Congenital complete heart block can manifest at any age. According to the guidelines established by the American College of Cardiology (ACC) and the American Heart Association (AHA), the implantation of a permanent pacemaker is considered essential for individuals experiencing symptomatic complete heart block.¹ Long-term right ventricular pacing is associated with various enduring adverse effects, notably the development of atrial arrhythmias, left ventricular dysfunction, and the potential progression to heart failure.² In cases where young patients require pacing for an extended duration, exploring alternative sites beyond the right ventricular apex becomes a viable option. In the current context, the consideration of permanent His bundle pacing (HBP) emerges as a practical solution. Multiple studies have validated the positive impact of adopting permanent HBP.³⁴ However, the use of HBP in cardiac interventions does come with certain limitations, including premature battery depletion, increased pacing threshold, and the inherent risk of lead revision due to escalating thresholds or dislodgment. These constraints mandate a careful examination of alternative pacing strategies and ongoing vigilance in managing potential complications to ensure the effectiveness and longevity of the therapeutic intervention.⁵ Left bundle branch area pacing (LBBAP) stands out as a promising solution to address these limitations, providing an optimal threshold along with sturdy lead stability.⁶

A 15-year-old male patient, weighing 53 kilograms and measuring 152 cm, was diagnosed with complete atrioventricular (AV) block during a routine check-up. The patient exhibits mild symptoms, particularly during exercise. Electrocardiography revealed AV dissociation with a ventricular rate of 53 beats per minute and a QRS duration of 90 msec (Figure Panel A). Echocardiography revealed a small and hemodynamically insignificant patent ductus arteriosus. A 24-hour Holter monitor recorded an average heart rate of approximately 48 beats per minute. We devised a strategy for implementing a permanent pacemaker in this patient with a reduced mean heart rate. Considering the patient's young age and the need for prolonged pacing, we presented the option of physiological pacing. During follow-ups, due to the possibility of threshold elevations and capture failures associated with micro and macro dislocations, as well as the potential for problems such as oversensing/undersensing, His bundle pacing was not preferred in our patient. With informed consent obtained, the procedure was performed under intravenous sedation. Continuous twelve-lead electrocardiography recording was conducted using an electrophysiology system. Following two distinct extra-thoracic left axillary venous punctures, a fixed shape C315 His catheter (Medtronic, Minneapolis, MN) was used to map the left bundle area. The lumenless 4.1F SelectSecure™ MRI SureScan™ 3830 lead (Medtronic, Minneapolis, MN) was introduced, and unipolar mapping was performed. Unipolar pacing at a depth of approximately 1 cm below the His bundle area produced a distinctive “W” pattern in lead V1. The lead was then rapidly rotated for eight rotations to penetrate deeply into the septum (Figure Panel B). The unipolar pacing showed a distinct appearance of the right bundle branch block morphology, along with discordance in the inferior leads; the QRS duration was 96 msec. The measured R-wave peak time (RWPT) during pacing in lead V6 was determined to be 55 msec, while the interpeak interval between V1 and V6 was also recorded as 42 msec. The transition from a higher to a lower output level resulted in a shift from nonselective to selective left bundle capture. The intrinsic rhythm displayed a prominent left bundle potential that preceded the local ventricular electrogram. The interval between the left bundle and local ventricular electrogram was measured as 28 msec. All these characteristics indicated a preference for the selective capture of the left bundle branch. The measured intrinsic R-wave amplitude was 12 mV, and the pacing impedance and threshold were determined to be 650 Ω and 0.3 V, respectively, with a pulse width of 0.4 msec. Subsequently, an atrial lead, utilizing another model 3830, was positioned in the free wall of the right atrium. Since the atrial lead was implanted into the free wall, during the procedure, the presence of phrenic nerve capture was tested, and it was observed that there was no capture with high-amplitude pacing. Both leads were connected to a Medtronic pulse generator that was equipped with a dual-chamber feature. The ultimate paced electrocardiogram displayed a right bundle branch block pattern with a QRS duration of 100 msec (Figure Panel C). The patient successfully recovered and was discharged on the third day after the procedure with stable device parameters and hardware (Figure Panel D). The device parameters were monitored steadily at 12 months (Table).

Cardiac pacing serves as the ultimate therapeutic intervention for managing symptomatic bradyarrhythmia. Given the significant hemodynamic issues associated with chronic right ventricular pacing, the exploration of alternative pacing sites has become essential. These alternatives include the right ventricular septum, right ventricular outflow tract, and the left ventricle.⁷ The concept of permanent HBP represents a refined and physiologically driven approach to cardiac pacing, wherein the pacing lead is carefully positioned in proximity to the His bundle conduction system. This technique aims to utilize the intrinsic physiological pathways of the heart's conduction system, preserving the native electrical activation sequence. By directly engaging the His bundle, permanent HBP seeks to optimize atrioventricular synchrony, reduce pacing-induced dyssynchrony, and alleviate the adverse effects associated with traditional right ventricular pacing. This method introduces a sophisticated paradigm in cardiac pacing strategies, underscoring the importance of maintaining physiological cardiac activation for improved hemodynamic performance and potentially mitigating long-term adverse outcomes linked to conventional pacing modalities.⁸ Following an enhanced understanding of the conduction system's anatomy, efforts have been made to selectively pace the left bundle branch.⁹ Placing the lead deep within the interventricular septum has resulted in favorable pacing parameters, accompanied by robust lead stability.

Patients with congenital heart disease are at a higher risk of developing a pacing requirement due to both underlying conditions and invasive interventions. With conventional pacing, pacing-induced cardiomyopathy, heart failure, and mortality might also occur in patients with congenital heart disease, and using conduction system pacing such as left bundle branch pacing can mitigate these adverse outcomes.

The Medtronic SelectSecure™ MRI SureScan™ 3830 lead is utilized for the implementation of LBBAP to manage symptomatic bradyarrhythmia. The lead is carefully inserted deep into the septum, guided either by a fixed-shape catheter (C315 His) or by a steerable catheter with a preshaped distal curve (SelectSite™ Deflectable C304 His). This pacing lead has some advantages and disadvantages. The absence of a central lumen and the utilization of a conductor cable instead of a coil result in enhanced redundancy in insulation, greater tensile strength, decreased overall volume, and increased lead durability. In cases where extraction is necessary, since it is a lumenless lead, it can easily be manually extracted with counterclockwise rotation from the body, or extraction devices can be used when needed. This pacing lead also offers adaptability for pacing in alternative locations. Different guiding catheters may be needed for placement in different implantation sites. The use of guiding catheters and splitters during implantation may slightly increase the dislocation rate.

It is crucial to maintain vigilant monitoring of paced QRS morphology and pacing impedance throughout the lead advancement into the septum to minimize the risk of perforation. To prevent septal perforation in children, during septal penetration of the electrode, it is important not to rotate the lead body too rapidly and uncontrollably, but rather to test pacing parameters and ECG after each few turns. Especially in the presence of a very thin septum, it may be necessary to penetrate only the distal cathode tip of the electrode and perform unipolar pacing if necessary.

Individuals requiring cardiac pacing are at risk of complications associated with prolonged right ventricular pacing. Specifically, congenital complete heart block involves a specific patient group requiring extended pacing starting early in life. Consequently, a thoughtful approach to physiological pacing becomes crucial within this subset, with options including HBP or LBBAP. This strategic selection aims to involve the native cardiac conduction system, promoting synchronized ventricular contractions. While this approach seems reliable in the adolescent demographic, its dependability remains uncertain in the childhood age group due to the thinness of the septum, potentially requiring extraction.