Factors related to AF originating from the SVC
Several previous studies have elucidated the relationship between some factors and AF originating from the SVC (SVC-AF). Almost all of these studies used pacing and/or drugs to induce SVC-AF. An anatomical report showed that SVC-AF is more likely to occur in patients with a smaller LA diameter 17. In a report on clinical features, SVC-AF tends to be more common in female patients, those with a lower body mass index, and those with certain genes (rs2634073 and rs6584555)18. The electrical characteristics were that SVC-AF is more common in patients with long SVC sleeves (>30 mm12,13), SVC firing is more likely to occur in patients with long SVC sleeves (>37 mm) or long SVC diameters (>17 mm) 19, and SVC-AF is more common in cases with a large potential (>1 mv 12).
In our electrophysiological study, the relationship between the SVC-ERP and SVC-AF was clarified. To the best of our knowledge, there are no reports that have examined the relationship between the SVC-ERP and SVC-AF. Our study revealed that the shorter the SVC-ERP, the more likely SVC-AF occurred at pacing, while the dispersion of the SVC-ERP did not contribute.
The present study revealed that the SIG had a higher proportion of patients with persistent AF. Past animal experiments using goats reported that AF leads to a marked shortening of the atrial ERP20, and this electrophysiological change is called electrical remodelling. Another previous study reported that electrical remodelling may also occur in the human SVC 16. Our study revealed the concordant result; patient with persistent AF had a shorter SVC-ERP than those with paroxysmal AF (240.0±37.6 vs 295.7±31.7 ms, p=0.002). We assumed that persistent AF caused the SVC sleeve to have a stronger electrical remodelling than that caused by paroxysmal AF, resulting in the acquisition of a shorter SVC-ERP and a greater vulnerability to pacing from the SVC.
Although previous studies using the same rapid electrical stimuli reported that the length of the SVC sleeve was longer in the SIG13, we did not find a difference between the two groups. The possible reason was that we selected only patients who could measure the SVC-ERP in all three portions. As a result of selecting a population with a relatively long SVC sleeve length, there may be no difference between the two groups in the present study.
A previous study reported that SVC firing is more likely to occur in patients with long SVC sleeves (>37 mm) or long SVC diameters (>17 mm) 19. Our study also revealed that the longer diameter of the SVC was significantly longer in the SIG (27.4±4.3 vs. 22.9±4.6 mm, p=0.03) compared to that of the non-SIG. Furthermore, we found that the SVC-ERP was significantly associated with pacing inducibility of AF after adjustment for the longer diameter of the SVC (adjusted odds ratio: 0.96 [1-ms increments], 95% confidence interval: 0.93–0.99; p=0.01). It was suggested that the SVC-ERP was also a factor related to SVC-AF.