CVS - ECG Flashcards
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?
Positive
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.
