Right Bundle Branch Pacing
Definition
Right bundle branch pacing (RBBP) is a right-sided conduction-system pacing modality in which a lead positioned in the right ventricular septal/His bundle region directly captures the right bundle branch (RBB), rather than the His bundle proximally or the left bundle transseptally. The paced wavefront travels retrogradely up the RBB to the His bundle, across the longitudinally dissociated His–LBB fibres, and anterogradely down the left bundle — so the left ventricle is activated through the conduction system, but later than during His bundle pacing. It is distinguished from HBP by a conduction-system potential-to-QRS interval <35 ms at the pacing site and by a paced V6 R-wave peak time that exceeds the native potential-to-V6 interval by ≥10 ms. (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
Key Concepts
Prevalence and how it is recognised
- RBBP was found in 19.6% (64/326) of patients in whom HBP was intended, and in 12.2% (40/326) at the working output of 3.0–3.5 V/0.4 ms. RBBP alone occurred in 11.0%, both RBBP and HBP in 8.6%, and HBP alone in 80.4% (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- The potential-to-QRS interval localises the lead: <35 ms suggests RBBP, 35–55 ms suggests HBP. Among patients with <35 ms, 90.6% (48/53) had RBBP; among the rest, 5.6% (16/273) did (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- The cut-off is imperfect. Within the <35 ms group, 9.4% still had HBP at some output, and 2.6% of the ≥35 ms group had RBBP at working output — explained by variable His bundle length, RBB takeoff level, conduction velocity, and longitudinal dissociation (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
The diagnostic criteria
Six criteria were proposed and tested; the third became the diagnostic standard (sources/right-bundle-branch-pacing-hrs-2023, rating: high):
| Criterion | Performance |
|---|---|
| 1. Double QRS transition during threshold testing | Present in all potential–QRS categories, but far more common <35 ms (22.6–50%) than ≥35 ms (3.5–8.2%); insufficiently specific |
| 2. Selective paced QRS differs from native conducted QRS | SN 64.1%, SP 91.1% |
| 3. Stimulus–V6RWPT > potential–V6RWPT (Δ ≥10 ms) | Diagnostic standard: Δ 17.8 ms in RBBP vs 0.5 ms in HBP; 100% specificity, and 100% sensitivity when HBP and RBBP coexisted |
| 4. Stimulus–sQRS > potential–QRS (Δ ≥10 ms) | SN 87.2%, SP 95.3%, AUC 0.944 |
| 5. Small V6RWPT increase (<20 ms) with loss of capture | SN 70.5%, SP 94.8%, AUC 0.888 |
| 6. Equal conduction-system and myocardial capture thresholds | SN 31.3%, SP 95.8% |
- The physiological core of the best criterion: during HBP the route from the His bundle to the LV lateral wall is the same in pacing and native conduction, so paced and native V6RWPT are equal — the same equality that underpins LBB capture criteria. During RBBP the wavefront must traverse RBB → His → LBB, so paced V6RWPT is longer than the native potential-to-V6RWPT. A Δ ≥10 ms separated RBBP from HBP in every case where the two could be compared (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- The latency criterion has a counterintuitive explanation: even with a preserved RBB, the RB-V interval during RBBP is set by left bundle activation of the septum, because QRS onset depends on the left-sided wavefront. The LBB–RBB conduction-time difference (5–20 ms) therefore determines how much the paced latency can exceed the native RB-V interval (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
ECG and capture characteristics
- Transition from ns-HBP to ns-RBBP prolongs V6RWPT by 11.6 ± 4.3 ms and QRS by 10.5 ± 5.4 ms (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- RBBP produces features of LV activation delay: smaller r and deeper S in V1–V3, delayed V6 R-wave peak, global QRS prolongation, and a pronounced pseudo-delta wave (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- Selective RBBP occurs only at low/near-threshold output; at working output RBBP is always nonselective, because of the ample myocardium surrounding the RBB. In complete RBBB, s-RBBP and HBP produce identical QRS morphologies, but the latency during selective RBB capture can be exceptionally long (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
Outcomes and clinical niche
