Abstract
BACKGROUND
His bundle pacing (HBP) and left bundle branch pacing (LBBP) both provide physiologic pacing which maintain left ventricular synchrony. They both improve heart failure (HF) symptoms in atrial fibrillation (AF) patients. We aimed to assess the intra-patient comparison of ventricular function and remodeling as well as leads parameters corresponding to two pacing modalities in AF patients referred for pacing in intermediate term.
METHODS
Uncontrolled tachycardia AF patients with both leads implantation successfully were randomized to either modality. Echocardiographic measurements, New York Heart Association (NYHA) classification, quality-of-life assessments and leads parameters were obtained at baseline and at each 6-month follow up. Left ventricular function including the left ventricular endo-systolic volume (LVESV), left ventricular ejection fraction (LVEF) and right ventricular (RV) function quantified by tricuspid annular plane systolic excursion (TAPSE) were all assessed.
RESULTS
Consecutively twenty-eight patients implanted with both HBP and LBBP leads successfully were enrolled (69.1 ± 8.1 years, 53.6% male, LVEF 59.2% ± 13.7%). The LVESV was improved by both pacing modalities in all patients (n = 23) and the LVEF was improved in patients with baseline LVEF at less than 50% (n = 6). The TAPSE was improved by HBP but not LBBP (n = 23).
CONCLUSION
In this crossover comparison between HBP and LBBP, LBBP was found to have an equivalent effect on LV function and remodeling but better and more stable parameters in AF patients with uncontrolled ventricular rates referred for atrioventricular node (AVN) ablation. HBP could be preferred in patients with reduced TAPSE at baseline rather than LBBP.
Recent studies found that His-Purkinje system pacing (HPSP), including His bundle pacing (HBP)[1] and left bundle branch pacing (LBBP) combined with atrioventricular node (AVN) ablation could help to improve heart failure (HF) and atrial fibrillation (AF).[2, 3] HBP provides truly physiologic ventricular pacing and LBBP provides physiologic left ventricular activation. They are effective in patients with narrow QRS maintaining and rescuing left ventricular (LV) dyssynchrony in typical left bundle branch block (LBBB) by His-Purkinje activation in AF and HF patients with reduced or preserved left ventricular ejection fraction (LVEF).[4] Few studies have compared the effects of HBP and LBBP directly.[5, 6]
We previously demonstrated both HBP and LBBP could be attempted successfully in the same AF patients.[6-8] LBBP yielded better and more stable parameters than that of HBP but showed comparable effects during the 6-month follow-up (intermediate effect).[7] LBBP is a physiological pacing mode which could achieve a similar cardiac electrical and mechanical synchronization but less interventricular synchrony and modest delay in right ventricular (RV) activation than that of HBP.[8]
The further study raised the question below: can electrical resynchronization effect and ventricular function and remodeling by LBBP be equivalent to results by HBP? Herein we report the results of a crossover comparison of HBP and LBBP in tachycardia AF patients referred for pacing.
METHODS
Patients’ Selection
This study was performed prospectively in Sir Run Run Shaw hospital on patients with symptomatic permanent AF, non-LBBB QRS and medication refractory uncontrolled ventricular rates (> 100 beats/min at rest) with pharmacologic treatment undergoing AV node ablation if they were 18 years or older and able to provide consent. Exclusion criteria were: (1) valve disease; (2) previous devices; (3) irreversible New York Heart Association (NYHA) class IV congestive heart failure; and (4) life expectancy of less than 12 months. All patients were prospectively enrolled from July 2018 to December 2019. The patients provided informed consent in a protocol approved by the investigational review board of our hospital and all patients were submitted by written informed consent. Moreover, patients were excluded if any coronary or vascular event occurred during the study.
