Normal P wave is no more than 2. It is either far right or far left axis deviation if it lies between o and o. The method of determining QRS axis will be explained in a later section. 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.
This electrical impulse causes the four chambers of the heart to contract and relax in a coordinated fashion. Studying these electrical impulses allows us to understand how the heart is functioning.
The P wave represents the depolarization of the left and right atrium and also corresponds to atrial contraction. Strictly speaking, the atria contract a split second after the P wave begins. Because it is so small, atrial repolarization is usually not visible on ECG. In most cases, the P wave will be smooth and rounded, no more than 2. These three waves occur in rapid succession. 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. Before you can start analyzing heart rhythms, atrial fibrillation, atrial flutter, ventricular tachycardia etc. Please take note of the study tips because these are common questions are exams. Remember from the electrical conduction lecture, that the SA node is responsible for this.
QRS Complex : The next area you see is a big spike. This spike is called the QRS complex. The bundle of His, bundle branches, and Purkinje fibers are responsible for this. The ventricles are so large that when they contract depolarize the form a large electrical impulse that presents the QRS complex.
Therefore, because they are so large when they relax repolarize they form a small electrical impulse that presents as the t-wave.
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