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Left bundle branch block

Left bundle branch block

• Septal depolarization is reversed [*]
1. Septal Q waves replaced by R waves
2. ST segment depression and T wave inversion are seen in leads with predominant R waves
• ST segment elevation and positive T waves are seen in leads with predominant S waves

Diagnostic criteria for LBBB [*]

• QRS duration 0.12 seconds or greater
• Broad, monophasic R waves in leads I, V5 and V6
• Absent Q waves in V5 and V6
• Associated features for LBBB
1. Displacement of ST segment and T wave deflections opposite to major QRS vector
2. Poor R wave progression across precordium
3. RS, rather than monophic R wave complex in V5 and V6
4. Left axis deviation is common