LBBB Criteria and Response to CRT

Study Questions:

Do the criteria for left bundle branch block (LBBB) influence the response rate to cardiac resynchronization therapy (CRT)?


The LBBB criteria that were evaluated in this multicenter retrospective study came from four sources: the European Society of Cardiology, the American Heart Association, the MADIT-CRT trial, and Strauss, et al. These criteria were applied retrospectively in 1,492 CRT patients. The primary endpoint was a composite of left ventricular assist device implantation, cardiac transplantation, and all-cause mortality.


Only 13.8% of patients met all four sets of criteria for LBBB. The primary endpoint was met in 32% of patients after a mean follow-up of 3.4 years. LBBB was associated with a relative risk reduction of 39-43% in the primary endpoint, regardless of which criteria were used to identify an LBBB.


The identification of LBBB depends to a major extent on the specific criteria applied during analysis of the electrocardiogram. However, all four definitions used in this study had a similar degree of prognostic value after implementation of CRT.


The differences between the four sets of criteria for LBBB evaluated in this study differ predominantly in the presence and location of notches in the QRS complex and presence or absence of a Q wave in leads I and aVL. The feature that most of the criteria share is a QRS duration ≥140-150 ms. Although the MADIT-CRT study used a QRS duration of >130 ms as a selection criterion, most of the patients had a QRS duration ≥150 and these were the patients who demonstrated the highest CRT response rate. The findings of this study indicate that an LBBB is predictive of a good response to CRT regardless of the specific criteria used to identify the LBBB, as long as the QRS duration is ≥140-150 ms.

Clinical Topics: Arrhythmias and Clinical EP, Cardiac Surgery, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Prevention, Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Cardiac Surgery and Arrhythmias, Cardiac Surgery and Heart Failure, Acute Heart Failure, Heart Transplant, Mechanical Circulatory Support

Keywords: Arrhythmias, Cardiac, Bundle-Branch Block, Cardiac Resynchronization Therapy, Electrocardiography, Heart Failure, Heart Transplantation, Heart-Assist Devices, Risk, Secondary Prevention

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