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. There are more accurate ways to determine heart rate from ECG, but in life-saving scenarios, this method provides a quick estimate.
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Thomas James, Director of Customer Experience. The Basics of ECG The information contained within a single lead electrocardiogram can be extensive. P Wave The P wave represents the depolarization of the left and right atrium and also corresponds to atrial contraction. Accepted or your money back. This interval represents the time between the onset of atrial depolarization and the onset of ventricular depolarization.
The QRS complex represents ventricular depolarization. Ventricular rate can be calculated by determining the time interval between QRS complexes. Click here to see how ventricular rate is calculated. The duration of the QRS complex is normally 0. This relatively short duration indicates that ventricular depolarization normally occurs very rapidly.
This can occur with bundle branch blocks or whenever a ventricular foci abnormal pacemaker site becomes the pacemaker driving the ventricle. Such an ectopic foci nearly always results in impulses being conducted over slower pathways within the heart, thereby increasing the time for depolarization and the duration of the QRS complex.
The shape of the QRS complex in the above figure is idealized. In fact, the shape changes depending on which recording electrodes are being used. The shape also changes when there is abnormal conduction of electrical impulses within the ventricles. The isoelectric period ST segment following the QRS and ending at the beginning of the T wave is the time at which both ventricles are completely depolarized.
This segment roughly corresponds to the plateau phase of the ventricular action potentials. The ST segment is very important in the diagnosis of ventricular ischemia or hypoxia because under those conditions, the ST segment can become either depressed or elevated.
The T wave represents ventricular repolarization. Generally, the T wave exhibits a positive deflection. The reason for this is that the last cells to depolarize in the ventricles are the first to repolarize. Normally it lasts no more than ms three 1-mm-divisions. It represents the time in which the ventricles depolarize and repolarize and is a measure of ventricular action potential AP duration.
Atrial and ventricular depolarization and repolarization are represented on the ECG as a series of waves: the P wave followed by the QRS complex and the T wave. 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.
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