QRSkomplex

The QRS complex is a waveform on the electrocardiogram (ECG) that represents ventricular depolarization. In English, the term is QRS complex; in German sources, QRS-Komplex is common. It occurs after the P wave and the PR interval and before the T wave. The QRS complex is composed of three deflections: Q, an initial downward deflection; R, a large upward spike; and S, a subsequent downward spike. The overall duration typically remains under 120 milliseconds in healthy adults and can vary with lead placement and heart axis.

Clinical significance: QRS duration and morphology reflect ventricular conduction. A normal, narrow QRS indicates rapid, coordinated activation via the conduction system. A widened QRS (greater than 120 ms) suggests delayed ventricular conduction, as in bundle-branch blocks, ventricular ectopy, or certain cardiomyopathies. Morphology changes can indicate myocardial infarction (pathological Q waves in contiguous leads) or preexcitation syndromes such as Wolff-Parkinson-White. Lead selection affects QRS appearance, and estimation of the QRS axis from limb leads aids diagnostic assessment.