Key Teaching Points
•
Patients with persistent left superior vena cava have a significantly enlarged coronary
sinus ostium, and the location of the slow pathway and His bundle area may be displaced,
making the atrioventricular nodal reentrant tachycardia (AVNRT) ablation more challenging
and increasing the risks of damage to the atrioventricular node.
•
The transseptal approach should be remembered and may be a simple, low-cost, and effective
choice for the ablation in this situation.
•
When a left-side AVNRT ablation is performed, it may be necessary to position the
ablation catheter in the ventricular aspect of the mitral annulus to achieve successful
slow pathway elimination.
Introduction
Atrioventricular nodal reentrant tachycardia (AVNRT) ablation presents a high success
rate with the classical approach, with the ablation catheter positioned in the right
posterior septal region. Persistent left superior vena cava (PLSVC), although rare,
is the most common venous anomaly in the chest, with a prevalence of 0.3%–0.5% in
the general population. Patients with PLSVC have a significantly enlarged coronary
sinus (CS) ostium, and the location of the slow pathway and His bundle area may be
displaced, making the procedure more difficult and increasing the risk of damage to
the atrioventricular (AV) node during ablation.
Here we describe a patient with successful ablation of a typical AVNRT associated
with PLSVC using the transseptal approach. Interestingly, the successful ablation
site was on the ventricular aspect of the mitral annulus.
Case report
A 47-year-old woman without prior cardiovascular disease, with several episodes of
paroxysmal supraventricular tachycardia refractory to drug treatment, was admitted
for radiofrequency (RF) ablation.
The electrophysiological study was performed after 8 hours of fasting and under general
anesthesia. Antiarrhythmic medication was suspended for at least 5 half-lives before
the procedure. Triple puncture of the femoral vein was performed with 2 7F decapolar
catheters positioned inside the CS and right chambers.
Atrial pacing with extrastimuli showed dual AV node physiology and inducted the clinical
tachycardia easily, with the earliest atrial activation seen at the His catheter with
a His–atrial time of 30 ms (Figure 1A). During tachycardia, an atrial extrastimulus
was delivered when the junction was refractory, with advancement of the next His potential
in 15 ms by early engagement of the slow pathway (Supplemental Figure 1), confirming
a common type (slow–fast) of AVNRT.
Figure 1
A: Atrial pacing with extrastimuli showed dual atrioventricular (AV) node physiology
and inducted the clinical tachycardia easily, with the earliest atrial activation
seen at the His catheter with a His–atrial time of 30 ms. B: Ablation catheter positioned
at the anatomic slow pathway area in the right atrium (unsuccessful target). C: Ablation
catheter positioned after transseptal access with a far-field atrial signal followed
by a large ventricular electrogram, suggesting the ventricular side of the mittral
annulus (successful target). D: Atrial pacing with extrastimuli confirmed the slow
pathway ablation. I, II, II, avF, V1, and V6 indicate electrocardiography leads. A
= atrial electrogram; Abl = Ablation catheter; d = distal; H = His electrogram; His
= His area; p = proximal; SC = coronary sinus; V = ventricular electrogram.
RF energy applications with a 4-mm catheter at the anatomic slow pathway area in the
right atrium with a typical intracardiac electrogram (Figure 1B) and in the roof of
the CS were unsuccessful despite the occurrence of a slow junctional rhythm.
Owing to the long duration of the procedure and difficulty in stabilizing the catheter
near the CS ostium, we performed CS venography, and the presence of a PLSVC was observed
(Figure 2A and B).
Figure 2
A, B: Coronary sinus (CS) venography in left anterior oblique (LAO; panel A) and right
anterior oblique (RAO; panel B) fluoroscopy views showing persistent left superior
vena cava (PLSVC). C, D: Position of the ablation catheter in the ventricular side
of the mitral annulus at the posterior septal region through transseptal access (LAO:
panel C; RAO: panel D).
