- The ST Segment
- The ST segment represents the period from the end of ventricular depolarization to the beginning of ventricular repolarization. The ST segment lies between the end of the QRS complex and the initial deflection of the T-wave and is normally isoelectric. It is clinically important if elevated or depressed as it can be a sign of ischemia and hyperkalemia.
Although the ST segment is isoelectric, the ventricles are actually contracting. AWiggers diagram can be used to illustrate the increase in ventricular pressure beginning at about half-way through the QRS complex and continues to the end of the T-wave. Pumping of blood does begins when ventricular pressure exceeds aortic pressure, causing the semi lunar valves to open. This is normally at the end of the QRS complex and start of ST segment.
- The animation below shows conduction during the ST segment. Note the isoelectric line on the EKG during the ST segment. Also note that the animation had been slowed about 10 times the normal heart rate to show the details.