With interest, we read the article recently published in Annals of Noninvasive Electrocardiology by Song‐Yun Chu et al. describing the left bundle branch pacing (LBBP) as a choice to correct the right bundle branch block (RBBB) (Chu et al., 2020). The article very well describes a novel mechanism of cardiac resynchronization therapy for RBBB. As is shown in article, the authors put forward an intriguing theory that unipolar pacing at 0.75V/0.4 ms captured the intra‐Hisian LBB then recruited the distal right bundle branch through transverse interconnection fibers (TF). This theory gives us a new understanding of the LBBP in the presence of RBBB.

In context, the authors did not describe how far away the LBB pacing lead location from His. What lead to present the ECG morphology of LBB pacing, if pacing was delivered at the point where His potential is recorded ?

Lazzara et al. 's study just explored the functional transverse interconnections (Lazzara et al., 1973), so the TF between the left and right bundle branches do not seem quite accurate. Beyond that, the anatomical structure of these fibers has not been clearly reported before, which requires further studies, especially in the human body.

However, we cannot conclude that it is TF transmitting an electrical signal from the left bundle branch to the right bundle branch. In unipolar pacing, increasing output might lead to the anodal capture. In bipolar pacing, the anodal ring might pre‐excite a portion of the right ventricular septum. When right ventricular anodal capture occurs, QRS duration is minimized, presumably because in this situation there are at least 2 depolarization waves fronts activating the ventricles, shortening conduction time from the left ventricle to the right ventricle (Mounsey & Knisley, 2009). To sum up, both of these pacing methods will cause a fusion of right ventricular septal excitation and left ventricular excitation. This is why the iso‐electrical interval fainted, the R wave disappeared in V1 and the QRS complex duration minimized (Figure 1b).

In addition, different to the authors' view that the typical LBBP would create RBBB morphology and might not be narrower than the intrinsic ones. We did observe narrower QRS complex in some patients with RBBB after implantation of selective LBBP (Figure 1a).

我们感兴趣的是，阅读了宋松珠等人最近发表在《无创心电学年鉴》上的文章。描述了左束支起搏（LBBP）作为纠正右束支传导阻滞（RBBB）的选择（Chu et al。，  2020）。这篇文章很好地描述了RBBB心脏再同步治疗的新机制。如文章所示，作者提出了一个有趣的理论，即以0.75V / 0.4 ms的单极起搏捕获Hisian内的LBB，然后通过横向互连纤维（TF）募集远端右束支。这种理论使我们对存在RBBB的LBBP有了新的认识。

在上下文中，作者没有描述LBB起搏导线位置距His的距离。如果起搏是在记录他的潜力的位置进行的，那么导致LBB起搏的ECG形态的原因是什么？

Lazzara等。的研究只是探讨了功能性横向互连（Lazzara等，  1973），因此左右束支之间的TF似乎不太准确。除此之外，这些纤维的解剖结构尚未得到明确报道，这需要进一步研究，尤其是在人体中。

但是，我们不能断定是TF从左束支流向右束支传输电信号。在单极起搏中，增加的输出可能会导致阳极捕获。在双极起搏中，阳极环可能会预先激发右心室间隔的一部分。当发生右心室阳极捕获时，QRS持续时间被最小化，大概是因为在这种情况下，至少有2个去极化波前沿激活了心室，从而缩短了从左心室到右心室的传导时间（Mounsey＆Knisley，  2009年））。综上所述，这两种起搏方法都会导致右心室间隔兴奋性和左心室兴奋性融合。这就是为什么等电间隔变弱，R波在V1中消失，QRS复数持续时间最小化的原因（图1b）。

此外，与作者的观点不同，典型的LBBP会产生RBBB形态，并且可能不会比固有的窄。我们确实观察到选择性LBBP植入后某些RBBB患者的QRS复合物较窄（图1a）。