Many causes must be investigated. Cannot post link
Here are some in ncib article
Structural heart disease: Coronary artery disease (CAD), hypertension, cardiomyopathies such as dilated, left ventricular noncompaction, stress, and hypertrophic cardiomyopathies, and aortic valve diseases like aortic stenosis and regurgitation
Degenerative changes: Age-related fibrosis, Lev disease, and Lenègre disease
Lev disease is a form of idiopathic, age-related progressive cardiac conduction disorder characterized by extensive calcification and fibrosis of the cardiac skeleton, including the aortic valve annulus, mitral valve annulus, and interventricular septum. This calcification can extend to involve the His bundle and the bundle branches, manifesting as bundle branch blocks, commonly LBBB, and varying degrees of atrioventricular block, which can progress to complete heart block. Lenègre disease involves age-related, progressive degeneration of the conduction fibers, leading to fibrosis and sclerosis. This degeneration typically affects the His bundle and its branches, leading to various conduction blocks, LBBB being the most common.
Infiltrative conditions: sarcoidosis or amyloidosis
Inflammatory cardiomyopathies: Infectious myocarditis or autoimmune disease
Iatrogenic: Following cardiac surgery involving the aortic valve or interventricular septum or after transcatheter aortic valve replacement (TAVR)
At least 30% to 50% of patients develop LBBB after TAVR, which independently predicts mortality in these patients.[5]
Electrolyte imbalance: Hyperkalemia
Medication: Anti-arrhythmic medications
Congenital structural heart disease
Idiopathic: Particularly in younger patients or individuals without significant cardiac risk factors