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Relationship between electrocardiographic characteristics and subclinical left ventricular systolic dysfunction in isolated left bundle branch block patients

Cardiovascular Ultrasound volume 23, Article number: 7 (2025) Cite this article

Abstract

Background

Early identification of subclinical left ventricular (LV) systolic dysfunction (LVSD) in patients with isolated left bundle branch block (LBBB) and preserved LV ejection fraction (LVEF), termed LBBBpEF, is clinically important. Electrocardiography (ECG) has been proposed as a potential screening tool for detecting subclinical LVSD in LBBBpEF patients, but its effectiveness has not been fully validated. This study investigated the relationships between specific ECG characteristics and subclinical LVSD in LBBBpEF patients.

Methods

The study included 111 patients with LBBBpEF. Two-dimensional speckle-tracking echocardiography was used to derive the LV global longitudinal strain (LV GLS), with LV GLS>-20% indicating subclinical LVSD. The recorded ECG characteristics included heart rate, QRS duration, P-R duration, QRS morphology, T-wave morphology, the presence of QS patterns, and discordant LBBB, among others. The presence of QS patterns was defined as the absence of R-waves in lead V1 (or R-waves < 1 mm with a scale of 10 mm/mV). Discordant LBBB was defined as an inconsistency between the T wave and QRS complex in leads I, V5, and V6.

Results

Among the patients, 52 exhibited subclinical LVSD. Compared with those with normal LV systolic function, patients with subclinical LVSD had longer QRS durations, a higher frequency of QS patterns, and more instances of discordant LBBB. A QRS duration of 153 ms was identified as the optimal cut-off for detecting subclinical LVSD, with a sensitivity of 75.00% and specificity of 72.88%. The combination of QRS duration, the presence of QS patterns, and discordant LBBB produced the highest area under the curve of 0.82. Incorporating the presence of QS patterns and discordant LBBB into the QRS duration model increased the integrated discriminant index from 0.07 to 0.15.

Conclusions

QRS duration, the presence of QS patterns, and discordant LBBB are independent predictors of subclinical LVSD in patients with LBBBpEF. An integrated ECG assessment may offer a straightforward screening method for identifying subclinical LVSD in this population.

Graphical Abstract

This study explores the relationship between ECG characteristics and subclinical left ventricular systolic dysfunction (LVSD) in patients with left bundle branch block and preserved ejection fraction (LBBBpEF). Through two-dimensional speckle-tracking echocardiography (2DSTE) and ECG analysis, QRS duration, QS patterns, and discordant LBBB were identified as independent predictors of subclinical LVSD. The integrated ECG assessment offers a simple, effective tool for early detection of LVSD in LBBBpEF patients, with potential clinical applications in risk stratification and management.

Peer Review reports

Background

Left bundle branch block (LBBB), caused by abnormal electrical conduction in the His bundle or its derivatives, is frequently diagnosed via electrocardiogram (ECG), characterized by a widened QRS complex along with other ECG features [1, 2]. Patients with structural heart diseases, such as ischemic or nonischemic cardiomyopathy, often have LBBB, which is associated with a poor prognosis [3, 4]. However, LBBB may also occur in asymptomatic patients without structural heart disease, commonly known as isolated LBBB [5]. Previous studies reported that subclinical left ventricular (LV) systolic dysfunction (LVSD) might have already existed in some patients with isolated LBBB and preserved LV ejection fraction (LVEF, LBBBpEF) [6, 7]. Moreover, during long-term follow-up, these patients were more likely to develop substantial cardiac diseases and had a higher mortality rate than patients with LBBBpEF without LVSD were [8]. Therefore, early screening for subclinical LVSD in patients with LBBBpEF remains an unmet need in real clinical practice.

Two-dimensional speckle-tracking echocardiography (2DSTE) has become a sensitive tool for detecting insidious LVSD in patients with preserved LVEF [9, 10]. However, performing comprehensive echocardiography, including 2DSTE, is time-consuming and highly dependent on the clinician’s expertise, with high intra- and inter-observability. Typically, echocardiography is conducted only when a patient presents with clinical symptoms. Thus, echocardiography has intrinsic limitations for rapid screening of isolated LBBB patients in the absence of any clinical symptoms. In contrast, ECG is a more cost-effective, portable, and rapid screening tool for cardiac disease, especially in the community or in large-scale populations. Previous studies have shown that ECG might serve as an effective tool for screening heart failure (HF) and predicting a poor prognosis in patients with HF [11, 12]. However, whether ECG might be used as a screening tool to detect insidious LVSD in asymptomatic patients with LBBBpEF has not yet been fully established. Therefore, this study aimed to investigate the relationships between ECG characteristics and subclinical LVSD in patients with LBBBpEF.

