It is well known that there is a wide variation in clinical responses to BVP in CHF patients. While studies have been performed to identify factors that may predict the responsiveness to BVP, few studies were specifically aimed to uncover the factors that may predict the responsiveness to LBBAP, another treatment to correct cardiac arrhythmias, such as bradycardia. In the present study, we examined a number of factors that might potentially affect the responsiveness to LBBAP treatment in CHF patients with CRBBB, CLBBB, or no BBB, respectively, and revealed that only QRSd was an independent predictor. Our study further suggests that the optimal cutoff point of QRSd for predicting the responsiveness to LBBAP is ≥153 ms, with a sensitivity of 81.3% and a specificity of 86.7%. Previous studies have shown that BVP can effectively shorten QRSd, increase heart rate and LVEF, and improve the clinical symptoms of CHF patients[8, 14]. However, some CHF patients with bradyarrhythmia showed no or poor response to treatment. On the other hand, BVP is expensive and technically challenging. As an alternative, LBBAP can also shorten the QRS duration of CLBBB patients and slightly increase the QRSd of patients with no BBB. Compared with RVP, LBBAP pacing parameters are more stable, and the QRSd is shorter. As a result, LBBAP can also increase LVEF and improve patient quality of life. In the present study, 16 patients (51.6%) responded to the treatment, and 15 (48.4%) had no response, which was higher than previously reported. This discrepancy might be attributed to the differences in patient selection criteria and the sample size in these two studies.
LBBAP paces the main branch of LBB, and LV is first tissue to be excited by the Purkinje fiber network. When the LBB is captured by pacing, an incomplete RBBB appears and the LVAT is suddenly shortened to between 65 and 80 ms in EKG[13,17−19]. In this study, patients in both groups had a successful LBBAP procedure. However, there were no significant differences between these two groups with regard to demographic and baseline clinical characteristics, indicating that they were not influential factors for the responsiveness to LBBAP treatment in CHF patients. Previously, LBBAP was shown to shorten the QRS duration of ECG in patients with CLBBB, reduce LVAT[15, 20], improve the synchrony of the left ventricle, ameliorate the symptoms of CHF patients, and reverse ventricular remodeling. On the contrary, LBBAP can increase the QRS duration of ECG and prolong LVAT in patients without BBB. However, we observed that there were significant differences in pre- and post-operative QRSd between these two groups. We further found that in the responsiveness group, the QRSd was significantly decreased after operation, while in the no-responsiveness group, the QRSd was significantly increased. We noticed that 13 of the 16 patients with LBBB responded to the treatment, and only 3 did not, which was probably the primary reason for shortened QRSd and decreased LVAT after LBBAP treatment in the responsiveness group, consistent with previous reports[15, 20]. In contrast, there were 10 CHF patients with no BBB before surgery, and the no-responsiveness group had 9 CHF patients, which was probably the main reason why there was an increase in QRSd and prolonged LVAT after LBBAP treatment. This could be the main reason for the lack of response to LBBAP treatment.
Studies have yielded conflicting results regarding the predictors for the response to CRT. For example, the PROSPECT Trial did not uncover any independent parameters related to the responsiveness to CRT, but a number of variables were identified in another study. In contrast, few studies were performed to examine the variables predictive of response to LBBAP, although LBBAP is a viable alternative treatment to the traditional CRT. In this study, although univariate binary logistic regression analysis revealed that preoperative QRSd, preoperative LVAT, and CLBBB were all significantly correlated with the responsiveness to LBBAP treatment, QRSd was the only independent predictor for the responsiveness as suggested by multivariate binary logistic regression analysis. When the QRSd exceeded 153 ms, CHF patients had a better response to LBBAP treatment. Therefore, we determined that the optimal cutoff value of QRSd was ≥153 ms, with a sensitivity of 81.3% and a specificity of 86.7%.
Some limitations of this study should be noted. For, this was a single-center retrospective study. Therefore, there could have been potential sampling bias. Also, our study had a limited sample size. Thus, the conclusions from this study need to be further corroborated by prospective studies with large cohorts in the future.
In summary, our data suggest that QRSd can be used as an easy and reliable indicator of LBBAP therapy for CHF patients with bradyarrhythmias to improve cardiac function, and that QRSd can be used to guide treatment.