Left anterior fascicular block

Left anterior fascicular block (LAFB) is an abnormal condition of the left ventricle of the heart, related to, but distinguished from, left bundle branch block (LBBB).

It occurs as a result of a conduction block in the left anterior fascicle, one of the offshoots of the left bundle branch. It manifests on the ECG as left axis deviation (LAD) and QRS prolongation.