DR. RIA MASLOG–MED INSIDER
Electrocardiography
We commonly hear about ECG. In routine general check up and when we are admitted especially if our symptoms are leading to chest discomfort, this laboratory called Electrocardiography, is done.
Electrocardiography or ECG records the sum of all the activities in the cardiac chambers.
The impulses in our heart are formed in the sinoauricular node (SA) in the wall of the right atrium.
From there , the impulses pass the atrioventricular node (AV) through the 3 internodal pathways.
Then, the impulse travels through the bundle of His embedded in the membranous septum before it divides into right and left main branches then to the right ventricular wall.
In normal circumstances the final portion of depolarization occurs in the posterior aspect of the left ventricle and upper wall of the septum.
So, what are these leads for that are attached to our chest, wrists and ankles, during ecg? The 12- lead ecg consists of
a. 3 bipolar or standard leads: lead I, lead II, and lead III.
b. 3 unipolar or augmented leads – AVR, AVL, AVF
c. 6 chest leads – V1 to V6
In children, 3 additional chest leads are routinely taken: V7, V3R, and V4R.
Lead I is connected to a positive left arm and a negative right arm while lead II is connected to positive left leg and a negative right arm and lead III is connected to positive left leg and negative left arm.
The unipolar limb leads, the electrode – is placed on the right arm for AVR, left arm for AVL and left leg for AVF. The right leg is used for electrical grounding of all the leads.
And for the chest leads, the electrode is placed across the chest wall starting on the right side of the sternum going to the left towards the apex and the axilla.
It is very important that during ecg taking, the client is comfortable and relaxed. In children, it is important that they are quiet because it will make a difference in the interpretation.