to aVR and S-wave amplitude in lead
V1 are
useful for differentiating between an Epi-VT/PVC originating from the
LV
epicardium remote from the left sinus of Valsalva (LSV) and that from
the LSV. Tissue tracking imaging is a
promising
modality for identifying the origin of OT-VT/PVCs and for
differentiating between
an Epi-VT/PVC originating from the LV
epicardium remote from the LSV and that from the LSV.
If the origin of the Epi-VT/PVC is identified within the
LSV, coronary and aortic angiography should be performed to assess the
anatomic
relationships between the Epi-VT/PVC origin and coronary arteries and
aortic
valve before the RF energy delivery. To
avoid
potential complications, RF ablation should be performed at the LSV
using a
maximum power of 35 watts and maximum temperature of 55°C. Epicardial mapping through the coronary venous
system and the presence of potentials recorded from the ablation site
within
the LSV and their changes before and after the RF energy applications
may be
useful for diagnosing Epi-VT/PVCs or predicting a successful catheter
ablation
from the LSV.
Key Words: Ventricular
tachycardia; left sinus of Valsalva; potential; premature ventricular
contraction; catheter ablation, tissue tracking imaging.
Introduction
Radiofrequency
(RF)
catheter ablation has been established as an effective and curative
therapy for
ventricular tachycardias (VTs) or symptomatic premature ventricular
contractions (PVCs) originating from the outflow tract (OT-VT/PVCs) in
structurally
normal hearts.1-6 Recenty, idiopathic
OT-VT/PVCs originating from the left ventricular (LV) epicardium
(Epi-VT/PVCs)
have been reported.6-13 These
OT-VT/PVCs are thought to originate from the LV epicardium around the
transitional area from the great cardiac vein to the anterior
interventricular
vein.13,14 Some can be
ablated through the coronary venous system15
or by percutaneous
epicardial instrumentation,16
but others can be ablated from the left
sinus of Valsalva (LSV).6-13 The
correct identification of the latter type
of OT-VT/PVC before the RF energy applications is important in order to
avoid
futile RF applications from the LSV and the ensuing complications.17,18
In this
article, we focused on the diagnosis
and RF catheter ablation of Epi-VT/PVCs which can be ablated from the
LSV.
Diagnosis
Characteristic
ECG findings originating from each portion
of the outflow tract and several ECG findings useful for
differentiating an
OT-VT/PVC from other OT-VT/PVCs originating from different portions of
the
outflow tract have been reported. The precordial
R-wave transition,3,6,19 QRS
morphology in lead I3,6, R-wave
duration in lead V1
or V2, and R/S-wave
amplitude ratio
in leads V1 or
V2 have been
reported as useful indices for differentiating OT-VT/PVCs originating
from the right side from those arising from the
left side (LVOT, LSV or LV
epicardium remote from the LSV)3,6,13. Furthermore,
the presence of
an S wave in lead V5 or V6 is
considered a characteristic, useful ECG finding in OT-VT/PVCs of LVOT
origin6,9.
Among those findings, the
usefulness of both
the R-wave duration index and R/S amplitude index in leads V1 or V2 for
identifying Epi-VT/PVCs has been reported (Fig. 1A).6,8 The R-wave
duration index is obtained by
dividing the QRS complex duration by the longer R-wave duration in lead
V1 or
V2, and the R/S-wave amplitude index is calculated as the greater value
for the
R/S-wave amplitude ratio in lead V1 or V2.6,8 A recent
study demonstrated that when the
R-wave duration index is >0.5 or the R/S-wave amplitude
index is >0.3,
there is a fair possibility that the OT-VT/PVC originates from the LSV
(Fig. 1A,
left panel) or LV epicardium remote from the LSV which cannot be
ablated from
the LSV (Fig. 1A, right panel).6 However,
both indices do not significantly differ when
differentiating between
Epi-VT/PVCs originating from the LSV and those originating from the LV
epicardium remote from the LSV.6 Instead, a Q-wave ratio of leads aVL to aVR
>1.4 or an
S-wave
amplitude >1.2 mV in lead V1 was useful for differentiating
between
an Epi-VT/PVC originating from the LV epicardium remote from the LSV
and that
from the LSV (Fig. 1).6 In a
previous report using a pace mapping techinique,13
the QRS
morphology during pacing from the proximal site of the anterior
interventricular vein (AIV) exhibited a deep S-wave in V1, and pacing
from the
distal portion of the great cardiac vein (GCV) revealed a high Q-wave
ratio of
aVL to aVR. Therefore, a high Q-wave
ratio for aVL to aVR or a deep S-wave in lead V1 may indicate that the
Epi-VT/PVC
originates from the LV
epicardium remote from the LSV around the transitional area from the
GCV to the
AIV.13,14 For determination
of the location of OT-VT/PVCs, including Epi-VT/PVCs, a recently
developed ECG
algorithm is useful.6
Figure 1. A.
