ECG Recording Paper
The electrocardiogram is recorded on paper full of squares, so if you want to know how to look on the electrocardiogram, the first thing you need to know is the meaning of these squares. In these squares, each thin vertical line is separated by 1mm, and each thin horizontal line is also separated by 1mm. They form a small grid of 1mm square. The thick lines are one every five small grids, and the distance between each thick line is 5mm. The horizontal and vertical thick lines form a large grid. The electrocardiogram recording paper moves according to the international standard speed, the moving speed is 25mm/s, which means that each small horizontal grid represents 0.04s; the distance between every two thick lines represents 0.2s. Internationally, there are also regulations on the applied voltage when recording the electrocardiogram, that is, when a voltage of 1mV is applied, the baseline should be accurately raised by 10 small divisions, that is, each small horizontal division represents 0.1mV, and each large division It means 0.5mV, and every two large divisions represents this 1mV.
One cardiac cycle will record a series of waveforms with different heights and widths on the ECG. Including P wave, QRS complex, T wave and (no) u wave.
P wave, the first round and blunt waveform with low amplitude, records the activation of the right and left atriums of the sinus node. Because the sinus node is located in the right atrium, the activation of the atrium begins with it, so the first half of the P wave records the activation of the right atrium, the middle part records the co-activation of the left and right atria, and the back represents the activation of the left atrium. . Except for the aVR lead, the P wave is basically upright. The height of the P wave in the limb leads should not exceed 0.25mV, and the height of the upright P wave in the front chest lead should not exceed 0.15mV. The width of the normal P wave should not exceed 0.11s.
QRS complex, a narrow but high amplitude complex that appears after the P wave. It is composed of q wave (with or without), R wave and S wave. It represents the excitement from the atrioventricular node into the cardiomyocytes through the atrioventricular bundle, the left and right bundle branches and the slender Purkinje fibers to stimulate the contraction of the ventricle, so it can be regarded as the ECG performance of the beginning of ventricular contraction.
Q wave is a clear downward wave that appears before the upward wave. If it is very small, the width is less than 0.04s, and the depth is less than 0.15mV, we will record it as a q wave; if it is high and wide, it is called a Q wave; of course, sometimes it is missing. Regardless of whether there is a Q wave, the first upward and sharp wave is the R wave; the next downward wave is the S wave, which can also be named S wave and S wave according to the depth. The upward wave that appears after that is called the R’(r’) wave, and the downward wave is called the S’(s’) wave. Because the height of the wave is different, it can be combined into many forms, but it is also limited. The most important thing is the time limit. Normally, the QRS complex time of a normal person is 0.08s, which can be in the range of 0.06～0.10s. fluctuation. As long as this time limit is exceeded, attention should be paid, especially if it exceeds 0.12s, it has pathological significance.
T wave, the wave that appeared after the last wave group paused, represents the repolarization of the ventricle (ventricular relaxation) in preparation for the next depolarization of the ventricle. When observing T waves, we must pay attention to its direction, shape and (height) depth. (1) Direction. Under normal circumstances, T waves are upright in leads I and II; upright, flat, two-way or even inverted T waves can appear in lead III; T waves are positive in lead aVR Inverted, and in leads aVL and aVF, it is consistent with the main direction of the QRS complex. The T wave in the front of the chest is usually upright. Of course, V1 and V3 sometimes have T waves inverted, but their depth usually does not exceed 0.25mV. When there is an inverted T wave in V3 , The first two leading T waves should also be inverted, otherwise it will be abnormal performance. (2) Form, usually the waveform of T wave is smooth and has a very natural top. T waves are generally asymmetrical, rising gently and descending slightly to the contour line. (3) Height (depth), each lead is not exactly the same, but in general, it rarely exceeds 0.5mV in the limb leads, and rarely exceeds 1.0mV in the chest leads. Abnormally high sharp T waves often appear in the early stages of myocardial infarction or hyperkalemia.
U wave, a very small wave after the T wave, the normal u wave is not obvious in every lead.