Steps for Performing Physiologic Pacing: The St. George Regional Hospital Experience

His bundle pacing (HBP) is considered an acceptable alternative to right ventricular (RV) endocardial pacing for patients with a bradycardia indication for pacing, especially if >40% RV pacing is anticipated. HBP produces more a physiological ventricular activation via the His-Purkinje conduction system vs non-physiologic activation. RV endocardial pacing is associated with slow transseptal conduction time and left ventricular (LV) wavefront propagation. By preserving physiological ventricular activation, HBP may prevent the development of RV pacing-induced cardiomyopathy.¹ Furthermore, HBP can often correct pre-existing bundle branch block, resulting in a reduction in QRS duration and improvement in ventricular activation time.² Pacing-induced cardiomyopathy is more common than previously thought, with an estimated incidence of up to 9%.³

Despite the excellent clinical outcomes of HBP, compared to RV stimulation, several challenges remain: thresholds tend to be higher with reduced battery longevity; HBP leads also tend to be initially less stable than RV leads, leading to a higher incidence of early lead revision; and finally, differences in sensing, AV intervals, and tissue capture characteristics can be difficult to troubleshoot when programming a HBP system. Left bundle branch area pacing (LBBAP) has now emerged as an alternative technique to overcome these limitations.⁴ Left bundle branches (LBBs) travel through the LV septum and form a wider target for pacing as compared to the His bundle. LBBAP has also been reported to offer low pacing thresholds and better sensing, and because the distal conduction system is targeted, it has a lower theoretical risk for development of distal conduction block.

St. George Regional Hospital is the first institution in Utah to perform LBBAP. A case is presented below.

Case Presentation

The patient is a 71-year-old male with history of hypertension, transient ischemic attack, obstructive sleep apnea, coronary artery disease, post CABG in 2013, with a 2-month history of syncope and presyncope associated with sinus pauses. His ejection fraction by echocardiography measured 65%. The baseline EKG showed normal sinus rhythm with an incomplete right bundle branch block (RBBB) (Figure 1). He was advised pacemaker implantation and underwent a successful insertion of a dual-chamber pacemaker with a LBBAP lead. Initial attempt at HBP with a 3830 lead and the fixed curve C315 His sheath (Medtronic) was suboptimal. The initial fixation caused persistent complete RBBB, non-selective HBP capture with a wide QRS, and a prolonged left ventricular activation time (LVAT) of 118 msec as measured from stimulation artifact to peak R-wave in lead V5 or V6 (Figure 2). Additionally, the HB capture threshold was suboptimal, measuring >3 V at 1 msec pulse width. Therefore, the lead was positioned for LBBAP, 2 cm deeper and posterior along the septum. Unipolar pacing resulted in a QRS complex with a “W” pattern in lead V1 and discordant polarities in leads aVR and aVL (Figure 3). The lead was then progressed through the septum by a series of 3-5 full clockwise revolutions until a small LBB potential was seen in the unipolar recording and a qR complex seen in V1. Impedance measurements and QRS configuration were assessed with each series of lead turns. At this point in the procedure, testing was carried out at 3V and 8V with LVATs of 91 msec and 74 sec, respectively. This finding indicated that the lead needed to advance slightly. The lead was then advanced by an additional 3 full clockwise turns, resulting in a larger LBB potential and a LVAT of 65 msec at low and high output (Figure 4). At 1V, the paced complex transitioned from nonselective LBBAP (NS-LBBAP) capture to selective LBBAP (S-LBBAP) capture and back, with stable LVAT and separation of the local stimulation artifact and ventricular EGM during selective capture (Figure 5). Bipolar R-wave measured 9.3 mV and capture threshold was 0.625V at 1 msec. The post-procedure 12-lead EKG was consistent with LBB capture with a QRS duration of 116 msec and was remarkably similar to the baseline QRS morphology (Figure 6). In follow-up, the patient felt well and had no recurrence of syncope or presyncope symptoms.

Discussion

Our steps for performing the LBBAP procedure are as follows:

– Prepare the C315-His catheter with an 80 cm .035” J wire.

– Set up recording system to display all 12 leads.

– Slave RV pacing cable through EP recording system. Adjust gain to highest setting without observing artifact.

– If there is LBBB present, the atrial lead is placed in the RV for ventricular backup pacing.

– The initial site at the right ventricular septal surface is guided by (1) localizing the distal His and marking the site on the fluoroscopy screen with impermanent marker in 30^° right anterior oblique (RAO), then moving the lead 1-2 cm towards the RV apex and (2) using the V1 “W” paced morphology pattern with the notch located at the nadir of the “W” as an ideal location.

– Unipolar tip pacing is performed (black alligator clip on lead pin, red clip to pocket) and impedance measurements are logged in the recording system.

– Ideal sites have the following features: (1) “W” pattern in V1, (2) discordance in aVR/aVL, negative R-wave in aVR, positive in aVL, and (3) R-wave in lead II to be more positive than lead III.

– Screwing the lead into the septum towards the LV surface is performed in the 30^° left anterior oblique (LAO) position, turning the lead clockwise 3-5 times in steps, each time assessing (1) movement of the notch in V1 towards the end of the QRS, (2) impedance rise, (3) recording LBB potential, and (4) the LVAT time (<85 msec and constant at varying outputs are ideal findings). Ensure the lead stays perpendicular to septum (1 o’clock in RAO, 2-3 o’clock in LAO).

– Screwing the lead into the septum is best done with a 2-hand technique while the scrub tech fixes the catheter.

– Pacing from the 3830 ring can be performed to confirm the presence of the ring at the RV septum.

– Sheath angiography to determine lead depth is rarely performed as it has not affected success or failure or helped avoid LV septal perforation in our cases.

– Reshaping the C315-His catheter with the dilator in place to avoid kinking the catheter can help localize to specific anatomic sites along the RV septum. Exchanging to the SelectSite C304-HIS deflectable sheath (Medtronic) prepared with a SS-SA-09 valve can aid positioning in difficult cases.

– Assess selective and non-selective LBBAP thresholds unipolar and bipolar.

– Assessing retrograde HB potential or antegrade LBB potential during pacing is not routinely performed.

Conclusion

Conduction system pacing can preserve the electromechanical ventricular synchrony that would normally be disrupted by chronic conventional permanent right ventricular pacing. When compared with HBP in this setting, we have found LBBAP to be associated with higher rates of implant success, significantly better electrical parameters (pacing threshold and sensed R-wave), and lower lead-related complications. From a technical point of view, LBBAP is easier than HBP owing to the larger anatomic target site, and therefore, has a shorter learning curve. The implant technique is safe and reliable when the appropriate steps are followed. Our experience at St. George Regional Hospital reflects a change in thinking as to the “best” site for physiologic conduction system pacing, with 100% of implants now involving an attempt at LBBAP. We have had a high rate of success (>95%) and have not experienced complications. LBBAP implants are now routine and have also been successfully performed in heart failure patients as part of a cardiac resynchronization therapy (CRT) platform and in conjunction with atrioventricular nodal ablation in patients with atrial fibrillation. LBBAP consistently narrows or preserves QRS duration and preserves or restores physiologic activation of the left ventricle. In patients with LV dysfunction and LBBB, LBBAP should be considered an acceptable alternative to CRT. 

Disclosures: The authors have no conflicts of interest to report regarding the content herein.

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