Left vs. Right Bundle Branch Block in COVID-19 Patients: Distinct Clinical Presentations and Prognostic Implications

<b>Background/Objectives</b>: COVID-19 is associated with multiple systemic effects, including cardiovascular complications. However, its interplay with cardiac conduction abnormalities remains underexplored. We compared the clinical profile of COVID-19 patients with pre-existing left bundle branch block (LBBB) or right bundle branch block (RBBB) at hospital admission. <b>Methods</b>: This study included 100 COVID-19 patients with antecedent BBB (50 LBBB, 50 RBBB). Critical cardiometabolic, renal, hematological, and inflammatory markers were measured. Logistic regression was used to identify key predictors differentiating COVID-19 patients with LBBB and RBBB. Spearman's correlations were applied to assess intra-strata associations for these variables. <b>Results</b>: COVID-19 patients with LBBB patients were significantly more likely to display lower systolic blood pressure (<i>p</i> = 0.012) but greater left atrial size (<i>p</i> = 0.008), left ventricular diameter (<i>p</i> = 0.001), and interventricular septal thickness (<i>p</i> = 0.023). Hematological and inflammatory markers differed, with LBBB patients being prone to exhibit higher red cell distribution width (<i>p</i> = 0.005), lymphocyte count (<i>p</i> < 0.001), neutrophil count (<i>p</i> = 0.045), and C-reactive protein (<i>p</i> < 0.001). This group also tended to show lower erythrocyte sedimentation rate (<i>p</i> = 0.013) and glycated hemoglobin (<i>p</i> = 0.045) but higher random glucose (<i>p</i> = 0.014). Absolute lymphocyte count, C-reactive protein, and left ventricular diameter were the most robust predictors distinguishing LBBB from RBBB. Significant associations were found exclusively for LBBB, all of them being weak. These predominantly negative relationships indicated an inflammatory origin, and most of them occurred for lymphocyte count. <b>Conclusions</b>: COVID-19 patients with LBBB and RBBB present distinct clinical profiles at hospital admission. The former group demonstrates a more adverse baseline clinical profile, particularly in terms of cardiac and inflammatory markers. These findings suggest that pre-existing BBB type may influence disease progression, potentially helping in risk stratification for COVID-19 patients.