As a cardiac electrophysiologist, I specialize in the study of the electrical activity of the heart. Repolarization is a critical phase in the cardiac cycle that follows depolarization. Here's a detailed explanation: Repolarization of the heart refers to the process by which the cardiac muscle cells, or myocytes, return to their resting membrane potential after a depolarization event. This is a crucial step in the cardiac cycle that allows the heart to prepare for the next contraction. The process of repolarization ensures that the heart muscle can contract in a coordinated and efficient manner. In the context of an electrocardiogram (ECG), repolarization is represented by specific components of the ECG waveform. The J point marks the end of the QRS complex and the beginning of the ST segment. The ST segment follows the J point and represents the period during which the ventricles are in a state of depolarization. The T wave represents the repolarization of the ventricles, and the U wave is a smaller wave that sometimes follows the T wave and is thought to be related to repolarization as well. It's important to note that the PQRST portion of the ECG, which includes the P wave (atrial depolarization), QRS complex (ventricular depolarization), and the T wave (ventricular repolarization), is significantly influenced by the autonomic nervous system, particularly the sympathetic nervous system. This system can affect the rate and force of the heart's contractions, which in turn can impact the shape and duration of the ECG waves. read more >>

The last event of the cycle is the repolarization of the ventricles. It is the restoring of the resting state. In the ECG, repolarization includes the J point, ST-segment, and T- and U-waves. The transthoracically measured PQRS portion of an electrocardiogram is chiefly influenced by the sympathetic nervous system.read more >>