Final answer:
On an ECG, a left posterior hemiblock is typically indicated by negative QRS complexes in the right precordial leads and positive QRS complexes in leads I and aVL, along with a right axis deviation.
Step-by-step explanation:
The ECG pattern that identifies a left posterior hemiblock is characterized by certain changes in the QRS complex and the axis of the heart's electrical activity. While the ECG abnormalities described do not specifically list the left posterior hemiblock, this condition generally presents as negative QRS complexes in the right precordial leads (V1-V2) and positive QRS complexes in leads I and aVL.
Additionally, there is usually a right axis deviation on the ECG. Left posterior hemiblock is a type of infra-Hisian block, which refers to blockages that occur after the bundle of His, such as in the fascicles of the left bundle branch. Clinically, the exact identification of left posterior hemiblock requires an analysis of multiple ECG leads, considering the normal wave of depolarization and whether it deviates from its usual pathway.