In left posterior fascicular block the current is conducted to the left ventricle via the left anterior fascicle, which makes the current travel upwards and leftwards producing small R waves in the lateral leads and small Q waves in the inferior leads. Depolarisation then spreads down and right, producing tall R waves in the inferior leads and deep S waves in the lateral leads.
Features of LPFB:
- There is Right Axis Deviation
- There are small R waves with deep S waves in leads I and aVL
- There are small Q waves with tall R waves in leads II, III and aVF
- QRS duration should be essentially normal
- R wave peak time is prolonged (over 45msec) in aVF
- There should be absence of right ventricular hypertrophy, or any other cause of right axis deviation
- Limb lead QRS voltage should be increased
Causes of Left Posterior Fascicle Block
- The left posterior fascicle has dual blood supply (LAD + AV nodal artery) so if ischaemic
heart disease is causing this phenomenon, it is SEVERE indeed.
- Could be myocarditis or some sort nof cardiomyopathy
Consequences of Left Posterior Fascicle Block
- This is an asymptomatic condition – usually doesn't amount to much.