We retrospectively evaluated 47 consecutive patients with severe native aortic stenosis referred for TAVR with the self-expandable Venus A valve (Venus Med Tech Inc., Hangzhou, China) from 2019 to 2021 at the Heart Center of Affiliated Zhongshan Hospital of Dalian University. The exclusion criteria included patients with PPM prior to TAVR (n = 2), intraoperative mortality (n = 1), valve-in-valve procedures (n = 3), and patients where 12-lead ECGs were unavailable (n = 2). Considering this, only 39 patients were included in the study. Surgical indications of patients were assessed and decided upon by a multidisciplinary team of doctors consisting of cardiac surgeons, cardiologists, echocardiologists, and anesthetists. A self-expandable aortic valve was deployed using the transfemoral approach in all patients. The study was approved by the ethics committee of Affiliated Zhongshan Hospital of Dalian University. The study also complied with the Declaration of Helsinki. All patients who participated in the study signed written informed consent forms.

All patients underwent immediate standardized (10 mm = 1 mV, 25 mm/s) 12-lead ECG before and one month post-operation with subsequent retrospective analysis of the data. Parameters included heart rate, rhythm, axis deviation, PR interval, type of AVB, QRS interval, type of bundle-branch block, QT interval, and corrected QT interval (cQT).

Categorical variables are expressed as numbers and percentages. All continuous data were expressed as means ± standard deviation (SD) or medians ± range as appropriate. Categorical variables were compared using Chi-squared or Fisher exact tests. Continuous variables were compared with the Student's t-test (2-tailed) or Wilcoxon signed-rank tests as appropriate. To identify predictors of patients with PPM dependency after TAVR, logistic regression, with Firth's correction due to the small sample size, was performed. All analyses were conducted using R (version 3.2.2; R Foundation for Statistical Computing, Vienna, Austria) or SAS Statistics (version 9.4; North Carolina, America). A p-value < 0.05 was considered statistically significant.

The most common indication for PPM implantation in those who underwent TAVR was complete AVB in our study, which had also been demonstrated previously (7, 8). Consistent with previous data, a sick sinus syndrome (37.5%), including relevant sinus and bradycardia, was a leading indication in patients who underwent PPM implantation (9).

The anatomic relationship between the aortic valve and the cardiac conduction system is the foundation of the conduction disturbances in patients undergoing TAVR. Anatomically, the proximity of this portion of the atrioventricular node (AVN), the bundle of His, and the membranous part of the interventricular septum makes it more susceptible to conduction disturbances. The left bundle branch is close to the bottom of the interleaflet triangle together with the location of the right coronary leaflets and non coronary aortic valve (10–12). The incidence of complete AVB after TAVR is due to a direct mechanical injury to the AVN and/or the left bundle branch that results in ischemia, edema, and hematoma according to necropsy studies (10). Due to the invention of a self-expandable valve possessing a subannular section, the release of the valve will produce radial force to the left ventricular outflow tract (LVOT). The implantation of a self-expandable valve may lead to conduction block (13). Therefore, it is crucial to improve the surgical manipulations among experienced surgeons in order to decrease the risk of complete AVB after TAVR.

Patients with a higher burden of PPM implantation following TAVR had a higher prevalence of abnormal clinical indications. Some abnormal clinical data before the procedure may be related to injury within the underlying conduction system during TAVR (11). Du et al. (12) demonstrated that patients with prior LBBB had a relatively higher risk of PPM implantation in the Chinese population. Gaede et al. (9) summarized that patients who already had aortic valve replacement prior to TAVR required a PPM implantation less frequently. Our study showed that severe AVS patients who required PPM following TAVR were likely to present with dyslipidemia and negative CrCl. STS Morbimortality also played an important role in evaluating patients with a high frequency of conduction disturbances after TAVR.

Previous studies have reported that renal dysfunction at baseline predicted a higher increase of myocardial injury after the procedure. Additionally, myocardial injury after TAVR could lead to conduction disturbances, which may contribute to the need for PPM implantation (14–16). Thus, lower average CrCl may lead to worse kidney function at baseline, which plays an important role in patients requiring PPM implantation after TAVR. Lindman et al. (17) showed that elevated blood lipid parameters were associated with higher risks of calcific AVS. On account of the thickening and remodeling of the aortic valve leaflets, the formation of calcific AVS will cause severe cardiac outflow tract stenosis. Prosthesis implantation may produce radial force to the cardiac outflow tract, which results in conduction block. It is therefore recommended that doctors focus more attention on reducing the risk factors before TAVR to decrease the need for subsequent PPM implantation.

