Electrophysiological Characteristics and Clinical Values of Left Bundle Branch Current of Injury in Left Bundle Branch Pacing

Authors, Journal, Affiliations, Type, DOI

• Authors: Lan Su and Tiancheng Xu (joint first authors); Mengxing Cai; Lei Xu; Pugazhendhi Vijayaraman; Parikshit S. Sharma; Xiao Chen; Rujie Zheng; Shengjie Wu; Weijian Huang (corresponding)
• Journal: Journal of Cardiovascular Electrophysiology 2020;31(4):834–842. Received 13 November 2019; accepted 13 December 2019. © 2020 Wiley Periodicals
• Affiliations: Department of Cardiovascular Medicine, The First Affiliated Hospital of Wenzhou Medical University; The Key Lab of Cardiovascular Disease of Wenzhou; Geisinger Heart Institute, Wilkes-Barre; Rush Heart Center for Women, Rush University, Chicago
• Type: Single-centre retrospective observational study — 117 consecutive patients with QRS <120 ms undergoing LBBP, August 2018 – March 2019; 115 had an LBB potential and were included; follow-up ≥6 months (12 months in 20 patients)
• DOI: 10.1111/jce.14377
• Funding: Key Research and Development Program of Zhejiang (2019C03012); Major Project of the Science and Technology of Wenzhou (ZS2017010). Disclosures: Vijayaraman — consultant to Abbott, Biotronik, Boston Scientific and Medtronic, and a patent pending for a His delivery tool; Sharma — speaker/consultant for Medtronic, Abbott and Biotronik

Overview

This is the first systematic study of current of injury at the left bundle branch itself. The signal is defined not on the ventricular electrogram but on the LBB potential-to-ventricle (PV) segment: more than 25% elevation or depression relative to the isoelectric baseline after lead fixation. Among 115 patients with a recordable LBB potential (98.3% of those attempted), an LBB COI was present in 77 (67.0%) and took three morphological forms — a visible high-frequency potential with an elevated PV arch, a large PV elevation that conceals the potential, and a deep negative deflection. The clinical associations are strong and one-directional: 100% of COI-positive patients achieved LBB capture below 1.5 V/0.5 ms versus 76.3% of COI-negative patients, and selective LBBP occurred in 54.5% of COI-positive patients but 0% of COI-negative patients. COI did not change thresholds or follow-up stability — both groups had stable parameters to 6 months — but it did mark the lead as being in contact with the conduction system, and its sudden disappearance alongside the ventricular COI signalled septal perforation.

Keywords

Capture threshold; Current of injury; Lead stability; Left bundle branch pacing; Left ventricular septal myocardial capture

Key Takeaways

The signal

• LBB COI is defined on the LBB potential channel, not the ventricular EGM: >25% PV-segment elevation or depression compared with the baseline isoelectric segment, appearing after lead fixation
• Recording: unipolar EGM with a bipolar pin box, 30–500 Hz for LBB potential/COI, 0.05–500 Hz for ventricular COI, 100 mm/s sweep; two blinded experienced physicians measured independently
• An LBB potential was recorded in 115/117 patients (98.3%) with narrow QRS and intact infra-Hisian conduction — far above the 63–67% previously reported. The authors attribute this to using the confirmed His position as the initial reference, and state that in narrow-QRS patients they "do not accept a location without documented LBB potential"
• The PV interval was 24.0 ± 4.5 ms; intrinsic LVAT in V5 69.3 ± 8.0 ms; intrinsic QRS 92.5 ± 8.1 ms; paced QRS 111.4 ± 10.3 ms

Three morphological types of LBB COI

• Type 2 is the one most easily missed, because the potential and the PV elevation merge into the ventricular EGM; the authors recommend watching for dynamic change and changing filter settings to expose the high-frequency signal
• Type 3 is interpreted as the helix penetrating the LBB sheath, with current leaking from surrounding fibres; the deep negative deflection is the marker
• COI persisted to case completion in 60/77 (78%), mean duration 21.0 ± 12.8 min

