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New Left Bundle Branch Block (LBBB) on EKG; What should we do?


Wassim Shaheen, MD

The use of EKG routinely with no clear defined clinical setting has become a common clinical practice. Hence more patients are currently diagnosed with LBBB, presumably new. This article will address the evaluation and prognostic implication of such a finding( Figure I).


Figure I: EKG showing LBBB.

The ECG shows wide QRS complexes (> 120 ms), increased intrinsecoid deflection time (80–120 ms), rS complexes inV1–V2, and loss or large reduction of Q waves in leads I and aVL. Likewise, repolarization forces mirror the electrical abnormality induced by the sequential activation of the two ventricles. Since they early originate from the right ventricle, leftleads (I, aVL) usually show a negative ST-T pattern.

The epidemiologic data reports that the prevalence of LBBB is 0.1-0.8%. As to its prognosis, there is no clear consensus. On one hand, The Framingham study published in 1979 and included 5,209 patients showed clear association with cardiac disease as CAD, CHF and hypertension.In this study 48% of patients developed CAD or CHF over 18 years period of follow up.Even worse the cardiac mortality was 50% at 10 years. However another published trial showed slightly different results. Fahy et al followed 110,000 patients for 9.5 years and showed no increased mortality associated LBBB. However 21% of patients with LBBB had underlying cardiovascular disease compared to 11% of controls. Data from different trials summarized in the next table.


Given the above-mentioned data, it is imperative to evaluate patients with new LBBB to make sure there is no underlying cardiovascular disease. That is why even US Federal Aviation Association (FAA) states that LBBB is a disqualification condition unless structural heart disease is excluded. Though there is no clear consensus on how to evaluate patients in general population with LBBB, we feel that additional testing is necessary based on patient’s risk factor and presentation. This is illustrated in the next figure.



PietroFrancia et al. Left Bundle Branch Block- Pathophysiology, Prognosis and Clinical Management. Clin. Cardiol.30 , 110-115 ( 2007).

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