Study Design and Implantation Procedures
After enrollment and consent, AF patients with uncontrolled ventricular rates referred for pacing were brought to the operating room. The HBP implantation procedure was firstly performed.[9-11] Briefly, the Select SecureTM lead (Model 3830, Medtronic, Inc., Minneapolis, MN) was advanced through the sheath (Model C315His; Medtronic, Minneapolis, Minnesota, USA) to the His bundle region in the atrioventricular septum for unipolar pacing. Then LBBP was performed according to the Huang technique.[11-13] If a HBP or LBB potential could be recorded during the intrinsic rhythm, the interval from the potential to the beginning of the QRS complex was measured and selective and non-selective HBP or LBBP were shown in intracardiac electrogram (EGM) (Figure 1). The differential criteria for the LBBP and LVSP was defined.[14, 15] The AVN ablation was done according to the report.[2] Patients with both HBP and LBBP achieved successfully were enrolled in our study. Subsequently, the HBP and LBBP leads were connected into atrial and RV ports respectively. Randomization, crossover and follow-up are described in Figure 2 as DDD pacing with maximal AV interval in HBP mode or VVI in LBBP mode. In accordance with the crossover design, patients were then randomized by HBP or LBBP modality. Each pacing modality was maintained for 6 months, with comprehensive testing at the end of each 6-month period. The paced percentage of HBP or LBBP was also assessed. A comprehensive assessment was also performed consisting of a medical questionnaire, physical examination, and quality of life assessments. Ventricular functions and remodeling were assessed by echocardiography with an modality of pacing who is blinded to the pacing mode.
Figure 1.
The fluoroscopic images, EGM by both HBP and LBBP in an AF patient.
AF: atrial fibrillation; HBP: His bundle pacing; LBBP: left bundle branch pacing.
Figure 2.
Enrollment, randomization and crossover procedures.
HBP: His bundle pacing; LBBP: left bundle branch pacing.
Clinical Follow-up and Data Collection
Patients were followed for 6 months at each setting. Clinical end-points included NYHA class, quality of life (QOL) assessment and echocardiographic assessments for LV function and remodeling including LVEF and LVESV. RV function was evaluated using TAPSE with a ≤ 14 mm threshold indicating severe RV impairment.[16] TAPSE was tracked in the apical four-chamber view using M-mode echocardiography. The severity of mitral regurgitation (MR) was assessed by the mitral jet area as a percentage of the left atrial area. The severity of tricuspid regurgitation (TR) was assessed by the proportion of the jet area in the right atrial area. The severity of valve regurgitation was classified as 0, none; 1, mild; 2, moderate; or 3, severe.[9, 10,16] Pulmonary artery systolic pressure (PASP) was calculated as 4 × [peak velocity of TR]2 + estimated right atrial pressure based on inferior vena cava diameter and collapsibility.[9, 10] QRS duration (QRSd) was measured in 12 contemporary ECG leads. Paced QRSd was measured from the pacing stimulus to the end of QRS complex.[17]
QOL Assessments
All patients underwent QOL measurements using the short-form general health survey (SF-36 Form) before, at 6 and 12-months follow up after different pacing modalities. The SF-36 form is a 36-item health status and quality of life inventory[18] which is to measure health concepts. The SF-36 assesses health status in eight areas including physical functioning, role disruption due to physical difficulties, role disruption due to emotion, social functioning, mental health, vigor, health perception and pain.
Statistical Analysis
This was a crossover feasibility study with no estimated power calculation. Descriptive statistics were used to summarize the clinical and echocardiographic outcomes. Continuous variables were expressed as mean ± SD or median (interquartile range [IQR]). Given the limited sample size, the student t test was used for paired and unpaired comparisons if the data was normally distributed. All data analysis was performed using SPSS version 22.0 (SPSS, Chicago, IL). A signed rank-sum test was applied for the comparison for an ordinal variable such as NYHA class and valve regurgitations. A P value ≤ 0.05 was considered statistically significant.