Capture and COI

• All 77 COI-positive patients achieved LBB capture at <1.5 V/0.5 ms, versus 29/38 (76.3%) of COI-negative patients (P < .001)
• The 9 patients without low-output bundle capture (7.8%) were all COI-negative
• Selective LBBP occurred in 42/106 (39.6%) overall — 54.5% of COI-positive versus 0% of COI-negative (P < .001)
• The COI-positive group more often had identical LBB and myocardial capture thresholds (Stim-LVAT constant, 34.3% vs 24.1%, P < .001), while the COI-negative group more often showed Stim-LVAT shortening with increasing output (75.9% vs 65.7%, P = .004)
• But COI does not equal capture: 23.7% of COI-negative patients still had low-threshold bundle capture, and the paper calls COI an additional marker on top of the LBB potential, Stim-LVAT and selective/nonselective pacing — not a substitute
• Lead depth was similar in both groups: distance from the lead tip 12.0 ± 2.4 mm (COI+) vs 12.6 ± 3.1 mm (COI−), angle 89.1 ± 14.6° vs 79.6 ± 13.7° (both NS), with similar septal thickness

Follow-up

• Unipolar LBB capture threshold: 0.67 ± 0.25 V at implant → 0.48 ± 0.13 V at day 1 (P < .001) → 0.67 ± 0.22 V at 6 months (P < .001 vs day 1)
• Unipolar LV septal capture threshold: 0.97 ± 0.48 V → 0.57 ± 0.18 V at day 1 → stable at 0.58 ± 0.13 V at 6 months
• R-wave amplitude (bipolar): 11.31 ± 5.43 → 12.06 ± 4.64 → 13.37 ± 4.90 mV at 6 months
• Impedance (unipolar): 586.0 ± 115.7 Ω → 476.1 ± 95.0 Ω at day 1 → 360.7 ± 43.6 Ω at 6 months
• No difference between COI-positive and COI-negative groups at any time point
• At 12 months (20 patients): LBB threshold 0.80 ± 0.22 V, R wave 15.04 ± 4.23 mV, impedance 353.3 ± 32.0 Ω — unchanged and not different between groups
• Loss of LBB capture during follow-up: 3/115 (2.6%), equally distributed (2 COI+, 1 COI−); these patients retained low LV septal capture (0.67 ± 0.29 V) and did not need revision

Perforation — the disappearance sign

• Two patients had septal perforation at implant and were repositioned. In both, the LBB COI and ventricular COI disappeared suddenly at the moment of perforation
• The illustrative case (Figure 3): LBBP was achieved at 0.5 V/0.5 ms with both LBB COI and ventricular COI recorded. Two additional rotations were made after the LBB COI appeared. Perforation followed: both COIs vanished, impedance dropped abruptly from 580 to 320 Ω, and LBB capture was then only achievable at 3 V/0.5 ms
• The practical lesson: once COI is recorded, stop rotating — the signal marks the target depth, and further turns trade capture for perforation

