Ventricular activation and the chest-lead QRS complex
THE CONTEXT
The shape of the QRS complex across the chest leads reflects the sequence of ventricular depolarisation. The left ventricle (LV) has the greater muscle mass and contributes the major component.
Sequence of activation
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The interventricular septum activates first, followed by the body of the LV and finally the right ventricle (RV).
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Chest leads V5 and V6 lie over the LV.
Resulting QRS deflections
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Septal depolarisation moves from left to right, generating a small initial negative deflection, the Q wave, in V6 and an initial positive deflection, the R wave, in V1.
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Activation of the body of the LV produces a large positive R wave in V6, with reciprocal changes in V1.
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The final phase of depolarisation involves the RV and produces a small negative S wave in V6.