Sinus Tachycardia with Left Bundle Branch Block (LBBB)

The ECG shows a regular rhythm at a rate of 130 bpm. P waves are not obvious in most leads. However, a positive P wave can be seen before each QRS complex in leads V4-V6 (*).

Sinus tachycardia with left bundle branch block
Sinus tachycardia with left bundle branch block

The PR interval is stable (0.14 sec). Using this PR interval, it can be seen that the negative deflection noted in leads V1-V2 (↑) as well as the positive deflection (↑) in leads I, aVL, and III are the P waves. This is, therefore, sinus tachycardia.

The QRS complex duration is prolonged (0.16 sec), and there is a pattern characteristic of left bundle branch block (LBBB; broad R wave in leads I and V5 and a QS complex in lead V1 [+]).

The axis in the frontal plane is leftward (positive QRS complex in lead I and negative QRS complex in leads II and aVF). The QT/QTc intervals are prolonged (320/470 msec) but are normal when corrected for the prolonged QRS complex duration (240/360 msec).