RESUTLS
Baseline Characteristics of the Patients and Implantation Procedures
Thirty-three patients that consented to the study were brought to the laboratory for attempted implantation. (1) Technical failure with HBP: one patient got HBP fixation failure and two patients got HBP threshold high during the procedure and were abandoned. (2) Failure of LBBP fixation: LBBP lead fixation failed in one patient with severe TR and another patient could not get LBB captured and got LVSP implanted. Finally, twenty-eight patients got both HBP and LBBP successfully at the time of implantation. One patient in HBP group with baseline normal RV function had his diuretics discontinued at 3 months and reused after 5 months and was found to have a widened QRSd and shortness of breath. Since the patient lost HB capture and thus exited from the study. His symptoms disappeared and diuretics discontinued when switched into LBBP modality. Three patients in LBBP group and one patient in HBP group lost follow up during first 6 months setting due to coronavirus pandemic and they kept stable and felt comfortable after the first 6-month follow up. Twenty three patients completed the full protocol with one-year follow-up and were included in the final analysis. Demographic data was given in Table 1. Six patients had symptomatic HF with baseline LVEF at less than 50%.
Table 1. Baseline characteristics of AF patients referred for both HBP and LBBP.
| Values are mean ± SD, n (%) or median (IQR). ACE/ARB: angiotensin-converting enzyme inhibitor or angiotensin receptor blocker; AF: atrial fibrillation; AVB: atrial ventricular block; BB: beta-blockers; DIU: diuretics; HBP: His bundle pacing; LBBP: left bundle branch pacing; LVEF: left ventricular ejection fraction; NYHA: New York Heart Association Functional Class; SPIR: spironolactone. | |
| Successful HBP | 30 (90.9%) |
| Successful LBBP | 31 (93.9%) |
| Both implanted successfully | 28 (84.8%) |
| Age, yrs | 68.5 ± 7.7 |
| Male | 20 (61.0%) |
| Coronary artery disease | 13 (39.4%) |
| Diabetes mellitus | 9 (27.3%) |
| Hypertension | 21 (63.6%) |
| NYHA | 2.7 ± 0.6 |
| Fluoroscopy duration, min | 6.2 ± 1.0 |
| Native QRS type | |
| Narrow | 24 |
| RBBB | 9 |
| QRS duration, ms | |
| Baseline | 107.4 ± 27.2 |
| HBP | 105.7 ± 13.2 |
| LBBP | 117.8 ± 15.3 |
| HBP threshold (V@0.4 ms) | |
| HBP threshold at the implantation | 0.8 ± 0.3 |
| LBBP threshold (V@0.4 ms) | |
| LBBP threshold at the implantation | 0.7 ± 0.2 |
| Medication: | |
| ACEI/ARB | 1 (5.3%) |
| BB | 9 (47.4%) |
| DIU | 14 (42.4%) |
| SPIR | 8 (24.2%) |
The fluoroscopic time, echocardiographic images as well as EGM and ECG of HBP and LBBP in AF patients were shown in Figure 1 which showed us the His potential (His p), left branch bundle potential (LBB p) and the potential injury after the pacing lead was screwed into targeted places. Briefly, the ECG and EGM characteristics of HBP were shown as Figure 1. (1) Almost the same pattern as the native pattern; (2) unusually with the Po His and potential injury; the interval from the Po His to the beginning of the QRS complex was approximately 30 to 50 ms (HV = 44 ms in Figure 1A); and (3) a low and high output of HBP with selective HBP (SHBP) and specific ECG changes with a discrete component in EGM (Figure 1A). The following ECG and EGM characteristics of LBBP were shown in Figure 1, as reported.[13]
Comparison of HBP and LBBP on Ventricular Remodeling
Figure 3 summarizes the clinical outcomes data for the 23 patients who completed the entire protocol. Both HBP and LBBP improved the quality of life, NYHA class and LVESV (n = 23). Both HBP and LBBP prevented the LV remodeling in AF patients. The baseline LVESV was 137.13 ± 36.20 mL with reduction at 6 months in the HBP mode reducing to 123.09 ± 21.78 mL and LBBP to 125.07 ± 25.99 mL (P = 0.02 and P = 0.04, respectively; HBP compared with LBBP not significant).
Figure 3.
