Current Role of Conduction System Pacing in Patients Requiring Permanent Pacing

Figures

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  Figure 1. Anatomy of the conduction system. (A) Tawara’s classic illustration of the atrioventricular conduction system from 1906. (B) A virtual dissection in cross section of the mid segment of the ventricles with conduction system highlighted in yellow and labeled depicting the complex three-dimensionality of the conduction system network. Modified with permission from Vijayaraman et al.27)

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  Figure 2. McAlpine style dissection of the atrioventricular node and proximal conduction system. (A) Careful McAlpine-style dissection was performed to show the macroscopic image of the atrioventricular node in the right anterior oblique direction. Overlay of the serial histology stained with Masson’s trichrome (reconstructed from a different case) was performed to show an estimated location of the left bundle branch viewed from this direction. Yellow denotes central components of the conduction system. (B) The ‘horizontal’ bisection was made at the membranous septum using the McAlpine’s approach. Overlay of the serial histology stained with Masson’s trichrome was performed to show the alignment of central components of the conduction system (yellow). Dotted line denotes the location of the septal attachment of the septal tricuspid leaflet. Modified with permission from Vijayaraman et al.27)

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  Figure 3. Conduction system pacing. Fluoroscopic images (A, B) show the His-bundle pacing (yellow arrowheads). Virtual simulation images viewed from the right anterior oblique direction (C, D) show the His-bundle pacing (red), and left bundle branch pacing (white, green). (C) Image shows the estimated location of components of the atrioventricular conduction system. (D) Image demonstrates the relevant structures, including the membranous septum and septal tricuspid leaflet. With permission from Vijayaraman et al.27)

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  Figure 4. Currently used delivery tools and leads for His bundle pacing.

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  Figure 5. His bundle pacing. HBP with progressively decremental output is depicted here in a patient with a right bundle branch block at baseline. At the highest output (blue) non-selective HBP is demonstrated with the presence of a small delta wave (red arrow) preceding the rapid QRS onset. The delta wave is lost when RV-septal capture is lost and selective HBP is demonstrated (green). The QRS is separated from the pacing artifact by an isoelectric line. Finally, at the lowest pacing output (yellow) the blocked right bundle branch recruitment is lost and selective HBP without correction of the RBBB is demonstrated. Stim-end of QRS as well as QRS duration are demonstrated with calipers. Electrogram from the HBP lead is shown in the inset with both His bundle and myocardial current of injury (black arrow). HBP = His bundle pacing; RV = right ventricular; RBBB = right bundle branch block.

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  Figure 6. Electrocardiographic observations during LBBAP lead implantation: Twelve lead ECG and intracardiac electrograms from the HBP and LBBAP lead are shown at sweep speed of 100 mms/sec during various stages of LBBAP lead fixation from the patient in Figure 1. (A) Prior to LBBAP lead fixation, pacing from the lead at demonstrates a QS pattern in surface lead V1 (circle). (B) During early fixation as the lead is driven deeper, the QS morphology changes to Qr pattern (circle) during unipolar pacing. Note the difference in pLVAT during pacing at 5V and 1V (95 and 105 ms). (C) At final fixation, unipolar pacing at 5V and 1V results in identical pLVAT of 65 ms. Note the LBB potential with injury current in the LBBAP lead. (D) During bipolar pacing at 3V there is anodal (RV septal) capture and at 1V there is nonselective LBBAP. Note the subtle changes in QRS morphology in leads V1 and V2 and the intracardiac electrograms in LBBAP lead. Pacing at 0.5V demonstrates selective LBBAP with a short isoelectric interval. More importantly note the presence of retrograde His (H) potentials (short stimulus-His interval) in the HBP lead during LBBAP at 1V and 0.5V confirming LBB capture. With permission…

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  Figure 7. Demonstration of LBB potential in a patient with LBBB. (A) Baseline LBBB with QRSd of 170 ms and HV interval of 45 ms is shown. Note the absence of potentials in the LBBAP lead due to proximal conduction block. (B) During threshold testing from LBBAP lead, nonselective (blue circle) to selective LBB capture (red circle) is seen. (C) Selective HBP with (blue circle) and without LBBB (red circle) correction is shown. During corrective HBP, LBB potentials with injury current (*) is clearly seen. (D) Sequential DDD pacing with RA to LBBAP at 150 ms delay shows normalization of QRS morphology due to fusion with native conduction via right bundle branch. QRSd and stimulus-QRS onset intervals during pacing are shown. With permission from Vijayaraman et al.33) HBP = His bundle pacing; LBB = left bundle branch; LBBAP = left bundle branch area pacing; LBBB = left bundle branch block; NS = non-selective; QRSd = QRS duration; RA = right atrial; S = selective.

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  Figure 8. Distribution and ROC curves for V6 RWPT during left bundle branch capture and left ventricular septal pacing. Results from patients with narrow QRS intervals or isolated RBBB (top) and results from patients with LBBB, NIVCD, a wide escape rhythm, or asystole (bottom) demonstrating considerable overlap between V6 RWPT values between presence and absence of left conduction system capture if left bundle branch area pacing. Modified with permission from Jastrzębski et al.35) AUC = area under the curve; LBBB = left bundle branch block; NIVCD = non-specific intraventricular conduction delay; ns-LBBP = non-selective left bundle branch pacing; RBBB = right bundle branch block; ROC = receiver-operating characteristic; SN = sensitivity; SP = specificity; V6 RWPT = R-wave peak time in lead V6.

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  Figure 9. Algorithm for confirming conduction system capture with LBBAP. Some of the steps may be skipped according to operator preference, experience or feasibility to perform particular measurements/maneuvers. With permission from Burri et al.39) DSP = deep septal pacing; IVCD = intra-ventricular conduction delay; LBBAP = left bundle branch area pacing; LBBB = left bundle branch block; ns-LBBP = non-selective left bundle branch pacing; RBBB = right bundle branch block; RBBP = right bundle branch pacing; RWPT= R-wave peak time; s-LBBP = selective left bundle branch pacing.

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  Figure 10. Site of conduction disease in patients with AV block. Conduction system pacing in 333 consecutive patients with AV block. AV = atrioventricular. With permission from Vijayaraman et al.44)

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  Figure 11. Geisinger pacing protocol. With permission from Vijayaraman et al.44) AV = atrioventricular; LBBB = left bundle branch block; LVEF = left ventricular ejection fraction; RBBB = right bundle branch block; RV = right ventricular.

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  Figure 12. Algorithm for cardiac physiologic pacing for patients with bradycardia indications. With permission from Chung et al.38) BiV = bi-ventricular; CRT = cardiac resynchronization therapy; HBP = His bundle pacing; LBBAP = left bundle branch area pacing; LBBB = left bundle branch block; LV = left ventricular; LVEF = left ventricular ejection fraction; RV = right ventricular; RVP = right ventricular pacing.