Methods

The current study was a retrospective observational study with a cross-sectional design that was conducted at the First Hospital of China Medical University from March 2018 to December 2020. We selected asymptomatic participants with LBBB who exhibited on standard 12-lead electrocardiograms (ECG) at our hospital’s physical examination center, who also exhibited normal LVEF with no evidence of other cardiac conditions. The included patients with LBBB were considered to have primary conduction abnormalities. Normal LVEF was defined as LVEF ≥ 52% in men or ≥ 54% in women according to the recommendations of the American Society of Echocardiography (ASE) [13].

The exclusion criteria for the present study were as follows: (1) arrhythmias other than LBBB, such as ventricular preexcitation, atrioventricular conduction abnormalities, atrial fibrillation, pacing rhythms; (2) structural heart diseases, including valvular heart disease, congenital heart disease, and restrictive, hypertrophic, or dilated cardiomyopathy; (3) history of ischemic heart disease, including chronic stable angina, unstable angina, non-ST-segment elevation myocardial infarction, or ST-segment elevation acute myocardial infarction, as well as positive results on an exercise test; (4) systemic diseases, including severe kidney or liver dysfunction, abnormal thyroid function, malignancy, autoimmune diseases, hypertension, and diabetes mellitus; (5) poor quality of echocardiography or ECG derived images.

The study protocol was approved by the China Medical University Ethics Committee and was conducted following the ethical guidelines of the 1975 Declaration of Helsinki.

Electrocardiographic parameters

Baseline standard supine 12-lead ECGs were recorded at a calibration of 10 mm/mV and a paper speed of 25 mm/s with a standard General Electric Healthcare device (type MACC 5500; Waukesha, WI, USA). The ECGs were identified by two experienced cardiologists, and any disagreements with the ECG readings were resolved by the third objective cardiologist. LBBB was defined according to the following criteria: (1) QRSd ≥ 140 ms in men and ≥ 130 ms in women; (2) QS or rS in leads V1 and V2; (3) mid-QRS notching or slurring in ≥ 2 contiguous leads of V1, V2, V5, V6, I, and aVL [14]. The absence of R-waves in lead V1 (or R-waves < 1 mm with a scale of 10 mm/mV) was attributed to the presence of QS pattern [15, 16]. Discordant LBBB was defined as an inconsistent T wave and QRS complex in leads I, V5, and V6 [17]. Other ECG parameters, including heart rate, QRS duration, P-R duration, QTc duration, QRS morphology, and T-wave morphology, were also recorded (Fig. 1).

Fig. 1
figure 1

Examples of QRS and T-wave morphologies in left bundle branchblock (LBBB). Mid-QRS notching (a) or slurring (b) in lead V5; QS (c) or rS (d) patterns in lead V1; concordant (e) or discordant (f) T-wave and QRS complex in leads V5 or V6. Abbreviations: LBBB left bundle branch block

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Echocardiography

The echocardiographic examination was performed on each patient within the time frame of half an hour after the ECG, using a Vivid E9 ultrasound system (GE Healthcare, Waukesha, WI, USA) with an M5S transducer. Images were acquired with patients in the left lateral decubitus position during normal respiration. Echocardiographic images were stored in cine-loop format for offline analysis. Three to five consecutive cardiac cycles were recorded. All echocardiography images were acquired and measured on the basis of the recommendation of the ASE guidelines by two experienced cardiologists who were blinded to any clinical data.

LV end-diastolic volume (EDV), end-systolic volume (ESV), LVEF, and left atrial (LA) maximal volume were measured via biplane Simpson’s method. The mitral peak early diastolic flow velocity (E), mitral peak late diastolic flow velocity (A), and average mitral peak early diastolic annular velocity (E’) were measured. The LA volume indices (LA maximal volume corrected by body surface area), mitral E/A, and mitral E/E’ were calculated. The LV end-diastolic dimension (EDD), interventricular septum, and inferolateral wall thickness were measured in the parasternal long-axis view. LV mass and relative wall thickness (RWT) were calculated via the linear method, and the LV mass index (LVMI) corrected by the body surface area was obtained. Accordingly, LV geometries, including normal geometry, eccentric hypertrophy, concentric remodeling, and concentric hypertrophy, were identified on the basis of the LVMI and RWT.

