L12: Understanding the ECG Flashcards
Define depolarisation?
Change within a cell of electrical charge distribution
Leading to less negative charge inside the cell
Happens through movement of ions (Na+, K+, Cl-)
Define repolarisation?
Change within a cell of electrical charge distribution
Leading to more negative charge inside the cell
Define resting membrane potential?
Separation of charge across cell membrane
Measure electrical imbalance between the inside and outside of the cell measured in mV
Define action potential?
Brief reversal of cell membrane electrical polarity that is then propagated from cell to cell
What is meant by deflection?
Deviation from straight line, upwards deflection or downwards deflection
What do ECG allow?
Electrocardiograms provide information about cardiac electrical activity from 12 separate views of the heart
Describe the electrical conduction across the heart?
Sinoatrial node
Intrinic rhythm–> spontaneously generate AP
Specialised cardiac myocytes–> pacemaker cells
Wave of depolarisation across the atria through gap junctions–> excitation-contraction coupling
Passes to the Atrioventricular node (AV node)
Slows electrical conduction down
Allowing time for atria to contract
Passes to Bundle of His–> passes through the Annular Fibrosis
Divides into Right Bundle branch of His and Left Bundle branch of His
Pass to purkinje fibres which result in depolarisation of the ventricles from the base upwards
Where is the sinoatrial node located?
Upper part of right atrium
Junction between RA and SVC
Where is the AV node located?
Interatrial septum
near Tricuspid valve
Where is the Bundle of His located?
Interventricular septum
What is the annulus fibrosis?
Fibrous skeleton of the heart
Anchor point for cardiac valves and myocardium
Insulator between atria and ventricles
Four fibrous rings joined together
What are the difference between the SA node and the AV node?
SA node–> fast depolarisation, 60-100bpm, sets HR and rhythm–> Sinus rhythm
AV node–> Slows conduction, allows atrial contraction to take place, Intrinsic firing rate slower 40-60bpm
Do the left and right bundle branches have intrinsic activity?
Intrinsic firing
Much slower 20-40bpm–> not sustainable
What does an ECG do?
Measure changes in electrical potential produced in the myocardium during the cardiac cycle via a series of leads
What does the ECG actually measure?
Electrical activity transmitted to the chest wall
What does ECG lead mean?
Can mean:
- Cable used to connect the electrode to the recorder
- View of the heart
How is an ECG recorded?
12 different views of the heart
10 different electrodes used
- 4 electrodes on limbs –> Right arm, right leg, left arm and left leg
- 6 electrodes on chest–> V1-6