C. Prognosis
In patients younger than age 50 with LBBB and struc¬turally normal hearts there is no adverse prognostic signi¬ficance; these individuals have idiopathic LBBB or early development of degenerative disease of the conduction system. New LBBB appearing after age 50 requires investigation. In the Framingham study 55 individuals developed new LBBB at about 62 years with cardiovascular disease manifested in 89%, and 50% died within 10 years. A marker of favorable prognosis is the ECG and echo-cardiographic absence of left atrial enlargement, which if present indicates severe left ventricular hypertrophy and significant disease. In patients with coronary artery disease, heart failure, hypertension, valvular heart disease, and cardiomyopathy the prognosis depends on the severity of the heart disease. In patients with underlying heart disease, greater than 25% are expected to die within 2 years and greater than 50% die suddenly. The prognosis is poor in individuals with LBBB who develop myocardial infarction or those in whom acute infarction causes LBBB. In these cases thrombolytic therapy or percutaneous coronary inter¬vention is necessary.

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