We chose to perform transseptal puncture under fluoroscopy, and the catheter was positioned
on the left posterior septal region (Figure 2C and D) with the intention of targeting
left-sided slow pathway inputs and an AV ratio of 1:8. Several RF energy applications
were performed, but tachycardia was still inducible. In a region where there was only
a small far-field atrial potential and a large ventricular electrogram, suggesting
the ventricular aspect of the mitral annulus (Figure 1C), RF pulses resulted in an
accelerated junctional rhythm. The tachycardia was no longer inducible, and tests
confirmed the slow pathway elimination (Figure 1D). The procedure was well tolerated,
with no complications. During 5 months of follow-up, the patient has remained clinically
free of symptoms, without medications.
Discussion
AVNRT ablation presents a high success rate with the classical approach, with the
ablation catheter positioned in the right posterior septal region. However, in less
than 1% of cases, the left approach may be necessary in cases when the right-sided
slow pathway ablation has failed.
1
PLSVC, although rare, is the most common venous anomaly in the chest, with a prevalence
of 0.3%–0.5% in the general population and of 3% in patients with congenital heart
defects. Usually, the left superior vena cava of the embryo involutes and becomes
the ligament of Marshall in the mature heart.
As an isolated anomaly PLSVC is most often detected during thoracic surgery or cardiac
catheterization.
2
It typically drains into the right atrium through the CS, which becomes dilated owing
to volume overload. Patients with PLSVC have a significantly enlarged CS ostium, and
the location of the slow pathway and His bundle area may be displaced, making the
procedure more difficult and increasing the risk of damage to the AV node during ablation.3,
4
Owing to these difficulties, several approaches besides fluoroscopy have been suggested
and reported, such as the use of 3-dimensional electroanatomic mapping,5, 6 intracardiac
echocardiography,
7
and even a magnet navigation system,
8
but to the best of our knowledge, this is the first case with the successful ablation
of a typical AVNRT associated with PLSVC using the transseptal approach. This simple
and low-cost strategy allowed for greater catheter stability and contact during the
attempted mapping and ablation.
Interestingly, as in the previous report by Green and colleagues,
9
the successful ablation site was on the ventricular aspect of the mitral annulus.
This region is accessed through the AV part of the cardiac septum, where the left
ventricular inlet shares a close relationship with the right atrium and slow pathway
location owing to the inferior displacement of the tricuspid valve relative to the
mitral valve, known as valvar offsetting (illustrated in Figure 3). While some morphologists
describe this part of the cardiac septum as the muscular portion of the AV septum,
some others argue that the region is not a true septum, since it carries a layer of
epicardial fibroadipose tissue with the artery originating in the U-turn of the dominant
coronary artery responsible for irrigation of the AV node. The proposed name for this
particular region is, according to such authors, “muscular atrioventricular sandwich.”
10
We believe that this anatomic particularity must be considered for an adequate mapping
of the slow pathway left inputs in all cases in which a left-side AVNRT ablation is
necessary.
Figure 3
A: Longitudinal section through the posteroinferior septal part of the atrioventricular
junction in a normal heart. Note the valvar offsetting, with the septal leaflet of
the tricuspid valve (T) inserting toward the apex relative to the mitral valve (Mi).
The asterisk shows the area of the so-called “muscular atrioventricular sandwich.”
B: Photomicrography of the septal structures at the atrioventricular junction. Note
the atrioventricular septum separating the right atrium (RA) from the left ventricle
(LV). The atrioventricular node is marked with arrows. The fibrous body is marked
with the asterisk. Masson’s trichrome. Original image from the Anatomy Lab of Heart
Institute – Incor, São Paulo, Brazil. MV = mitral valve; TV = tricuspid valve.
Conclusion
In cases where the classic AVNRT ablation approach fails, CS venography may diagnose
PLSVC; and knowing the particularities of this association, the transseptal approach
should be remembered and may be a simple, low-cost, and effective choice for the ablation
of these arrhythmias. It may also be necessary to position the ablation catheter in
the ventricular aspect of the mitral annulus to achieve successful slow pathway elimination.