Discussion
Although IVC is known as a possible source of non-PV foci in AF
patients, the prevalence is very low. Nie et al. recently reported from
a single center that the incidence of AF triggered from the IVC was
0.91% (6/661).1 However, a total of only 7 isolated
reports (8 cases) had been reported as of July
2022.2-8 In line with the rarity of previously
published cases, there were only 2 cases (0.04%) among 4,500 AF
ablation procedures in our hospital.4 Thus, the
prevalence of AF triggers in the IVC is considered to be much lower in
the real world than the recent report.1
Hashizume et al. described that the IVC histologically has the same
arrhythmogenicity as the thoracic veins (PVs, superior vena cava
[SVC], coronary sinus) with cardiac musculature extending from the
RA in humans. However, the myocardial sleeve in the IVC was much shorter
than that in the SVC (18 mm vs. 45 mm).9 In addition,
the IVC is considered to be electrically more silent than the SVC
because of the frequent absence of longitudinal myocardial
fibers.10 These different electrophysiological
features may relate to different developmental processes between the two
venous systems; the SVC is embryologically derived from the anterior
cardinal vein, whereas the terminal segment of the IVC is derived from
the right vitelline vein.11
In the clinical setting, the precise localization of the APC origin in
the IVC is often difficult due to the proximity of the coronary sinus
ostium and lower part of the RA. In previous reports, although nine
cases anatomically demonstrated the origin of the trigger from the IVC
using a contact 3D-EAM system, the definition of the border between the
IVC and RA was unclear.1,6-8 In the present case, the
concealed IVC firings (bigeminy) observed in the IVC strongly suggested
an origin inside the IVC rather than at the RA-IVC junction. This is the
first case demonstrating the limited excitation area with a low voltage
in the IVC by detailed 3D-EAM.