Jonathon T. answered 11/21/22
Experienced Cell Biology Instructor and Practicing PA-C
The simplest way to answer this question is that a wide QRS complex refers to the heart being paced by a site of ,cardiac tissue in the ventricles rather than the atria.
There are more complex things to consider however, but the above is your most basic answer if that is what you are looking for. The heart is normally paced by the SA node or the sinoatrial node located in the right atrium. Where there is damage to the heart, say for example you had a previous heart attack which caused the death of heart muscle, this can damage the ability of a region of the heart to conduct. You can have ectopic pacing, where different areas of the atria other than the SA node take charge in pacing the heart. You can even have random regions of the atria pacing and electrical signals, for lack of a better description, running into each other causing the atria to quiver rather than pump which can lead to atrial fibrillation. Pulseless ventricular tachycardia is a wide QRS complex with relatively regular QRS patterns, but even though there is rapid conduction by the ventricles, there is no appropriate time or relaxation of the muscle to fill or pump blood effectively to the rest of the body and this is where emergency response teams will initiate CPR and use defibrillation. Polymorphic ventricular tachycardia is a wide QRS complex with a ribbon like appearance and is often due to electrolyte abnormalities like low magnesium levels (in fact Mg is provided for patients with this rhythm without laboratory confirmation of electrolyte abnormalities). You can have wide QRS complexes with bundle branch blocks, and for this just think of the physiology of the heart and the bundle branches which split from the bundle of his in the interventricular septum. Think of decreased or blocked conduction to the right or left branches. You can distinguish by looking in different leads of the EKG, primarily V2, V3, V5 and V6 for an interesting, wide QRS complex which actually form a characteristic RSR' wave.
Note that a patient can be stable and relatively asymptomatic with both wide and narrow QRS complexes.
George B.Your answer could not be more incorrect. A wide QRS does not whatsoever indicate the level from which the heart is being paced. It represents the time required for ventricular depolarization.