CVS - ECG Flashcards Preview

CJ: UoL Medicine Semester Two (ESA2) > CVS - ECG > Flashcards

Flashcards in CVS - ECG Deck (32)
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1
Q

What is ‘sinus rhythm?’

A

The is when the rhythm of the heart’s contraction is set by the sinoatrial node. It has the fastest rhythm in the heart - around 60-100

2
Q

Where is the left anterior division of the Bundle of His found?

A

Left ventricle

3
Q

What are Purkinje fibres?

A

Fine branches of the Bundles of His. They send a rapid spread of depolarisation throughout the ventricular myocardium

4
Q

Outline the cardiac cycle?

A
  • SA node depolarises and impulse spreads through atria
  • impulse held up at AV node and spreads to the ventricle via the Bundle of His
  • spreads rapidly down left and right bundles and Purkinje fibres
  • myocytes of the intraventricular septum are depolarised first
  • apex and RV and LV are depolarised next
  • base of the ventricles are last to be depolarised, then repolarisation of the ventricles happens in the reverse order
5
Q

What does an ECG record?

A

Records changes on extracellular surface of cardiac myocytes during wave of depolarisation and repolarisation. It does this from the surface of the body using electrodes pasted on the skin

6
Q

If the impulse moves towards a positive electrode, will the deflection be positive or negative?

A

Positive

7
Q

What direction would the electrical impulse move in if the complex is tall and positive?

A

From the top of the heart to the bottom - towards the apex

8
Q

What direction would the electrical impulse be going in if there is a small positive complex?

A

Across the heart, slightly towards the electrode

9
Q

What direction is the electrical impulse travelling in if there is a large negative complex?

A

From left ventricle to right atrium, directly away from the electrode

10
Q

Where is the sinoatrial node located?

A

Top right hand corner of the right atrium, near junction of superior vena cava and right atrium

11
Q

How does atrial depolarisation spread across the heart?

A

Spreads along atrial muscle fibres and intermodal pathways throughout left and right atria. Produces a small upward deflection on ECG (p-wave).

12
Q

Why is there a delay at the AV node?

A

It allows time for atrial contraction to fill the ventricle. This forms the flat line section of the ECG between the P wave and the QRS complex

13
Q

What is the function of the fibrous ring between the atria and ventricles?

A

It ensures that there is no direct contact between atrial and ventricular myocytes, so that depolarisation can only travel via the bundle of His

14
Q

How does the interventricular septum depolarise?

A

It goes from left to right. This produces a small downward deflection in the ECG wave because it is moving obliquely away from the electrode (‘Q wave’)

15
Q

What does depolarisation of the apex and ventricular wall look like on an ECG trace?

A

A large positive deflection, because the depolarisation is moving directly towards the electrode, and there is a large amount of muscle mass so there is more electrical activity.

16
Q

How would left ventricle hypertrophy affect the R wave?

A

It would be correspondingly taller

17
Q

What is the T wave caused by?

A

A wave of repolarisation of the ventricles moving away from the electrode, which spreads in the opposite direction to depolarisation

18
Q

How many electrodes are attached in a 12 lead ECG?

A

10 electrodes - 4 on limbs, 6 on chest

19
Q

What are ‘leads’ in an ECG?

A

Views of the heart

20
Q

How many views of the heart do the four limb leads provide?

A

6 views in the vertical plane

21
Q

Which leads are better for looking at the inferior surface of the heart?

A

Leads II, III and AVF

22
Q

Which leads are better for looking at the left side of the heart?

A

Leads I and aVL

23
Q

What view of the heart does the chest leads provide?

A

6 views of the heart in the horizontal plane

24
Q

Why do different chest leads have different shapes of QRS complex?

A
  • Right heart leads have no Q waves, a small R wave and large S waves.
  • Septal heart leads have larger R waves and smaller S waves
  • Left heart leads have large R waves and small S waves.

This is due to their differing proximities to parts of the heart

25
Q

What is the horizontal axis on an ECG?

A

Time - 5 large squares = one second

26
Q

What is the vertical axis on an ECG?

A

Voltage

27
Q

How can heart rate be calculated from a single PQRST wave?

A

Count number of large boxes between complexes (count R-R interval). Divide 300 by number of boxes. This is the heart rate

28
Q

How is heart rate calculated from an ECG if the rhythm is irregular?

A

Count number of QRS complexes in 6 seconds then multiply by 10

29
Q

How long should the PR interval be?

A

0.12 - 0.20 seconds

30
Q

How long should the QRS internal be?

A

Less than 0.12 seconds

31
Q

What is sinus bradycardia?

A

Sinus rhythm with rate of less than 60 beats per minute

32
Q

What is sinus tachycardia?

A

Sinus rhythm with a rate of more than 100 per minute

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