Physiology practical 1

Question 1

define an electrocardiogram

Answer 1

The entire electrical sequence accompanying the beat

Question 2

why is atrial depolarisation not seen on a ECG

Answer 2

Atrial repolarisation occurs during ventricular depolarisation (the QRS) so is not seen in the normal EGG)

Question 3

how do you set up the volunteer

Answer 3

 Select a volunteer; ask them to lie quietly on the bench. It is important to make sure the patient is warm and relaxed during the test because we want to reduce muscle tremors and movement as much as possible since they can impair the quality of recordings. When a patient is cold, he/she may tense or shiver which can cause muscle artifact on the tracings. The patient’s arms should lay flat along the side of the body. If the patient does not fit comfortably on the exam table, due to size, have them cross their arms on their stomach to reduce muscle tension.
 Patients should not read or talk when an ECG test is being performed.
 The build-up of skin oils and residues increase the resistance to the conduction of the electrical signal, therefore, it is important to prepare the skin properly by rubbing with either
isopropyl alcohol or soap and water to remove skin oils.
 Electrodes are best placed in fleshy areas rather than bone which is a poor conductor and
ideally avoiding areas where there is a lot of muscle movement. Inner surface of the wrists and legs (just above the ankles) are good places.

Question 4

describe how to connect limb leads

Answer 4

• electrodes are stuck on to both the wrists and ankles
• colour coded
• 3 initial limb leads form einthovens triangle
• there is also 3 augmented leads

Question 5

limb leads …

Answer 5

measure the activity of the heart in the vertical plane

Question 6

where do you attach the chest leads

Answer 6

V1 - right 4th intercostal space 
V2: left 4th intercostal space
V3: halfway between V2 and V4
V4: left 5th intercostal space, mid-clavicular line V5: horizontal to V4, anterior axillary line
V6: horizontal to V5, mid-axillary line

Question 7

describe why different electrodes show different ECG patterns

Answer 7

Rule 1. Depolarisations moving TOWARDS the POSITIVE recording electrode cause the trace to RISE. Depolarisations moving AWAY FROM the POSITIVE recording electrode cause the trace to FALL.
Rule 2. Depolarisations that are PARALLEL to the electrodes being used give LARGE traces. Depolarisations that are AT RIGHT ANGLES to the electrodes being used give SMALL OR ZERO traces.