First look at an ECG Flashcards
Where is the different standard leg limbs measured from
SLL I = left arm wrt right arm
SLL II = left leg wrt right arm
SLL III = left leg wrt left arm
In an ECG what does the P wave correspond to
atrial depolarisation
In an ECG what does the QRS complex correspond to
ventricular depolarisation
In an ECG what does the T wave correspond to
Ventricular re-polorisation
A wave of approaching depolarisation cause what on an ECG
an upward Blip
What events record better on an ECG
Fast events
What does an ECG look for
Look for disorders of rhythms or conduction
What is examples of disorder or rhythms of conduction
atrial flutter, atrial fibrillation,
ventricular fibrillation
What is the action of a defibrillator
puts all cells into refractory period so that they can restart conduction
A typical ECG shows what limb lead
Standard limb lead II recording from the left leg (+) with respect to the right arm (-)
If a wave of depolarisation moves towards left leg(+) what outcome does this show on the ECG
Positive blip
as creates a positive potential in relation to the arm
If a wave of depolarisation moves towards the right arm (-) what is the outcome on the ECG
Negative blip
as a positive wave is moving towards the negativity of the arm = negative potential
If a wave of re-polarisation moves toward the right arm what is the outcome of the ECG
Positive blip,
a negative wave is moving towards the negativity of the arm = cancel each other out creating a positive potential
What is the PR interval and what is it mainly due to
Time from artirial depolarisation to ventricular depolarisation
What is PR interval mainly due to and how long is transmission
transmission through AV node
~0.1-0.2 sec
What is the QRS and how long does this take
Time for the whole of the ventricle to depolarise
(~ 0.08 sec)
What does the QRS prove
How well the Purkinje fibers are working
What does the QT interval show
time spent while ventricles are depolarised
What does the length of depolarisation depend on for the QT interval
Varies with Heart rate
What is the length of the QT interval
0.42 sec at 60 bpm- resting HR
Why cant you see arterial re-polorisation on an ECG
Because atrial repolarisation coincides with ventricular depolaristion. Ventricular depolarisation involves much more tissue depolarising much faster so it swamps any signal from atrial repolarisation.
Why is the QRS complex so complex
Because different parts of the ventricle depolarise at different times in different directions
What is the three directions of the QRS complex
1st – the interventricular septum depolarises to the right
2nd – the bulk of the ventricle depolarises from the endocardial to the epicardial surface going down the septum transverse
3rd – the upper part of the interventricular septum depolarises to the left
Where is the summation of the QRS complex
add all togethers by wave of depolorisation going down the septum transverse
Why is the T wave a positive blip if it is due to ventricular re-polarisation
The re-polarisation travels back the way towards the arm opposing direction of depolarisation, this is a negative charge moving in a negative direction therefore this negative double negative creates a net gain of a positive
signal moves away from recording electrode and produce this positive blip
what is the interval from the beginning of the QRS to the apex of the T wave called
absolute refractory period
what is the last half of the T wave refers to as
relative refractory period
Why is the R wave bigger in SLL II compared to the others
as the main vector of depolorisation is is line with the recording of the left leg to the right arm going along the septum tranversum
if hypertrophy occurred and the heart shifted towards the left where would the R wave be the biggest
Would get a bigger recording in SLL I
if hypertrophy occurred and the heart shifted towards the right where would the R wave be the biggest
Would get a bigger recording in SLL III
What is augmentended limb lead recording
recording from one limb lead with respect to the other two combined
- Electrical angles of the heart
What is the benefit of augmented limb leads
it gives you 3 other perspectives on events in the heart
What is the three other perspective gained from augmented limb lead recording
aVR, aVL and aVF
Augmented limb lead recording produces what over all
give you 6 different views of events occurring in the frontal (or vertical) plane
How is precordial chest leads aligned
These are arranged in front of the heart and therefore look at the same events, but in the transverse plane
What are the results of the precordial chest leads
Look at the spread of depolarisation showing progression
flipping negative to positive waves
What is the differentiation between limb leads and precordial chest leads
Limb meads look at: spread of depolarisation (and repolarisation) from 6 angles in the frontal plane
Precordial leads look at: the same events from 6 angles in the transverse plane
What measuring technique one will affect the results of the ECG and why
precordial due to change in the spread of depolarisation
What is the normal Heart rate, brachycardia, tachycardia
Normal - 60bpm
Brachy - < 60bpm
Tachy - > 60bpm
What information does a rhythm strip tell me
Heart rate
How do you measure heart rate on a rhythm strip
Measure the R - R interval
count how many occur in 60 seconds
or count how many occur in 30 large squares and multiply by 10
What other information can be gathered by a rhythm strip
Is each QRS complex preceded by a P-wave
Is the PR interval too short (<0.12 sec) or too long (>0.2 sec)
Is the QRS complex too wide (>0.12 sec)
Is the QT interval too long (>0.42 sec at 60 bpm)
What is elevated in a STEMI myocardial infarction
ST
What does NSTEMI means
no ST elevated myocardial infarction
What myocardial infarction is worse
STEMI
