What does a QRS complex greater than 120 ms typically indicate?

The QRS complex represents the electrical activity of the ventricles during depolarization and is a crucial component of the electrocardiogram (ECG). A QRS duration greater than 120 ms typically indicates abnormal ventricular conduction. This is most commonly associated with a bundle branch block, where there is a delay or obstruction in one of the branches of the conduction system that normally transmits electrical impulses to the ventricles.

In a bundle branch block, the electrical signal takes longer to travel through the affected branch, leading to a wider QRS complex. This widening occurs because the ventricles are not activated simultaneously; instead, one ventricle is depolarized before the other, resulting in a longer duration of the QRS. Recognizing this pattern on an ECG is vital for diagnosing various cardiac conditions, and it informs the clinician regarding potential underlying heart disease or conduction system dysfunction.

While ventricular hypertrophy can also influence the QRS complex, it usually does not manifest as QRS widening to this extent. Normal conduction would present with a narrower QRS, and regular atrial involvement does not directly extend the QRS duration but affects the atrial waveforms instead. Understanding these nuances helps clarify why the correct answer is indicative of abnormal conduction related specifically to