ECG

Question 1

Name the standard limb leads

Answer 1

SLL I= left arm wrt right arm
SLL II= left leg wrt right arm
SLL III=left leg wrt left arm

Question 2

Basic principles of SLL

Answer 2

• When the electrical activity of the heart travels towards a lead you get a positive deflection.
• When the electrical activity travels away from a lead you get a negative deflection.

Question 3

SLL II reading from the LL relative to the RA

Answer 3

Wave of depolarisation
»RA wrt LL= positive
&laquo_space;LL wrt RA= negative

Question 4

Describe the PQRST wave

Answer 4

P=atrial depolarisation
QRS= ventricular depolarisation
T=ventricular repolarisation

Question 5

What is the PR, QRS + QT interval?

Answer 5

PR interval=time from atrial depolarisation to ventricular depolarisation due to transmission through the AV node

QRS= time for whole ventricle to depolarise

QT interval= time spent while ventricles are depolarised ( dependent on HR)

Question 6

Why isn’t atrial repolarisation seen on the PQRST wave?

Answer 6

-atrial repolarisation occurs at same time as ventricular depolarisation. This involves more tissue depolarising faster overpowering any signal from atria repolarisation

Question 7

Describe ventricular depolarisation

Answer 7

Different parts of the ventricle depolarises at different times;

1. Intraventricular septum depolarises from left ot right
2. bulk of the ventricle depoalrises from the endocardial to the epicardial surface
3. The upper part of the IV septum depolarises

Question 8

Why is the T wave positive going?

Answer 8

-The AP is longer in endocardial cells vs epicardial cells, so the wave of repolarisation runs in the opposite direction to the wave of depolarisation. The wave of repolarisation moving away from the recording elecreode produces another positive going blip

Question 9

Why is the R wave bigger in SLL II than in SLL I or SLL II

Question 10

What would happen if heart was rotated to the left/developed hypertrophy on the left/atrophy on the right?

Answer 10

• axis deviation

- Extra heart muscle causes a stronger positive signal to be be picked up by leads

Question 11

What extra information fo the augmented limb give you?

Answer 11

-recordinfs from SLLs I, II, III and aVR, aVL, aVF give you 6 different views of events occuring in the frontal(or vetrical) plane

Question 12

What extra info do the precordial ( chest) leads give you? Pericardial ( chest leads) vs Limb leads

Answer 12

Limb leads
- look at the spread of depoalrisation/repolarisation from 6 angles in the FRONTAL plane.

Pericardial leads
-Looks at same events from 6 angles in TRANVERSE plane
arranged infront of heart, so look at the same events but in the horizontal(transverse) plane.

• Since main vector of depolarisation is as shown, it will produce a negative blip going when recorded from V1, a positive going blip from V6 and flip over at V3/V4.
• '’progression’’

Question 13

How to calculate HR from the rythmn strip

Answer 13

Heart rate:
Measure the R-R interval and work out how many occur in 60 sec, or better ..
Count the R waves in 30 large squares (= 6 sec) and multiply by 10
60-100 beats per min = normal
Below 60 beats per minute = bradycardia
Above 100 beats per minute = tachycardia

Question 14

What is the STEMI malarkey?

Answer 14

STEMI = ST elevated myocardial infarction
NSTEMI = non-ST elevated myocardial infarction

ST elevation indicates a heart attack. Can be used to classify severity of it. STEMI is worse than NSTEMI