Synchronized left anterior/posterior fasciculars pacing - a modified strategy for difficult left ventricular lead implantation during CRT-D: A case report

Abstract

Cardiac resynchronization therapy - defibrillator (CRT-D) is an effective treatment for ischemic heart failure (HF). But, it is a tricky challenge for left ventricular lead implantation difficulties during CRT-D. We report an ischemic cardiomyopathy patient with complete right bundle branch block (cRBBB) underwent CRT-D. During the implantation, the left anterior fascicular (LAF) region pacing was not ideal, and the implantation of left ventricular lead in lateral posterior or posterior wall was difficult. Then, leads were changed to be implanted into anterior septal region (near the LAF) and posterior septal region (near the LPF) from right ventricle, respectively. Synchronized pacing of LAB and LPB was performed to replace the pacing of left bundle branch region and left ventricular lateral posterior wall. Then, the QRS duration was shortened from 160ms to 100ms. During one month in follow-up, the patient’s quality of life was good and the pacing parameters were stable. This case illustrates a technically feasible, hypothesis-generating bailout approach for selected patients when conventional coronary sinus left ventricular lead placement and standard conduction system pacing are unsuccessful.

Introduction

Heart failure (HF), the end-stage of many heart diseases, affects 1-3 % of the population and kills >50 % within five years; lifetime cost per patient exceeds $126,000.^1,2 Ischemic heart disease drives 65 % (men) and 48 % (women) of HF cases. When optimal drugs fail, cardiac resynchronization therapy-defibrillator (CRT-D) is indicated for sinus-rhythm patients with EF < 35 %, bundle-branch block and NYHA II–IV ≥ 40 days post-MI. Ideal pacing couples left-bundle-branch area with lateral-posterior LV wall, but anatomical variants or absent veins thwart 7.5-10 % of LV lead placements.^3–5 We describe an ischemic cardiomyopathy patient with complete RBBB whose target anatomy was unsuitable; successful CRT-D was achieved by simultaneous pacing of the left anterior and posterior fascicles instead, offering a safe fallback for difficult LV lead implantation.

Case report

A male in his early 50s presented a recurrent chest pain with dyspnea on exertion for 3 years, and admitted in The Second Affiliated Hospital of Guangxi Medical University at Apr, 2024. Coronary angiogram revealed a 70% stenosis in the distal segment of the left main coronary artery, 60%-90% diffuse stenosis in the middle segment of the left circumflex artery, left anterior descending artery was occluded in the proximal segment, and the right coronary artery was occluded in the middle segment. The echocardiography indicated that the left ventricular ejection fraction was 35%, left atrial diameter was 45 mm, left ventricular end-diastolic diameter was 60 mm, systolic motion of the anterior septum and anterior left ventricular wall was reduced. Electrocardiograph (ECG) indicated complete right bundle branch block (cRBBB) with a 160ms duration (Figure 1(a)). Cardiac resynchronization therapy - defibrillator (CRT-D) was then performed. The reporting of this case report conforms to the CARE guidelines. ⁶

Figure 1.

(a) ECG before implantation. (b, c, d) Location of the lead in LBB, LAF, and in LA and LPF. (e) Synchronized LAF/LPF pacing. (f) ECG after implantation. LA, left atrium; LAF, Left anterior fascicular; LPF, Left posterior fascicular; PP, P potential.

The right ventricular (RV) active lead (3830, Medtronic Inc, USA) was implanted from the right ventricular septal plane at a depth of 9 mm. But the parameters were not ideal after pacing in this region inducing a wide QRS with 134 ms, time to peak of threshold with 1.6 V, sensing value of 8.0 mv, and impedance with 690 Ω (Figures 1(b)–1(c)). True LBB capture was considered unsuccessful because no clear LBB potential/no abrupt shortening of stimulus-to-left ventricular activation time/no output-dependent transition between non-selective LBB capture and septal myocardial capture/no typical V1 terminal R-wave pattern; and the stimulus-to-V6 R-wave peak time was 100ms. Coronary sinus angiography found that posterior lateral vein and lateral veins were absent. Unfortunately, it was difficult to implant the left ventricular (LV) lead (3830, Medtronic Inc, USA) into the anterior lateral vein even under the support of the sheath tube. Thus, pacing on LAF and LPF regions were considered. P potential (Discrete fascicular potentials) could be recorded in the posterior septum of right ventricle, which was near the LPF region, and the ventricular lead was implanted into the LAF region from the anterior septum of the RV, where P potential can be recorded, with threshold of 0.6 V, sensing value of 6.0 mv, and impedance of 520 Ω (Figure 1(d)). According to the anatomy, it was near the LAF region, and the QRS wave was shorted to 101ms with synchronization pacing on LAF and LPF regions. Additionally, the cRBBB pattern disappeared and QRS duration was shorten than before. Then, the atrial (5076-52, Medtronic Inc, USA), defibrillation lead (4196, Medtronic Inc, USA), and resynchronization defibrillator (DTBC2D1, Medtronic Inc, USA) were implanted, respectively (Figure 1(e)). The two septal 3830 leads were connected as follows: anterior septal/LAF-area lead to LV port; posterior septal/LPF-area lead to RV port. ECG showed a narrow QRS duration of 100ms, and RBBB pattern was disappeared (Figure 1(f)). Neither acute nor delayed complications were noted. After one months, the lead was fixed well and the parameters were ideal. LVEF decrease to 25%, left atrial diameter was 43 mm, left ventricular end-diastolic diameter was 57 mm.

