The implantation technique in His-bundle pacing: evolution and perspectives

This editorial refers to ‘Electrical characteristics of pacing different portions of the His bundle in bradycardia patients’, by Y. Hu et al., on pages ii27--ii35. Permanent His-bundle pacing (HBP) has emerged as a promising approach for delivering physiological pacing and maintaining long-term ventricular synchrony.1–3 According to early experience with permanent HBP, lead implantation at the His-bundle (HB) was performed by using standard pacing leads and reshaping various stylets with the aim of positioning the lead at a site near the His bundle identified by a mapping catheter under fluoroscopic views.4 With the accelerating development of delivery systems, mapping the HB using the lead itself became more feasible, followed by more stable lead fixation, and resulted in a substantial improvement in implantation success rates.5 In addition, this standard implantation technique in HBP has been further improved by using three-dimensional (3D) electroanatomic mapping system, dual-lead method, and tricuspid valve annulus angiography.6 In this article, we discuss the evolution and perspectives of implantation technique in HBP. In early times, localization and placement of a fixation lead at the HB were challenging due to lacking efficient tools.1 The implantation required operators to use a mapping catheter via femoral access to locate the HB region and to reshape various stylets to position the lead at HB region that was identified by the mapping catheter.4 Undoubtedly, this technique was very time-consuming and associated with lower success rate, higher fluoroscopy exposure, and higher incidence of procedure-related complication.7 The application of this implantation technique was first described in 2000 by Deshmukh et al.4 in clinical practice, showing that the success rate was only 66.7% (12 of 18 patients) and the incidence of lead-related complications during follow-up was 16.7% (2 of 12 patients). To improve this inferior implantation technique, Medtronic SelectSite™ pacing lead (Model 3830, Medtronic Inc., Minneapolis, MN, USA) and the delivery system (Model 10635) were designed.8 Zanon et al.5 used this new lead-delivery system to investigate the feasibility of HBP, showing that the implanting success rate could be improved to 92% (24/26). However, the implantation technique in this stage also needed a combination of mapping and implantation. With the further improvement of SelectSite™ delivery system, including the C315 HIS (non-deflectable) and/or the C304 HIS (deflectable), many experienced implanters no longer used mapping catheters because mapping for the HB electrogram could be achieved using this delivery system.1 The implantation technique has gradually become maturing and standardized.9 After obtaining venous access, the C315 HIS sheath is inserted into the right ventricle (RV) beyond the tricuspid annulus over a guidewire. Subsequently, the 3830 pacing lead is advanced to the tip of sheath with its tip just beyond the distal part of the sheath for HB potential recording and unipolar pacing. Unipolar connections are achieved between the tip of the lead and subcutaneous tissue. C304 HIS sheath can be helpful in challenging anatomical situation (dilated right atrium, etc.). Sharma et al.10 assessed the comparison between this standard implantation technique and conventional RV pacing, demonstrating that HBP was successful in 80% patients (75/94). Fluoroscopy time was comparable to those of the RV pacing patients (12.7 ± 8 vs. 10 ± 14 min; median 9.1 vs. 6.4 min; P = 0.14). Therefore, HBP is now routinely performed worldwide using this standard implantation technique.11 A recent meta-analysis about HBP showed that the overall implant success rate was 84.8%.12 Among early stage with stylet delivery, the implant success rate was only 54.6%, whereas the implant success rate among current stage with catheter delivery was 92.1% (P < 0.001). All these demonstrate that the SelectSite™ delivery system serves as the cornerstone of HBP implantation being standardized. Although the ‘stylet-less’ 3830 lead and the C315/C304 catheter-delivered system is the first choice for permanent HBP implantation, challenging issues still remain with these tools, particularly in patients with anatomic variations. A study reported by Orlov et al.13 showed the experience with stylet-driven leads (SDLs) (Model 8107/8109, Boston Scientific Inc., USA) delivered through coronary sinus (CS) sheaths (Model 4471/7742, Boston Scientific Inc., USA) in HBP implantation. His-bundle pacing with SDLs was successful in 24 of 27 patients (89%) compared with 15 of 17 patients (88%) in the SelectSite™ catheter-delivered system group. There was no significantly difference in fluoroscopy and procedural times between the two groups. Hence, a telescoping system with a lead having a stiff, shapeable stylet may allow improved accessibility to the HB region in patients with anatomic