Time : 2022-11-25
When we get an ECG report, we always get confused in the up and down lines, and can only judge several typical ECG changes based on past experience. However, these lines actually hide more secrets.
To understand these secrets, the first step is to understand what the waves, wave groups, peaks, bands, and intervals of each lead look like in a normal ECG.
Measurement of each band of ECG
1. P wave
Potential changes reflecting depolarization of atrial myocardium.
1. Time: The P wave time of normal people is generally less than 0.12s.
2. Amplitude: P wave amplitude is generally less than 0.25mV in limb leads and less than 0.2mV in chest leads.
2. PR interval
Reflects the time from the onset of atrial depolarization to the onset of ventricular depolarization.
Time: When the heart rate is in the normal range, the PR interval is 0.12-0.20s.
3. QRS complex
Potential changes reflecting ventricular depolarization.
1. Time: The QRS time of normal people generally does not exceed 0.11s, and most of them are between 0.06-0.10s.
2. Shape and amplitude:
1) In the chest leads, the V1 and V2 leads of normal people are mostly rS type, and the R wave of V1 generally does not exceed 1.0mV; the V5 and V6 lead QRS complexes can be qR, qRs, Rs or R type, and R Wave generally does not exceed 2.5mV;
The R wave in the chest leads gradually increases from V1 to V5, and the R wave in V6 is generally lower than the R wave in V5; usually the S wave in V2 is deeper, and the S wave in leads V2 to V6 gradually becomes shallower;
The R/S of V1 is less than 1, and the R/S of V5 is greater than 1; in lead V3 or V4, the amplitude of R wave and S wave is roughly equal.
2) In the limb leads, the main wave of the QRS complex in leads I and II is generally upward, and the main wave of the QRS complex in lead III is changeable;
The main wave direction of the QRS complex in lead aVR is downward, which can be QS, rS, rSr` or Qr type; the QRS complex in leads aVL and aVF can be qR, Rs or R type, or rS type;
In normal people, the R wave in lead aVR is generally less than 0.5mV, the R wave in lead I is less than 1.5mV, the R wave in lead aVL is less than 1.2mV, and the R wave in lead aVF is less than 2.0mV.
3) The QRS wave group amplitudes of the 6 limb leads (the absolute value of the positive wave and the negative wave amplitude) should generally not be less than 0.5mV, and the QRS wave group amplitudes of the 6 chest leads (the positive wave and the negative wave amplitude) should not be less than 0.5mV. The sum of the absolute values of negative wave amplitudes) generally should not be less than 0.8mV, otherwise it is called low voltage.
4. R peak time
It reflects the activation time of the ventricular wall, and refers to the distance from the QRS starting point to the vertical line at the top of the R wave.
1. Time: The normal R peak time generally does not exceed 0.03s in leads V1 and V2, and generally does not exceed 0.05s in leads V5 and V6.
2. Prolonged R peak time is seen in ventricular hypertrophy, pre-excitation syndrome and intraventricular conduction block.
Five, Q wave
The first negative wave of the ECG reflects the potential change of depolarization of the interventricular septum.
1. Time: The Q wave duration of normal people generally does not exceed 0.03s, except that the width of the Q wave in lead III can reach 0.04s and a wider Q wave or QS wave can appear in lead aVR.
2. Amplitude: Under normal circumstances, the depth of the Q wave does not exceed 1/4 of the amplitude of the R wave in the same lead.
3. In normal people, Q waves should not appear in leads V1 and V2, but occasionally QS waves may appear.
Six, J point
Refers to the transition point between the end of the QRS complex and the beginning of the ST segment.
1. Most of the J points are on the equipotential line, which shifts with the shift of the ST segment.
2. Due to tachycardia and other reasons, the coexistence of ventricular depolarization and atrial repolarization causes the atrial repolarization wave (Ta wave) to overlap with the posterior part of the QRS wave group, and the J point may move down.
7. ST segment
Reflecting the potential change of slow ventricular repolarization, it refers to the line segment between the end of the QRS complex and the beginning of the T wave.
1. Most of the normal ST segment is an equipotential line, and sometimes there may be a slight shift. However, in any lead, the ST segment shift generally does not exceed 0.05mV.
2. Adult ST-segment elevation is more obvious in leads V2 and V3, up to 0.2mV or higher, and the degree of elevation is generally greater in males than in females.
3. In leads V4-V6 and limb leads, the degree of ST-segment elevation rarely exceeds 0.1mV.
4. In some normal people (especially young people), due to the early repolarization of myocardial cells in the local epicardial area, the J point of some leads may move upward, and the ST segment presents a concave upward elevation (often in V2-V5 leads and II, III, aVF leads), commonly known as early repolarization, are mostly normal variations.
Eight, T wave
Potential changes reflecting rapid ventricular repolarization.
1. Morphology: The shape of normal T wave is asymmetrical in both limbs, with a slow slope in the front half and a steep slope in the second half; the direction of the T wave is mostly consistent with the direction of the main wave of the QRS complex;
The direction of T wave is upward in leads I, II, V4-V6, downward in lead aVR, upward, bidirectional or downward in lead III, aVL, aVF, V1-V3; if the direction of T wave in V1 is upward, then V2 The -V6 lead should no longer be down.
2. Amplitude: Except for leads III, aVL, aVF, and V1-V3, the amplitude of the T wave in other leads should generally not be lower than 1/10 of the R wave in the same lead.
It is normal for the T wave to be as high as 1.2-1.5mV in the chest leads.
Nine, QT interval
It reflects the time required for the whole process of depolarization and repolarization of ventricular myocardium, and refers to the distance from the beginning of the QRS complex to the end of the T wave.
1. Time: The length of the QT interval is closely related to the speed of the heart rate. The faster the heart rate, the shorter the QT interval, and vice versa;
When the heart rate is 60-100 beats/min, the normal range of QT interval is 0.32-0.44s.
2. There are certain differences in the QT interval between different leads. In normal people, the QT interval difference between different leads can reach up to 50ms, and the QT interval in V2 and V3 leads is the longest.
Ten, u wave
After T wave 0.02-0.04s, the wave with very low amplitude and small amplitude is more obvious in the chest leads, especially V2-V3.
1. Morphology: Normally, the slope of the first half is steeper, while the slope of the second half is gentler, which is just the opposite of T wave.
2. Direction: generally consistent with the T wave.
3. Amplitude: The amplitude of u-wave is related to the speed of heart rate. When the heart rate increases, the amplitude of u-wave decreases or disappears, and when the heart rate slows down, the amplitude of u-wave increases.
4. Significantly higher U wave is common in hypokalemia; U wave inversion can be seen in hypertension and coronary heart disease.
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