Results of an ECG record
By means of electrodes located on the thorax, arms and legs, after amplifying them, a detailed record of cardiac rhythm can be obtained, which are transmitted by the body tissues from the heart to the skin. From the different locations of the electrodes, various readings of the heart waves are obtained.
The anatomical sites for positioning the electrodes are standardized by means of different derivations, which refer to the measurement of the voltage that passes between two electrodes. These are:
A. Derivations of extremities:
a. I: Between the right arm (-) and left arm (+).
b. II: Between the right arm (-) and left leg (+).
c. III: Between the left arm (-) and left leg (+).
B. Unipolar shunts:
a. aVR: Between right arm (+) and derivation III.
b. aVL: Between left arm (+) and shunt II.
c. aVF: Between left leg (+) and shunt I.
C. Precordial shunts
a. V1. Fourth right intercostal space, next to the sternum.
b. V2. Fourth left intercostal space, next to the sternum.
c. V3. In a place equidistant between V2 and V4 (halfway along the line that joins the two branches).
d. V4. Fifth left intercostal space on the midclavicular line.
e. V5. Fifth left intercostal space, in the anterior axillary line.
f. V6. Fifth left intercostal space in the midaxillary line.
The ECG is structured in the measurement of the electrical potential between several body points. The I, II and III leads are peripheral and measure the potential difference between the electrodes located on the limbs. The unipolar leads of the aVR, aVL, and aVF limbs are obtained from the same electrodes as leads I, II, and III. However, they “see” the heart from different angles. . The electrodes for the precordial leads (V1, V2, V3, V4, V5, and V6) are placed directly on the chest, and because of their proximity to the heart, they do not need to be increased.
As we can see, there are different types of electrocardiogram, which differ from where they were obtained and the shape of their wave, but regardless of this, they will mean the same thing, providing better information about the heart for a more accurate diagnosis.