variations, in whom the fixed curve C315 sheath is inadequate. The standard HBP under fluoroscopic guidance to identify clear His potential usually entails higher fluoroscopy exposure.6 High-fluoroscopy exposure may significantly increase the risk of cancer or genetic abnormality for both patients and implanters.14 In this age of accelerating scientific technologies, interventional therapy in the field of cardiac arrhythmia has stepped into a new era of non-fluoroscopic 3D mapping. Some mapping systems have been applied as a convenient and efficient way of visualizing HB region with low or zero fluoroscopy.6 The Ensite NavX™ system (St. Jude Medical, Inc., St. Paul, MN, USA), a non-contact endocardial mapping system, enables reconstruction of the right atrial (RA) geometry and tagging of His potential with extremely low fluoroscopy or zero exposure15 (Figure 1). Besides, it is recommendable for HBP implantation as it has some distinctive advantages: compatibility with any type of electrophysiology catheter; electroanatomic mapping and HB region mapping with zero fluoroscopy; allowing either unipolar or bipolar mapping and visualization of the lead tip within or beyond the C315 HIS. Sharma et al.16 for the first time described low-fluoroscopy HBP using Ensite NavX system. His-bundle pacing was successful in 100% cases (4/4) using this system. The mean His lead fluoroscopy time (HL-FT) was only 0.25 min and no procedure-related complications were observed. Hu et al.17 enrolled 15 patients in HBP implantation using Ensite NavX system. Fourteen (93.3%) patients successfully underwent HBP guided by Ensite NavX system. Compared with the conventional fluoroscopy group, the total fluoroscopy doses (1.4 ± 0.5 vs. 16.1 ± 2.2 mGy, P < 0.001) and His lead fluoroscopy doses (0.4 ± 0.3 vs. 12.5 ± 2.2 mGy, P < 0.001) in the NavX group were significantly lower. Permanent His-bundle pacing in sinus node dysfunction using EnSite NavX system. (A) Electroanatomic map with the final location of the 3830 lead tip (blue arrows) and with tagged proximal His-bundle points (yellow dots) in RAO and LAO projections. (B) Only His (H)-ventricular (V) potential recorded and paced morphology with selective HBP. HBP, His-bundle pacing; IVC, inferior vena cava; LAO, left anterior oblique; RAA, right atrial appendage; RAO, right anterior oblique; SVC, superior vena cava; TV, tricuspid valve. Permanent His-bundle pacing in sinus node dysfunction using EnSite NavX system. (A) Electroanatomic map with the final location of the 3830 lead tip (blue arrows) and with tagged proximal His-bundle points (yellow dots) in RAO and LAO projections. (B) Only His (H)-ventricular (V) potential recorded and paced morphology with selective HBP. HBP, His-bundle pacing; IVC, inferior vena cava; LAO, left anterior oblique; RAA, right atrial appendage; RAO, right anterior oblique; SVC, superior vena cava; TV, tricuspid valve. The CARTO-3 system (Biosense Webster, Inc., Irvine, CA, USA), a magnetic navigation mapping system, enables accuracy of information on anatomic structures with low fluoroscopy.18 High resolution of anatomic and electric mapping is achievable. Sharma et al.16 reported their experience of HBP using CARTO-3 system. His-bundle pacing was successful in 83.3% cases (5/6) using this system. The mean HL-FT was only 0.132 min. None of the patients was noted to have any procedure-related complications or increase in HB capture threshold at follow-up. Although featuring advantages in guiding HBP, CARTO-3 system has some obvious limitations. This expensive system may not visualize the lead tip unless it is within the matrix created unlike the Ensite system that can track the lead tip all the way down from the venous system.18 The KODEX-EPD™ (EPD Solutions, a Philips company, Best, The Netherlands) is a novel catheter-based cardiac electrophysiological system.19 Acquiring the electromagnetic information through all conductors in-touch with the patient body, the system allows extremely accurate real-time localization and visualization of any intra-cardiac catheter, as well as acquisition and display of HD CT-like cardiac images either as a conservative reconstructed 3D image or as a flattened 3D panoramic view (PANO™). Hua et al.19 have conducted this cardiac imaging and navigation system guided permanent HBP implantation in a 76-year-old man (Figure 2). The final HBP had a capture threshold of 1.5 V/1.0 ms, with an R-wave of 4.6 mV. No procedure-related complications were observed during follow-up. However, prospective clinical research will be necessary to further assess the feasibility and safety of HBP using KODEX-EPD ™. Right atrial anatomy and final permanent His bundle lead position imaged by KODEX-EPD (EPD Solutions, Philips, Best, The Netherlands). (A) Right anterior oblique view. (B) Panoramic view. All anatomical landmarks were correctly depicted and the His bundle position was tagged. (C) Intracardiac signals of His potential obtained from the KODEX EPD