The clinical outcomes data for the 23 patients who completed the entire protocol.
LVEF% and LVESV comparison in all patients (A & B); LVEF% and LVESV comparison in patients with LVEF < 50% (C & D). HBP: His bundle pacing; LBBP: Left bundle branch pacing; LVEF: left ventricular ejection fraction; LVESV: left ventricular endosystolic volume.
Among the patients with baseline LVEF of less than 50% (n = 6), the baseline average LVEF was 36.56 ± 4.94% with improvement at 6 months in the HBP mode improving to 52.55% ± 5.24 % and LBBP to 57.26% ± 11.23% (P < 0.001 and P = 0.002, respectively; HBP compared with LBBP not significant). The baseline LVESV was 183.57 ± 20.16 mL with reduction at 6 months in the HBP mode reducing to 136.08 ± 12.38 mL and LBBP to 140.45 ± 8.39 mL (P < 0.001 and P < 0.001, respectively; HBP compared with LBBP not significant). The NYHA class improved from 2.7 to 2.1 and 2.0 for HBP and LBBP respectively (P < 0.001 and P < 0.001, respectively; difference between HBP and LBBP not significant).
Clinical Outcomes and QOL Assessments
18 of 23 patients who had symptomatic HF had oral diuretics at the baseline. At the 6-month follow-up, 17 patients had their symptoms improved with cessation of diuretics and another patient had a diuretic dosage reduction at the 3-month follow-up and the diuretic was discontinued at the 6-month follow up while this kept during the entire 6-month crossover comparison.
The TAPSE was improved by HBP and not by LBBP after 6 months follow up. In four patients with reduced RV function (TAPSE of less than 14 mm) before implantation, they got edema and discomfort when switched into LBBP mode though the LVEF did not worsen (Figure 4).
Figure 4.
The clinical data of TAPSE in the patients who completed the entire protocol with baseline normal (A) and reduced TAPSE (B).
HBP: His bundle pacing; LBBP: left bundle branch pacing; TAPSE: tricuspid annular plane systolic excursion.
Patients had statistically significant improvements on the physical function, role-physical function, mental health index, vitality score, social functioning, role emotional function and general health function but not pain index by HBP or LBBP (Figure 5).
Figure 5.
Quality of life assessments of HBP or LBBP in AF patients.
The quality of life score was both improved by HBP and LBBP. AF: atrial fibrillation; HBP: His bundle pacing; LBBP: left bundle branch pacing.
Pacing Threshold, Sensitivity and Impedance of HBP or LBBP
The capture threshold for HBP was higher than LBBP (Table 2). Among them, 4 patients had threshold problem during the whole 12-month follow-up. Two patients got HBP threshold increased to 2.5 v at 0.4 ms during the first 6 months. While 3 patients got HBP threshold to 2.5 v and one patient got HBP threshold to 3.5 v after 12 months. During the whole 12 months, the LBBP threshold kept stable and kept lower than HBP.
Table 2. Leads parameters of HBP and LBBP at the baseline and during the follow-up.
| 24 h after implantation | Post 6 months | Post 12 months | |
| Capture threshold, **P < 0.001 vs. HBP lead values. Sensing, &P < 0.001 vs. HBP lead values. Impendence, ##P < 0.01 and ###P < 0.001 vs. HBP lead values. HBP capture threshold increased after 6 months. HBP: His bundle pacing; LBBP: left bundle branch pacing. | |||
| HBP lead | |||
| Capture threshold, V | 0.95 ± 0.39 | 1.28 ± 0.83** | 1.39 ± 0.81** |
| Threshold increased to absolute value > 2 V, Number | 0 | 2 | 4 |
| Sensing | 3.94 ± 3.04 | 3.55 ± 3.16 | 3.43 ± 3.20 |
| Impendence, Ohm | 449.52 ± 77.60 | 441.00 ± 73.54 | 419.13 ± 75.74 |
| LBBP lead | |||
| Capture threshold | 0.68 ± 0.23** | 0.71 ± 0.22 | 0.70 ± 0.22 |
| Threshold increased to absolute value > 2 V, Number | 0 | 0 | 0 |
| Sensing | 12.01 ± 3.86& | 11.93 ± 3.88 | 12.07 ± 3.93 |
| Impendence, Ohm | 567.83 ± 168.89## | 579.57 ± 166.14### | 551.65 ± 135.11 |
DISCUSSION
The major findings of this study are: (1) LBBP is comparable to HBP in helping in LV function and remodeling in uncontrolled AF patients with fast ventricular heart rate combined with AVN ablation in a prospective crossover study design; (2) RV function indicated by TAPSE was improved by HBP but not by LBBP; and (3) during the implantation and the whole 12-months follow-up, parameters of HBP and LBBP remained stable though in 4 patients the HBP capture threshold got increased.
