ECG Patterns Identify Early Left Ventricular Dysfunction in Asymptomatic Bundle Branch Block

Standard electrocardiogram markers can identify early subclinical left ventricular systolic dysfunction in asymptomatic patients diagnosed with isolated left bundle branch block who retain a preserved ejection fraction, according to findings from a retrospective observational study conducted by researchers at the First Hospital of China Medical University. Left bundle branch block, a condition originating from abnormal electrical conduction within the His bundle or its derivative branches, manifests on surface electrocardiography as a widened QRS complex alongside characteristic morphological alterations. While the condition frequently appears alongside structural cardiovascular disorders such as ischemic or nonischemic cardiomyopathies, where it denotes an unfavorable clinical prognosis, it can also manifest in asymptomatic individuals displaying no overt structural anomalies. In this subset of patients with preserved left ventricular ejection fraction, insidious contractile impairments may already be present and silently advancing. When subclinical systolic dysfunction remains undetected over extended periods, affected individuals face an increased likelihood of progressing toward substantial cardiac diseases and experiencing higher long-term mortality rates compared to peers whose systolic function remains preserved.

Although two-dimensional speckle-tracking echocardiography serves as an established and highly sensitive imaging method to detect insidious systolic failure by quantifying myocardial strain, widespread clinical deployment faces notable barriers. Comprehensive echocardiographic assessments, particularly those relying on speckle tracking, require extensive examination time, rely heavily on operator expertise, and demonstrate variability between different observers and across repeated readings. Consequently, detailed imaging examinations are overwhelmingly performed only after patients present with overt cardiovascular symptoms, limiting their practical utility as rapid initial screening instruments for asymptomatic populations. By comparison, standard twelve-lead electrocardiography represents a widely available, highly portable, rapid, and cost-effective modality suitable for broad community-level screening. Prior clinical research established that surface electrocardiograms can aid in screening for heart failure and forecasting adverse outcomes in symptomatic cohorts; however, the explicit ability of electrocardiographic characteristics to uncover hidden myocardial contractile deficits among individuals presenting with isolated left bundle branch block and preserved ejection fraction had not been systematically validated.

To investigate whether specific electrocardiographic indices correlate with insidious contractile impairment, the investigative team selected 111 asymptomatic participants evaluated at their medical center between March 2018 and December 2020. The retrospective cross-sectional cohort included 59 female patients, and the overall study population presented a mean age of 61.1 ± 10.7 years. All enrolled subjects exhibited isolated primary conduction abnormalities satisfying formal criteria for left bundle branch block: a QRS duration of at least 140 milliseconds in men or at least 130 milliseconds in women, QS or rS patterns in leads V1 and V2, and mid-QRS notching or slurring spanning at least two contiguous leads among V1, V2, V5, V6, I, and aVL. Crucially, all participants retained normal baseline left ventricular ejection fraction, established in accordance with American Society of Echocardiography guidelines as an ejection fraction of at least 52 percent in male patients and at least 54 percent in female patients, without any clinical evidence of underlying cardiac pathology.

Rigorous clinical exclusion criteria were enforced during patient enrollment to ensure that observed myocardial alterations stemmed strictly from primary conduction pathology rather than secondary systemic or structural disease. Investigators excluded individuals displaying alternative arrhythmias, including ventricular preexcitation, atrioventricular conduction blockages, atrial fibrillation, or artificial pacing rhythms. The presence of overt structural abnormalities, such as valvular pathology, congenital cardiac defects, or restrictive, hypertrophic, or dilated cardiomyopathies, warranted immediate study exclusion. Furthermore, patients with documented histories of ischemic heart disease, encompassing chronic stable angina, unstable angina, non-ST-segment elevation myocardial infarction, ST-segment elevation acute myocardial infarction, or positive results on provocative exercise testing, were systematically omitted. Concomitant systemic illnesses capable of influencing ventricular remodeling—including severe hepatic or renal dysfunction, thyroid abnormalities, active malignancies, autoimmune diseases, hypertension, and diabetes mellitus—also led to exclusion, alongside any imaging examinations of inadequate diagnostic quality.

