Question

Describe the various component of ecg in normal functioning and abnormal functioning of the heart

Answer 1

Electrocardiography

At every beat, the heart is depolarized to trigger its contraction. This electrical activity is transmitted throughout the body and can be picked up on the skin. This is the principle behind the ECG. An ECG machine records this activity via electrodes on the skin and displays it graphically. An ECG involves attaching 10 electrical cables to the body: one to each limb and six across the chest.

ECG terminology has two meanings for the word "lead":

the cable used to connect an electrode to the ECG recorder

the electrical view of the heart obtained from any one combination of electrodes

Carrying out an ECG

Ask the patient to undress down to the waist and lie down

Remove excess hair where necessary

Attach limb leads (anywhere on the limb)

Attach the chest leads (see Figure 1) as follows:

V1 and V2: either side of the sternum on the fourth rib (count down from the sternal angle, the second rib insertion)

V4: on the apex of the heart (feel for it)

V3: halfway between V2 and V4

V5 and V6: horizontally laterally from V4 (not up towards the axilla)

Ask the patient to relax

Press record



Figure 1

Standard attachment sites for chest leads.

The standard ECG uses 10 cables to obtain 12 electrical views of the heart. The different views reflect the angles at which electrodes "look" at the heart and the direction of the heart's electrical depolarization.

Limb leads

Three bipolar leads and three unipolar leads are obtained from three electrodes attached to the left arm, the right arm, and the left leg, respectively. (An electrode is also attached to the right leg, but this is an earth electrode.) The bipolar limb leads reflect the potential difference between two of the three limb electrodes:

lead I: right arm–left arm

lead II: right arm–left leg

lead III: left leg–left arm

The unipolar leads reflect the potential difference between one of the three limb electrodes and an estimate of zero potential – derived from the remaining two limb electrodes. These leads are known as augmented leads. The augmented leads and their respective limb electrodes are:

aVR lead: right arm

aVL lead: left arm

aVF lead: left leg

Chest leads

Another six electrodes, placed in standard positions on the chest wall, give rise to a further six unipolar leads – the chest leads (also known as precordial leads), V1–V6. The potential difference of a chest lead is recorded between the relevant chest electrode and an estimate of zero potential – derived from the average potential recorded from the three limb leads.

Answer 2

Explanation:

Describe the various component of ecg in normal functioning and abnormal functioning of the heart