As a cardiac electrophysiologist with extensive experience in interpreting electrocardiograms (ECGs), I can provide a detailed explanation of the S wave in an ECG. The S wave in an ECG is the first downward deflection that follows the R wave within the QRS complex. The QRS complex represents the electrical activity of the ventricles as they depolarize during a heartbeat. The S wave is particularly significant in leads that are looking at the heart from a direction where the depolarization wave is moving away from the electrode. It's important to note that an S wave may not be present in all ECG leads for a given patient. The size and presence of the S wave can vary depending on the lead and the patient's specific anatomy and physiology. In a normal ECG, the S wave is typically most prominent in the lead V1, and its amplitude tends to decrease as you move across to lead V6, where it may be almost nonexistent. The S wave is not only a normal finding but can also be indicative of certain conditions when abnormally large or deep, such as left ventricular hypertrophy (LVH) or other pathologies affecting the heart's conduction system. read more >>

The S wave is the first downward deflection of the QRS complex that occurs after the R wave. However, a S wave may not be present in all ECG leads in a given patient. In the normal ECG, there is a large S wave in V1 that progressively becomes smaller, to the point that almost no S wave is present in V6.read more >>