Representative
12-lead ECGs of premature ventricular contractions (PVCs) originating
from the
left sinus of Valsalva (LSV; Patient 1) and left ventricular (LV)
epicardium
remote from the LSV (Patient 2). Both
PVCs have an R-wave duration index in lead V2 >0.5,
indicating that these
PVCs originate from the LV
epicardium. The Q-wave ratio of aVL to
aVR was <1.4 and S-wave amplitude <1.2 mV in lead V1 in
patient 1,
and the Q-wave ratio of aVL to aVR was >1.4 and S-wave amplitude >1.2
mV in patient 2. The former PVC could be
eliminated by an RF energy application from the LSV, but the latter
could not be
ablated from the LSV. B. Twelve-lead ECG
of a PVC and pace mapping (PM) from the LSV. The
configuration of the 12-lead QRS complex
that was induced by stimulation through the ablation catheter within
the LSV
matched that of the spontaneous PVC. An
RF application at this site eliminated this PVC.
Although
rare (3%), some OT-VT/PVCs have demonstrated dynamic changes in the QRS
morphology following the RF catheter ablation, requiring additional RF
ablation
applications at a different portion of the outflow tract to cure the
OT-VT/PVCs20.
These OT-VT/PVCs consistently showed a change
in the R wave amplitude in the inferior leads between the 1st
OT-VT/PVC
and 2nd OT-VT/PVC, while the earliest
ventricular activation
during
either the 1st or 2nd
OT-VT/PVC was recorded from
the LSV20.
When an increase in the R-wave amplitude in
the inferior leads follows the RF catheter ablation of the 1st
OT-VT/PVC from an
endocardial site of the RVOT or LVOT, the earliest ventricular
activation
during the 2nd OT-VT/PVC
may be recorded at the LSV. On
the other hand, when a decrease in the R-wave
amplitude in the inferior leads follows the RF catheter ablation from
the LSV,
the earliest ventricular activation during the 2nd OT-VT may be
recorded from
an endocardial site of the RVOT or LVOT. Therefore,
detailed continuous observation of the QRS
morphology of
OT-VT/PVCs, especially the R wave amplitude in the inferior leads, is
important
for identifying the changes in the QRS morphology during the RF
catheter
ablation of OT-VT/PVCs.
Recently, tissue tracking imaging
(TTI) has been
demonstrated as a novel non-invasive modality for identifying the
origin of OT-VT/PVCs.21 TTI is
an ultrasonographic technique that
measures the myocardial motion amplitude toward the transducer in each
region
during systole, identifying regional myocardial displacement on the
basis of
myocardial velocities using color Doppler myocardial imaging principles.22,23
It allows
rapid semiquantitative visual
assessment of the systolic distance of the tissue motion along the
Doppler axis
using a graded color display.21-23 In this
technique, the
origin of the OT-VT/PVC could be recognized as the site where the
earliest
color-coded signal (ECCS) appeared on the myocardium at the onset of
the OT-VT/PVC
(Fig. 2).21 The OT-VT/PVCs in
which the earliest ventricular activation was recorded from the LSV had
the
ECCS in the myocardium above the pulmonary valve, and most of them in
which the
ECCS appeared close to the pulmonary valve could be ablated from the
LSV (Fig.
2B).21
The distance between
the attachment of the pulmonary valve to the septum and the center of
the ECCS (8±4
mm) in these OT-VT/PVCs with a successful ablation from the LSV was
significantly
shorter than that in those with a failed ablation (18±6 mm,
p<0.05). On the other hand, the ECCS
was always found
below or at the level of the pulmonary valve in all arrhythmias which
could be
ablated from the RVOT(Fig. 2A). These
results indicate that TTI can provide detailed and accurate information
on the
arrhythmia origin of OT-VT/PVCs and may be useful for
differentiating between an OT-VT/PVC
originating from the LV
epicardium remote from the LSV and that from the LSV.
Figure 2. Tissue
tracking images obtained from 2 patients
with idiopathic premature ventricular contractions (PVC) originating
from the
outflow tract. A. The earliest
color-coded signal (ECCS; blue arrow) appeared at the level of the
pulmonary
valve during a PVC. This PVC was
successfully eliminated by an RF energy application to the septum of
the right
ventricular outflow tract (RVOT) just beneath the pulmonary valve. B. The ECCS (blue arrow) appeared in the
myocardium 8 mm above the pulmonary valve during a PVC.
This PVC was successfully ablated from the left
sinus of Valsalva. LA= left
atrium; LV=
left ventricle; PA= pulmonary artery.
