What is the significance of a "QRS duration" greater than 0.12 seconds?

A QRS duration greater than 0.12 seconds is significant as it typically indicates an abnormality in the electrical conduction system of the heart, particularly suggesting a bundle branch block or a ventricular-origin beat.

In a healthy heart, the QRS complex reflects the depolarization of the ventricles, which should normally occur in a timely manner. When the QRS duration exceeds 0.12 seconds, it signifies that the electrical impulse is taking longer than normal to travel through the ventricles. This delay can arise from a blockage in one of the bundle branches—right or left—resulting in a slower and potentially dysfunctional ventricular contraction.

Additionally, a prolonged QRS duration can also indicate beats originating from the ventricles themselves, known as ventricular ectopic beats. These are often wider and can vary significantly in shape compared to normal QRS complexes.

Normal conduction through the heart would not manifest in a QRS duration greater than 0.12 seconds, as that would be indicative of a conduction delay. It is also not considered a normal variant, particularly in young adults, and is unrelated to the heart rate exceeding 150 beats per minute. Instead, changes in the QRS duration are more closely associated with structural and functional abnormalities within the heart