Conduction System Pacing Using Stylet-Driven Leads. What Is the Difference?
Article Category: Case presentation
Published Online: Sep 08, 2022
Page range: 108 - 112
DOI: https://doi.org/10.2478/rjc-2022-0020
Keywords
© 2022 Cătălin Pestrea et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.
Conventional right ventricular myocardial pacing is characterized by non-physiological ventricular activation, which in turn creates biventricular electrical and mechanical dyssynchrony, similar to what has been described with left bundle branch block [1]. Physiological pacing, in the form of either His bundle or left bundle branch (LBB) pacing, has been, for the last decade, the next step in permanent cardiac pacing. The main argument behind these procedures is a synchronous electrical biventricular activation, leading to a significant reduction in pacing-induced cardiomyopathy occurrence [2].
The vast majority of implanters worldwide gained experience in physiological pacing with the (until recently) only available delivery kits: the Medtronic C315 His pre-curved sheath and the lumenless 4.1 French Medtronic SelectSecure 3830 lead (Medtronic, Minneapolis).
The feasibility studies for His bundle pacing and left bundle branch pacing showed acute success rates of around 80% and 90%, respectively [3,4]. Procedural failure is mostly related to patient anatomy, the delivery tools used, and operator skills. Patient anatomy is a non-modifiable factor, and the current success rates are reported only in highly experienced centers with skilled operators. Improvement of technology is probably the sole hope for better results.
With this in mind, we present our initial experience with physiological pacing using conventional stylet-driven leads in two case reports and share our first impressions regarding how the technique compared to the lumenless lead technique.
The procedure using His Bundle pacing was performed as follows: after gaining venous access through the axillary vein, a preformed shaped 8.7 Fr. Biotronik Selectra 3D delivery catheter (Biotronik, SE & CO), similar in design to the Medtronic C315 His, was advanced to the atrioventricular junction where the two curves placed the tip of the catheter at the anteroseptal part of the tricuspid annulus. Because this catheter can accommodate stylet-driven leads, we selected the Biotronik Solia 60 cm 5.9 Fr. lead. Before introducing the lead, the helix was exposed with at least 20 turns from the fixation tool on the connector pin of the lead. The lead was then advanced through the catheter with the stylet inserted completely, and mapping for the His bundle was performed in a unipolar fashion. After the signal was found and pacing revealed acceptable His bundle capture, the assistant kept the sheath in place, and the operator rotated the lead clockwise with a two-handed technique for 5–6 turns. To prevent potential helix retraction during manual clockwise rotation, another 3–5 turns with the fixation tool on the connector pin were performed in the end. Before the withdrawal of the sheath, the stylet was retracted approximately 10 cm. Then, while maintaining the lead in place, the sheath was gently retracted so that the lead would make a U-shaped slack, similar to what is recommended with the lumenless lead. In the end, the sheath was removed with the provided slitter.
Similar to the lumenless lead technique, the Selectra 3D catheter was advanced from the His position 1–1.5 cm towards the apex and maintained perpendicular to the septum. The “sweet spot” to start screwing was selected using the same criteria described by Huang et al. in 2017 [5]: a “W” shaped QS complex in V1 with electrical discordance in DII vs. DIII and aVL vs. aVR. Before screwing, the Biotronik Solia lead was also prepared by exposing the helix. With the stylet completely inserted and the assistant keeping gentle counterclockwise torque on the sheath to maintain perpendicularity on the septum, the lead was rotated clockwise manually with both hands while monitoring, under fluoroscopy, for advancement into the septum. Once this was achieved, the morphology of the paced QRS showing a qR or a right bundle branch pattern in lead V1 and a short left ventricular activation time (less than 80 ms) suggested left bundle branch capture.
In the end, the stylet was retracted to expose the distal part of the lead, and the sheath was removed gently while being cautious to avoid dislodgement of the lead.
A 62-year-old, hypertensive, and dyslipidemic female patient with paroxysmal atrial fibrillation was hospitalized with complaints of dizziness and extreme fatigue following episodes of fast and irregular palpitations. The initial 12 lead electrocardiogram (ECG) was suggestive for second-degree type II, alternating with third-degree sinoatrial block. Laboratory workup revealed a mild and transitory elevation of liver enzymes, without other significant changes. The transthoracic echocardiography (TTE) showed normal cardiac chambers, with preserved left and right ventricular systolic function and no significant valvular abnormalities.
Figure 1
a. His bundle recording shows a sharp His bundle electrogram (black arrow). b. Pacing at that site resulted in nonselective His bundle capture (first two beats) transitioning with lower amplitudes to selective His bundle capture (last two beats). c. Posteroanterior fluoroscopic image showing the final position of the Biotronik Solia lead in the His bundle region (white arrow). The atrial lead was placed as a backup at the RV apex during ventricular lead implantation and afterward implanted in the right atrial appendage.
Figure 2
a. Baseline ECG. b. Left bundle branch pacing with a right bundle branch morphology in V1 and a short left ventricular activation time (79 msec). c. Left anterior oblique fluoroscopic image after contrast injection showing the depth of penetration into the septum (the atrial lead was placed as a backup at the RV apex during ventricular lead implantation and afterward implanted in the right atrial appendage). d. Echocardiographic parasternal short-axis image showing the lead tip reaching the left endocardium (white arrow).
A sinus node disease was diagnosed, and implantation of a dual-chamber device with permanent His bundle pacing was planned.
