The QRS complex associated with a third-degree AV block is always wide.

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The site of block in a third-degree AV block may be the AV node or, more commonly, the bundle of His or the bundle branches. A secondary pacemaker (either junctional or ventricular) stimulates the ventricles; therefore the QRS may be narrow or wide, depending on the location of the escape pacemaker and the condition of the intraventricular conduction system.

The QRS Complex Associated with a Third-Degree AV Block Is