The QT/QTc intervals are prolonged (460/500 msec) but are normal when the prolonged QRS complex duration is considered (400/440 msec). The QRS complex is leftward between 0° and -30° (QRS complex positive in lead I and II-after accounting for the deep S wave-and negative in aVF). As a result, abnormalities of the left ventricle cannot be definitively established. An LBBB represents left ventricular conduction directly through the myocardium and not the normal His-Purkinje system. Therefore, abnormalities affecting the left ventricle can be established. Of note, an IVCD represents slow conduction through the normal His-Purkinje system. Therefore, this is an intraventricular conduction delay (IVCD). Indeed, the terminal S wave is more consistent with a right bundle branch block. There should be no terminal S waves in leads I or V6, which represent left-to-right forces. With an LBBB, all forces are directed in a right-to-left direction. Moreover, there is a terminal broad S wave in lead V6 (↑). Because septal activation is from a small septal (median) branch from the left bundle branch, when an LBBB is present, septal forces are absent. However, there is a small septal Q wave in leads I and aVL (*) and a septal R wave in lead V1 (↓). The QRS complex duration is increased (0.16 sec), and there is a morphology of a left bundle branch block (LBBB) with a deep S wave in lead V1 (←) and a broad R wave in lead I (→). The rhythm is regular at a rate of 72 beats/min, although one longer RR interval is seen (↔).
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