ECG1 Flashcards
What are electrodes?
They are in contact with the skin- foam or plastic
What are cables/ wires?
They connect the electrodes to the machine
What are leads?
They are the lines on the ECG machine
What is an isoelectric line on an ECG?
Represents no net change in voltage. I.e. the vectors are perpendicular to the lead.
What does the width of deflection show?
The duration of the event
What are upward deflections?
Towards the cathode
What are downward deflections?
Towards the anode
What does the steepness of the line indicate?
Steepness of the line denotes the velocity of the AP.
Another word for this is the amplitude
What is the p-wave?
electrical event that stinulate contraction of the atria
(atrial systole)
What does the QRS complex signify?
The electrical signal that stimualtes contraction of the ventricles
(ventricular systole)
What does the T wave signify?
The electrical signal that signifies relaxation of the ventricles.
(ventricular diastole)
Ventricular repolarisation- ventriuclar myocytes repolarise back to resting membrane potential.
The delay?
There is a notable delay between the electrical signal peaks (ECG) and pressure changes. LEARN THE SHAPES OF THE GRAPHS
What is the PR segement?
The pause between the atrial and ventricular depolarisation- caused by the AV node which is a block to the conduction.
What does the AV node do?
Delays the impulse to allow for filling
Describe the bundle of His
comprised of purkinke cells that conduct rapidly;
conducts then bifurcates to left and right bundle branches to deliver impulse to base of heart to allow base up contraction
left bundle branch not insulated as much as right; allows septum to contract first before the ventricular walls
The conduction velocity differences along the conduction system
The SAN and AVN have similar conduction speeds (curves)- basically negligible compared to all the other cells and structures inside the heart.
Bundle of his has the largest conduction velocity.
As the curves have been stacked up on top of each other, you can see the delay in initiation of contraction.
Cardiac vectors: SAN
Responsible for the P wave.
Comprised of autorhythmic myocytes that cause atrial depolarisation.
Cardiac vectors: AVN
Isoelectric point- responsible for the PR segment
AVN depolarisation, slow signal transduction (2-5ms)
Protective function for the heart cos the fours chambers can’t all contract together.
Cardiac vectors: Bundle of His
The very last bit of the PR segment (straight bit).
This is small because its so rapid.
Very insulated therefore high conduction speed.
Cardiac vectors: Bundle branches
The small deflection downwards before the QRS complex.
This is due to the septal depolarisation.
Cardiac vectors:Purkinje fibres (1)
Ventricular depolarisation
(1) is the upwards deflection of the QRS complex
Cardiac vectors: Purkinje fibres 2
Late ventricular depolaristation
The small downward deflection of the QRS complex (just before S)
Cardiac vectors: Fully depolarised ventricles
The S-T segment
Isoelectronic ECG, no electrical activity at this point.
Cardiac vectors: Repolarisation
The T wave
Ventricular repolarisation
Upward deflection, heading to the negative electrode
deflection and anodes
A downward deflection is towards the anode. The anode is near the feet so this makes sense
An upward deflection is towards the cathode (which is actually on the right arm). This also makes sense.
Just think about it.
