Impact of Newly Diagnosed Left Bundle Branch Block on Long-Term Outcomes in Patients with STEMI

<b>Background/Objectives</b>: This study assessed the long-term prognostic implications of newly developed left bundle branch block (LBBB) in patients with ST-elevation myocardial infarction (STEMI) and a single coronary lesion, following primary percutaneous coronary intervention (PCI). <b>Methods:</b> Among 3526 patients admitted with acute myocardial infarction between January 2011 and December 2013, 42 were identified with STEMI, a single coronary lesion, and newly diagnosed LBBB. A control group of 42 randomly selected STEMI patients without LBBB was also included. All participants were prospectively evaluated with a median follow-up duration of 9.4 years. Demographic, clinical, and laboratory data were analyzed to assess the impact of LBBB on long-term outcomes. <b>Results:</b> The baseline characteristics were similar between the groups. The STEMI with new LBBB group had significantly higher rates of new myocardial infarction, revascularization, and mortality, highlighting the severe prognostic implications and elevated risk for adverse outcomes compared to STEMI without LBBB. The multivariate Cox regression analysis demonstrated that the presence of LBBB (HR: 2.15, 95% CI: 1.28-3.62, <i>p</i> = 0.003), lower LVEF (HR: 1.45, 95% CI: 1.22-1.72, <i>p</i> < 0.001), and longer pain-to-admission time (HR: 1.32, 95% CI: 1.09-1.61, <i>p</i> = 0.008) were significant independent predictors of adverse outcomes. <b>Conclusions:</b> Newly acquired LBBB in STEMI patients is associated with poorer long-term outcomes. Early identification and management of factors such as reduced LVEF and timely hospital admission, specifically in patients with new-onset LBBB, can improve prognosis.