Interventricular mechanical delay (IVMD) is the time difference between the onset of the QRS wave on a surface ECG and the start of blood ejection from the left ventricle (LV) and right ventricle (RV). This interval is measured using pulsed-wave Doppler in the outflow tracts of both ventricles.

Two-dimensional speckle-tracking echocardiography

Offline image analysis was performed using an EchoPAC 203 workstation (GE Healthcare) on apical views. The endocardial border of the LV was delineated manually, and the software automatically drew the LV epicardial border. The width of the regions of interest was adjusted manually to match the actual endocardial and epicardial borders. The software automatically tracked the 18 segments of myocardial speckle patterns in the LV frame by frame during the cardiac cycle. We measured the regional longitudinal strain (LS) of each LV wall. LV global LS (LV GLS) was calculated by averaging the values of all LV segments from apical views. LV GLS<-20% is considered normal, while LV GLS > -20% is regarded as subclinical LVSD. The LV septal LS was calculated by averaging six septal segments, and the LV lateral LS was obtained by averaging six lateral wall segments [13].

The time-to-peak systolic LS (Ts) was measured as the interval from the onset of the QRS to the peak negative systolic of LV LS throughout the cardiac cycle. Ts-SD is the standard deviation (SD) of Ts from 18 LV segments. Ts-Dif is the maximal difference in Ts between any 2 of 18 segments of the LV [18].

We randomly selected 30 subjects to assess the intra-observer and inter-observer variability of LV GLS measurements. Intra-observer variability was evaluated by performing repeated measurements on the original dataset under blinded conditions, with intervals of four weeks or longer between measurements. To assess inter-observer variability, a second experienced operator evaluated the loops without access to the original dataset.

Statistical analysis

Continuous variables were presented as the means ± standard deviations (SDs) or medians (interquartile ranges [IQRs]) on the basis of a normal distribution, and categorical variables were presented as percentages. Continuous variables were compared between two groups via the independent t test or the Mann–Whitney U test. Chi-square or Fisher exact test was used to compare the categorical variables. The variability of LV GLS measurements was assessed by calculating the intraclass correlation coefficient (ICC) for both intra-observer and inter-observer measurements [19]. ICCs equal or lower to 0.40 indicate poor to fair agreement, 0.41–­0.60 moderate, 0.61–­0.80 good, and over 0.80 excellent agreement. Univariate and multivariate logistic regression analyses were performed to investigate the associations between ECG characteristics and subclinical LVSD in patients with LBBBpEF. Variables for the multivariate model were selected on the basis of significant univariate associations and prior knowledge experience (age, sex, and LVEF) [20]. The associations were expressed as odds ratios (ORs) and 95% confidence intervals (CIs). Receiver operating characteristic (ROC) analysis was performed to evaluate the discrimination power of the selected variables or their combination for predicting subclinical LVSD in patients with LBBBpEF. The net reclassification improvement (NRI) and integrated discrimination index (IDI) were calculated to evaluate the incremental value of adding the selected parameters to the existing model. A 2-tailed p value of < 0.05 was considered statistically significant for all the parameters. All the statistical analyses were performed via the SPSS 22.0 software package (SPSS version 17, Chicago, IL, USA)(Fig. 2).

Fig. 2
figure 2

Flowchart illustrating the patient exclusion criteria for the current study. Abbreviations: ECG electrocardiogram, LBBB left bundle branch block, LVEF left ventricle ejection fraction

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Results

Clinical parameters of LBBBpEF

A total of 111 patients with LBBBpEF (59 females; mean age, 61.1 ± 10.7 years) were ultimately included in the final data analysis (Fig. 2). 52 patients (25 females; mean age, 61.0 ± 8.8 years) with LBBBpEF had subclinical LVSD, whereas the remaining patients (34 females; mean age, 61.2 ± 12.2 years) had normal LV systolic function. Age, sex, blood pressure, and lipid profile were similar in the 2 groups of patients with LBBBpEF (p > 0.05)(Table 1; Fig. 3).

