What are the criteria for Left Bundle Branch Block (LBBB)?

From the Guidelines

Left Bundle Branch Block (LBBB) is diagnosed based on a QRS duration ≥120 ms, with more specific criteria including broad notched or slurred R wave in leads I, aVL, V5, and V6, and ST and T waves usually opposite in direction to QRS, as stated in the 2009 AHA/ACCF/HRS recommendations 1. The diagnosis of LBBB is crucial in clinical practice, as it can have significant implications for patient management and outcomes.

• The QRS duration is a key factor in diagnosing LBBB, with a duration of ≥120 ms being a common criterion 1.
• Other electrocardiographic criteria for LBBB include broad notched or slurred R wave in leads I, aVL, V5, and V6, and ST and T waves usually opposite in direction to QRS 1.
• The presence of LBBB can mask ECG signs of myocardial infarction and may indicate underlying heart disease such as coronary artery disease, hypertension, cardiomyopathy, or valvular heart disease.
• In patients with heart failure, LBBB with a QRS duration ≥150 ms is an indication for cardiac resynchronization therapy (CRT) to reduce total mortality, reduce hospitalizations, and improve symptoms and quality of life (QOL) 1.
• The 2022 AHA/ACC/HFSA guideline for the management of heart failure recommends CRT for patients with LVEF ≤35%, sinus rhythm, LBBB with a QRS duration ≥150 ms, and NYHA class II, III, or ambulatory IV symptoms on guideline-directed medical therapy (GDMT) 1. Based on the most recent and highest quality evidence, the criteria for LBBB include a QRS duration ≥120 ms, with specific electrocardiographic criteria, and the presence of LBBB can have significant implications for patient management and outcomes, particularly in patients with heart failure 1.

From the Research

Criteria for Left Bundle Branch Block (LBBB)

The criteria for LBBB have been studied and proposed by various researchers. Some of the key criteria include:

• QRS duration:
  • ≥ 140 ms for men and ≥ 130 ms for women 2
  • ≥ 120 milliseconds in duration 3
  • ≥ 130 milliseconds for patients with LBBB being considered for cardiac resynchronization therapy 3
• QRS complex morphology:
  • QS or rS in V1-V2 2
  • Mid-QRS notching or slurring in ≥ 2 contiguous leads 2
  • Notch width of the QRS complex in the lateral leads (I, aVL, V5, V6) 4
• Other criteria:
  • Absence of initial portion of the QRS complex (the "septal Q waves") 3
  • QRS prolongation should not be gradual 3

Comparison of LBBB Criteria

Different studies have compared the diagnostic accuracy of various LBBB criteria, including:

• Conventional LBBB criteria (QRSd ≥ 120 ms) vs. strict LBBB criteria (QRSd ≥ 140 ms for men and ≥ 130 ms for women, and mid-QRS notching in ≥ 2 contiguous leads) 2, 5
• European Society of Cardiology (ESC) 2013 definition vs. ESC 2021 definition 6
• High-density electroanatomical mapping vs. ECG criteria 4

Diagnostic Accuracy of LBBB Criteria

The diagnostic accuracy of LBBB criteria has been evaluated in various studies, with results showing:

• Strict LBBB criteria had 100% specificity, while conventional criteria had 48% specificity 5
• The notch width/left ventricular end-diastolic diameter (Nw/LVd) ratio had a sensitivity of 56% and a specificity of 91.7% for diagnosing true complete LBBB 4