br Results As shown in Table the

Results As shown in Table 1, the amplitude, and the onset or the end of LA potentials were successfully determined via visual inspection. Among 19 patients with AP, LA potentials were detected in 7 (37%), all in an LA → CSM activation sequence (Fig. 2). In contrast, among 21 patients with CCW AFL, LA potentials were visible in 14 (67%), all in a CSM → LA activation sequence (Fig. 3). This difference was highly significant (P<0.0001). The prevalence of LA potentials was not significantly different between both study groups (P=0.1119), and the overall prevalence was 53%. In the left anterior oblique fluoroscopic projection, most LA potentials were located between 3 and 6 o׳clock in patients with AP and between 4 and 5 o׳clock in patients with AFL (Fig. 4). In a single case with left-sided AP presenting CS double potentials, we compared the relative timing of far-field LA potentials in the CS recordings with LA potentials directly recorded during successful ablation procedure, by using trans-septal approach (Fig. 5). The far-field potential was recorded simultaneously with LA potential at the successful ablation site during retrograde conduction over AP, whereas no far-field potential was observed after the elimination of AP, providing further confirmation that the far-field potentials in the CS recordings reflect LA activation. Furthermore, although not enrolled in the present study, we present two interesting cases in which unique CS double potentials were observed. The diagnosis of the first case was a manifest Wolff-Parkinson-White (WPW) syndrome and AVRT attributable to ventricular-CS connection that was confirmed by its successful ablation inside a mid-cardiac vein [8]. During ventricular pacing before the ablation, LA potentials following CSM potentials were noticed in the proximal CS recordings (Fig. 6). The second case had typical clockwise (CW) AFL that was electrophysiologically confirmed. During the ongoing tachycardia, in AZD3264 to typical CCW AFL, LA potentials preceding CSM potentials were registered on the proximal CS recordings (Fig. 7).
Discussion Until recently, most clinical electrophysiologists believed that the CS electrograms reflected strictly the LA activation. However, the recognition of far-field LA potentials distinct from the near-field potentials of the CSM has gradually increased, after a detailed human anatomical study revealed a distinct spatial relationship of the CSM and the LA such that the former is near and the latter is away from the catheter located inside the CS [2]. Kasai et al. first reported that the far-field LA and near-field CSM potentials recorded from the CS, which seemed to be fused, could be separated by functional block over the CSM → LA connection caused by extrastimulation [9]. We reported the recording of double CS potentials, consisting of LA and CSM potentials, visible only during retrograde AP conduction in patients in whom there were few LA → CSM connections, except in the proximal CS [7,10]. The activation pattern of the double potentials varies, depending on the differences in the conductive properties of the LA-CSM connections [7,10,11]. Double potentials were also recorded inside the CS during atrial fibrillation, and during typical or perimitral AFL in patients with LA → CSM connections that were impaired by an ablation attempt [11–14]. Nevertheless, far-field LA electrograms distinct from CSM potentials have been much less reported than expected. However, they were visible in approximately 50% of patients in this study, suggesting that, if persistently looked for during sequential LA → CSM activation, far-field LA potentials adjacent to near-field potentials are not rare, regardless of individual variations in the LA-CSM connections. In other words, even if multiple LA-CSM connections are present, activation of LA and CSM is not strictly simultaneous, and as noticed in the subjects included in the present study, a far-field LA potential is not fully superimposed on near-field CSM potential during sequential activation of LA and CSM. That is, at least the onset of LA potential not superimposed on CSM potential is visible during retrograde conduction over left-sided AP, and at least the offset of LA potential not superimposed on CSM potential is visible during CCWAFL. When the activation direction of CSM potential is identical to that of LA potentials as shown in Fig. 2, Rough ER is possible that multiple LA-CSM connections are present. Under these conditions, the detection of the LA potentials may depend on the distance between the LA wall and the recording catheter inside the CS. No detection of an LA potential suggests that the recording catheter inside the CS is not located adjacent to the LA wall, and does not mean that the LA muscle near CS is absent or injured. As shown in Fig. 4, there seemed to be a difference in recording sites of LA potentials between the two groups, probably because the difference might be attributable to the conductive direction of the LA wavefront relative to the axis of the CS recording catheter. The bipolar recording with the standard CS catheter could detect the LA wavefront that propagated almost parallel to the recording catheter, such as during CCW AFL. It may be less incident to record the LA wavefront that propagated nearly perpendicular to the catheter, such as during retrograde conduction over the left-sided AP. We did not routinely insert a distal tip of the CS catheter into a great cardiac vein to record LA potential only of which the recording may make it easier to differentiate LA potential from CSM potentials. In addition, we did not record the CS electrograms with a low sensitivity setting to observe the whole CSM potentials, instead, we always recorded those with a high sensitivity setting in order to detect tiny LA potentials.