Electrocardiography Revisited w/ pictures Flashcards
What is the clinical relevance of the ECG?
Conduction abnormalities
Structural abnormalities
Perfusion abnormalities
Are electrodes, cables / wires, and leads all the same thing?
No Electrodes - sticky parts that stick onto the skin e.g. chest, limbs
Cables / wires - connect to the electrodes
Leads - views of the heart (i.e. the graph on the ECG)
What is the job of the leads?
What is a vector?
Pick up cardiac vectors
A quantity that has both, magnitude and direction
What are the advantages of ECGs?
Relatively cheap and easy to undertake
Reproducible between people and centres
Quick turnaround on results/report
What happens if the wave of excitation travels toward the negative electrode?
Downward deflections are towards the anode (-)
What happens if the wave of excitation travels toward the positive electrode?
Upward deflections are towards the cathode (+)
What does the isoelectric line represent?
Represents no net change in voltage. i.e. vectors are perpendicular to the lead
What does the steepness of the line relate to?
What does the width of the line relate to?
Steepness of line denotes the ‘velocity’ of action potential
Width of the deflection denotes the ‘duration’ of the event
What is the P wave?
What is the QRS complex?
What is the T wave?
The electrical signal that stimulates contraction of the atria (atrial systole)
The electrical signal that stimulates contraction of the ventricles (ventricular systole)
The electrical signal that signifies relaxation of the ventricles
What comprises the SAN?
Autorhythmic myocytes
Small amount of muscle that points more positive than negative
What does the action of the SAN show on an ECG?
Deflection is wide (slow)
Not very high (thin muscle)
Positive
What does the action of the AVN show on an ECG?
AVN depolarisation
Isoelectric ECG
Slow signal transduction
Protective
What does the Bundle of His divide into?
What does the action of the bundle branches show on an ECG?
2 bundle branches
Sharp but small downward spike - due to thin wall of muscle
What does the action of the purkinje fibres show on an ECG?
Ventricular depolarisation, followed by late ventricular depolarisation
Upward stroke, QRS peak
What does the action of the ventricular repolarisation show on an ECG?
Period of isoelectric status
Slow, domed T-wave
Where do you place the leads?
Rule of L’s:
Lead I (one L) Right Arm to Left Arm
Lead II (two L’s) Right Arm to Left Leg
Lead III (three L’s) Left Arm to Left Leg
What is the rule of reading for the leads to figure out which are the anodes / cathodes?
English is read left to right and top to bottom.
Polarity does that too.
Drawn as a triangle and reading left to right and top to bottom the first electrode of each pair you reach is the anode (-ve)
Right arm anode
Left Leg cathode
Left arm both
Where are the V1, V2, V3 and V4 electrodes placed?
V1 - Right sternal border In the 4th intercostal space
V2 - Left sternal border In the 4th intercostal space
V3 - Halfway between V2 and V4
V4 - Mid-clavicular line In the 5th intercostal space
Where are the V5 and V6 electrodes placed?
V5 - Anterior axillary line at the level of V4
V6 - Mid-axillary line at the level of V4
An ECG graph paper has big squares, that are further divided up into smaller squares?
What do each of these squares represent?
Big square - 0.2s, 0.5mV
Little square - 0.04s, 0.1mV