His–Purkinje pacing reshapes cardiac resynchronisation practice

Cardiac resynchronisation therapy (CRT) has traditionally relied on biventricular pacing through a coronary sinus lead. His–Purkinje conduction system pacing offers a more physiological alternative by engaging the native electrical network directly. His bundle pacing (HBP) and left bundle branch area pacing (LBBAP) can restore ventricular activation with a narrower QRS and may provide useful options when coronary sinus lead placement is difficult or conventional CRT produces limited benefit.

The technique has moved quickly from a niche electrophysiology procedure to an important part of contemporary pacing practice. The clinical challenge is no longer simply whether conduction system pacing can be performed, but which patients are most likely to benefit, how implantation should be standardised, and how operators can manage thresholds, lead stability and follow-up. This update considers practical implantation, patient selection and Australian service realities.

Why conduction system pacing matters

His–Purkinje conduction system pacing aims to preserve or restore rapid electrical activation through the specialised pathways below the atrioventricular node. HBP captures the His bundle directly and can correct some forms of bundle branch block. LBBAP places a transvenous lead deep within the interventricular septum to capture the left bundle or the surrounding left ventricular conduction system. The latter approach is increasingly used because it generally offers a larger target and more stable pacing thresholds than traditional HBP.

For patients with reduced left ventricular ejection fraction and a wide QRS, conventional biventricular CRT remains an established treatment with substantial outcome data. Conduction system pacing is best viewed as an alternative or complementary strategy, rather than a universal replacement. It may be particularly attractive in patients with left bundle branch block, a high anticipated burden of right ventricular pacing, pacing-induced cardiomyopathy, or a failed or unsuitable coronary sinus lead.

The physiological rationale is compelling, but electrical improvement must translate into clinical benefit. Operators should assess QRS duration and morphology, ventricular function, heart failure symptoms, atrial rhythm, scar burden and the likelihood of meaningful ventricular capture. In patients with atrial fibrillation and heart failure, the wider CRT context is explored in this review of CRT in atrial fibrillation, including the importance of achieving a consistently high effective pacing percentage.

Selecting between His and left bundle approaches

HBP remains the most anatomically direct form of conduction system pacing. Selective His capture produces a discrete ventricular electrogram and a paced QRS resembling native conduction, while non-selective capture also activates adjacent myocardium. His capture can correct proximal conduction disease, but distal block may remain unresolved. High or rising capture thresholds, low sensing amplitudes and lead revision are practical concerns, especially when long-term battery longevity is important.

LBBAP has therefore become a common first-line conduction system strategy in many centres. The lead is advanced through the membranous or muscular septum towards the left bundle region, usually from the right ventricular side. Evidence supporting left bundle branch capture includes a short stimulus-to-left ventricular activation time, appropriate paced QRS morphology, a left bundle potential where visible, and a change in QRS or timing with output reduction. No single criterion is sufficient in every patient, so a combination of surface ECG, intracardiac electrograms and pacing manoeuvres is preferable.

Patient anatomy influences feasibility. Marked septal hypertrophy, extensive scar, right-sided implants, mechanical tricuspid valve considerations and venous occlusion may require a modified plan. In patients with a conventional CRT indication, the decision should be discussed by the heart failure and electrophysiology teams. A conduction system lead may be used as the primary resynchronisation lead, as a rescue after coronary sinus failure, or alongside a left ventricular lead when there is concern about incomplete capture or uncertain long-term thresholds.

Implantation technique and electrical confirmation

A reliable procedure begins with a pre-implant 12-lead ECG, imaging review and a clear definition of the target. The implanting team should document baseline QRS morphology, the presence of atrioventricular block, expected pacing dependence and the intended endpoint. Venography can be useful when prior devices or central venous access raise concern about obstruction. A delivery sheath with adequate support is essential, particularly for deep septal lead deployment.

For HBP, the His region is identified using a mapping catheter, a specialised lead or both. The operator records the His potential and tests unipolar pacing at different outputs. A narrow paced QRS, correction of bundle branch block and a consistent relationship between the pacing stimulus and ventricular activation support successful capture. The final position should balance a low capture threshold with acceptable sensing and mechanical stability. When the threshold is borderline, a backup ventricular lead may be prudent in a pacing-dependent patient.

LBBAP requires controlled lead advancement and frequent assessment of depth, orientation and electrical response. A right bundle branch block pattern in lead V1 is common, but it should not be treated as proof of left bundle capture. The paced QRS duration, stimulus-to-V6 peak time, V6–V1 interpeak interval and evidence of left septal or left bundle activation should be interpreted together. Contrast injections, stored fluoroscopic views and, where available, three-dimensional mapping can help identify an excessively deep trajectory or septal perforation.

