Restoration of Cardiac Function in Left Bundle Branch Block-Induced Cardiomyopathy via Conduction System Pacing: A Case Report

Introduction

The prevalence of left bundle branch block (LBBB) in the general population is reported to range from 0.1% to 0.8%, with incidence typically increasing with age [1]. Left bundle branch block-induced cardiomyopathy (LIC) is not classified among the unclassified cardiomyopathies or nongenetic forms of dilated cardiomyopathy (DCM) [2]. Patients with LIC exhibit a continuous deterioration of cardiac function, ultimately progressing to a clinical phenotype resembling DCM [3]. This subtype of cardiomyopathy, solely induced by LBBB, is referred to as LIC and is defined by the following criteria: 1) a history of LBBB for more than 1 year; 2) left ventricular ejection fraction (LVEF) greater than 50% at the time of LBBB diagnosis; 3) a progressive decline in LVEF to less than 40% and the development of New York Heart Association (NYHA) functional class II to IV; 4) the absence of any other identifiable cause for cardiomyopathy; and 5) echocardiographic evidence of dyssynchrony (interventricular mechanical delay greater than 40 ms; aortic pre-ejection delay greater than 140 ms; septal to lateral wall delay greater than 65 ms) [4]. LBBB on 12-lead electrocardiography (ECG) is defined as a QRS duration greater than 130 ms in women and greater than 140 ms in men, along with the presence of mid-QRS notching or slurring in at least 2 consecutive leads (I, aVL, V1, V2, V5, or V6) [4,5]. For the treatment of patients with LIC, timely correction of LBBB may lead to a complete reversal of symptoms and return of cardiac function [6]. Cardiac resynchronization therapy (CRT) effectively resynchronizes electrical and mechanical coupling, improves chronic left ventricular systolic dysfunction, reverses left ventricular remodeling, and enhances survival rates in patients with an LVEF of 35% or lower [7]. Liu et al reported a case of LIC characterized by an LVEF of 15% and LBBB, which were ultimately reversed through His bundle pacing (HBP) [8]. Currently, conduction system pacing (CSP) has been validated as an alternative effective strategy for managing this specific subtype of cardiomyopathy [9,10].

This report describes a 57-year-old woman diagnosed with LIC following the onset of LBBB over the course of 1 year. Remarkably, her LVEF improved to nearly normal levels after undergoing CSP.

Case Report

Our patient was a 57-year-old retired woman who had consistently undergone health checkups. A baseline ECG recorded on December 4, 2020, indicated a narrow QRS duration of 78 ms (Figure 1A). An echocardiogram performed on July 14, 2021 demonstrated a preserved LVEF of 55%. In January 2022, she began to experience progressive dyspnea and a decrease in exercise tolerance. Further evaluation at another hospital resulted in a diagnosis of DCM. Guideline-directed medical therapy (GDMT) was initiated, which included sacubitril/valsartan 50 mg twice daily, spironolactone 20 mg once daily, furosemide 20 mg once daily, and metoprolol succinate extended-release 47.5 mg once daily.

Despite 6 months of optimized medical therapy, the patient’s symptoms persisted, leading to her referral to our institution. Her family and medical history were unremarkable, and she denied any illicit substance use. Upon examination, her heart rate was recorded at 72 bpm, and her blood pressure was measured at 103/62 mmHg, with no significant murmurs detected during cardiac auscultation. Laboratory test results, listed in Table 1, revealed no notable abnormalities, and cardiac biomarkers (MYO, CK-MB, TNI) were within normal limits, effectively ruling out acute myocardial injury.

The ECG demonstrated sinus tachycardia with complete LBBB, a QRS duration of 132 ms, and mid-QRS notching/slurring in leads I, aVL, V5, and V6 (Figure 1B). An echocardiogram performed on August 15, 2022, indicated a reduced LVEF of 38% (Figure 2A). Holter monitoring revealed sinus rhythm with complete LBBB, an average heart rate of 76 beats per minute, and a total of 104 469 heartbeats. Occasional premature ventricular contractions were noted, amounting to 12 isolated events.

