The QRS complex is a component of the heart’s electrical activity, appearing as a distinct pattern on an electrocardiogram (ECG). It represents the rapid electrical activation of the heart’s lower chambers, the ventricles.
A combination of the Q wave, R wave and S wave, the “QRS complex” represents ventricular depolarization. This term can be confusing, as not all ECG leads contain all three of these waves; yet a “QRS complex” is said to be present regardless.
The QRS complex, normally beginning with a downward deflection, Q; a larger upwards deflection, a peak (R); and then a downwards S wave. The QRS complex represents ventricular depolarization and contraction.
The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the central and most visually obvious part of the tracing.
The QRS complex shows ventricular depolarization — the signal spreads through the ventricles, causing them to contract. This is the most critical part: if the QRS is wide or abnormal, the ventricles aren’t conducting electricity properly.
Normal QRS width is 70-100 ms (a duration of 110 ms is sometimes observed in healthy subjects). The QRS width is useful in determining the origin of each QRS complex (e.g. sinus, atrial, junctional or ventricular). Narrow complexes (QRS < 100 ms) are supraventricular in origin.
QRS duration is the time interval from the onset to the end of the QRS complex. A short QRS complex is desirable as it proves that the ventricles are depolarized rapidly, which in turn implies that the conduction system functions properly.
A practical, emergency medicine–focused guide to the QRS complex. Learn how QRS width, amplitude, morphology, axis, and transition zone reflect hypertrophy, infarction, bundle branch block, and low voltage ECG patterns.