Antitachycardia Pacing at the His Bundle is Safer than Conventional Right Ventricular Antitachycardia Pacing in a Canine Myocardial Ischemic Injury Model
Authors, Journal, Affiliations, Type, DOI
- Authors: Annie M. Hirahara, Muhammad S. Khan, Omar Gharbia, Matthias Lange, Yuki Ishidoya, Douglas Smego, Ravi Ranjan, Gregory J. Stoddard, Craig Selzman, Derek J. Dosdall
- Journal: Journal of Cardiovascular Electrophysiology 2023 May;34(5):1249–1256
- Affiliations: Department of Biomedical Engineering, Nora Eccles Harrison Cardiovascular Research and Training Institute, Department of Surgery (Division of Cardiothoracic Surgery), Department of Internal Medicine and Clinical and Translational Science Institute — University of Utah
- Type: Preclinical animal study (canine ischaemia-reperfusion model)
- DOI: 10.1111/jce.15916
Overview
This preclinical study tested whether antitachycardia pacing (ATP) delivered from a His-bundle lead is more effective and safer than conventional right ventricular (RV) apical ATP. Six mongrel dogs underwent left anterior descending artery occlusion followed by reperfusion, with pacing leads in the RV apex and His bundle; 83 VT episodes were induced and 128 ATP trials were delivered, crossing over between sites when the first failed. His ATP terminated VT at a similar rate to RV ATP (23 vs 25 successful trials), but caused significantly fewer episodes of VT acceleration (6 vs 14, p = 0.05) and degeneration into ventricular fibrillation (1 vs 7, p = 0.02). Epicardial sock mapping showed more complete myocardial capture from the His lead, which the authors attribute to Purkinje-mediated spread and a less curved activation wavefront. The study is the first test of conduction-system ATP and concludes that His ATP is safer, but not more effective, than RV ATP.
Keywords
His bundle pacing; antitachycardia pacing; ventricular tachycardia; VT acceleration; conduction system pacing
Key Takeaways
Methods
- Six adult mongrel dogs of both sexes (two male) were anaesthetised; pacing leads were implanted in the right atrium, RV apex and His bundle.
- His capture was confirmed by a His potential between the P wave and QRS and by a narrow, sinus-like paced QRS.
- A 2-hour occlusion of the paraconal interventricular branch (human LAD equivalent) plus collateral circulation created an ischaemia-reperfusion injury; the terminal study followed 4–7 days later.
- A 128-electrode epicardial sock mapped ventricular activation; VT was induced by programmed RV stimulation and was considered sustained after 5 seconds.
- ATP was delivered at 88% of the VT cycle length in trains of 8 pulses, 2 ms pulse width, at twice the diastolic threshold, up to 3 trains per site.
- The first ATP site was randomised; if it failed, ATP was attempted at the other site. Mixed-effects logistic regression accounted for repeated treatments within animals.
VT characteristics and ATP delivery
- 83 VT episodes, 128 ATP trials and 309 ATP trains (152 RV, 157 His) were analysed.
- Mean VT rate was 336 ± 70 bpm — fast, canine VT.
- Capture thresholds were 1.1 ± 0.3 mA at the RV lead and 3.3 ± 0.9 mA at the His lead.
- Overall success for a set of trains at both sites was 38%.
Efficacy
- RV ATP terminated 23 trials and His ATP 25 trials (of 64 each; 36% vs 38–39%, not significant).
- The sites were discordant in both directions: 6 episodes terminated only by His ATP and 6 only by RV ATP; 35 episodes were refractory to both.
- No significant difference by mechanism: re-entrant VT 10 vs 12 terminations, focal VT 13 vs 13.
Safety
- There were 20 VT accelerations and 8 degenerations into VF.
- Acceleration occurred 6 times after His ATP and 14 times after RV ATP (p = 0.05); degeneration into VF occurred 1 and 7 times respectively (p = 0.02); all adverse outcomes combined favoured His ATP (p = 0.01).
- The mixed-effects model estimated acceleration at 10 ± 2.4% (RV) vs 4 ± 1.5% (His), and VF at 11 ± 9.5% vs 2 ± 3.7%.
- At the train level (Figure 3), any adverse outcome occurred in 13.8% of RV trains vs 4.4% of His trains; acceleration 9.2% vs 3.8%; VF 4.6% vs 0.6%.
- 17 of the 20 accelerations occurred during re-entrant VT (12 RV, 5 His), and all VF occurred during re-entrant VT. All classifiable VF cases followed incomplete myocardial capture.
Myocardial capture and mechanism
- Incomplete capture by the end of the ATP train occurred in 39 RV cases (43%) vs 21 His cases (25%) (p = 0.05); the model estimated 32 ± 11% vs 21 ± 8%.
- The His-Purkinje system interfaces with ventricular myocardium across the lower third of both ventricles, so His pacing recruits a larger volume of tissue and may reach the VT circuit or excitable gap earlier in the train.
- Wavefront curvature is proposed as the mechanism for the safety difference: point pacing from the RV produces a more curved wavefront that can detach around an ischaemic obstacle and re-initiate a spiral, whereas Purkinje-mediated His activation behaves more like multi-site or line stimulation.
Limitations of the document
- Animal model, induced VT. All episodes were induced by programmed stimulation in dogs; canine VT is faster with a narrower excitable gap than typical human VT, and spontaneous clinical VT may respond differently.
- Small sample. Six animals and 83 episodes; the study is powered for the primary comparison, not for subgroup or safety analyses.
- Homogeneous lesion close to the RV lead. The ischaemic injury was in a similar location and size in every animal and sat near the RV apex, potentially favouring RV ATP by proximity to the circuit.
- Non-selective His capture. His thresholds were three times RV thresholds, and ATP was delivered at twice diastolic threshold; the stimulus therefore also captured surrounding septal myocardium, so results may differ from selective His ATP.
- Acute preclinical endpoints only. No shocks, mortality, quality of life or chronic lead performance were measured.
- Industry and intellectual-property ties. Medtronic donated the 3830 SelectSecure leads; two authors are inventors on a University of Utah patent related to the technology and have filed further intellectual property; one author consults for Abbott, Medtronic and Biosense Webster.
Key Concepts Mentioned
- concepts/His-Bundle-Pacing — the ATP delivery site
- concepts/Conduction-System-Pacing — the broader pacing strategy
- concepts/ICD-Programming — ATP is the therapy being reprogrammed here
- entities/ICD — the device platform
- concepts/Left-Bundle-Branch-Area-Pacing — the distal conduction-system site tested in the companion study
Key Entities Mentioned
- University of Utah — coordinating institution
- Medtronic — donated the 3830 SelectSecure pacing leads
- Fischer Medical — Bloom DTU-215B external electrophysiology stimulator
- MathWorks — Matlab, used for electrogram analysis
- StataCorp — Stata, used for the mixed-effects models
Wiki Pages Updated
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