What does the QRS complex represent in an ECG?

The QRS complex in an electrocardiogram (ECG) specifically represents ventricular depolarization. This phase of the cardiac cycle is crucial because it indicates the electrical activation of the ventricles, which leads to their contraction and allows for the ejection of blood to the lungs and the rest of the body.

The QRS complex is typically a sharp, high-voltage deflection on the ECG tracing, and its duration is usually less than 0.12 seconds, reflecting the rapid spread of the electrical impulse through the ventricles. This process begins when the electrical signal from the atrioventricular (AV) node travels through the bundle of His and into the right and left bundle branches, ultimately reaching the Purkinje fibers, which cause the ventricles to contract.

Understanding this representation is essential for diagnosing various cardiac conditions because changes in the QRS complex size, shape, or duration can indicate underlying issues such as bundle branch blocks, ventricular hypertrophy, or myocardial infarction. Other options relate to different electrical activities in the heart that occur at other points in the cardiac cycle and do not reflect the depolarization of the ventricles.