Programming and follow-up after implantation

Device programming should be tailored to the capture strategy. In HBP, the programmed output must provide an appropriate safety margin above the His capture threshold, which can differ from the myocardial capture threshold. Threshold testing at implantation and during follow-up should distinguish selective from non-selective capture and identify any loss of conduction system recruitment. Automatic algorithms may not reliably interpret these transitions, so manual review remains important.

For LBBAP, the key questions are whether the lead continues to capture the intended conduction system and whether ventricular synchrony is maintained at the programmed output. A 12-lead ECG during device interrogation is valuable, especially when the paced QRS changes, the threshold rises or heart failure symptoms recur. Remote monitoring can identify lead impedance changes, loss of capture and arrhythmia episodes, but it does not replace periodic clinical and electrocardiographic assessment.

Follow-up should include symptoms, wound and venous status, pacing percentage, atrial arrhythmia burden, threshold trends and ventricular function where clinically indicated. Digital tools can support adherence and symptom surveillance; the role of digital AF interventions is relevant when atrial fibrillation management is part of the wider CRT pathway. A fall in effective pacing during atrial fibrillation may require rate control, rhythm control or atrioventricular node ablation, depending on the patient’s goals and overall condition.

Evidence, complications and service planning

The evidence base for conduction system pacing is expanding, with observational studies, comparative cohorts and emerging randomised data. Benefits commonly reported include narrower paced QRS complexes, improved left ventricular function and fewer limitations related to coronary sinus anatomy. However, studies vary in definitions of capture, procedural expertise, follow-up duration and patient selection. Hard outcomes such as mortality and heart failure hospitalisation require careful interpretation, particularly when comparing modern LBBAP with established biventricular CRT.

Complications include lead dislodgement, septal perforation, rising thresholds, loss of capture, pocket infection and venous obstruction. LBBAP also raises specific concerns about deep septal lead extraction, although long-term extraction experience is developing. HBP can be affected by micro-dislodgement and threshold increase. A documented rescue plan is therefore essential: this may involve repositioning, an additional ventricular lead, coronary sinus lead placement or a change in pacing strategy.

Australian implementation must account for unequal access to specialist electrophysiology. Patients in Sydney, Melbourne and Brisbane may have access to high-volume implant programs, while those from regional Western Australia, Queensland or the Northern Territory can face long travel and limited local device expertise. Public hospital pathways, private insurance arrangements and Medicare-supported follow-up can differ, so discharge planning should include remote interrogation, local cardiology communication and a clear escalation pathway.

The Australian device market also affects procedural planning. Lead and delivery-system availability, operator training and technical support vary between institutions and manufacturers. Centres adopting LBBAP should maintain a registry of implant success, thresholds, complications, revisions and clinical outcomes. Training through supervised cases, stored ECG review and multidisciplinary case conferences is particularly valuable. Culturally safe care and practical support for Aboriginal and Torres Strait Islander patients, including travel coordination and continuity with community health services, should be part of the pathway rather than an afterthought.

Integrating the approach into modern CRT practice

The most useful technique update is a change in decision-making rather than a single preferred lead position. Conventional biventricular CRT remains highly appropriate for many patients, particularly when the coronary sinus lead can be placed in a favourable vein and reliable resynchronisation is achieved. Conduction system pacing expands the options for patients with challenging venous anatomy, non-response, pacing-induced dysfunction or a strong physiological pacing rationale.

A structured implant report should state the target location, capture type, threshold at tested pulse widths, sensing amplitude, paced QRS measurements, programmed output and any evidence of septal perforation. These details improve longitudinal care when patients move between tertiary centres, rural cardiology services and device clinics. They also create the data needed to compare outcomes across Australian programs.

Research priorities include randomised comparisons with biventricular CRT, clearer definitions of left bundle capture, long-term extraction outcomes and patient-centred measures such as exercise capacity and quality of life. Registries should include diverse populations and reflect real-world Australian practice, including older adults, people with chronic kidney disease, patients with atrial fibrillation and those who travel long distances for follow-up.

Clinicians can strengthen practice by reviewing current electrophysiology evidence, incorporating conduction system pacing into CRT conferences and reporting procedural outcomes transparently. Explore the Journal of Arrhythmia’s research and educational collections, apply these principles to local device pathways, and contribute well-designed Australian data to the evolving evidence base.