What is represented by the QRS complex in an electrocardiogram?

The QRS complex in an electrocardiogram represents ventricular depolarization. This phase of the cardiac cycle occurs when the ventricles, which are the lower chambers of the heart, receive electrical signals that trigger their contraction. The depolarization results from the rapid influx of sodium ions through channels in the cardiac muscle cells, leading to a synchronized contraction of the ventricles.

The QRS complex is a critical part of interpreting an ECG, as it reflects how well the electrical signals are conducted through the ventricles, which is essential for effective pumping of blood to the lungs and the rest of the body. Understanding this aspect is important, as any alteration in the normal shape or duration of the QRS complex could indicate underlying cardiac issues, such as conduction abnormalities or ventricular hypertrophy.