system. CS, coronary sinus; HB, His-bundle; IVC, inferior vena cava; RAA, right atrial appendage; RV, right ventricle; SVC, superior vena cava; TV, tricuspid valve. Adapted with permission from Hua et al.19 Right atrial anatomy and final permanent His bundle lead position imaged by KODEX-EPD (EPD Solutions, Philips, Best, The Netherlands). (A) Right anterior oblique view. (B) Panoramic view. All anatomical landmarks were correctly depicted and the His bundle position was tagged. (C) Intracardiac signals of His potential obtained from the KODEX EPD system. CS, coronary sinus; HB, His-bundle; IVC, inferior vena cava; RAA, right atrial appendage; RV, right ventricle; SVC, superior vena cava; TV, tricuspid valve. Adapted with permission from Hua et al.19 More physiological and non-fluoroscopic is the development direction of cardiac pacing. His-bundle pacing guided by 3D electroanatomic mapping system, featuring extremely low-fluoroscopy exposure, is recommendable as it has some distinctive advantages. However, this implanting technique requires implanters to enhance dual expertise in HBP and electrophysiology mapping.17 Despite that pacing lead can be deployed in the HB region with the assistant of SelectSite™ delivery system, there exists a longer learning curve to achieve the standard implantation technique in HBP due to lack of a clear visualized anatomic marker.20 Besides, many new beginners remain confused with the HB position in fluoroscopy view, especially for those patients with anatomical variations.21 They have difficulty in placing the pacing lead at an appropriate location for HBP. In addition, the pacing parameters of leads implanted in the region of the HB are very different from those of leads implanted in the proximal or distal HB.22 These mentioned above are major factors limiting the widespread adoption of HBP in clinical practice. From the perspective of anatomy, the HB is composed of two segments: the penetrating and branching portions.23 The penetrating HB is located near the tricuspid septal leaflet, whereas the branching HB is located on the posterior sites of the muscular interventricular septum just inferior to the tricuspid septal leaflet, suggesting an anatomic association between HB and the tricuspid valve annulus (TVA)1 (Figure 3). The study by Sharma et al.21 first reported using the tricuspid valve ring as an anatomic landmark for localizing the HB region and improving the HBP implantation in the ventricular side. Besides, Gu et al.24 demonstrated the feasibility of visualization of the TVA by contrast injection under the fluoroscopic image to purposely place the pacing lead tip at the desired location for HBP. During the procedure, the pacing lead placement was attempted for atrial-sided HBP (aHBP) in two patients, ventricular-sided HBP (vHBP) in five patients, and first for aHBP then vHBP in one patient. The aHBP was selective and had a capture threshold of 1.6 ± 0.5 V/1.0 ms and R‐wave amplitude of 1.2 ± 0.4 mV. Ventricular‐side His bundle capture was selective in four patients and non-selective in two patients. The vHBP capture threshold was 0.8 ± 0.4 V/1.0 ms (P < 0.05 vs. aHBP) and R‐wave amplitude was 4.1 ± 1.5 mV (P < 0.05 vs. aHBP). Fluoroscopic image during His-bundle pacing implantation on the atrial (A) and ventricular side (B). Fluoroscopic image during His-bundle pacing implantation on the atrial (A) and ventricular side (B). The distal HB is the most ideal pacing site for HBP, followed by several reasons: distal HB is closely adjacent to ventricular side, covered with less myocardial fibres, and hence usually the HB and RV capture threshold is acceptable.25 With the assistance of TVA angiography, Gu et al.26 showed distal HB pacing (DHBP) in a patient with atrioventricular block and left bundle branch block. Pacing distal site revealed three types of eletrocardiogram (ECG). Pacing with a low output of 0.4 V generated ECG QRS morphology with right bundle branch block and selective capture of the left bundle branch (LBB). When the output was increased to 0.5 V, ECG QRS morphology became relatively narrower, suggesting capture of the LBB and local ventricular tissue. When the pacing output was further increased to 1.1 V, HBP capture was non-selective with relatively normal ECG QRS complex, suggesting capture of both the left and right bundle branches. Besides, Hu et al.27 demonstrated the feasibility and efficacy of DHBP by TVA angiography in a challenging HBP implantation. According to the imaging results, the position of distal HB lies ∼14 mm (the distance measured between the distal lead tip and proximal lead ring) towards the membranous septum–apex axis by TVA angiography. Recently, a single-centre study by Hu et al.28 reports the electrical characteristics of pacing different portions of the HB using TVA angiography. This is the pioneering investigation of HBP implantation based on image-guided lead placement to compare pacing characteristics between aHBP and vHBP. His-bundle pacing by