The QRS Complex. Normal Activation of the Ventricles

The ventricular conduction system starts below the His bundle, where it bifurcates into the right and left bundle branches that taper out to the subendocardial Purkinje network, which activates the ventricular myocardium. This system is responsible for the synchronized and almost simultaneous activation of both ventricles. On the surface ECG, the ventricular conduction system lies in the terminal portion of the PR interval, whereas the QRS complex is comprised of the electrical currents originating from ventricular depolarization. This article reviews the main electroanatomical features of the ventricular conduction system and the effects of its delay on the QRS.