In this study, we compared the clinical responses of permanent HBP or LBBP directly in tachycardia AF patients combined with AVN ablation in a prospective crossover study design. HBP and LBBP are two types of His Purkinje system pacing which keep LV synchrony in pacing dependence patients.[4] We were able to demonstrate that LBBP is comparable to HBP in preserving LV synchrony in AF patients which showed us a clinical response on LV function and remodeling that was like that of HBP. HBP can achieve optimal ventricular synchrony. By locating the lead at a more ventricular site, across the tricuspid valve, distal HBP can be achieved and results in a relatively low pacing threshold and acceptable R-wave amplitude. However, difficultly in achieving distal HBP can be a potential issue. HBP can achieve optimal cardiac resynchronization, but its higher pacing thresholds and inability of correcting LBBB in patients with block in the proximal left bundle have been major limitations of this approach.[19] LBBP seems to be easier to target and capture but still limited by paced RBBB pattern which could possibly worsen RV synchrony though a growing number of studies have demonstrated that a paced RBBB pattern during LBBP do not negatively impact the LV cardiac function. Our results also indicate the significant improvements of LVEF and NYHA functional class by HBP or LBBP in AF patients with reduced LVEF.[3] Even with loss of bundle capture, LV septal pacing could allow back up pacing with relative ventricular resynchronization.[20]
However, if the left bundle is stimulated before the stimulus enters the His-Purkinje system (negative delays), then pacing completely overwrites intrinsic activation, RV activation is slow, and interventricular dyssynchrony increases which is already shown in our previous study.[8] With positive delays, the patient’s intrinsic rhythm induces a wave traveling from the atria to the ventricles that activates the RV.
LBBP with optimized AV delay is comparable to HBP.[21] In our study, in AF and pacing dependence patients, AV delay could not be optimized. RV function is crucial for outcome in patients with chronic HF, especially in patients with significant LV dysfunction.[22] AF is often associated with HF.[23] HF patients who developed persistent AF displayed greater reduction in RV function.[24] A simple and established method for determining global RV function in the traditional two-dimensional imaging is an evaluation of TAPSE which is also reliable in AF patients.[25] The paced morphology of LBBP was typical right bundle branch block (RBBB) pattern. There is an association between RV systolic function and RBBB. Ignoring RV physiology in RBBB patients leads to underscoring of RV performance.[26] RBBB can result in delayed ejection of the RV,[27] which can impact RV systolic function, much like in cases of LBBB. RV function is now receiving more attention by researchers. In our study, TAPSE was improved by HBP but not by LBBP. In four patients with worsened RV function before implantation, patients got better by HBP but got edema after switching to LBBP mode indicating in patients with reduced RV function before the implantation, HBP rather than LBBP should be preferred.
