ECGs

Question 0

Why do we perform an ECG?

Answer 0

To confirm that the heart rhythm is normal or abnormal, an arrhythmia is present, and to indicate if damage has been done to myocardial activity.

Question 1

Asides from an ECG, what are other alternative ways to diagnose heart conditions?

Answer 1

• CXR (cardiac x-ray)
• pathology
  = troponin
  = CK-MB
  = CK
  = FBE
  = electrolytes
• exercise stress test
• nuclear imaging
• CT scan

Question 2

What is an ECG?

Answer 2

• diagnostic tool
• reflects the electrical activity from a range of reference points
• ECG is obtained by placing disposable electrodes in standard positions on the skin of the chest wall and extremities
• ECG machine can vary in size

Question 3

Name six indications for having an ECG.

Answer 3

• chest pain
• clinical history of palpitations
• cardiac disease
• life-threatening conditions
• syncope/collapse
• shortness of breathe
• overdose
• interventions (pre/post surgery an ECG)
• envenomation (bitten by a snake)

Question 4

Name three types of ECG monitoring.

Answer 4

• continuous cardiac monitoring
• 12 lead electrocardiography
• ambulatory monitoring (long distance monitoring)
• stress testing
• telemetry (monitoring of time)

Question 5

What are the deflecting points labelled on an ECG? Explain each.

Answer 5

P wave - firing of SA node and depolarisation of atria
QRS complex - depolarisation of ventricles and repolarisation of atria (hidden in QRS)
T wave - repolarisation of ventricles

Question 6

The ECG records the potential difference in charge between two electrodes as the depolarisation and repolarisation waves move through the heart, but is not conducted to the surface of the skin. True or false.

Answer 6

False.

It is conducted to the skin surface.

Question 7

The shape of the tracing is determined by what?

Answer 7

The direction in which the impulse spreads through the heart muscle in relation to electrode placement.

Question 8

Explain the PR interval.

Answer 8

• distance from the beginning of the P wave to the beginning of the QRS complex
• represents time of impulse from the SA node to ventricles
• takes 0.12-0.20 seconds

Question 9

Explain the QRS complex.

Answer 9

• the first downward deflection is the “Q” wave (not everyone has a Q wave)
• first upward deflection is the “R” wave
• any deflection following the “R” wave is the “S” wave

Question 10

What is the QRS complex duration?

Answer 10

This is the time taken to spread through the ventricles.

<0.12 seconds

Question 11

Explain the ST segment.

Answer 11

• it is from the end of the QRS to beginning of T
• ST depression may indicate myocardial ischaemia
• ST elevation may indicate myocardial injury

Question 12

Explain the T wave.

Answer 12

• should look round and smooth
• tall, inverted or pointy Ts may indicate myocardial injury or hyperkalaemia
• inverted or flattened Ts may indicate ischaemia
• notched or jacked up Ts may indicate pericarditis

Question 13

Explain how we count the boxes on an ECG to determine the regular and irregular heart rhythms.

Answer 13

Regular heart rhythms
- count the number of small boxes within an RR interval and divide by 1500

Irregular heart rhythms
- count the RR waves for 6 seconds and multiply number by 10

Question 14

To be a sinus rhythm, the ECG must have what?

Answer 14

• normal rate
• a regular rhythm
• one P wave per QRS complex
• a PR interval within normal range
• normal QRS duration.

Question 15

Name the location of all the precordial leads.

Answer 15

V1 - 4th intercostal space, right of the sternal boarder
V2 - 4th intercostal space, left of the sternal boarder
V3 - halfway between V2 and V4
V4 - 5th intercostal space, inline with the mid-clavicular line
V5 - 5th intercostal space, left anterior axillary line (between V4 and V6)
V6 - 5th intercostal space, left of the mid-axillary line

Question 16

What are some reasons for ECG errors and interference?

Answer 16

• attaching leads to the wrong limbs
• electrical interference
• metallic interference
• somatic tremor due to patient shivering
• loose connections

Question 17

Name eight common arrhythmia causes.

Answer 17

• accessory pathways
• cardiomyopathy
• myocardial cell degeneration
• valve disease
• connective tissue disorder
• drug effects
• near drowning
• conduction deficits
• heart failure
• myocardial infarction
• acid base imbalances
• alcohol
• tobacco and caffeine
• electrical shock
• emotional crisis
• hypoxia