The Biotronik Selectra 3D catheter was placed at the anteroseptal part of the tricuspid valve where the tip of the Biotronik Solia lead recorded a sharp His bundle signal (Figure 1a). Pacing at this site resulted in a transition from nonselective to selective His bundle capture (Figure 1b). The lead was then fixed, and the sheath removed (Figure 1c). The final parameters showed a detection threshold of 3 mV and a pacing threshold of 1.5 V at 1 msec pulse for nonselective His bundle capture and 0.5 V at 1 msec pulse width for selective His bundle capture. The three months follow-up recorded stable sensing and pacing thresholds.
A 70-year-old hypertensive female patient was admitted to our hospital after an episode of syncope preceded by dizziness. The initial 12-lead ECG showed sinus rhythm, with a grade I atrioventricular block (PR 240 ms) and flattened T waves in DI and aVL leads (Figure 2a). Continuous ECG monitoring showed intermittent 2:1 AV block. Laboratory workup was unremarkable. Her TTE showed a mild degenerative aortic stenosis, a normal-sized left ventricle with preserved ejection fraction, and mild mitral insufficiency. A left bundle branch area pacing strategy was chosen.
The Biotronik Selectra 3D catheter was placed perpendicular to the basal interventricular septum, and the lead was advanced until a right bundle branch block pattern was recorded in V1 with a left ventricular activation time of 79 msec (Figure 2b). The depth of penetration was assessed during the procedure with contrast injection to delineate the right side of the septum (Figure 2c) and with echocardiography after the procedure (Figure 2d). The final sensing threshold was 10 mV, and the pacing threshold was 0.5 V at 0.4 msec pulse width, which remained constant at the three-month follow-up.
If ventricular depolarization is at least partially accomplished by engaging the conduction system, it is superior to the slow cell-to-cell depolarization encountered in conventional right ventricular pacing. That is why conduction system pacing is supported by strong pathophysiological arguments and generally agreed upon amongst electrophysiologists. The main struggle in implementing these techniques was to overcome the technical difficulties and to standardize the procedures so the results would be similar in most centers.
It is important to take into consideration that, in the lumenless technique, the implanter maneuvers the sheath and the lead., while in the stylet-driven lead technique, the operator also has to maneuver the stylet, which adds more complexity to the procedure.
His bundle pacing is potentially more difficult because the target zone is only a few millimeters long and a millimeter wide. The first challenge is to reach the His bundle and afterward to capture it with acceptable amplitudes [6].
The design of the Selectra sheath is similar to the C315 His sheath, so it is to be expected that the His bundle location will be reached similarly. Nevertheless, one possible advantage of the thicker and stiffer 8.7 F sheath is the preservation of its curvatures for a longer period while in contact with blood. On the other hand, the same sturdiness decreases the maneuverability, e.g., making it harder to turn it counterclockwise (especially in smaller hearts) to reach more inferior positions. Once the His bundle electrogram is found, the sheath must be held steady and the lead screwed in. In this regard, the lumenless lead offers an advantage because of its smaller size and less driving force, which decreases the risk of dislodgement while manually rotating the lead. In contrast, the stylet-driven lead is bulkier and requires finer movements (in our cases with the help of an assistant and a two-handed rotation technique) to fix the lead without pushing too much on the septum and thus risking small dislodgements from the initial position. But, if there is adequate fixation, the larger diameter may capture a wider area and the chance of engaging the His bundle increases.
The same arguments do not apply to LBB pacing. For this type of conduction system pacing, the target zone is much wider, but the prerequisite for success is the penetration of the septum to reach the left side. Some studies reported difficulties in advancing the lead through the septum, and these have been attributed mostly to the thickness and/or increased fibrosis of the septum [7]. Nevertheless, all of these studies have been performed with a thin and soft lumenless lead. Compared to His bundle pacing, in LBB pacing it is all about the magnitude of the perpendicular force applied on the septum while screwing. In this instance, the much sturdier ensemble of the Selectra sheath and the Solia lead seems significantly greater for pushing and penetration. Different screwing techniques have been described (one-handed vs. two-handed, fast vs. slow rotations). The wider outer diameter of the stylet-driven lead provides better grip during fixation. Furthermore, the presence of the stylet conducts the rotations applied at the proximal end to the tip of the lead, so it is our opinion that very fast initial rotations pose the risk of septal perforation if the advancement of the lead is not closely followed with fluoroscopy.
Recently, De Pooter et al. [8] reported a study that compared the efficacy of lumenless vs. stylet-driven leads for LBB pacing, showing that there is no significant difference between the two strategies in achieving procedural success.
There is also the concern of complications with the stylet-driven-leads for conduction system pacing. Unfortunately, there is no data yet in this regard. For His bundle pacing, we do not expect a higher rate of complications because, apart from the slightly larger diameter of the lead, the helix length is identical to the lumenless lead, and the degree of fixation should be similar.
For left bundle branch pacing, possible procedural complications described with the lumenless lead are septal hematoma, septal coronary artery fistula, and late septal perforations [9]. Although rarely encountered, and difficult to completely avoid without knowing the anatomy of the septal arteries, it is intuitive to believe that the risk for such complications could be higher with a larger lead diameter.
The experience with LBB pacing leads extraction is lacking, but the possibility to retract the helix in the case of stylet-driven leads may be associated with easier removability.
We have now at hand new delivery tools for conduction system pacing with advantages and disadvantages comparable with the already known and widely used lumenless system. The stylet-driven leads could prove beneficial especially for left bundle branch pacing because of their superior stiffness, and thus their ability to penetrate the septum. In the end, having more options for each patient will only increase the procedure's success. It would be ideal to use noninvasive preprocedural tests, like echocardiography, to describe the width and the density of the septum to choose the most appropriate tools and maximize success.