Bigeminal superior vena cava activity with potent arrhythmogenicity

Superior vena cava is one of the important AF triggers. Superior vena cava bigeminy acts as a trigger of AF. Attention should be paid to the bigeminal activities of the thoracic veins in AF catheter ablation. Superior vena cava (SVC) is known as one of the important trigger veins of AF as pulmonary veins (PVs) are.1 PV bigeminy is reported as an indicator of potent arrhythmogenicity.2, 3 The electrophysiological properties of SVC resemble to those of PV; however, it has not been clarified whether SVC bigeminy indicates potent arrhythmogenicity. Here, we report a case in which repetitive SVC bigeminy followed by AF firings. Isolated SVC fibrillation after SVC isolation could be also observed, suggesting potent arrhythmogenicity as a trigger as well as a substrate of the SVC in the present case. A 72-year-old woman with drug-resistant paroxysmal AF was referred to our institution for catheter ablation. Pulmonary vein antrum isolation was performed under sinus rhythm by radiofrequency catheter ablation. After bidirectional block between left atrium and PVs was confirmed, existence of non-PV triggers was evaluated according to our institutional protocol. Following a termination of induced AF with direct current (DC) cardioversion, atrial bigeminy with a coupling interval (CI) of 350 ms appeared. After a short while, an immediate recurrence of AF (IRAF) was induced following the atrial bigeminy (Figure 1). The earliest activation site of the atrial bigeminy was located in the high right atrium on a BeeAT catheter (Japan-Life-Line), which implied that the atrial bigeminy originated from the SVC. A twenty-pole circular mapping catheter was positioned to the SVC (Figure 2A), and then atrial burst pacing and the termination of induced AF by DC cardioversion were performed again. This time, a concealed SVC bigeminy with a CI of 115 ms was observed 8 s after AF termination. Subsequently, IRAF was re-induced from the SVC following the concealed SVC bigeminal activity 17 s after AF termination (Figure. 2B). SVC sleeve length from SVC-HRA junction to the top of the twenty-pole circular mapping catheter in the fluoroscopic image was as long as 41 mm. SVC isolation was performed under AF rhythm. Sinus rhythm restoration was achieved during radiofrequency application to the SVC, and isolated SVC fibrillation or tachycardia was observed simultaneously (Figure 3). The isolated SVC tachycardia appeared intermittently. After confirming the bidirectional block between the right atrium and SVC, AF was not induced anymore. To date, AF did not recur during 12 months of follow-up without resuming any antiarrhythmic drugs. In the present case, repetitive AF firing following SVC bigeminy was observed. In addition, isolated SVC fibrillation/tachycardia was observed after SVC isolation. These electrophysiological findings suggested that the SVC bigeminy was an indicator of potent arrhythmogenicity. Although Takasugi and colleagues4 reported SVC bigeminy that acts as a trigger of AF, there are few reports regarding SVC bigeminal activities. It has been reported that the prevalence of PV bigeminy in AF patients is 4.9–11%.2, 3 Reithmann and colleagues5 reported that PV bigeminy appears under sinus rhythm and is classified into two types; one is the conducted PV bigeminy which has electrical conduction to the atrium, and the other is the concealed PV bigeminy which does not conduct to the atrium. They reported that CI determined the type of PV bigeminy. While mean CI of the conducted PV bigeminy was 375 ± 25 ms, mean CI of the concealed PV bigeminy was 230 ± 17 ms. Possible mechanisms of PV bigeminy have been reported as follows; abnormal automaticity, triggered activity, and reentrant mechanisms. In most cases, PV bigeminy appears incessantly and is of short duration, which makes it difficult to validate the mechanisms with an electrophysiological study. Mukai and colleagues3 reported that the bigeminal PV potential exhibited decremental conduction properties in response to atrial extra stimuli, suggesting a reentrant mechanism. In general, PV bigeminy indicates potent arrhythmogenicity of the PV. It has been reported that the prevalence of AF firing from the PV with bigeminy is as high as 76.7%–89%.2, 3 The present case suggests that SVC bigeminy as well as PV bigeminy is an indicator of potent arrhythmogenicity that triggers AF. It may be useful to focus on the bigeminal activities of the thoracic veins in AF catheter ablation. The authors declare no conflict of interest for this article. N/A. Written informed consent was obtained from the patient to publish this report. N/A.