QRS

QRS refers to the QRS complex, a characteristic series of deflections seen on an electrocardiogram (ECG) that reflects the rapid depolarization of the ventricles. It follows the P wave, which represents atrial depolarization, and precedes the T wave, which corresponds to ventricular repolarization. The QRS complex is a key component in assessing cardiac rhythm and conduction.

The QRS complex is composed of three possible deflections: the Q wave, the R wave, and the S wave. The Q wave is a small, initial negative deflection; the R wave is the first positive deflection, and the S wave is a subsequent negative deflection after the R wave. In many leads, a Q wave may be absent or very small, while the R and S waves form the typical spike pattern. The overall morphology of the QRS complex can vary by lead and individual anatomy.

Normal duration is a primary diagnostic parameter. In adults, the QRS duration is typically between 0.06 and 0.10 seconds, with a maximum of about 0.12 seconds. A longer duration suggests impaired intraventricular conduction, such as a bundle branch block or ventricular rhythm. Other features of the QRS complex, including its amplitude and axis, can indicate ventricular hypertrophy, electrolyte disturbances, or myocardial scarring.

Abnormal QRS patterns have clinical relevance. Pathologic Q waves can indicate prior myocardial infarction, while changes in QRS morphology help differentiate ventricular tachycardia from other wide-complex arrhythmias. The QRS complex is routinely analyzed in 12-lead ECGs to diagnose conduction abnormalities, acute ischemia, and other cardiac conditions.