Discussion

We report a case of CRT-D implantation in a patient with ischemic cardiomyopathy with cRBBB who underwent synchronization pacing of the left anterior and left posterior branches to shorten the QRS duration as the left ventricular lead implantation was difficult. This case should be interpreted in the context of established conduction system pacing. Current consensus statements define LBBAP as capture of the left septal sub-endocardial area with or without conduction-system capture and distinguish it from deep septal myocardial pacing.^7,8 In our case, the initial LBBAP attempt did not meet the available criteria for reliable LBB capture, and conventional coronary sinus LV lead placement was not feasible; therefore, the final configuration is best described conservatively as dual septal fascicular-area pacing rather than proven selective fascicular pacing.

In general, CRT is recommended for patients with complete left bundle-branch block at a higher grade than for those with right bundle-branch block, and the effect seems to be better, possibly because CRT not only improves electrocardiographic dyssynchrony, but also reduces mitral regurgitation caused by dyssynchrony of the anterior and posterior left ventricular papillary muscles. For patients without LBBB, the effect of CRT is not consistent. For cRBBB, CRT can restore electrical conduction delay (QRS wave narrowing), but the right ventricle is a volume reservoir/capacitance chamber, and correction of right-sided conduction delay alone may not restore left ventricular systolic function. What’s more, restoring septal and LV function by CRT increases workload in RV free wall and may explain why patients with RV failure respond poorly to CRT.^9,10 The indication for CRT-D in RBBB therefore requires caution. Patient-level meta-analysis data suggest that CRT benefit is substantially weaker in RBBB than in LBBB or nonspecific intraventricular conduction delay. In the present case, the decision was individualized because of ischemic cardiomyopathy, reduced LVEF, wide QRS, symptomatic HF despite medical therapy, and the need for defibrillator protection; nevertheless, the RBBB morphology limits the generalizability of this approach.

For this patient, coronary angiography showed that the LAD artery and the RCA were occluded, which supply the blood of the anterior septum, the anterior wall of the left ventricle, and the posterior septum, respectively. Echocardiography showed that the systolic motion of anterior septum and anterior wall of left ventricle was weakened notably, which was consistent with the site of vascular lesions. What’s more, these regions were also consistent with the regions distributed in the left anterior branch and the left posterior branch. When pacing on the posterior septal, though the ECG changed from cRBBB to incomplete right bundle branch block, the QRS duration was not shortened significantly. A previous case reported a patient underwent a mechanical aortic valve replacement, diagnosed with heart with complete atrioventricular block, and right ventricular (RV) escape rhythm. He was performed CRT with synchronization pacing of the LAF and the LPF, and the curative effect was satisfactory. ¹¹ In this case, the QRS duration was significantly shortened after resynchronization pacing of the LAF region and the LPF region, indicating that the lowest site of contraction in left ventricle may be included in the conduction way after left and right bundle branch pacing.

The QRS complex of the surface ECG is the integrated division vector of the left and right ventricles. After implantation, the pattern of right bundle branch block disappeared with a near normal narrow QRS duration, indicating that the conduction of the left and right ventricles was improved, and the right bundle branch of the original block was not participated in the way of conduction after pacing. Pacing the LV from multiple locations is an attractive method to solve the problems caused by ischemic scar or other areas of slow conduction velocity that reduce the efficacy of CRT by affecting the LV paced wave front. ¹² Thus, we considered that the site of right bundle branch block may be relatively high, and the low contraction of left ventricular maybe associated with ischemic scar. Pacing on the LAF region and the LPF region not only shortened the duration of the whole left ventricle, but also paced the right ventricle, which might be transmitted backward through the left bundle branch or spread through the ventricular septum to the distal area of the right bundle branch block. In other words, the mechanism for this implantation to correct the wide QRS wave in RBBB may be that the lead implantation site spans the block area, and paced on the downstream of the block area.

Pharmacological therapy should also be considered when interpreting clinical improvement. Contemporary guideline-directed medical therapy for HFrEF includes beta-blockers, renin-angiotensin system inhibition/ARNI, mineralocorticoid receptor antagonists, and SGLT2 inhibitors. Therefore, postoperative improvement should not be attributed solely to pacing unless medical therapy is stable.

The main limitations are the single-case design, the absence of complete intracardiac electrogram documentation, lack of output-dependent capture testing, short follow-up, and incomplete objective imaging data. These limitations mean that this report can only support feasibility, not efficacy.

Conclusion

The implication of this case is that in patients with ischemic cardiomyopathy, more adequate consideration needs to be given to whether conduction block is related to scarring or infarction in the diseased vascular supply territory at the time of CRT (-D) implantation. When conventional coronary sinus LV lead implantation and standard LBBAP are not feasible, dual septal fascicular-area pacing may be considered as an individualized bailout option. This case report should be interpreted cautiously until longer follow-up, device interrogation, and objective imaging data are available.

ORCID iD

Hao Liu https://orcid.org/0000-0002-4105-8474

Ethical considerations

This case report was approved by the Ethics Committee of The Second Affiliated Hospital, Guangxi Medical University [2024-KY(0494)].

Consent to participate

Written informed consent was obtained from the patient for participation in this case report.

Data Availability Statement

Original contributions presented in the case report are included in the article.*