Pattern: Wide, notched QRS with a slurred onset in lateral leads and absence of q waves in I and V6.

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Recognizing left bundle branch block on ECG involves a wide QRS with a broad, notched appearance and a slurred onset, especially in the lateral leads (I, aVL, V5, V6). This pattern reflects delayed activation of the left ventricle, so the depolarization is prolonged and discordant, producing a QRS duration typically over 120 ms and a characteristic “M” or notch in the lateral leads. The absence of initial q waves in those same lateral leads (I and V6) is another clue, because normal septal activation that creates those tiny q waves is disrupted by the delay in left ventricular conduction. In contrast, right bundle branch block would show an rsR' pattern in the right precordial leads and a different pattern in the lateral leads, not the broad, notched, slurred QRS described here. A normal QRS would lack widening and notching, and short QT syndrome concerns the QT interval rather than QRS morphology.