During the whole 12-months follow-up, parameters remained stable though in some patients the HBP capture threshold increased shown as Table 2. No patients had lead dislodgements and one patient had a stroke during the follow-up. A variety of modifications were mentioned including dual-lead method that could make the technical aspects of implantation easier and feasible.[28] During the 12-month follow up, HBP threshold could increase and the mean change in the HBP threshold was 0.44 ± 0.58 v at 0.4 ms. Despite the limitations described, we were able to detect an equivalent 6-month response on LV remodeling and function using typical physical pacing using HBP or LBBP. In patients with baseline reduced LVEF, HBP and LBBP both improved LV remodeling and function,[3] which showed that it is feasible to adopt LBBP combined with AVN ablation to normalize the LV synchrony in AF patients, consistent with our previous publications[7, 29] though in our study HBP but not LBBP could help in some patients with baseline reduced RV function. A larger series and better selection of patients will be required to detect significant differences in ventricular remodeling and function between HBP and LBBP. We found in most of the patients based on the data presented herein and elsewhere, that it would be reasonable to perform a study in which such patients were randomized to HBP or LBBP. In the meantime, it may be reasonable to consider LBBP for AF candidates who for one reason or another cannot receive HBP lead or in whom HBP elicits a response but with high threshold. At a minimum, the relative advantages of LBBP include: (1) a simpler method that could easily be achieved; (2) a lower threshold at the time of implant and stability during the follow up; and (3) the possibility of equivalent effect as HBP as to the LV remodeling and function.
In addition, direct left conduction system capture was confirmed in all patients[14,15] in our study. As defined in a recent study[30] they were divided: (1) proximal LBB capture (P-LBBP) was diagnosed if all of the following were observed: (a) LBB potential to QRS (PV) interval value within the range of 35–25 ms; and (b) inferior or intermediate QRS axis. (2) Left bundle fascicular pacing (LBFP): (a) Fascicular Purkinje potential to QRS interval within the range of 24–0 ms or absence of a potential. Additionally, LBFP was subdivided into: (a) Left posterior fascicle pacing (LPFP): superior QRS axis (leads II and III predominantly negative). (b) Left anterior fascicle pacing (LAFP): inferior QRS axis (leads II and III positive). (c) Left septal fascicle pacing (LSFP): intermediate QRS axis (lead II predominantly positive, and lead III with negative component). PV interval in our study is 16.4 ± 4.9 ms. Among all patients with LBBP successfully (n = 31), the percentage of P-LBBP was 9.7% (n = 3). While the percentage of LBFP was 90.3% (n = 28) including LPFP (39.3%, n = 11), LAFP (25.0%, n = 7) and LSFP (35.7%, n = 10), respectively.
Study Limitations
The major limitation of this study is its size. Given the small sample size, it is unlikely that we would have detected a significant difference between HBP and LBBP. Additionally, the small sample size likely contributed to the absence of significant echocardiographic changes including RV function from baseline for either HBP or LBBP. The observations reported provide important and novel insights that could be used to design a large randomized comparison of the two pacing strategies. Technically the greatest limitation we encountered was the absence of His-bundle–specific pacing systems, especially critical in this setting of diseased His–Purkinje tissue in which high thresholds are likely to be encountered. In our study, HBP could possibly have a beneficial effect over RV function in patients with worsened RV function before implantation. This postulate should be addressed in a prospective study of HBP on the basis of RV function. However, the current study emphasizes the importance of assessing RV function before and after pacing for optimal patients’ management. In the present study, it should be emphasized that a 6-month period may be too short to show the entire impact of HBP vs. LBBP. Our study population was small. However, the cross-over design reduced inter-individual variation, thereby enabling the reproducible effects of LBBP on ventricular function and remodeling to be demonstrated even with a limited number of specific subjects.
Conclusions
LBBP was found to have an equivalent effect on LV function and remodeling but better and more stable parameters in AF patients with uncontrolled ventricular rates referred for AVN ablation in comparison with HBP. HBP could be preferred in patients with reduced TAPSE at baseline rather than LBBP.
ACKNOWLEDGEMENTS
We thank Weijian Huang, MD, PhD, for sharing his experience in His bundle pacing and left bundle pacing with us. This work was supported by Medical Science and Technology Project of Zhejiang Province (Grant Number 2020KY220 and 2022506537) and the funding from Clinical research project of Zhejiang Medical Association (No. 2016ZYC-A28).
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