Left Bundle Branch Area Pacing as a Rescue Strategy After Failed Cardiac Resynchronization Therapy in a Patient With Persistent Left Superior Vena Cava, Absent Coronary Sinus Branches, After Bilateral Maze Procedure: A Case Report

Introduction

Conduction system pacing (CSP) is a physiological pacing strategy that activates the ventricles through the native His–Purkinje network [1]. Placement of a coronary sinus (CS) lead for conventional cardiac resynchronization therapy (CRT) can fail in patients with complex venous anatomy, particularly in the presence of persistent left superior vena cava (PLSVC), which frequently drains into a large, funnel-shaped coronary sinus lacking suitable lateral branches.

PLSVC is the most common congenital anomaly of systemic venous return, occurring in approximately 0.3% to 0.5% of the general population and up to 10% of patients with congenital heart disease [2]. In such cases, CSP provides a practical alternative for achieving ventricular resynchronization [3].

Case Report

A 78-year-old man with a history of mitral valve replacement with a bioprosthesis, tricuspid valve repair, and a bilateral Maze procedure (2020) was followed for chronic heart failure with reduced left ventricular ejection fraction (LVEF 35%). On January 27, 2025, he was indicated for implantation of a cardiac resynchronization pacemaker (CRT-P, SJM Allure RF) for sick sinus syndrome with tachy-brady arrhythmia, with an LVEF of 35% and left bundle branch block (LBBB) morphology with a QRS duration of 190 ms. The NT-proBNP level at that time was 4636 ng/L. The timeline of the patient’s clinical course is presented in Figure 1.

During the procedure on January 27, 2025, bilateral venography revealed a persistent left superior vena cava. A biventricular pacemaker (Abbott Allure RF) was implanted with a right atrial lead positioned in the right atrial appendage and a ventricular lead placed in the right ventricular septum. The left ventricular port was capped with the prospect of future surgical implantation of an epicardial bipolar Abbott Myodex lead (model 1084T). Computed tomography was not performed, as it is not routinely indicated in this setting and was not expected to provide additional clinically relevant information.

Following ventricular lead implantation, high pacing thresholds and a persistently wide QRS complex were observed, with subsequent deterioration of left ventricular function and a decline in LVEF to 25% by August 12, 2025. The NT-proBNP level increased to 7741 ng/L. The patient subsequently met the indication criteria for implantable cardioverter defibrillator (ICD) implantation according to current guidelines, specifically the 2023 focused update of the 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure [4].

During the procedure on September 12, 2025, venography revealed venous drainage into a markedly dilated coronary sinus with a wide main trunk and no identifiable lateral branch (Figure 2). Because no suitable coronary sinus branch could be identified and conventional coronary sinus cannulation was not feasible, conduction system pacing (CSP) was selected as an alternative strategy for left ventricular activation. Using a right subclavian approach, a right atrial lead (Tendril 2088TC, Abbott) was positioned in the right atrial appendage, and a defibrillation lead (Durata 7122Q, Abbott) was actively fixed in the apical septal region of the right ventricle. The defibrillation lead served solely for defibrillation, while ventricular pacing was provided by a bipolar lead (QuickFlex 1258T). The lead was advanced to the basal interventricular septum under fluoroscopic guidance and progressively screwed into the septum while monitoring the paced QRS morphology (Figure 3). During lead advancement, a transition from a left bundle branch block-like morphology to a right bundle branch block-like morphology (R-prime pattern) in lead V1 was observed, consistent with engagement of the left bundle branch area. Non-selective left bundle branch area capture was achieved. Periprocedural electrical parameters were excellent: paced QRS duration 120 ms, V6 RWPT 75 ms, V1–V6 Δ = 31 ms, capture threshold 0.5 V at 0.5 ms, impedance 340 Ω, and R-wave amplitude > 12 mV.

Following successful right-sided ICD implantation with ventricular pacing provided by left bundle branch area pacing, the previously implanted left-sided cardiac resynchronization therapy pacemaker (CRT-P) system was completely extracted using simple traction, as the leads had been in place for less than 1 year (Figure 4). A chest X-ray focused on the implanted leads obtained on postoperative day 1 is shown in Figure 5. An electrocardiogram (ECG) demonstrating left bundle branch area pacing (LBBAP) is shown in Figure 6.

At the 2-month follow-up visit on November 5, 2025, the patient remained clinically stable (NYHA class II), without angina, syncope, or heart failure decompensation. Echocardiography demonstrated improvement of left ventricular ejection fraction to 30–35%. The ICD system with LBBAP (Unify Assura) was functioning in DDDR mode with a lower rate limit of 60 bpm. Device parameters were stable: RA impedance 400 Ω, RV impedance 410 Ω (defibrillation function), LV impedance (CSP lead) 340 Ω, pacing threshold 0.5 V at 0.5 ms, and R-wave sensing > 12 mV. Paced QRS duration was 120 ms. Device diagnostics showed atrial pacing 90%, LBBAP pacing 94%, and atrial tachyarrhythmia/atrial fibrillation burden < 1%.

Discussion

The 2023 HRS/APHRS/LAHRS guideline on cardiac physiologic pacing recognizes conduction system pacing as an acceptable and effective strategy in situations where conventional coronary sinus lead placement is not feasible or fails to achieve adequate resynchronization [5]. It can help minimize the adverse hemodynamic consequences associated with long-term right ventricular pacing, including pacing-induced dyssynchrony, functional deterioration, and pacing-induced cardiomyopathy [6].

To the best of our knowledge, this case represents a unique combination of persistent left superior vena cava, absence of suitable coronary sinus branches, and prior bilateral Maze procedure, successfully managed using right-sided ICD implantation with left bundle branch area pacing.

Conclusions

Persistent left superior vena cava (PLSVC) is encountered in approximately 0.5% of patients undergoing cardiac device implantation and can complicate implantation of cardiac implantable electronic devices due to altered venous drainage and dilation of the coronary sinus. In such situations, conduction system pacing (CSP) is an alternative strategy to conventional biventricular pacing, and its use has been increasing as device therapy moves toward more individualized approaches [7].

Rodriguez-Queralto et al described successful conduction system pacing in a patient with persistent left superior vena cava in whom conventional CRT implantation was not feasible. In that report, a modified implantation approach enabled physiological ventricular activation and clinical improvement [8].

Left bundle branch area pacing (LBBAP) is generally considered technically easier and more stable over time than His bundle pacing, typically providing higher R-wave amplitudes and lower and more durable capture thresholds. By directly engaging the left bundle branch region, LBBAP can effectively restore physiological ventricular activation in patients with left bundle branch block or pacing-induced dyssynchrony [9].

These findings suggest that LBBAP can serve not only as a rescue strategy when coronary sinus lead implantation fails but also as a potential primary pacing strategy in patients with persistent left superior vena cava and unfavorable coronary sinus anatomy.