As a medical professional with expertise in cardiology, I can explain the concept of the S wave in the context of an electrocardiogram (ECG). An S wave is a deflection seen in the ECG that follows the R wave. The R wave is the first large positive deflection of the QRS complex, which represents the depolarization of the ventricles. The S wave, which stands for "septal," is the subsequent downward deflection in the QRS complex. It is particularly notable because it represents the spread of the electrical impulse through the ventricles as it moves away from the interventricular septum. It's important to note that the presence of an S wave can vary among different ECG leads. Some leads may not show an S wave at all, while others may have a prominent one. The size and depth of the S wave can also be significant in diagnosing certain cardiac conditions, such as hypertrophy or strain. 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.read more >>