As a medical professional with expertise in cardiology, I can explain that the J point on an ECG (Electrocardiogram) is a critical point that marks the end of the QRS complex and the beginning of the ST segment. The QRS complex represents the ventricular depolarization, which is the process of the ventricles contracting to pump blood out of the heart. The J point is the very moment when this depolarization is complete. Following the J point, the ST segment begins, which represents the period of ventricular repolarization, where the ventricles are relaxing back to their resting state. Any changes in the ST segment, such as elevation or depression, can be indicative of various cardiac conditions, particularly ischemia, which is a lack of blood flow to the heart muscle. The T wave follows the ST segment and represents the repolarization of the ventricular muscle. The T wave is typically upright and in the same direction as the QRS complex, which is a normal finding. Here is the translation of the above explanation into Chinese: read more >>

On the ECG, the repolarization phase starts at the junction, or j point, and continues until the T wave. The ST segment is normally at or near the baseline. Minor STT changes are not necessarily associated with cardiac ischemia[1]. The T wave is usually concordant with the QRS complex.read more >>