ST segment reflects the current flow associated with phase 2 of ventricular repolarization. Since there is no current flow during this plateau phase of repolarization, the ST segment is normally isoelectric with the baseline. The T wave represents the current of rapid phase 3 ventricular repolarization see diagram above. The polarity of this wave normally follows that of the main QRS deflection in any lead.
The ventricles are electrically unstable during that period of repolarization extending from the peak of the T wave to its initial downslope. A stimulus e. The PR interval extends from the beginning of the P wave to the beginning of the QRS, whatever the first wave of this complex may be. This interval measures the time from the initial depolarization of the atria to the initial depolarization of the ventricles and reflects a physiological delay in AV conduction imposed by the AV node.
Normal range is — ms 3 to 5 1-mm-divisions and no longer. This interval should be determined in the ECG lead where it is longest. Normal QT c is ms or less. The J-point is where you start to see an upward stroke after the S wave. The segment ends at the beginning of the T-wave. The ST-segment represents when the ventricles are relaxing, also called repolarizing. Now test your knowledge on how well you grasp the material by taking this quiz.
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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. One of the quickest ways is called the sequence method. To use the sequence method, find an R wave that lines up with one of the dark vertical lines on the ECG paper. If the next R wave appears on the next dark vertical line, it corresponds to heart rate of beats a minute. The dark vertical lines correspond to , , , 75, 60, and 50 bpm.
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