Components of ECGEach ECG cycles consists of 5 waves: P, Q, R, S, T corresponding to different phases of the heart activities. The P wave represents the normal atrium (upper heart chambers) depolarization; the QRS complex (one single heart beat) corresponds to the depolarization of the right and left ventricles (lower heart chambers); the T wave represents the re-polarization (or recovery) of the ventricles. To interpret ECG, one needs to focus on the frequency (heart rate), regularity, shape and size of each individual waves and the timing and interaction between waves. The following diagram shows the components of a ECG cycle. Show
P WaveThe P wave occurs when both left and right atria are full of blood and the SA node fires. The signal causes both atria to contract and pump blood to the ventricles (lower chambers). Any abnormality is generally associated with the SA node and the atria. Lead II and V1 are the best leads to observe p-waves. General characteristics :
Examples of abnormal P waves
PQ SegmentWhen the signal from the SA node arrives the AV node, the signal is slowed and paused for a short period to allow blood from the atria to fill the ventricles. General characteristics :
Examples of abnormal PR interval
Q WaveThe Q wave is generated when the AV nodes releases the signal that travels through the inter-ventricular septum. General characteristics :
R WaveR wave is the first positive deflection after the P wave regardless whether a Q wave exists or not. As the signal continues from the AV node and spreads to the ventricles, the signal triggers a contraction on the left ventricle that pumps blood out of the ventricle. There may be multiple R waves. S waveS wave is generated when the basal parts of the ventricles are depolarized resulting in the contraction of the right ventricle. QRS ComplexThe Q, R and S waves together are referred to as QRS complex (even if some of its components are missing). It is the electrical forces generated by ventricular depolarization and represents the pumping action of the ventricles. General characteristics :
ST SegmentThe ST segment marks the time for the ventricles to pump the blood to the lung and body. In normal situations, it serves as the base line from which to measure the amplitudes of the other waveforms. Examples of abnormal ST segment
T WaveAfter the contraction empties the blood in the ventricles, they begin to relax, which is marked by the T wave. General characteristics :
Examples of abnormal T wave
Which of the following waves should an EKG technician use to determine the regularity?NHA EKG. Which interval should the tech use to determine the regularity of ventricular depolarization?Study material. Which method can be used to calculate regular and irregular rhythms?Count the number of QRS complexes over a 6-second interval. Multiply by 10 to determine heart rate. This method works well for both regular and irregular rhythms and for bradycardias. It's recommended for irregular rhythms and for bradycardias.
Which of the following waves would an EKG technician measure to evaluate for atrial enlargement?Which of the following waves would an EKG technician measure to evaluate for atrial enlargement? The P wave is the only wave that is measured outside of an interval or a complex.
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