What is the J point?

As a cardiac electrophysiologist, I specialize in the study of the electrical activity of the heart and its disorders. When it comes to the J point, it's an important concept in the field of electrocardiography (ECG or EKG), which is a diagnostic tool used to assess the heart's electrical activity. The J point is the precise point at which the QRS complex ends and the ST segment begins. The QRS complex represents the depolarization of the ventricles, which is the process by which the ventricles are stimulated to contract and pump blood. The ST segment, on the other hand, represents the period of repolarization of the ventricles, during which the ventricles are in a state of contraction and are not being stimulated by electrical impulses. The J point is significant because any deviation from its normal position can be indicative of various cardiac conditions. For instance, a raised J point or ST segment elevation can be a sign of acute myocardial infarction (heart attack), while a depression of the ST segment (known as ST depression) might suggest ischemia or other heart conditions. In summary, the J point is a critical junction on the ECG that marks the transition from ventricular depolarization to repolarization and is a key observation point for diagnosing cardiac abnormalities.

The J point is the the junction between the termination of the QRS complex and the beginning of the ST segment.