Discussion
This study is the first to compare LBBAP using lumen-less pacing leads with fixed helix design to standard stylet driven leads with extendable helix design. The main findings of this study are that LBBAP with stylet-driven leads yields comparable implant success and similar pacing characteristics at implant and short-term follow up without affecting procedural safety.
LBBAP is a novel pacing technique aiming to capture the conduction system of the heart at the left side of the interventricular septum.4 Compared to HBP, LBBAP aims to pace the conduction system more distally on the left bundle branch. Although no direct comparisons between HBP and LBBAP have been published, current evidence shows promising effects of LBBAP in terms of maintaining physiologic ventricular activation, hemodynamic benefits and the potential for cardiac resynchronization in patients with LBBB and heart failure.3, 5, 13, 17 Moreover, LBBAP is associated with lower pacing thresholds, and higher sensing values compared to HBP. As such, LBBAP might overcome the limitations of HBP, as HBP has been associated with high pacing thresholds, especially in the setting of bundle branch block or infranodal disease, and is associated with two to three times more lead revision compared to RVP.8, 9, 18
Until now, LBBAP has been exclusively performed with a 4.1Fr thin lumen-less lead with a fixed helix (SelectSecure 3830 lead, MDT) delivered though a fixed curved delivery sheath (C315HIS, Medtronic).4, 6, 7, 10, 11 This approach has been shown to yield high implant success and is associated with excellent pacing threshold both in patients with narrow QRS, atrioventricular block and bundle branch blocks. The main advantage of this type of lead is the isodiametric shape between the lead tip and the lead body which facilitates screwing the lead into the ventricular septum. Stylet-driven leads with extendable screws however lack the isodiametric shape at the location where the helix exits the helix case, which might limit lead penetration into the septum. Recently, the first two cases of LBBAP with an SDL delivered through a new preshaped sheath (Selectra 3D sheath) have been reported by Zanon et al.15 In these two cases, HBP with the SDL failed and the same lead was implanted successfully at the area of the left bundle branch. In our experience, the combination of a standard stylet-driven lead (Solia S60) delivered through the Selectra 3D sheath performed excellent to achieve LBBAP with similar success rates as compared to thin lumens-less leads. Neither the larger lead diameter (5.6 Fr), nor the non-isodiametric lead design limit the screwing of the lead towards the left side of the septum. On the contrary, the larger outer diameter of the SDL allows more grip on the lead body when applying manual rotations. The screwing of an SDL into the septum was further facilitated by the extra support of the stylet and the wider (8,7 Fr) and sturdier Selectra 3D sheath. As described by Zanon et al15, we tend to extend the helix and routinely add additional tension on the inner coil of the lead before screwing into the septum. This approach avoids unwinding of the inner coil and partial retraction of the helix when manual rotation on the outer lead body is applied and allows the applied torque to be transferred predictably to the lead tip.
In our experience, LBBAP with LLL and SDL reveals comparable procedural characteristics and safety. Despite the larger lead diameter, the use of an inner stylet and a wider delivery sheath, LBBAP with SDL did not result in more septal perforations. However, we detected an asymptomatic septal coronary artery fistula on echocardiography in one patient who underwent LBBAP with SDL. Although perforation of septal coronary artery branches could occur with any transseptal lead, the risk might be considered higher with larger pacing lead diameters. This complication highlights the importance of routine echocardiographic screening to assure integrity of the interventricular septum after LBBAP.
Our study shows that both types of leads tend to have comparable LBBAP thresholds immediately post implant and at short term follow up. Both leads have an electrical active pacing helix and use steroids at the helix, although the steroid location differs. The LLL helix is steroid-coated, whereas the SDL leads contain steroids within a capsule at the distal lead tip. A recent study showed that with HBP, SDL leads with steroid containing capsules presented with higher acute HBP thresholds compared to LLL with steroid coated helices. Although no such difference in acute pacing thresholds was detected in our patients with LBBAP, further studies are needed to assess whether differences in lead design and steroid location could affect long-term LBBAP pacing thresholds.