Case presentation
We herein report a male in his 40s who was referred for catheter
ablation due to drug refractory paroxysmal atrial fibrillation (PAF) and
frequent atrial premature contractions (APCs). Informed consent was
obtained from the patient for publication of this case report. An
electrocardiogram recording of the APCs demonstrated a negative P-wave
morphology in the inferior leads and a positive P-wave morphology in the
I and aVL leads (Figure 1A) . Other examinations, including a
cardiac echocardiogram, chest X-ray, and laboratory tests, showed
results within the normal range. After successful pulmonary vein
isolation using a third-generation cryoballoon system (Arctic Front
Advance Cardiac Cryoablation Catheter, Medtronic), frequent
mono-morphological APCs remained. We therefore mapped the APC focus with
a multielectrode mapping catheter (PentaRay; Boisense Webster, Diamond
Bar, CA, USA) on a high-density three-dimensional electroanatomical
mapping (3D-EAM) system (CARTO3; Boisense Webster). The activation map
showed a focal activation pattern from the inferior vena cava (IVC). The
earliest activation site was located at the posteromedial part within
the IVC (6.2 mm below the IVC ostium), and the local signal demonstrated
a very low amplitude of 0.05 mV (Figure 1B ). In addition, the
voltage map (>0.05 mV) demonstrated the short IVC sleeve
from the ostium (9.3 mm) (Figure 1C) . Interestingly, sustained
continuous IVC firings (bigeminy) were observed, which propagated to the
right atrium (RA) only when the coupling interval was prolonged from 190
msec to 200 msec (Figure 2) . We next mapped the concealed
bigeminy alone, which revealed the confined tiny excitable area within
the IVC (0.1 cm2) with low-voltage fragmented
potentials recorded at the earliest site (Figure 3A and 3B) .
Catheter ablation was performed at the transit area between the IVC and
RA to isolate the IVC. The APCs and concealed IVC firings disappeared
after a total of 4 radiofrequency applications (30 W, 192 seconds), and
dissociated activity was observed immediately after IVC isolation. After
four months of follow-up, there was no AF recurrence without any
anti-arrhythmic drug, and the number of APCs was within normal limits.