Pacing Beyond the Site of Block: Left Bundle Branch Area Pacing in a Patient With Infranodal AV Block Following TAVR

Background

His bundle pacing (HBP) has been shown to improve clinical outcomes compared to right ventricular pacing. By accessing the native conduction system, HBP allows for physiologic activation of the ventricles, which is not possible through typical right ventricular pacing (RVP). HBP minimizes the potential for adverse structural remodeling, heart failure, and increased mortality.¹ HBP has been shown to be feasible in patients with infranodal AV block and bundle branch block; however, the pacing thresholds are often high and may not be achievable in some patients with distal disease.²

Transcatheter aortic valve replacement (TAVR) is being increasingly utilized to manage severe aortic stenosis in elderly patients. As high as 20-43% of patients undergoing TAVR may require permanent pacemaker implantation due to AV block resulting from injury to the conduction system.³ While HBP has been shown to be feasible in patients with AV block following TAVR, the success rate is low.⁴ Deep septal left bundle branch area pacing (LBBP) is a novel form of physiological pacing that utilizes the native conduction system. LBBP has been shown to be a feasible option for patients with AV block with or without left bundle branch block (LBBB).⁵

Case Presentation

An 86-year-old woman with a history of symptomatic severe aortic stenosis, coronary artery disease, hypertension, and left ventricular ejection fraction (LVEF) >70% underwent successful TAVR using a SAPIEN 3 transcatheter heart valve (26 mm) (Edwards Lifesciences). Post procedurally, the patient developed persistent LBBB but without any evidence for AV block. The patient was discharged two days later with a 14-day mobile cardiac outpatient monitor.

Five days after discharge, the patient developed recurrent episodes of symptomatic complete heart block (CHB) and was admitted to the hospital through the emergency department. Because of complete AV block with an unstable, wide complex escape rhythm, an emergent temporary transvenous pacing wire was inserted (Figure 1). The following day, permanent pacemaker implantation with His-Purkinje conduction system pacing (HPSP) was attempted.

HPSP was performed using a SelectSecure 3830 pacing lead and a C315HIS delivery sheath (Medtronic). The His bundle region was mapped, and the lead was temporarily fixed in this region. HBP at this location resulted in LBBB correction, but only at high outputs (Figure 2). Despite extensive mapping of the His region, LBBB correction at low output could not be achieved. The fluoroscopic location of the distal His bundle region was used as a reference point for LBBP (Figure 3). In the right anterior oblique (RAO) 30º fluoroscopic view, the lead was advanced 1 cm towards the right ventricular apex.⁵ LBBP was performed as previously described.⁶ Unipolar pacing in this region demonstrated a mid-QRS notch with a “W” pattern in the surface ECG lead V1. The active fixation screw of the lead was fixed into the RV septum at this location. The sheath was advanced close to the lead tip to better support the lead. The sheath was rotated counterclockwise to achieve perpendicular orientation of the sheath tip to the RV septal wall, and four to five rapid rotations of the lead body were performed. Unipolar pacing impedance increased from 520 Ohms pre-fixation to 640 Ohms, immediate post fixation. Unipolar pacing demonstrated right bundle branch block morphology in lead V1. Sheath angiography performed in the left anterior oblique (LAO) 30º fluoroscopic view confirmed that the lead was about 11 mm deep in the septum. (Figure 3)

Sensed R waves were 8 mV and the unipolar pacing threshold was excellent at 0.5V at 0.5 ms. Bipolar pacing demonstrated anodal (RV septal) capture in addition to left bundle branch and left ventricular septal capture up to 1.8 mV at 0.5 ms, resulting in normalization of the QRS morphology and duration (110 ms). Nonselective (LV septum + LBB) to selective LBB capture was noted at 1V and 0.5V at 0.5 ms, respectively (Figure 4). A right atrial pacing lead was placed and a dual-chamber pacemaker was subsequently implanted in the left pectoral region. There were no procedural complications, and the patient was discharged home the following day. The final 12-lead ECG is shown in Figure 5. The LBBP lead’s electrical characteristics remained stable during six-month follow-up (R waves >12 mV, anodal capture threshold of 1.75V, and LBBP threshold of 0.5V @ 0.4 ms).

Discussion

Complete AV block and LBBB are not uncommon following the TAVR procedure in elderly patients. Many patients with aortic stenosis develop LV systolic dysfunction and heart failure. RVP in these patients with underlying LV systolic dysfunction and/or LV hypertrophy may lead to worsening of heart failure. While biventricular pacing with a lead placed in the coronary sinus branch may be beneficial, HPSP (HBP or LBBP) promotes physiological ventricular activation by accessing the native conduction system and avoids pacing-induced ventricular dyssynchrony. While HBP can be successfully performed in patients with infranodal AV block, it is not feasible in ~25% of patients due to high capture thresholds as noted in this patient or inability to capture the distal conduction system.² Deep septal LBBP has been shown to be feasible in patients with LBBB and/or infranodal AV block with extremely low thresholds and excellent sensing characteristics.⁵ Bipolar LBBP in this patient resulted in near-normalization of the QRS morphology.

Prior study by our group had shown the feasibility of HBP in patients with AV block following valve surgery.⁴ However, HBP was successful in only 50% (two of four) of patients following TAVR, limited by high thresholds. By transvenously placing the lead in the left bundle branch region in the LV septum, pacing beyond the site of the conduction block (distal left-sided His bundle) was feasible in this patient. LBBP provides the ability to perform HPSP in nearly all patients with infranodal AV block. While the long-term safety of this approach is not known, early reports are promising.

Summary

HBP is the preferred form of physiologic pacing. However, HBP in patients with block in the distal His bundle, as seen in patients undergoing TAVR, is often not feasible. In this case report, we describe the feasibility of pacing beyond the site of block in the proximal left bundle in a patient with LBBB and complete infranodal AV block following TAVR. LBBP was associated with excellent pacing parameters. 

Disclosures: The authors have no conflicts of interest to report regarding the content herein. Outside the submitted work, Dr. Subzposh reports personal fees (speaker) from Medtronic; Dr. Vijayaraman reports a grant and personal fees (speaker, research, consultant, fellowship support) from Medtronic, personal fees (consultant) from Abbott and Boston Scientific, and personal fees (speaker and consultant) from BIOTRONIK.

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