ECG instrumentation

Question 1

What is an electrocardiograph?

Answer 1

An machine that measures the electrical activity of the heart

Question 2

What is an electrocardiogram?

Answer 2

The trace produced by an electrocardiograph

Question 3

Name the components of a biopotential system and explain their role

Answer 3

Transducer, converts one form of energy into another
Processor- processes the signal, digitalizes or amplifies it
Display- the output, e.g., chart recorder, aim it to get the input and output signal to be as similar as possible

Question 4

What is a biopotential system?

Answer 4

Biopotentials are electrical signals produced by the cells in our bodies, creating ionic flows measured in a system

Question 5

X axis & y Axis on ECG

Answer 5

Y axis is voltage (mV)
X axis is time (m/s)

Question 6

If the pen moves up on an ECG then…..

Answer 6

The current is moving towards the electrode & vice versa if the pen moves down

Question 7

State the equipment specifications

Answer 7

• input impedance
• CMRR
• Time constant
• Patient isolation
• Linearity
  These are all unable to be changed, set during manufacturing, influence can occur during patient isolation

Question 8

Name operator adjustable components of ECG machine

Answer 8

• Sensitivity
• Paper speed
• Frequency

Question 9

State Ohms law

Answer 9

The law states that the current is proportional to the voltage across it and is inversely proportional to the resistance
V=IR

Question 10

AHA states that Input impedance

Answer 10

should be greater than 0.5 ohms

If not, ECG will show reduced amplitude, input impedance should be high, but cannot be changed

Question 11

What is CMRR

Answer 11

Stands for common mode rejection ratio
Electrodes pick up background noise, it is the ability of the amplifier to reduce this common mode noise

Question 12

AHA states that CMRR

Answer 12

The ratio should be 1000:1, between 45-65 Hz, when imbalanced ECG will be noisy, affecting interpretation of results

Question 13

Define linearity

Answer 13

If points on a graph occur in a straight line, it is said to be linear

Question 14

AHA states that linearity

Answer 14

The maximum error must be less than 5% of chart width, if not met ECG waves will be distorted, leading to a possible misdiagnosis. ECG should be as linear as possible, but this cannot be changed

Question 15

Define time constant

Answer 15

The ability of an ECG to process slow or low-frequency signals, it is the time taken for the amplitude to decay due to a change in voltage

Question 16

AHA states that time constant

Answer 16

It must be greater than 3.2 seconds, if not met low frequency areas of ECG will be distorted. This cannot be changed set by manufacturers

Question 17

Define Patient isolation

Answer 17

The maximum amount of current that can be passed to a patient, needs to be checked, prevents shocking the patient and can also influence the quality of impedance
current should be as low as possible

Question 18

AHA states that patient isolation

Answer 18

should be less than 10 microamps, if not met mild sensations or burns could occur

Question 19

Importance of sensitivity

Answer 19

Amplitude could decrease/ increase based on sensitivity
common choices are 5mmV, 10mmV & 15mmV

Question 20

AHA states that sensitivity

Answer 20

Must be 1mV for every 10mms, if not met amplitude may be distorted, leading to a possible misdiagnosis
If changes to sensitivity made, make a note of it to ensure correct interpretation

Question 21

Importance of paper speed

Answer 21

To prevent overlapping of waves,

Question 22

AHA states that paper speed

Answer 22

25mm is equal to one second, if not met HR may appear higher or lower, leading to misdiagnosis

Question 23

Define frequency response

Answer 23

The range of frequencies over which an ECG works

Question 24

AHA states that frequency response

Answer 24

AHA states that frequency should equal to 0.5-150Hz, if not met wave will be distorted, as frequency affects wave shape, clearly annotate if filter is on. Switch on filter when all external noise has been excluded