Left Bundle Branch Block May Be Key Indicator of Progressive Heart Failure

Left bundle branch block (LBBB) may be a key indicator of progressive heart failure in asymptomatic individuals with structurally normal hearts, a recent study published in the JAMA Network Open reported.¹

LBBB is characterized by electrical abnormalities within the heart ventricles that delay or block signals to the lower chambers of the heart. This can reduce the heart’s ability to pump blood efficiently, causing the left ventricle to contract in a sporadic manner.² This type of contraction, over time, results in dilation (stretching or thinning of the heart chamber), cardiac remodeling (structural changes in size and shape of the heart), and systolic dysfunction (reduced pumping ability of the heart).

The study aimed to identify any association between LBBB and increased risk of heart failure (HF), decline in the left ventricular ejection fraction (LVEF), or risk of death. LBBB is also common in patients with HF and dilated cardiomyopathy (enlarged and weakened left ventricle); however, researchers believe LBBB may also cause cardiomyopathy due to the reversibility of systolic dysfunction by cardiac resynchronization therapies.¹

Left bundle branch block may be an significant indicator of heart failure succeeding previous risk-factors like diabetes and hypertension. | Image Credit: AdobeStock_phonlamaiphoto.jpeg

“We cannot exclude the possibility that LBBB is an early manifestation of cardiomyopathy, which later manifests as HF or an LVEF decline (as opposed to the underlying hypothesis that an LBBB causes subsequent systolic dysfunction),” the study authors explained. “However, again, given the common success of cardiac resynchronization therapy in many other cohorts, LBBB is almost certainly causal in contributing to HF and an LVEF decline in many patients.”

Other established risk factors of heart failure include age, sex, race, income, body mass index, hypertension, diabetes, myocardial infarction, coronary artery disease, smoking status, alcohol use, left ventricle (LV) mass index, and atrial fibrillation (AF); however, the study results showed that LBBB was associated with an increased risk of HF that surpassed that compared with other established risks.¹ Additionally, LBBB was also associated with higher odds of LVEF decline (OR, 4.73; 95% CI, 1.70-13.70; P = .003).

Participants were obtained from a longitudinal cohort study that began in 1987 and recruited 5201 men and women, all of whom underwent biannual physical examinations and check-ins and a 12-lead electrocardiography (ECG). ECGs were repeated after 5 years and then assessed, and LVEF function was categorized into mildly, moderately, or severely reduced. The cohort evaluated in the current study consisted of 4541 participants with a mean age of 72.6 years. Of them, 2697 (59.4%) were female, and 1% (n = 44) exhibited a baseline LBBB. Of those with LBBB at baseline, 21 (47.7%) developed heart failure compared with the 1300 (28.9%) of 4497 individuals without LBBB. After adjusting for other risk factors of HF, LBBB at baseline was associated with a higher risk of HF (HR, 4.98; 95% CI, 2.18-11.39; P < .001).

Furthermore, 336 participants were admitted to the hospital with HF with reduced ejection fraction (HFrEF), and 566 patients were admitted with HF with preserved ejection fraction (HFpEF). Of the 14 participants with LBBB at baseline, 11 (78.6%) had either mild, borderline, or low LVEF upon admission compared with 472 of 864 individuals (54.6%) without. LBBB at baseline was associated with a higher risk of admission for HFrEF (HR, 5.98; 95% CI, 1.43-25.00; P = .01); however, in the adjusted model, the risk of admission with HFpEF was not statistically significant. The risk of death was also associated with a greater risk amongst participants with LBBB at baseline (HR, 1.75; 95% CI, 1.26-2.44; P = .001)

“Taken together, these observations suggest that the presence of an LBBB, even in the absence of other evidence of structural heart disease, may be an important independent risk factor for future systolic HF,” the study authors wrote.

Key limitations of the study included the long follow-up period, and while researchers acknowledged its strength for assessing long-term outcomes, it may have introduced bias, as there have been changes to diagnostic and therapeutic therapies over time.

“Currently, the finding of asymptomatic LBBB does not prompt further testing or management,” the study authors noted. “Our findings raise the question as to whether early interventions should be considered for these patients to prevent cardiac remodeling, hypertrophy, and, ultimately, HF, or if, perhaps, the presence of an asymptomatic LBBB should trigger regular, protocolized surveillance (such as with serial echocardiograms) to detect the development of systolic dysfunction.”

References

1. Thein AS, Dixit S, Soliman E, et al. Left bundle branch block as a risk factor for heart failure. JAMA Network Open. 2025;8(8):e2525801. doi:10.1001/jamanetworkopen.2025.25801

2. Smiseth OA, Aalen JM. Mechanism of harm from left bundle branch block. Trends Cardiovasc Med. 2019; 29(6): 335-342. doi:10.1016/j.tcm.2018.10.012