What does the PQRST complex on an ECG represent?

The PQRST complex on an ECG represents the electrical activity of the heart during each heartbeat. Specifically, it illustrates the sequence of depolarization and repolarization of the heart's atria and ventricles.

The "P" wave signifies atrial depolarization, which is the electrical activation of the atria. The "QRS" complex reflects ventricular depolarization, representing the contraction of the ventricles after they have been electrically activated. Finally, the "T" wave indicates ventricular repolarization, when the ventricles prepare for the next cycle of depolarization.

Understanding this progression is crucial for interpreting cardiac function and identifying potential abnormalities. Other options, while related to cardiac health, do not directly reflect what the PQRST complex represents. For instance, heart rate variability is a measure of the variations in time intervals between heartbeats and is not directly depicted on the ECG complex itself. Myocardial infarction refers to a specific condition caused by reduced blood flow to the heart muscle, which may affect the ECG but is not depicted as part of the PQRST sequence. Cardiac output, a measure of the blood the heart pumps in a minute, is an outcome of heart activity but is not represented directly by the PQRST waves