Bundle Branch Block Recognition

Expansion

WiLLiaM MaRRoW:

• WiLLiaM: a W pattern in V1 and an M pattern in V6 means Left bundle branch block
• MaRRoW: an M pattern in V1 and a W pattern in V6 means Right bundle branch block

Both require a QRS of 120 ms or more. Under 120 ms the pattern is an incomplete block.

Right bundle branch block

• RSR’ in V1, the rabbit ears, with a slurred S wave in I and V6
• Causes: often normal variant, especially incomplete; pulmonary embolism, cor pulmonale, atrial septal defect, ischaemic heart disease, Brugada syndrome, right ventricular hypertrophy

Left bundle branch block

• Broad notched or slurred R wave in V6 and I, deep S in V1, absent septal Q waves
• Appropriate discordance: the ST segment and T wave point opposite to the main QRS deflection. This is expected and normal in LBBB
• Causes: almost always pathological, being ischaemic heart disease, hypertension, aortic stenosis, cardiomyopathy, or conduction system disease

LBBB obscures the usual ST criteria for infarction. The Sgarbossa criteria identify infarction despite it: concordant ST elevation of 1 mm or more, concordant ST depression of 1 mm or more in V1 to V3, or excessively discordant ST elevation, being over 25 per cent of the depth of the preceding S wave in the modified criteria.

Bifascicular block is right bundle branch block with left anterior or posterior hemiblock; adding first degree block gives “trifascicular block”, which warrants attention in the context of syncope.