Within thirty minutes of obtaining baseline standard twelve-lead electrocardiographic tracings recorded at a standard paper speed of 25 millimeters per second and calibration of 10 millimeters per millivolt, each participant underwent comprehensive transthoracic echocardiography using dedicated ultrasound platforms. Myocardial mechanics were evaluated through offline two-dimensional speckle-tracking analysis across apical acoustic windows, tracking eighteen individual ventricular myocardial segments frame by frame throughout the cardiac cycle. Left ventricular global longitudinal strain was computed by averaging the values of all eighteen segments, with a strain value greater than minus twenty percent serving as the established diagnostic threshold indicating subclinical left ventricular systolic dysfunction. To ensure measurement fidelity, intra-observer and inter-observer reliability assessments performed across thirty randomly chosen participants yielded intraclass correlation coefficients of 0.94 and 0.93 respectively, demonstrating excellent analytical consistency across blinded evaluations.

Electrocardiographic analyses evaluated heart rate, PR interval duration, QRS duration, corrected QT interval, specific QRS morphologies, and repolarization patterns across all leads. Two specialized morphological configurations received targeted evaluation: the presence of a QS pattern and the occurrence of discordant left bundle branch block. The presence of a QS pattern was defined by the complete absence of R-waves in lead V1, or the appearance of minimal initial R-waves measuring less than 1 millimeter under a 10 millimeter per millivolt scale. Discordant left bundle branch block was defined by an inconsistency in orientation between the T wave and the dominant QRS complex across leads I, V5, and V6. Across the overall cohort of 111 patients, speckle-tracking echocardiography identified subclinical systolic dysfunction in 52 individuals, while the remaining 59 patients exhibited preserved longitudinal contractile function. Baseline demographic characteristics and clinical profiles, including age, sex distribution, resting blood pressure, and circulating lipid measurements, showed no statistically significant differences between the two functional groups.

Comparative evaluations revealed distinct structural and electrical divergences between the patient cohorts. Functionally impaired participants demonstrated significantly longer mean QRS durations than those exhibiting normal systolic function, averaging 159.6 ± 10.2 milliseconds compared to 150.1 ± 12.1 milliseconds. While PR intervals and corrected QT durations showed no meaningful differences between the groups, morphological features exhibited pronounced divergence. Specifically, patients harboring subclinical dysfunction presented a significantly higher prevalence of QS patterns in lead V1, observed in 73.1 percent of impaired patients versus 44.1 percent of controls. Similarly, discordant left bundle branch block occurred in 71.2 percent of those with subclinical dysfunction compared to only 35.6 percent among preserved systolic controls. Echocardiographic parameters corroborated these mechanical discrepancies: patients with subclinical dysfunction exhibited lower ejection fractions, worse global longitudinal strain, greater interventricular mechanical delays, increased mechanical dispersion, and a higher prevalence of eccentric ventricular hypertrophy.

Univariable logistic regression established that prolonged QRS duration, the presence of QS patterns, and discordant repolarization were each significantly associated with insidious left ventricular systolic impairment. Following multivariable adjustments incorporating age, biological sex, and resting left ventricular ejection fraction, all three electrocardiographic markers retained independent predictive significance. In multivariable models, prolonged QRS duration yielded an odds ratio of 1.07 with a 95 percent confidence interval spanning 1.02 to 1.13. The presence of a QS pattern produced an odds ratio of 0.19 with a 95 percent confidence interval of 0.08 to 0.57, and discordant left bundle branch block demonstrated an odds ratio of 0.32 with a 95 percent confidence interval of 0.11 to 0.91, confirming that each electrocardiographic variable contributes independent prognostic information regarding subclinical myocardial compromise.

Receiver operating characteristic curve analyses highlighted the diagnostic discrimination provided by individual parameters and integrated models. Evaluated as an isolated marker, QRS duration yielded an area under the curve of 0.75, which exceeded the discrimination achieved by isolated QS patterns, which recorded an area of 0.65, or discordant morphology, which demonstrated an area of 0.68. Within this cohort, a QRS duration threshold of 153 milliseconds emerged as the optimal single cut-off value for detecting subclinical systolic impairment, providing a diagnostic sensitivity of 75.00 percent alongside a specificity of 72.88 percent. Diagnostic accuracy improved progressively when combining parameters: incorporating QS patterns alongside QRS duration elevated the area under the curve to 0.78, while combining discordant repolarization with QRS duration yielded an area of 0.79.

