How is the QRS complex characterized in rhythms that originate above the ventricles?

In rhythms that originate above the ventricles, such as atrial rhythms or junctional rhythms, the QRS complex is typically characterized as a narrow QRS complex. This is due to the conduction impulse traveling through the normal conduction pathways of the heart, namely the atria, the AV node, and then down the His-Purkinje system.

When the impulse follows this pathway, the ventricles depolarize in a coordinated and efficient manner, resulting in a QRS complex that is usually less than 0.12 seconds in duration. Narrow QRS complexes indicate that the impulse is originating from a site above the ventricles and that there is efficient conduction through the His-Purkinje system without significant delays or blockages.

In contrast, a wide QRS complex typically indicates that the impulse is originating from the ventricles themselves or there is a conduction delay through the ventricular pathways. Irregular QRS complexes can be seen in various arrhythmias but do not specifically characterize rhythms from above the ventricles. A flat QRS complex is an abnormal finding that can suggest other cardiac issues but is not characteristic of rhythms originating in the atria or junctional areas.