Figure 2:A: Atrial fibrillation (AF) was induced using an S1S1 pacing
protocol at 260 ms.
B: A three-dimensional electroanatomical mapping of the right atrium
shows the presence of a Persistent Left Superior Vena Cava (PLSVC). The
mapping electrode located within the superior vena cava (SVC) recorded
potentials in the posterior-anterior view.
C: The mapping electrode (yellow) displays regular electrical potentials
in the SVC, which are slower in frequency relative to those in the
coronary sinus (CS) (green).
D: The three-dimensional electroanatomical map of the right atrium with
the mapping electrode positioned in the PLSVC records rapid and
disorganized potentials in the anterior-posterior view.
E: The mapping electrode (yellow) in the PLSVC shows prolonged,
fragmented, and regular potentials, which are faster than those in the
coronary sinus (green).
F: A three-dimensional model from the right anterior oblique perspective
showing the ablation points (pink) at the proximal end of the PLSVC.
G: A three-dimensional model from the left anterior oblique perspective
also showing the ablation points (pink) at the proximal end of the
PLSVC.
H-K: Three types of PLSVC configurations.
H: The PLSVC drains into the right atrium via the coronary sinus.
I: The PLSVC drains into the left atrium via the coronary sinus.
J: The PLSVC drains directly into the left atrium.
K: The PLSVC drains into the left atrium and is associated with
pulmonary vein anomalies.
Outcome and follow-up:
After the ablation, isoproterenol infusion and atrial pacing were used
to repeatedly verify that the patient did not experience atrial
fibrillation. The patient was then followed up via telephone for six
months, with monthly check-ins. The follow-up outcomes were defined as
the patient experiencing palpitations accompanied by ECG-confirmed
atrial fibrillation, or the presence of atrial fibrillation lasting more
than 30 seconds on a 24-hour Holter monitor, indicating a recurrence of
atrial fibrillation. Regardless of the presence of palpitations, the
patient underwent a 24-hour Holter monitor every three months. During
the entire follow-up period, monthly phone calls and Holter monitoring
showed no arrhythmias.
Discussion:
AF is the most common cardiac arrhythmia, characterized by rapid and
irregular contractions of the atrial myocardial cells. The incidence of
AF increases with age and has been rising annually. It often occurs due
to spontaneous depolarization of atrial tissue outside the sinoatrial
node, primarily due to ectopic activity that commonly originates from
the pulmonary veins (95%) and, less frequently, from the inferior and
superior vena cava (5%)1. Rarely, it arises from
abnormal structures such as the Persistent Left Superior Vena Cava
(PLSVC)2,3.
In terms of treatment, rhythm control is preferred for patients with
concomitant heart failure or severe symptoms4,5.
PLSVC is a common congenital venous anomaly, also known as bilateral
superior vena cava. Normally, the left superior vena cava regresses to
form the ligament of Marshall. However, in approximately 0.3% to
0.5%6,7 of the population, this regression does not
occur, resulting in the formation of PLSVC. Most PLSVC cases drain into
the right atrium via the coronary sinus, while in some patients, the
right superior vena cava is atretic, and in very rare cases, the PLSVC
drains into the left atrium8 (Figures 2H-K).
Studies have shown that in patients with AF combined with PLSVC, 68.8%
of the PLSVC can act as an ectopic trigger or maintenance substrate for
AF, necessitating electrical isolation of the left superior vena cava.
Additionally, 44.4% of these patients may have other types of
arrhythmias, including atrial flutter, AVNRT (Atrioventricular Nodal
Reentrant Tachycardia), and junctional tachycardia8.
The mechanism of arrhythmias in PLSVC is complex and may be related to
residual tissues from cardiac development during embryogenesis. During
embryonic development, the primitive heart tube exhibits autonomic
electrical activity, initially occurring in the sinus horn and main
veins. As the heart matures, the pacemaker function gradually shifts to
the sinoatrial node in the right heart. However, in some cases, such as
with PLSVC, the original pacemaker tissue may not completely regress and
remains in the PLSVC. These residual pacemaker tissues can cause
electrophysiological abnormalities, particularly at the junction between
the PLSVC and the coronary sinus. This structural abnormality can form
ectopic trigger points, thereby initiating and maintaining AF.
Additionally, overlapping myocardial sleeves in the PLSVC can also be a
potential source of abnormal electrical activity and
arrhythmias8,9.
Different scholars have varied strategies for the ablation of PLSVC.
Successful catheter ablation has been reported at the proximal, mid, and
distal segments of the PLSVC. Regarding ablation power settings, some
researchers have used a maximum power control mode of 65°C and 30W with
a flow rate of 30 mL/min, while others have suggested using a power of
15-20W for ablation within the PLSVC, with each ablation point limited
to a maximum duration of 20 seconds and a flow rate of 17 mL/min,
targeting a maximum temperature of 43°C9.
Additionally, some scholars have employed cryoablation, which has also
been successful in eliminating AF10.
During the procedure, it is crucial to consider the anatomical proximity
of surrounding tissues. The left phrenic nerve descends along the
anterolateral side of the PLSVC, extending down to the pericardium at
the obtuse margin of the left ventricle11. Therefore,
when performing ablation on the anterolateral side of the PLSVC, phrenic
nerve pacing should be employed to avoid nerve damage.
In this case report, the patient was initially admitted with persistent
atrial fibrillation. The preoperative echocardiogram showed a left
atrial end-systolic diameter (LA) of 50mm and an ejection fraction (EF)
of 33%. After nine months of rhythm control to maintain sinus rhythm, a
follow-up echocardiogram revealed a reduction in heart size and
normalization of the ejection fraction, further confirming that rhythm
control is the preferred treatment for AF patients with heart failure to
improve cardiac function.
Additionally, atrial substrate mapping identified the PLSVC as the
trigger for paroxysmal AF, further confirming that AF can originate from
abnormal structures. For ablation, the strategy involved targeting the
fragmented potentials at the proximal PLSVC with an AI index of 280-300
and performing a 10-second ablation. Under the protection of phrenic
nerve pacing, electrical isolation of the PLSVC during AF successfully
terminated the tachycardia, providing an effective treatment strategy
for arrhythmias originating from similar anatomical anomalies.
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