Fig. 3
figure 3

Bull’s-eye maps showing regional longitudinal strain in LBBB patients with (a) and without (b) subclinical LVSD, and ROC analysis of ECG variables for identifying subclinical LVSD in LBBBpEF. (c) Abbreviations: LVSD left ventricle systolic dysfunction, LBBB left bundle branch block, QRS QRS duration, QS Presence of QS in lead V1, Dis-T T-wave orientation discordant with QRS complex in leads I, V5, and V6

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Echocardiographic characteristics of LBBBpEF

As expected, LBBBpEF patients with subclinical LVSD had worse LV GLS, LVEF, and E’ as well as greater LVMI, IVMD, Ts-SD, and Ts-Dif than those with normal systolic function. Moreover, LBBBpEF patients with subclinical LVSD were more likely to have eccentric hypertrophy than those with normal systolic function (Table 1). In addition, LBBBpEF patients with subclinical LVSD had a worse regional LS of each LV wall as well as more reduced septal LS and lateral LS than did those with normal systolic function (Table S1). Regardless of the LV systolic status, LBBBpEF patients presented more pronounced ventricular septal dyskinesia than dyskinesia in the LV lateral wall (Table 1; Fig. 3).

Table 1 Baseline and echocardiographic characteristics of the study population
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Consistency of LV GLS

The ICCs for LV GLS were 0.94 for intra-observer reliability and 0.93 for inter-observer reliability, indicating good consistency.

ECG characteristics of LBBBpEF

In patients with LBBBpEF, the QRS duration was longer in those with subclinical LVSD than in those without LVSD (159.6 ± 10.2 ms vs. 150.1 ± 12.1 ms, p < 0.001). However, there was no significant difference in PR or QTC duration between the two groups of patients with LBBBpEF (p > 0.05). Similarly, LBBBpEF patients with LVSD were more likely to have QS (73.1% vs. 44.1%, p = 0.002) and discordant LBBB (71.2% vs. 35.6%, p < 0.001) than were those with normal LV systolic function. However, there was no significant difference between the two groups of patients with LBBBpEF in terms of the R-wave notch in different leads (Table 2).

Table 2 ECG characteristics according to the presence of LVSD in LBBBpEF
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According to the univariable logistic regression analysis, longer QRS duration, the presence of QS, and discordant LBBB were associated with subclinical LVSD in patients with LBBBpEF. Moreover, even after correcting for age, sex, and LVEF in patients with LBBBpEF, QRS duration (p = 0.007, OR = 1.07, 95% CI: 1.02–1.13), the presence of QS (p = 0.003, OR = 0.19, 95% CI: 0.08–0.57), and discordant LBBB (p = 0.03, OR = 0.32, 95% CI: 0.11–0.91) remained significantly associated with LVSD (Table 3).

Table 3 Univariable and multivariable regression analysis of the ECG characteristics for LVSD in LBBBpEF
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The results of the ROC analysis for predicting subclinical LVSD in LBBBpEF patients were presented in Table 4; Fig. 3. QRS duration, the presence of QS, and discordant LBBB were significant predictors of subclinical LVSD in LBBBpEF patients. Notably, the area under the curve (AUC) of the QRS duration (AUC, 0.75) was greater than that of the presence of QS (AUC, 0.65) or discordant LBBB (AUC, 0.68) in identifying subclinical LVSD in LBBBpEF patients. Furthermore, the QRS duration of 153 ms was identified as the cut-off value to determine subclinical LVSD in patients with LBBBpEF., with a sensitivity of 75.00% and specificity of 72.88%.

Table 4 Receiver operating characteristic analysis of ECG variables to identify LVSD in LBBBpEF
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Moreover, adding QS and discordant LBBB to the QRS duration 0.75 (95% CI, 0.66–0.83) model increased the AUC for identifying subclinical LVSD to 0.78 (95% CI, 0.69–0.85) and 0.79 (95% CI, 0.71–0.86), respectively. The combination of QRS duration, presence of QS, and discordant LBBB had the highest AUC for identifying subclinical LVSD in LBBBpEF patients (AUC, 0.82; 95% CI, 0.74–0.89; p < 0.001), with a sensitivity of 80.77% and a specificity of 81.36%. In addition, when the presence of the QS feature was added to the risk classification model based on the existing model of QRS duration, the reclassification was improved (NRI = 0.50, p = 0.006; IDI = 0.07, p = 0.004). Furthermore, when the presence of QS was added to the joint risk classification model of QRS duration and discordant LBBB, the NRI and IDI were significantly improved (NRI = 0.55, p = 0.001; IDI = 0.15, p < 0.001; Table 5), suggesting that the integrated assessment of QRS duration, the presence of QS, and discordant LBBB performed better than any single parameter in evaluating subclinical LVSD in patients with LBBBpEF.

