How can ECG be analyzed?
ECG can be interpreted by two basic methods, one is by remembering all the patterns that appear on the ECG and the other is by deeply understanding the exact electrical graphs related to the electrophysiology of the heart. Most doctors or clinicians know both of these methods of interpretation. Most people know that the appearance of a flat line on the ECG machine shows that the person is dead, while the waves show that the person is alive and the heart is beating. But the physiology of understanding cardiac leads and electrical impulses is not that easy. There is much more to it.
Electrodes are the sticky patches or sensors placed on the patient's chest to measure their heart's activity during the ECG test. These conductive metal pads connect with the wire to the monitor of the ECG machine and record the cardiac electrical signals by displaying them on the machine in the form of waves. Electrodes are usually 10 to 12, depending on the type of test being performed.
Channels on ECG
Channels are sometimes also called "leads." The 12 channel ECG machine displays the 12 waves graphically on the ECG monitor and each of the 12 tracks are printed on one slot.
Electrophysiological basis of electrocardiogram (ECG) machine
The basic foundation of cardiac electrophysiology is mastering the functions of heart rhythms and the contraction of cardiac muscles. The cardiac electrical activity can be analyzed by the differentiation of the potential or voltage. The charged particles characterized into intracellular and extracellular ions move and produce the electrical current. The flow of sodium, potassium, and calcium ions occurs between the cells through the gap junctions.
The difference in electrical potential or voltage occurs when the electrical impulses travel in the heart between the two points of measurement. During electro cardiology, the two points of potential difference are detected between the two electrodes on the skin. The electrocardiogram amplifies and measures the potential difference recorded by the electrodes and displays the results in the form of ECG leads.
Lead for ECG machine
The leads are displayed on the ECG as curves or waves. Different ECG machines are available but the standard type of ECG has 12 leads. The leads exhibited in the graph on the cardiac monitor determine the complexity of the diagnosis of the heart condition. The direction of deviation of leads on the ECG apparatus displays whether the electrical impulses travel toward the electrode or away from the electrode. This, in turn creates the positive and negative deviation of electrical impulses. The upright curve from the baseline is determined positive and the downward curve reflects negative deflection. The waves on the ECG graph are also termed as P, Q, R, S, T, and U waves.
Six leads on the graph are examined as the precordial leads considering they are placed on the precordium or chest, while the other six leads are considered the limb leads because of their placement on the legs and arms of the patient. The limb leads are presented on the graph with the letters I, II, III, aVL, aVR, aVF, and precordial leads or chest leads with V1, V2, V3, V4, V5, and V6.
Limb leads anatomy
The limb leads presented on the graph are obtained by placing four electrodes on the upper and lower extremities of the individual. The position of leads on upper limbs is left and right wrist while on lower limbs, the position is on the left and right ankle. The electrodes are placed in all these places in order to complete the circuit of electrical impulses on the cardiac monitor machine. The limb leads view the heart vertically. The one neutral electrode placed on the left leg acts as a reference lead. The limb leads observe the left ventricle of the heart as follows:
Inferior limb leads
Lead II, aVF, and III obtain electrical impulses from the inferior wall of the heart.
Lateral limb leads
aVL, I, -aVR obtain or observe the electrical impulse from the lateral walls of the heart.
Precordial lead anatomy
The six leads are placed on the chest anteriorly on the rib cage. The primary method to determine the exact position of placing electrodes is by first finding the "angle of Louis" and then moving your fingers to the right side and placing each six of the leads on intercoastal spaces. Chest leads view the heart horizontally.
The placement of chest leads is as follows:
V1: placed on the right margin of the rib cage on the 4th intercoastal space
V2: placed on the left margin of the rib cage on the 4th intercoastal space
V3: placed between the V2 and V4V4: placed on the center of clavicle line
V5: placed on the anterior side of the axillary line
V6: placed on the mid-axillary line
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