- Sensing is the clear advantage: acute 5.6 (3.6–8) vs 3.2 (2.3–5) mV and chronic 5.6 (4–12.5) vs 3.2 (2–5.6) mV versus HBP, with no undersensing in RBBP (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- Thresholds are equivalent: acute 1.3 vs 1.1 V, chronic 0.8 vs 0.8 V. No RBBP patient had a threshold rise >3 V or a lead revision, versus 5.6% and 3.9% in HBP — but the differences were not significant (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- Echocardiographic outcomes and 3-year mortality did not differ: ΔLVEF +2% vs +1%, ΔLVEDD −3 vs −1 mm, mortality 28.6% vs 23.2% (P = .28) — an underpowered comparison in an elderly cohort (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- Advantages beyond sensing: obligatory myocardial backup capture at working output; no transseptal access, which may facilitate lead extraction and is relevant to leadless conduction-system pacing; a para-RBB midseptal position with faster access to the distal conduction system if RBB capture is lost (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- Disadvantages: more delayed LV activation than HBP or LBBP; paced QRS is usually <150 ms, possibly enough to prevent pacing-induced cardiomyopathy but likely insufficient for optimal CRT response; and RBBP cannot correct LBBB, so it cannot serve as the sole pacing mode for most CRT candidates (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- The proposed niche: dual-branch pacing (RBBP + LBBP) to restore both sides of the conduction system, or RBBP combined with coronary venous pacing when fusion with intrinsic RBB conduction is impossible (e.g., AF)
Contradictions / Open Questions
- There is no direct electrophysiological proof of RBB capture. The diagnostic standard is an ECG interval difference (ΔV6RWPT ≥10 ms), an inference validated against a double transition in only 28 patients. The additional 36 cases classified as RBBP without a double transition are identified by the criterion under test, which makes the validation partly circular. Direct capture — a retrograde His potential or an anterograde RBB potential — has not been demonstrated for this modality (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- The criteria were derived and tested in the same 326 patients, without external validation or confidence intervals. The reported sensitivity and specificity are in-sample optima; a second cohort could move them materially (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- The 19.6% prevalence is population-specific. It describes patients targeted for HBP with preserved infranodal conduction after excluding H-V >55 ms and LBBB. RBBP's prevalence among LBBP-directed implants, or among unselected CSP candidates, is unknown — and the excluded LBBB group is precisely where RBBP cannot help (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- Whether RBBP is better than HBP is unresolved. Sensing is clearly superior, but thresholds, echocardiographic remodelling and mortality were not different, and the numerically lower threshold rise and revision rates in RBBP did not reach significance. No randomised comparison exists, and the outcome analysis is unadjusted for age, comorbidity, indication and ventricular pacing burden (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- Is nonselective RBBP the same entity as selective RBBP? At working output, all RBBP is nonselective because of surrounding myocardium; the selective state the criteria identify appears only near threshold. Nothing in the data shows that selective RBBP confers a clinical advantage, and the outcome analyses describe the nonselective state (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
- Where RBBP sits relative to LBBP is undefined. Both activate the LV through the conduction system; LBBP corrects LBBB and gives faster LV activation, while RBBP avoids transseptal access and gives better sensing. The suggestion that dual-branch RBBP + LBBP may be superior is a hypothesis with no outcome data (sources/right-bundle-branch-pacing-hrs-2023, rating: high)
Connections
- Related to concepts/Conduction-System-Pacing — the umbrella taxonomy
- Related to concepts/His-Bundle-Pacing — the proximal right-sided target and the comparator
- Related to concepts/Left-Bundle-Branch-Area-Pacing — the left-sided counterpart; dual-branch pacing combines the two
- Related to entities/CRT — RBBP cannot correct LBBB and is not a standalone CRT strategy