EKG: Precordial leads

Ever wondered why leads have the shape they have?

  • Electricity propagates downward, to the left and a bit forward. If your lead “receives” the vector (imagine you are in a train statin and the train is coming towards you), the QRS complex will be positivo (tall R wave). This is true for V5 and V6.
  • If depolarization pulls away from you (the train is leaving the station and you are watching it go far away) then the QRS complex will be mostly negative. This is true for the septum leads: V1 and V2. They have a close relationship with the right bundle branch. In fact, you can see a RBBB in both V1 and V2 (rR’).
  • If your vector is close to the anterior wall, depolarization initially comes closer and then it pulls away (You are in the train station and the train just passes by). This is true for V3 and V4.
  • Take a look at the illustration:
Precordial leads. Notice how V1 starts pointing down (deep S) and it moves towards the positive as leads are placed on the left of the patient (Tall R in V6).
And here’s why… Click to enlarge and download!

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