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Trace
Sinus rhythm, first-degree AV block (long and fixed PR) with left bundle branch block: QRS width > 120 ms (184 ms); absence of q wave, along with wide and notched R wave in leads I, aVL, V5 and V6 with delayed intrinsicoid deflection > 60 ms; QS and rS pattern in V1 and V2; ST segment depression and negative T wave in leads I, aVL, V5 and V6;
Exergue
Left bundle branch block is characterized by a disruption of all ventricular depolarization vectors; activation of the right ventricle is normal while that of the left ventricle is slow and delayed with reversal of the direction of septal activation.
In a left bundle branch block, activation of the right ventricle is normal whereas that of the left ventricle is delayed since its slowly depolarized by an activation wavefront originating from the right bundle branch.