The greatest overall discriminatory capability emerged from a fully integrated diagnostic assessment that combined QRS duration, QS morphology, and discordant left bundle branch block simultaneously. This combined triple-marker model achieved an area under the receiver operating characteristic curve of 0.82, accompanied by a 95 percent confidence interval ranging from 0.74 to 0.89. The integrated model yielded an enhanced diagnostic sensitivity of 80.77 percent and a specificity of 81.36 percent. Risk reclassification metrics further substantiated the incremental predictive utility of combining these parameters. Incorporating QS pattern evaluation into a baseline model founded on QRS duration alone generated significant reclassification gains, reflected by a net reclassification improvement of 0.50 and an integrated discrimination index of 0.07. When the presence of a QS pattern was integrated into a joint model comprising both QRS duration and discordant morphology, discriminatory performance improved even more substantially, producing a net reclassification improvement of 0.55 and an integrated discrimination index of 0.15.

The underlying pathophysiological mechanisms linking these specific surface conduction features to contractile deficits reflect progressive mechanical and metabolic derangements. Left bundle branch block inherently disrupts synchronized electrical activation, which precipitates mechanical dyssynchrony between the interventricular septum and lateral ventricular walls, ultimately impairing left ventricular filling and ejection dynamics. Prolonged QRS duration directly mirrors worsening delays in inter-myocyte electrical transmission, which intensifies mechanical dyssynchrony and degrades overall contractile efficiency. In turn, asynchronous activation compromises local coronary blood flow, impairs regional myocardial perfusion, and disrupts normal glucose metabolism. Concurrently, an absent initial R-wave in lead V1 signifies an absence of residual septal conduction from left to right; in such cases, septal activation occurs exclusively via the right bundle branch through slower myocyte-to-myocyte transmission, exacerbating mechanical delay. Meanwhile, discordant T-wave morphology indicates abnormal ventricular repolarization, often reflecting underlying subendocardial ischemic stress or early cardiomyopathic remodeling.

Despite these encouraging findings, several methodological limitations characterize the study design and warrant cautious interpretation. The retrospective single-center framework involved a modest sample size of 111 participants, introducing potential selection biases that necessitate future validation within expansive, prospective, multi-center cohorts. Because patient data were captured at a single cross-sectional time point without longitudinal follow-up, researchers could not evaluate temporal progression or confirm direct causal relationships between specific electrocardiographic patterns and long-term clinical decompensation. Furthermore, the duration of pre-existing bundle branch block burden could not be ascertained from medical records, leaving unmeasured the potential influence of chronicity on mechanical remodeling. The diagnostic criteria applied were those established during the historical study window rather than updated consensus definitions. Nevertheless, this investigation provides the first systematic evidence demonstrating that integrated analysis of routine twelve-lead electrocardiographic features can serve as an accessible, rapid, and cost-effective screening approach to identify subclinical systolic impairment in patients with isolated left bundle branch block.

Subject of Research: Screening for subclinical left ventricular systolic dysfunction in isolated left bundle branch block using electrocardiography

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

Article References: Li, G., Wang, Y., Pang, B., Yang, J., & Ma, C. (2025). Relationship between electrocardiographic characteristics and subclinical left ventricular systolic dysfunction in isolated left bundle branch block patients. Cardiovascular Ultrasound, 23(1), Article 7. https://doi.org/10.1186/s12947-025-00342-6

Image Credits: AI Generated

DOI: 10.1186/s12947-025-00342-6

Keywords: Left bundle branch block, Subclinical left ventricular systolic dysfunction, Preserved ejection fraction, Electrocardiography, Two-dimensional speckle-tracking echocardiography, Global longitudinal strain, QRS duration, QS pattern, Discordant LBBB, Cardiac dyssynchrony, Echocardiography, Receiver operating characteristic, Integrated discrimination index, Cardiovascular screening, Retrospective cross-sectional study, Cardiac conduction abnormalities