The patient exhibited progressive dyspnea and palpitations over the course of a year, accompanied by a decline in LVEF. Although initial ECG and echocardiography results were normal, the subsequent development of LBBB coincided with a deterioration in left ventricular systolic dysfunction. This temporal association suggests a potential LIC; however, other etiologies, including infiltrative, hypertensive, or idiopathic DCM, must also be considered. To evaluate disease progression and identify the underlying cause, a comprehensive diagnostic workup was conducted. Tissue synchronization imaging demonstrated delayed peak systolic contraction in the basal to mid-segments of the anterior and inferior interventricular septum, inferior wall, and basal to mid-segments of the inferolateral wall (Figure 2B), with the latest delay observed at 460 ms (Figure 2C). The posterior-to-septal wall delay was measured at 134 ms, resulting in a cardiac synchrony index of 9.98%. Coronary angiography indicated normal coronary arteries.

Cardiac magnetic resonance imaging (CMRI) revealed an LVEF of 31% (Video 1), interventricular dyssynchrony (Video 2), and thinning of the interventricular septum (Figure 3A), with normal wall thickness and no gadolinium-delayed enhancement (Figure 3B). These results are consistent with alterations observed in LIC.

The patient’s LVEF was recorded at below 35% in the context of LBBB, thereby fulfilling the criteria for CRT [11]. Considering cost-effectiveness, CSP was proposed as an alternative. After a shared decision-making process, the patient chose to proceed with CSP. The procedure was conducted as previously described [12–14]. A SelectSecure 3830 pacing lead (Medtronic, Inc., Minneapolis, MN, USA) was delivered through a C315 delivery sheath (Medtronic, Inc.) and positioned at the interventricular septum under fluoroscopic guidance (Figure 4). At a pacing rate of approximately 60 beats per minute, CSP successfully corrected the LBBB, reducing the QRS duration to 95 ms. The acute pacing threshold was recorded at 1.5 V with a pulse width of 0.4 ms.

Serial echocardiograms documented the natural progression of the response to resynchronization therapy utilizing CSP. The LVEF increased to 50% at 4 months and further to 54% at 6 months (Figure 2D). The left ventricular longitudinal strain ranged from −4.8% to −29.1% (Figure 2E), while the time to peak left ventricular systolic strain varied between 217 ms and 369 ms (Figure 2F). The cardiac synchrony index improved to 2.24%, which was accompanied by significant enhancements in exercise capacity and NYHA class after 6 months. The interventricular dyssynchrony delay was reduced to 35 ms, with a QRS duration of 82 ms (Figure 5A). Notably, a reappearance of the LBBB was observed following the prolongation of the atrioventricular interval (Figure 5B). At the most recent follow-up on February 24, 2025, the patient remained clinically stable. Electrocardiography indicated a QRS duration of 82 ms, and transthoracic echocardiography revealed an LVEF of 56%. Pacemaker interrogation showed a pacing threshold of 0.625 V. Changes in echocardiographic and cardiac synchrony parameters before and after CSP are presented in Table 2. The timeline of diagnosis and interventions is illustrated in Figure 6.

Our final diagnosis was LBBB-induced cardiomyopathy and heart failure with reduced ejection fraction, successfully treated with CSP.

Discussion

We described the case of a woman who developed LBBB. This development, on ECG, was followed by a progressive reduction in LVEF. Concurrent cardiac evaluation demonstrated both interventricular and intraventricular mechanical dyssynchrony. CMRI failed to identify an alternative etiology for the cardiomyopathy. Taken together, these findings fulfill the diagnostic criteria for LIC as proposed by Ponnusamy et al [4]. Normalization of post-CSP cardiac function provided diagnostic confirmation of LBBB-induced cardiomyopathy. The relationship between cardiomyopathy and LBBB remains a topic of ongoing debate [15]. Ernest et al proposed that LBBB and cardiomyopathy may interact through multiple mechanisms, including direct causation, shared pathological pathways, secondary triggering, and bidirectional amplification [16]. Based on the extent of LBBB involvement in cardiomyopathy, these cases are classified as follows: LIC, LBBB non-ischemic cardiomyopathy, or ischemic cardiomyopathy with LBBB [17–19].