TVA angiography was successfully performed in 45 patients (90% success rate with 44.4% aHBP and 55.6% vHBP). The capture threshold was lower in vHBP than aHBP at implant (vHBP: 1.1 ± 0.5 vs. aHBP: 1.4 ± 0.4 V/1.0 ms, P = 0.014) and 3-month follow-up (vHBP: 0.8 ± 0.4 vs. aHBP: 1.7 ± 0.8 V/0.4 ms, P < 0.001). The R-wave amplitude was higher in vHBP than in aHBP at implant and at follow-up. No aggravation of tricuspid valve regurgitation was observed in most patients and echocardiographic assessment of cardiac function remained in the normal range in all patients during the follow-up. Hence, the TVA angiography can act as an ideal anatomical landmark to guide aHBP/vHBP, or even DHBP, when compared with simply probing other areas of the high RV septum and coming to the same site eventually. His-bundle pacing using TVA angiography was of feasibility while the safety without affecting tricuspid valve function and no procedure-related complications were observed.24,26 However, long‐term follow‐up will be necessary to further assess the safety and clinical outcomes. Despite advantages of HBP, challenging HBP implantation still remains, similar to unstable success rate and high acute pacing threshold.12 Su et al.25 shared their experience of the dual-lead method: the first 3830 lead could act as an anatomic landmark, a superior site for HBP could be located by the second lead within a small region. From their single-centre experience, the permanent HBP implantation rates increased from 77.3% to 85.7% (P < 0.001) and the acute HB capture threshold reduced from 1.30 ± 0.7/0.5 to 1.11 ± 0.6 V/0.5 ms (P < 0.001), compared with conventional HBP implantation. However, the limitations of the dual-lead method were also obvious: increased expenditure and inability to help the second lead delivered to the due location with precision albeit with the first 3830 lead acting as an anatomical landmark. The TVA angiography combined with this method may be helpful, the operator would be able to figure out the position between the first lead and the distal HB region so as to purposely guide the delivery of the second lead to distal HB region.24 For patients with dilated RA/RV, SelectSite™ delivery system could not play a role in HBP implantation in clinical practice.1 While the deflectable C304 sheath is versatile in reaching the atrioventricular annular septal region in a normal sized heart, lead fixation is not perpendicular to the tissue surface of the dilated RA/RV due to lack of a septal curve. The C315His sheath, in contrast, has a secondary septal curve that allows excellent lead fixation. Mapping and lead fixation with the current tools can be challenging in dilated RA/RV. A sheath-in-sheath technique by Vijayaraman and Ellenbogen29 removed the proximal 10–15 cm off the CS sheath and pre-slit the sheath. The C315HIS sheath was then advanced through the outer sheath over a guidewire. They demonstrated that by adjusting the length of the outer sheath, the desired His region could then be easily reached using the C315 HIS sheath. The success rate was >95% by using this technique in HBP lead implantation. With the incessant deepening of clinical research on cardiac pacing, the traditional right ventricular apex pacing has been replaced by HBP to deliver more physiological form of pacing, which depicts the movement of continuous exploration and improvement in cardiac pacing for cardiac electrophysiologists.1,10 The advent of the SelectSite™ delivery system plays a basis role in standard HBP implantation technique and procedure. Three-dimensional electroanatomic mapping system reduces implanters’ pressure in fluoroscopy exposure and doses. The TVA and tricuspid septal leaflet revealed by right ventriculography can be used as a landmark to help quickly identify the HBP site and aHBP/vHBP or even DHBP can be performed purposely. Dual lead method makes it into possibility to find the sites with better pacing parameters. Sheath-in-sheath technique covers the shortage of SelectSite™ delivery system using in dilated RA/RV patients. Various HBP implantation techniques increase the confidence of electrophysiologists worldwide conducting permanent HBP in clinical practice (Table 1). In the future, the development of the newer steerable sheath, combined with 3D mapping system, could greatly facilitate the implementation of permanent HBP efficiently. We are holding promise that more patients will benefit from physiological HBP. The new implantation technique in His-bundle pacing aHBP/vHBP, atrial-sided HBP/ventricular-sided; DHBP, distal HB pacing; HBP, His-bundle pacing; RA/RV, right atrial/right ventricle. The new implantation technique in His-bundle pacing aHBP/vHBP, atrial-sided HBP/ventricular-sided; DHBP, distal HB pacing; HBP, His-bundle pacing; RA/RV, right atrial/right ventricle. Conflict of interest: none declared. The opinions expressed in this article are not necessarily those of the Editors of Europace or of the European Society of Cardiology.