What does the QRS complex indicate?

The QRS complex on an electrocardiogram (EKG) represents ventricular depolarization, which is the electrical activity that triggers the ventricles to contract and pump blood out of the heart. This is a critical phase in the cardiac cycle as it initiates the mechanical contraction of the ventricles, leading to the ejection of blood into the pulmonary artery and the aorta.

The QRS complex appears as a series of sharp, narrow peaks on the EKG trace. Its duration and morphology can provide valuable information about the health of the ventricular conduction system. The normal duration of the QRS complex is less than 0.12 seconds; if it is prolonged, it may indicate issues such as a bundle branch block or other forms of ventricular conduction delay.

Understanding the QRS complex is vital for diagnosing various cardiac conditions, as it reflects the state of the ventricles. This electrical activity does not encompass atrial depolarization or repolarization, nor does it directly indicate heart rate—those aspects are represented by different parts of the EKG, such as the P wave for atrial depolarization and the QT interval for repolarization activity.