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

Flashcards in CVS - ECG Deck (32)
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What is 'sinus rhythm?'

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


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

Left ventricle


What are Purkinje fibres?

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


Outline the cardiac cycle?

- 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


What does an ECG record?

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


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



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

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


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

Across the heart, slightly towards the electrode


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

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


Where is the sinoatrial node located?

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


How does atrial depolarisation spread across the heart?

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


Why is there a delay at the AV node?

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


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

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


How does the interventricular septum depolarise?

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')


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

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.


How would left ventricle hypertrophy affect the R wave?

It would be correspondingly taller


What is the T wave caused by?

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


How many electrodes are attached in a 12 lead ECG?

10 electrodes - 4 on limbs, 6 on chest


What are 'leads' in an ECG?

Views of the heart


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

6 views in the vertical plane


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

Leads II, III and AVF


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

Leads I and aVL


What view of the heart does the chest leads provide?

6 views of the heart in the horizontal plane


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

- 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


What is the horizontal axis on an ECG?

Time - 5 large squares = one second


What is the vertical axis on an ECG?



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

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


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

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


How long should the PR interval be?

0.12 - 0.20 seconds


How long should the QRS internal be?

Less than 0.12 seconds

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