The patient had no history of syncope, and Holter monitoring revealed no episodes of ventricular tachycardia. CMRI showed no LGE, indicating the absence of myocardial fibrosis. The patient’s LVEF was below 35%, which could make prophylactic implantable cardioverter-defibrillator (ICD) implantation a potential option. However, her short disease history and the possibility of reversing cardiac dysfunction by correcting the LBBB contraindicated ICD implantation [11]. This underscores the importance of prioritizing personalized care based on the patient’s individual characteristics and clinical outcomes, rather than rigidly adhering to guidelines and traditional dogmas [7].

CSP may serve as an effective treatment for LIC, demonstrating significant functional recovery in patients with LIC [20]. While this aligns with previous findings indicating that certain patients with LBBB and left ventricular systolic dysfunction may benefit from early electrical resynchronization, the generalizability of this observation remains uncertain [21].

While biventricular pacing (BiVP) is well-established in CRT, it faces considerable limitations, including anatomical constraints, suboptimal resynchronization, and a non-response rate of approximately 30% [11]. Liu et al [8] reported a case involving a 61-year-old woman with a 4-year history of left ventricular systolic dysfunction and LBBB, characterized by a QRS duration of 172 ms. Following HBP, her QRS duration decreased to 120 ms, and her LVEF improved to 50% within 3 months. LIC was diagnosed based on the therapeutic response observed. Notably, the patient did not undergo ICD implantation. Intracardiac electrograms confirmed the presence of His bundle-ventricular block. However, the case report was limited by the absence of data from cardiac synchronization imaging and CMRI. CSP includes HBP and left bundle branch area pacing (LBBAP), which have emerged as more physiological alternatives to conventional right ventricular pacing [9]. CSP aims to restore synchronized ventricular activation and preserve cardiac function. Although HBP is considered the most physiological pacing method, its clinical applicability is constrained by technical challenges, including low implantation success rates, high and unstable pacing thresholds, and diminished ventricular sensing over time [22]. Furthermore, long-term safety data regarding CSP remain limited. While LBBAP is generally easier to perform and more stable than HBP, it requires deep septal lead implantation, which raises concerns regarding complications such as lead perforation, fibrosis at the fixation site, and challenges in lead extraction or replacement [23]. Variations in implantation techniques or excessive lead tension may also result in unintended consequences.

Tricuspid valve regurgitation is a significant consideration in CSP [24]. Leads that traverse the tricuspid valve can disrupt leaflet coaptation, potentially leading to or exacerbating tricuspid valve regurgitation [25]. This concern, already acknowledged with right ventricular pacing leads, may be even more pertinent in CSP due to lead looping or fibrosis near the tricuspid valve apparatus. The long-term effects of CSP on tricuspid valve function, particularly in patients with pre-existing valve disease, remain under investigation.

We report a case involving a woman diagnosed with LIC, who experienced a rapid deterioration of cardiac function within 1 year. Cardiac synchronization imaging confirmed the presence of ventricular dyssynchrony attributed to LBBB, while CMRI revealed a typical septal flash. Postoperative evaluations indicated that CSP successfully restored both intraventricular and interventricular synchrony, resulting in a reversal of cardiac dysfunction. However, it is noteworthy that intracardiac electrogram data during the procedure were not available. Although surface ECG findings were consistent with CSP – particularly HBP – direct evidence confirming the correction of LBBB through HBP was lacking.

Conclusions

LIC is a newly recognized condition characterized by the development of LBBB, which subsequently leads to left ventricular dysfunction and mechanical dyssynchrony. We present a case of LIC with a symptom duration of less than 1 year, which demonstrated significant clinical improvement following CSP, underscoring the critical importance of early intervention.