Address for Correspondence:
Mathew D. Hutchinson, MD, FACC, FHRS
University of Arizona College of Medicine Tucson
1501N. Campbell Ave, 4142B
Tucson, AZ 85724, USA
Email: MathewHutchinson@shc.arizona.edu
The right ventricular outflow tract (RVOT) is the most common location
of idiopathic ventricular arrhythmias (VA). Due to low procedural risk
and high success rates, catheter ablation of VA originating from the OT
has been routinely performed for decades. From an attitudinal
perspective, the RVOT is oriented anteriorly and leftward relative to
the left ventricular (LV) OT, and is bounded superiorly by the pulmonic
valve and inferiorly by the RV inflow region. The topography of the RVOT
below the pulmonic valve is commonly conceptualized as opposing
“septal” and “free wall” surfaces; this schema is useful both in
predicting site of VA origin from 12-lead ECG and in performing
catheter-based mapping. The junction of these two surfaces is the most
superior and leftward aspect of the heart, and arrhythmias from this
region typically have a left bundle branch block configuration, a
rightward frontal plane axis, and tall inferior R waves on ECG.
The proximity of coronary arteries to the aortic cusps and LVOT is well
understood, therefore imaging of the coronary arteries is frequently
performed during catheter ablation in the LVOT to prevent collateral
injury. However, the three-dimensional relationship between the coronary
arteries and the RVOT, and consequently the risk of potential collateral
damage to the coronary arteries when ablating in the RVOT, is often
overlooked.1
The study by Dilling-Boer et al2 in this issue of theJournal illustrates a rare and underappreciated hazard associated
with ablation in the RVOT. The authors report acute or subacute injury
to the left anterior descending (LAD) coronary artery in five patients
after ablation in the RVOT. All patients required coronary intervention,
four with acute vessel occlusion. This manifested as acute ST segment
elevation in the precordial leads during catheter ablation in three of
the patients, and as nonspecific ST segment flattening and depression in
one. Review of the coronary angiogram demonstrated occlusion of the LAD
segment between the first and second diagonal branches in four patients
and the LAD segment between the second and third diagonal branches in
one patient. Follow-up ambulatory monitoring data is reported for three
of the patients, all of whom had VA suppression at last follow-up.
The manuscript is a welcome addition to the existing literature
concerning OT VA ablation and the authors are congratulated for their
important effort. The manuscript figures combine multimodality imaging
platforms to highlight the proximity of the RVOT to the intraseptal
course of the LAD and the anterior interventricular vein. There are
several important observations from the report. First, there is
remarkable similarity in 12-lead ECG VA morphology between the five
reported patients: left bundle branch block pattern with late (V4)
precordial transition and a right inferior frontal plane axis. These VAs
have a tall R wave amplitude in the inferior leads with lead III greater
in magnitude compared to lead II. The authors’ Figures 5B and C
illustrate well the cranial and relatively leftward position of this
region compared to the interventricular septum. Also note the lack of
initial r wave in V1, coupled with a relatively slurred QRS onset in
these patients. Many of these ECG features are reminiscent of
arrhythmias successfully ablated in the anterior interventricular or
intraseptal veins.3,4
Consider next the extent of ablation performed in these patients. We
have relatively complete ablation data from only three patients, and the
total radiofrequency ablation duration was 40 and 26 minutes in patients
1 and 3 respectively. Patients 2 and 4 had VA suppression coincident
with a steam pop and pericardial tamponade respectively, thus the
relatively short total duration of ablation likely underestimates the
extent of the lesions applied. Only one patient underwent mapping of the
LV or coronary venous system, thus it is reasonable to speculate whether
there may have been alternative safer or more proximate sites for
ablation compared to the RVOT. Neither pacemapping nor activation
mapping data are included in the report to inform the reader in this
regard.
In considering the ECG morphologic data and the extent of ablation
performed, it is reasonable to conclude that most of the patients
reported in this manuscript had intramural origin for their VAs. It is
well known that VAs from this region can be approached from the RVOT,
LVOT, or coronary venous system. Extensive mapping is required to locate
a site to ablate that provides the best balance between safety and
efficacy. More extensive ablation is likely to create collateral damage,
and the authors’ report illustrates this concept well. In select cases,
one might consider novel techniques such as coronary venous ethanol
ablation rather than more aggressive endocardial strategies like
simultaneous unipolar or bipolar ablation.5 It is also
reasonable to conclude that LAD injury is quite rare in patients with
idiopathic VAs originating from the endocardial aspect of the RVOT in
whom early suppression during ablation is achieved. Nonetheless, the
manuscript underscores a distinct ECG signature for VAs originating in
proximity to the mid LAD, allowing the operator to optimize patient
consent and procedural workflow. Specifically, the use of preoperative
tomographic imaging or intraprocedural coronary angiography may be
appropriate in certain cases, particularly those with underlying
cardiomyopathic processes or failed prior ablation procedures. Such
images can be imported and co-registered with the electroanatomic
mapping system to provide greater anatomical context. When ablating in
this region, the operator should also be mindful of any ST segment
deviation that may suggest coronary injury. These changes can be more
difficult to appreciate on electrophysiology recording systems due to
increased sweep speed. Particular vigilance is needed in patients under
general anesthesia in whom the presence of symptoms cannot be assessed.
In summary, the study by Dilling-Boer et al highlights the anatomical
relationship of the RVOT with the intraseptal course of the LAD with
attendant risk of vessel occlusion during ablation. A thorough
understanding of spatial anatomy of this region and ablation biophysics
will help the practicing electrophysiologist both to anticipate possible
complications specific to this region and to tailor ablation strategies
to mitigate procedural risk.
REFERENCES:
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Horowitz BN, Shivkumar K. Catheter ablation of right ventricular outflow
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10.1111/j.1540-8167.2006.00483.x
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Schurmans J, Phlips T, Didenko M, Vijgen J. Damage to the left
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