Mapping
and Ablation Technique
Under
guidance with
fluoroscopy, catheters were introduced into the RV apex, RVOT and/or
His bundle
region via the right femoral vein. If
the clinical arrhythmia did not occur spontaneously, programmed
ventricular
stimulation from the RV apex and RVOT or incremental burst pacing were
performed. If the clinical arrhythmia was
not induced in the baseline state, intravenous isoproterenol (0.5 to
2.0 μg/min)
was administered to induce the clinical arrhythmia. Activation
mapping and pace mapping were performed
during the clinical arrhythmia. Mapping
of the OT-VT/PVC was initially started in the RVOT region.
If suitable ablation sites were not found in
the RVOT, the endocardium of the LVOT and aortic sinus of Valsalva were
mapped. If the origin of the OT-VT/PVC was
mapped to a location above the aortic valve, coronary and aortic
angiography were
performed to assess the anatomic relationship between the OT-VT/PVC
origin and coronary
arteries and aortic valve before the RF energy delivery (Fig. 3).6-9,12,13
Figure 3. Left coronary
artery (left)
and fluoroscopic images during the radiofrequency catheter ablation
(right)
obtained in the right anterior oblique (RAO 35°) and left anterior
oblique (LAO
45°) projections showing the ablation sites. The
tip of the catheter at the successful ablation sites
(Abl) was
located about 10 mm below the left coronary artery ostium. An RF energy delivery at this site terminated
the tachycardia. GCV-AIV=2-Fr
octapolar electrode
catheter placed from the great cardiac vein and anterior
interventricular vein; HRA=high
right
atrium; RV= right ventricle.
It is believed that an RF
application from the LSV does not ablate the valve or aortic wall
itself, but destroys
the epicardium above the septum.9 In our laboratory, a 7 Fr quadripolar catheter
with a 4-mm
distal
electrode, embedded thermistor, interelectrode spacing of 2-5-2 mm, and
deflectable tip was usually
used for mapping and ablation (Fig. 3).
To avoid
potential complications, the RF
ablation was performed at the aortic sinus of Valsalva using a maximum
power of
35 watts, maximum electrode-tissue interface temperature of 55°C
and maximum of
6 RF applications.
9 The
applications of RF energy were 60 to 90 sec in duration.
If an application of RF energy was
unsuccessful, the ablation site was changed under fluoroscopic guidance.
Pace mapping from the LSV was possible (
Fig.
1B), and several studies reported that a perfect pace mapping
could be
obtained
from the successful ablation site.
9,13 However,
the pacing threshold was usually too
high (>8 V) to capture the myocardium through the LSV,
9
and no
studies have sufficiently examined whether or not an RF energy
application at a
site where a perfect pace map is obtained can always result in
successful
ablation, or whether or not an RF energy application at a site where a
perfect pace
map cannot be obtained results in a failed ablation.
Utility of Epicardial Mapping
through the Coronary Venous System
It is well
known that
even if the earliest ventricular activation of the Epi-VT/PVC is at the
LSV, RF
catheter ablation at that site is not always effective.
Because the tip temperature should be
maintained at <55°C to
avoid potential complications,9
the distance between the ablation site within
the LSV and origin of the Epi-VT/PVC will mainly affect the results of
the RF
ablation from the LSV. Therefore, some
Epi-VT/PVCs
with the earliest ventricular activation in the LSV cannot be ablated
from the
LSV because of the distance from the LSV. No
criterion based on the electrograms for predicting a
successful catheter
ablation from the LSV has been established. However,
when the earliest ventricular activation during the
clinical
arrhythmia was found within the LSV, the placement of a 2-Fr octapolar
electrode catheter from the GCV to the AIV (GCV-AIV) and obtaining 7
bipolar
electrogram recordings from the adjacent electrodes of the catheter
placed
along the GCV-AIV may be helpful in diagnosing Epi-VT/PVCs and
predicting the successful
RF catheter ablation from the LSV.24 In Epi-VT/PVCs, the earliest ventricular
activation during
the
arrhythmias is usually found at the LSV or GCV-AIV.13,14
Therefore, several studies have attempted to
evaluate the utility of epicardial mapping through the coronary venous
system
for diagnosising and treating Epi-VT/PVCs.6,8,9,13 However, their results differ.
