What does a QRS complex that is wider than 0.12 seconds often indicate?

A QRS complex that is wider than 0.12 seconds typically indicates a disruption in the normal conduction pathway through the ventricles of the heart, which is often caused by a bundle branch block. In a healthy heart, electrical impulses travel down the bundle of His and through the right and left bundle branches, leading to a coordinated contraction of the ventricles. When there is a blockage in one of these branches, the electrical impulse takes longer to travel through the affected ventricle, resulting in a wider QRS complex on the EKG.

In contrast, normal conduction typically results in a QRS duration of less than 0.12 seconds. Atrial fibrillation, while it can have an irregular rhythm and unpredictable intervals, does not specifically cause a widened QRS complex; it primarily affects the atria rather than ventricular conduction. Premature ventricular contractions can occur with a wide QRS, but they do so on an occasional basis and typically do not indicate a permanent state of conduction delay as seen with a bundle branch block. Thus, a QRS complex wider than 0.12 seconds is most consistently associated with a bundle branch block.