ecg_lbbb

ECG:
- QRS duration > 0.11sec
- M shape in leads I, V5 or V6
- QS complex usually present in leads facing RV ie. V1
  - but <50% have small r wave in V1
- ST elevation common in V1-4 with ST-T waves opposite in direction to terminal QRS direction
aetiology:
- normal hearts but extremely rare in children
- IHD - these pts have high incidence of LV dysfunction & CCF
- cardiomyopathy
- degenerative diseases
management:
- if present, cannot make diagnosis of LVH & Dx of AMI is difficult (see ECG Diagnosis of AMI )
  - ECG Dx of AMI in patient with LBBB:
    - ST-segment elevation of >= 1 mm concordant with (in the same direction as) the QRS complex = score of 5
    - ST-segment depression >= 1 mm in lead V1, V2, or V3 = score of 3
    - ST-segment elevation >= 5 mm discordant with (in the opposite direction from) the QRS complex = score of 2
    - a total score of 3 or more suggests AMI, however, studies suggest this rule is less useful than reported.
    - see Sgarbossa's scoring system in NEJM Feb 1996
- in general, new LBBB in a setting of ischaemic chest pain is managed as for ST elevation MI until proven otherwise
- patients with a trifascicular block (eg. LBBB with 1st degree AV block, or alternating LBBB with RBBB) should be considered for a ventricular demand pacemaker if symptomatic bradycardias or in the setting of acute MI when risk of complete heart block is higher.