Kanagaratnam et al. reported simultaneous
endocardial and percutaneous epicardial mapping in patients with
Epi-VTs
eliminated by an RF application from the LSV.7 They found that the Epi-VT/PVC had an earlier
activation on the epicardial surface than at the endocardial site.7 However,
Hachiya et al. reported that the
ventricular
activation recorded from the LSV must be earlier than the earliest
ventricular
activation recorded in the GCV-AIV in Epi-VT/PVCs which can be ablated
from the
LSV.9 A
recent study reported
the usefulness of comparing the earliness of the ventricular activation
recorded
from the LSV and earliest ventricular activation of 7 bipolar
recordings from
the GCV-AIV during the Epi-VT/PVCs for predicting a successful catheter
ablation from the LSV.24 In
patients
in whom the earliest ventricular activation was found at the LSV or
GCV-AIV,
the earliest ventricular activation in the GCV-AIV preceding the
ventricular
activation from the LSV by less than 10 ms identified a successful RF
catheter
ablation from the LSV with a sensitivity of 88 %, specificity of 100%,
positive
predictive value of 100 % and negative predictive value of 75%.24
Significance
of
Potentials recorded
at the Ablation Site within the Left Sinus of Valsalva
It
is well known that a potential preceding the QRS complex is often
recorded at
the ablation site within the LSV (Fig.
4A).8,12,13,25
However, it is unclear if complete
elimination of Epi-VT/PVCs can always be achieved with an application
of RF
energy at the site where this potential is recorded. In
a recent study in which a quantitative
analysis of the electrograms was performed in 23 patients
with symptomatic Epi-VT/PVCs that
underwent RF applications from the LSV, this
potential was found at 19 (90%) of 21 successful ablation sites.26 However, it was also
recorded at 19 (79%) of 24 unsuccessful
ablation sites, and there was no
significant difference in the
incidence of the potentials
between the successful and
unsuccessful ablation sites (p=0.5). In
addition, there were no significant differences in the amplitude
(p=0.12) or interval
from the potential to the QRS complex (p=0.10) between the successful
and
unsuccessful ablation sites. Therefore,
the presence of this potential may not help in identifying successful
ablation
sites within the LSV.
Another
potential recorded in the late phase of the QRS complex during sinus
rhythm in
patients with Epi-VT/PVCs has been reported (Fig. 4B).8
A recent study demonstrated that this
potential was more often observed at the successful ablation sites than
at the
unsuccessful ablation sites before the ablation (p<0.05), and the
difference
between the two groups became greater after the ablation (p<0.001)26:
In the unsuccessful ablation sites, this potential was absent (Type 1)
or its
location did not change before and after the ablation (Type 4). However, this potential appeared at 38% of the
successful ablation sites (Type 2), and pre-existing potentials were
more
delayed after the ablation at 53% of the successful ablation sites
(Type 3),
demonstrating significant differences in the pattern of this potential
between the
successful and unsuccessful ablation sites (p<0.001).
As a result, type 2 or
type 3 patterns for this potential
identified a successful ablation with a sensitivity of 100%,
specificity of 92%,
positive predictive value of 90% and negative predictive value of 100%26.
Therefore,
this
potential is also characteristic of Epi-VT/PVCs, and may be more useful
in
identifying successful ablation sites than the former potential
recorded during
the Epi-VT/PVCs. However, the precise
mechanism responsible for these two potentials recorded during the
Epi-VT/PVCs
(the former) or during sinus rhythm (the latter) is still unclear. There is a possibility that the analysis of
the electrograms recorded at the successful and unsuccessful ablation
sites in
the same patient might be affected by the effects of the RF energy
applications. Therefore, the significance
and utility of
these 2 potentials recorded within the LSV have not been sufficiently
clarified.
Figure 4.
Intracardiac
recordings from
the successful ablation site within the left sinus of Valsalva. A. A sharp potential preceding the QRS
complex (arrow) was recorded during a premature ventricular contraction
(PVC). B. Intracardiac recordings during
sinus rhythm. Before ablation, no potentials
following the QRS complex were recorded. After
the application of radiofrequency
energy at this site, a potential following the QRS complex after the
successful
ablation (arrows) appeared during sinus rhythm. Abl= ablation catheter; Bi.= bipolar
recording; d= distal;
HRA= high
right atrium; HBE= His bundle electrogram; p= proximal; Uni.= unipolar
recording.
Conclusions
With an RF
energy application from the LSV, some Epi-VT/PVCs
can be abolished. However, RF catheter
ablation within the LSV runs the risk of potential complications. Thus, attempting to diagnose these types of
VT/PVCs non-invasively before the ablation procedure, performing
detailed mapping
and assessment of the electrograms obtained during the procedure, and
obtaining
a precise assessment of the anatomic relationships between the
arrhythmia
origin and coronary arteries and aortic valve, are crucial for avoiding
futile
RF applications from the LSV and the ensuing complications, and for
successfully
eliminating this type of Epi-VT/PVC.
Acknowledgements
The
author gratefully thanks all the cardiac physicians and the nursing,
echo
laboratory, clinical engineering and radiology staff members in the
cardiac
wards at Gunma Prefectural Cardiovascular
Center, Maebashi,
for
their kind support.
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