Ecg what is the s wave

The QRS complex represents the electrical impulse as it spreads through the ventricles and indicates ventricular depolarization. As with the P wave, the QRS complex starts just before ventricular contraction. The convention is that the Q wave is always negative and that the R wave is the first positive wave of the complex.

If the QRS complex only includes an upward positive deflection, then it is an R wave. The S wave is the first negative deflection after an R wave.

Under normal circumstances, the duration of the QRS complex in an adult patient will be between 0. It can also be thought of as the start of the ST segment. The J-point also known as Junction is important because it can be used to diagnose an ST segment elevation myocardial infarction. A T wave follows the QRS complex and indicates ventricular repolarization.

Unlike a P wave, a normal T wave is slightly asymmetric; the peak of the wave is a little closer to its end than to its beginning. When a T wave occurs in the opposite direction of the QRS complex, it generally reflects some sort of cardiac pathology.

If a small wave occurs between the T wave and the P wave, it could be a U wave. The biological basis for a U wave is unknown.

Overdose: TCA. Ventricular Fibrillation. Ventricular Tachycardia. Diagnosis, Wenckebach Squared? P wave Q wave R wave T wave. EKG Library. We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits.

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Performance performance. Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors. Some leads may display all waves, whereas others might only display one of the waves. Regardless of which waves are visible, the wave s that reflect ventricular depolarization is always referred to as the QRS complex.

Naming of the waves in the QRS complex is easy but frequently misunderstood. The following rules apply when naming the waves:. The QRS complex can be classified as net positive or net negative, referring to its net direction. The QRS complex is net positive if the sum of the positive areas above baseline exceeds that of the negative areas below baseline. Refer to Figure 6 , panel A. These calculations are approximated simply by eyeballing.

Panel B in Figure 6 shows a net negative QRS complex, because the negative areas are greater than the positive area. Depolarization of the ventricles generate three large vectors, which explains why the QRS complex is composed of three waves. It is fundamental to understand the genesis of these waves and although it has been discussed previously a brief rehearsal is warranted.

Figure 7 illustrates the vectors in the horizontal plane. Study Figure 7 carefully, as it illustrates how the P-wave and QRS complex are generated by the electrical vectors. Note that the first vector in Figure 7 is not discussed here as it belongs to atrial activity.

The ventricular septum receives Purkinje fibers from the left bundle branch and therefore depolarization proceeds from its left side towards its right side. The vector is directed forward and to the right. The ventricular septum is relatively small, which is why V1 displays a small positive wave r-wave and V5 displays a small negative wave q-wave.

Thus, it is the same electrical vector that results in an r-wave in V1 and q-wave in V5. The vectors resulting from activation of the ventricular free walls is directed to the left and downwards Figure 7. The explanation for this is as follows:. As evident from Figure 7 , the vector of the ventricular free wall is directed to the left and downwards. Lead V5 detects a very large vector heading towards it and therefore displays a large R-wave.

Lead V1 records the opposite, and therefore displays a large negative wave called S-wave. The final vector stems from activation of the basal parts of the ventricles. The vector is directed backwards and upwards. It heads away from V5 which records a negative wave s-wave. Lead V1 does not detect this vector. Prolongation of QRS duration implies that ventricular depolarization is slower than normal.

This is very common and a significant finding. The reason for wide QRS complexes must always be clarified. Clinicians often perceive this as a difficult task despite the fact that the list of differential diagnoses is rather short. The following causes of wide QRS complexes must be familiar to all clinicians:. A QRS complex with large amplitudes may be explained by ventricular hypertrophy or enlargement or a combination of both.

The electrical currents generated by the ventricular myocardium are proportional to the ventricular muscle mass. Hypertrophy means that there is more muscle and hence larger electrical potentials generated. However, the distance between the heart and the electrodes may have a significant impact on amplitudes of the QRS complex.

For example, slender individuals generally have a shorter distance between the heart and the electrodes, as compared with obese individuals. Therefore, the slender individual may present with much larger QRS amplitudes. Similarly, a person with chronic obstructive pulmonary disease often display diminished QRS amplitudes due to hyperinflation of thorax increased distance to electrodes.

Low amplitudes may also be caused by hypothyreosis. In the setting of circulatory collapse, low amplitudes should raise suspicion of cardiac tamponade. It is important to assess the amplitude of the R-waves. High amplitudes may be due to ventricular enlargement or hypertrophy. To determine whether the amplitudes are enlarged, the following references are at hand:. R-wave peak time Figure 9 is the interval from the beginning of the QRS-complex to the apex of the R-wave.

This interval reflects the time elapsed for the depolarization to spread from the endocardium to the epicardium. R-wave peak time is prolonged in hypertrophy and conduction disturbances. R-wave progression is assessed in the chest precordial leads.

Normal R-wave progression implies that the R-wave gradually increases in amplitude from V1 to V5 and then diminishes in amplitude from V5 to V6 Figure 10 , left hand side.