Limitations of the document

Authors' own stated limitations

• None are stated. The article has no limitations section

Additional limitations evident in the study

• The "LBB COI" measured here is not the same signal as the ventricular COI used in other studies. It is defined on the LBB potential–ventricle segment and requires a recordable LBB potential, whereas the Zhongshan and other series define COI on the unipolar ventricular EGM (ST elevation ≥25% of the R wave). This makes the 67% incidence and the three-type classification non-comparable with the later 92.6% tip-COI figures, and less usable when no LBB potential is obtainable
• The population is deliberately narrow and favourable: QRS <120 ms, a recordable LBB potential, age 18–90, and 6-month follow-up. It excludes LBBB, wide QRS, and the patients in whom LBB capture and COI are hardest to interpret — so the 98.3% potential rate and 67% COI rate should not be generalised to CRT or LBBB cohorts
• Retrospective, single-centre, unblinded at the point of decision. The operators were not following a COI-guided protocol; they monitored COI while implanting and later analysed it. The association between COI and selective capture may reflect lead position and operator technique rather than a causal property of the signal
• No control group and no protocol for acting on COI. The "wait rather than reposition" and "stop rotating" recommendations are drawn from illustrative cases, not from a comparison of management strategies
• The 98.3% LBB-potential rate is an outlier against the 63–67% in the literature, and the paper attributes it to the His-referenced technique and to a policy of not accepting sites without a potential. Both are operator-dependent, and the figure is unlikely to reproduce in lower-volume or less LBBP-specialised centres
• The three-type classification is descriptive, with 18–38 patients per type, no reproducibility data, and no demonstration that the types carry different clinical consequences. The authors themselves note COI type was not associated with differences in electrical parameters
• Follow-up is short for the durability claim: 6 months in the main cohort, 12 months in only 20 patients, and no data beyond that
• Electrical endpoints only — no echocardiographic remodelling, heart failure events, or mortality
• The perforation signal is supported by 2 events plus one illustrative case, so "sudden disappearance of COI = perforation" is a mechanistic inference with a very small evidence base, even if it is physiologically plausible and consistent with the larger Zhongshan series
• The relationship between COI and capture is confounded by the fact that both depend on lead depth and contact. COI-positive leads were slightly deeper (12.0 vs 12.6 mm — actually shallower in the COI-negative group, which weakens a simple depth explanation), and the paper does not adjust for depth, angle, or operator
• Rating rationale: rated medium. It is the primary description of LBB COI, with a reasonable sample (115 patients), a clear morphological classification and 6–12-month electrical follow-up, and its perforation observation is clinically important. But it is retrospective, single-centre, narrow-QRS-selected, uncontrolled, without a limitations section, its COI definition is not the one later studies use, and its management recommendations rest on illustrative cases rather than comparative data

Key Concepts Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — the technique; this paper defines LBB current of injury
• concepts/Conduction-System-Pacing — the umbrella category
• LBB current of injury (COI) — >25% PV-segment elevation or depression after fixation; evidence that the helix is in contact with the conduction system
• PV segment — the LBB potential-to-ventricle interval; the segment on which the COI is measured here
• The three COI morphologies — elevated arch with visible potential (type 1), PV elevation concealing the potential (type 2), deep negative deflection (type 3)
• Ventricular COI — the separate myocardial injury signal; its simultaneous disappearance with LBB COI marks perforation
• Stim-LVAT — stimulus-to-LV activation time; constant or abruptly shortening depending on whether LBB and myocardial thresholds differ
• Selective vs nonselective LBBP — capture states whose frequency differed sharply by COI status
• Threshold recovery — the fall from implant values to day 1, followed by a small rise at 6 months
• Impedance trajectory — 586 Ω at implant, 476 Ω at day 1, 361 Ω at 6 months

Key Entities Mentioned

• concepts/Left-Bundle-Branch-Area-Pacing — primary concept page
• The First Affiliated Hospital of Wenzhou Medical University and the Key Lab of Cardiovascular Disease of Wenzhou — the investigating centre and one of the originators of LBBP
• Geisinger Heart Institute (Vijayaraman) and Rush University (Sharma) — co-authoring centres
• Weijian Huang; Shengjie Wu; Lan Su — the Wenzhou group
• Medtronic 3830 lead and C315 His sheath — the implant system used in every patient
• Medtronic 2290 analyser; GE CardioLab 2000 — pacing and EP recording systems
• Kenneth A. Ellenbogen — acknowledged reviewer of the manuscript
• Wiley Periodicals / Journal of Cardiovascular Electrophysiology — publisher

Wiki Pages Updated

• Created: wiki/sources/lbb-current-of-injury-jce-2020.md
• Updated: wiki/concepts/Left-Bundle-Branch-Area-Pacing.md
• Updated: wiki/concepts/Conduction-System-Pacing.md
• Updated: wiki/sourceindex.md
• Updated: wiki/wikiindex.md