Table 5 LVSD reclassification of QRS duration, discordant LBBB and presence of QS
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Discussion

Early rapid screening for LVSD in patients with isolated LBBB and preserved LVEF is of important clinical significance. In this study, we used 2DSTE to assess subclinical contractile function in patients with LBBBpEF. This facilitated the evaluation of ECG characteristics. The principal findings of the study can be summarized as follows: (1) LBBB patients with subclinical LVSD had longer QRS durations, more presence of QS, and discordant LBBB. (2) QRS duration, the presence of QS, and discordant LBBB were independent predictors for identifying subclinical LVSD in LBBBpEF patients. (3) Among all single ECG parameters, the cutoff value of the QRS duration of 153 ms had the greatest AUC for determining LVSD in patients with LBBBpEF. (4) Compared with any single parameter, the combined assessment of QRS duration, QS presence, and inconsistent LBBB had greater AUC values for identifying subclinical LVSD in patients with LBBBpEF.

The prognosis of patients with isolated LBBB varies, with some patients potentially progressing to LVSD and even HF. The impact of isolated LBBB on LV function can be explained through several factors. Firstly, LBBB causes electrical activation and mechanical contraction to become desynchronized, which may impair the LV’s ability to fill and eject blood effectively [21]. Additionally, LBBB may lead to LV remodeling, asymmetric myocardial hypertrophy, and LV dilation. This asynchronous electrical activation can affect coronary blood flow, myocardial perfusion, oxygen demand, and glucose metabolism, ultimately resulting in deteriorating myocardial function [22]. Therefore, early identification of isolated LBBB patients with cardiac dysfunction is crucial in clinical practice. The LV GLS, derived from 2DSTE, is a recommended parameter for assessing overall LV systolic function. It can detect early subclinical changes in contractility and provide incremental information about LV function, even when LVEF remains within the normal range. However, 2DSTE is time-consuming and highly dependent on the clinician’s expertise, making it unsuitable for early and widespread screening of cardiovascular diseases. In contrast, ECG is a simple, cost-effective, and widely used tool for screening cardiovascular conditions. Research has already demonstrated that specific ECG characteristics can effectively identify both structural and functional heart diseases [23, 24].

Prior to this, several studies have shown that QRS duration was negatively associated with LVEF in patients with LBBB and that QRS duration was an independent risk factor for increased cardiac morbidity and mortality [25, 26]. The results of the current study were consistent with those of previous studies. One of the potential explanations for how the QRS duration affects LV systolic function in patients with LBBB might be that patients with LBBB have already had insidious underlying cardiac structural or functional abnormality regardless of clinical symptoms, which results in delayed electrical activation between cardiac myocytes and subsequently prolonged QRS duration [27]. Accordingly, prolonged QRS duration further deteriorates ventricular electrical activation and leads to mechanical contraction asynchrony, resulting in further worsening of cardiac contractile efficiency [28]. Moreover, asynchronous electrical activation and dyssynchronous contractile motion further affect coronary blood flow, myocardial perfusion, and subsequent glucose metabolism, which together contribute to the deterioration of myocardial contractile function [29, 30].

Previous studies have shown that the presence of QS is associated with cardiac systolic dysfunction and systolic desynchrony in patients with LBBB [31]. Consistent with previous studies, the present study also revealed that the presence of QS in lead V1 was more likely to be present in patients with LBBBpEF and LVSD than in their counterparts without LVSD, and it was an independent predictor of LVSD. Moreover, several studies have shown that the presence of QS in lead V1 in LBBB as a criterion for CRT candidate selection might be associated with a better response to CRT therapy [32, 33]. In addition, the initial r wave of ≥ 1 mm in V1 leads has been considered a marker of residual conduction from the left to the right ventricular septum in patients with LBBB. Thus, the presence of QS and absent r wave (or r wave < 1 mm for a scale of 10 mm/mV) in lead V1 suggest a lack of residual conduction [31]. Proximal LBBB occurs in patients with QS, and activation of the ventricular septum occurs through the right bundle branch and further activates the LV during myocyte-to-myocyte activation [34]. Compared with LBBB patients with residual conduction, those with QS have a more significant electrical activation delay and mechanical contraction asynchrony, resulting in less effective myocardial work and being more likely to present with LVSD.