Few studies have evaluated the relationship between new-onset LBBB and the risk of PPM implantation after TAVR. In our cohort, a new-onset LBBB and T wave magnitude in lead I were the predictors for the patients requiring a PPM implantation after TAVR. However, prior RBBB at baseline was identified as an independent predictor in some previous studies (7, 11, 18, 19). In contrast to our study, smaller studies have shown that prior RBBB plays an important role in cardiac conduction system disorders after TAVR (8, 9, 20, 21).

The predictors of PPM implantation in patients receiving TAVR have been examined in seven studies (9, 12, 22–26). All studies were cohort studies. RBBB prior to TAVR was considered to be a predictor in most of the selected studies (9, 12, 22, 24, 26) in Table 4. However, the association of new-onset LBBB with PPM implantation after TAVR has not been fully characterized. A study by Chorianopoulos et al. (22), in which 46 patients with PPM implantation and 83 patients without PPM implantation were enrolled, showed that prior RBBB was the only predictor. A retrospective cohort study by Muillet et al. (23) showed that post-TAVR QRS duration and depth of implantation were the predictors of PPM implantation in patients receiving TAVR. In a cohort study by Luise Gaede et al. (9), in which 176 patients with PPM implantation and 849 patients without PPM implantation were enrolled, not only prior RBBB but also higher MPG and post-dilatation of the prosthesis were observed to be the predictors. A study focusing on 38 Chinese patients with PPM implantation and 218 Chinese patients without PPM implantation showed that prior RBBB, tricuspid aortic valve (TAV), and implantation depth at the non-coronary sinus side were the predictors, especially in Chinese population (12). The study of Kiani S, et al. (24) showed the history of syncope, prior RBBB, QRS duration ≥138 ms, and valve oversizing >15.6% were the predictors. Ferreira T et al. (25) demonstrated that increased H-V interval, which showed in post-TAVR electrophysiological study, was the best predictor of PPM implantation undergoing TAVR. A previous study by Johny Nicolas et al. (26) showed that RBBB before TAVR was the only predictor.

A positive correlation between PPM implantation after TAVR and new-onset LBBB was demonstrated in our study. However, no correlation was found between PPM implantation and prior RBBB or 1° AVB. We attribute the finding to mechanical injury that mainly affected the left bundle branch. Preexisting damage to the right bundle branch may lead to complete AVB when exposed to TAVR. The mechanism of the relationship between T wave magnitude in lead I and PPM implantation is unknown. Meanwhile, other predictors, including the type of the valve and the depth of prosthesis implantation, were not confirmed in our cohort (27–30). To date, no detailed guidelines for the management of new-onset LBBB following TAVR are available. Consequently, any recommendation about the management of new-onset LBBB after TAVR should be treated with caution and further investigation is warranted.

The limitations of our study are as follows. First, our study had a small sample size and a short follow-up time. The patients undergoing TAVR were also from a single center. The numbers of patients with PPM implantation and without PPM implantation were low, which limits the statistics of the study. However, the data were revised with Firth's correction due to the small sample size. All analyses were conducted using R (version 3.2.2; R Foundation for Statistical Computing, Vienna, Austria) or SAS Statistics (version 9.4; North Carolina, America). Thus, we strongly believe that our findings are reliable. Second, following discharge, we observed the patients only after a one-month follow-up. The interpretation may differ based on six-month or one-year follow-up periods. Finally, other variables, such as the position of the valve and valve type, may have generated a significant variation to the risk of conduction abnormalities after TAVR. Although our study cohort was small, only involved a single center, and was limited to a short follow-up time, we strongly believe that our findings are representative and may assist in providing valuable insight toward future identification of high-risk cases requiring PPM. Hence, our findings about PPM implantation after TAVR contributes to not only patients but also doctors for improving the postoperative quality of life of patients.