Moreover, the present study further classified patients with LBBBpEF into two categories according to the consistency of the T-wave in leads I, V5, and V6 with the direction of the QRS complex, namely, concordant LBBB (T-wave orientation concordant with the QRS complex) and discordant LBBB (T-wave orientation discordant with the QRS complex) [35]. Prior studies have shown that discordant LBBB is associated with more severe coronary artery disease and HF and a worse prognosis than concordant LBBB is [11, 36, 37]. In addition, the incidence of ventricular tachycardia/ventricular fibrillation/death was greater in patients with discordant LBBB than in those with concordant LBBB [38]. Similarly, in the present study, the discordant type of LBBB was more likely to be present in LBBBpEF patients with subclinical LVSD than in those without subclinical LVSD. When the QRS axis is normal, an abnormal T-axis direction usually indicates a primary repolarization abnormality, which might also be due to underlying myocardial ischemia or early cardiomyopathy, leading to endocardial damage and resulting in a misalignment of repolarization [37].

Finally, the present study incorporated QRS duration, the presence of QS, and discordant LBBB simultaneously in the model, which significantly improved both the accuracy and the predictive value of subclinical LVSD in patients with LBBBPEF. Overall, these findings suggest that ECG might serve as a rapid, effective, and cost-effective clinical screening diagnostic method for detecting subclinical LVSD in patients with LBBBpEF, aiming to improve the efficiency of daily clinical practice.

Limitations

Our study has several limitations. First, the sample size was relatively small, and there may be selection bias. Future studies should incorporate multi-center designs and larger sample sizes to validate these findings. Second, this study was a retrospective cross-sectional analysis that collected data at a specific time point, lacking long-term or regular follow-up. Consequently, we were unable to assess the impact of temporal changes on the outcomes, nor can we conduct an accurate causal assessment. Additionally, since this is a retrospective study, the ECG diagnostic criteria used were those in effect at the time, rather than the latest standards. Furthermore, date on the duration of LBBB burden in participants were unavailable, which may affect the results. Nevertheless, this study is the first to investigate the association between ECG characteristics and subclinical left ventricular systolic dysfunction in patients with LBBBpEF, highlighting the need for further validation in future research.

Conclusion

In conclusion, ECG characteristics, including QRS duration, the presence of QS, and discordant LBBB, are independent predictors of subclinical LVSD in patients with LBBBpEF. The integrated ECG assessment might serve as a simple, effective, and rapid screening tool for predicting subclinical LVSD in patients with LBBBpEF.

Data availability

No datasets were generated or analysed during the current study.

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Funding

This work was supported by the National Natural Science Foundation of China (grant number U21A20387), and the Department of Science and Technology of Liaoning Province supports China Medical University’s high-quality development science and technology funding program (grant number 2023JH2/20200096).

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Authors and Affiliations

  1. Department of Cardiovascular Ultrasound, First Hospital of China Medical University, Shenyang, Liaoning, China

    Guangyuan Li, Yonghuai Wang, Bo Pang, Jun Yang & Chunyan Ma

  2. Clinical Medical Research Center of Imaging in Liaoning Province, Shenyang, Liaoning, China

    Guangyuan Li, Yonghuai Wang, Bo Pang, Jun Yang & Chunyan Ma

Authors
  1. Guangyuan Li
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Contributions

All the authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Guangyuan Li and Bo Pang. The first draft of the manuscript was written by Guangyuan Li. Yonghuai Wang and Jun Yang revised the manuscript. Chunyan Ma agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All the authors read and approved the final manuscript.

Corresponding author

Correspondence to Chunyan Ma.

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Ethical approval

This study was performed in accordance with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of China Medical University (Reference number: AF-S0P-07-1.1-01).

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Informed consent was obtained from all individual participants included in the study.

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All the participants gave their consent for publication.

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Li, G., Wang, Y., Pang, B. et al. Relationship between electrocardiographic characteristics and subclinical left ventricular systolic dysfunction in isolated left bundle branch block patients. Cardiovasc Ultrasound 23, 7 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12947-025-00342-6

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Keywords

Cardiovascular Ultrasound

ISSN: 1476-7120

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