L12 Electrocardiogram Flashcards Preview

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Flashcards in L12 Electrocardiogram Deck (38):

What is ECG?

ECG = recording at surface of body of electrical activity originating from the heart


Does ECG record individual AP or total depolarisation?

Individual AP = 70-80 mV change cannot detect

whole heart depolarizes can detect


Does ECG record accurate AP values or just the wave/ shape of depolarisation

movement of wave of AP, not actual value


Relate all of P-Q-R-S-T to electrical events

P wave= atrial depolarization (initiation of AP)

QRS complex – ventricular depolarization (rapid depolarization phase)

T wave – ventricular repolarization (end of ventricular AP)


Dissect the QRS complex and relate to different parts of the heart.

 Q – interventricular septum
 R – main body of ventricular muscle (dominated by larger
left ventricle)
 S – upper septum + high posterior walls (dominated by right ventricle)


Slow AP cells and Fast AP cells. Which belongs to which?

Slow AP = AV and SA node
Fast AP= Atrial and ventricular muscle and Purkinje fibre


What is bipolar and unipolar ECG? What are the names of the electrodes?

Bipolar = between 2 points on the body surface ( +/- electrodes) = record p.d.

Unipolar= from one point on body surface relative to ground (exploring and indifferent electrodes)


What 2 events can give positive deflection?

1. Depolarisation moving towards exploring electrode (in direction from which the electrode views the heart)

2. Repolarisation moving away from the electrode


What 2 events give Negative deflection?

1. Repolarisation towards the electrode

2. Depolarisation moving away from the electrode


What is cardiac vector?

Total electrical activity of heart:
 = sum of all individual movements of potential waves
 Has both magnitude and direction


How can unipolar leads voltage signal be augmented?

May record between 1 limb and other 2 limbs = augmented (aVR, aVL, aVF) = increases size of
voltage signal


What gives no deflection?

Depolarisation / repolarisation moving at 90° to the electrode


Limb leads views the heart in what plane?



Unipolar limb leads view the heart from what direction?

From the direction of the exploring electrode


Bipolar limb leads view the heart from which direction?

A direction halfway between the +ve and the OPPOSITE of the -ve electrode


Limb leads are equally spaced or not.

yes. 120 degrees in between


Whilst limb leads view the heart in vertical plane, what do precordial leads close to heart view the heart in?

In the horizontal plane


What structure gives larger deflection in precordial leads?

Structures close to the electrode


How many precordial leads are there?

V1 to V6


Run through the location of each precordial exploring electrode.

V1 = 4th ICS, Right sternum border
V2= 4th ICS, Left sternum border
V3= halfway between V2 and V4
V4= Left 5th ICS intersect MCL
V5= Left 5th ICS intersect Left Anterior axillary line
V6= Left 5th ICS intersect Left MAL


Where are the exploring precordial electrodes located over the heart?

V1 and V2 located over RV

V3 and V4 over inter-ventricular septum

V5-V6 over left ventricle


What are the expected wave magnitude for each of the 6 precordial leads?

V1 - 2: S > R wave
V3 - 4: S=R wave
V5 - 6: R>S wave


Where are VR, VL and VF limb leads placed?

VR= Right arm
VL= Left arm


Bipolar standard limb leads has +ve and -ve electrodes.
There are three ways to place the electrodes. List all three.

Lead I:
-ve = Right arm (VR)
+ve = Left arm (VL)
viewing angle= left horizontal

Lead II
-ve = Right arm (VR)
+ve = Left leg (VF)
v.a.= +70 degrees to horizontal (same as
ventricular depolarization)

Lead III
-ve = Left arm (VL)
+ve = Left leg (VF)

v.a.= 30 degrees to right from directly down


Bipolar lead 1,2,3 and unipolar lead VR VL VF gives how many viewing angles?

Total 6 viewing angles from vertical plane


Atrial depolarisation
What is the route of impulse spread?
Direction of spread?

SA node > AV node

 Downwards
 To the left


Ventricular depolarisation
What is the route of impulse spread?
Direction of spread?

Majority = through ventricular muscle:
inner > outer surface

 Down
 To the left
(L ventricle has greater bulk than R ventricle: thicker wall , more muscle cells = more AP)


Ventricular repolarisation
What is the route of impulse spread?
Direction of spread?

Myocardium: outer (epicardial) > inner
(endocardial) surface

**Repolarization** away =
 Downwards
 To the left
 (Also dominated by left side)


What are the average vectors of three electrical events?
Atrial depolarisation Ventricular depolarisation Ventricular repolarisation

Atrial depolarisation
+45°from horizontal

Ventricular depolarisation
+60° from horizontal

Ventricular repolarisation
~ +35°to +40°


What can you expect from Bipolar limb lead 1 ECG?

R, T almost same height:
 R: bigger magnitude but more perpendicular
 T: smaller magnitude but more aligned


What can you expect from Bipolar limb lead 2 ECG?

Gives largest R wave >
used for calculating HR

Vent. depolarisation is in exact direction to Lead 2


What can you expect from Bipolar limb lead 3 ECG?

Shallow P, T waves*
Moderate R wave as vent. depol. is less than 90 degrees from viewing lead

*Atrial depolarisation (P) and ventricular repolarisation (T) are almost 90 degrees from viewing angle


What does PR interval tell? QT interval?

PR= conduction time in AV node
QT= ventricular AP


What timing info can be obtained from ECG? (2)

1. Rate (no. of R waves / min)
2. Rhythm (regular / irregular time interval)


What is a heart block?

2-to-1 AV block (not all atrial depolarization are transmitted to ventricles)
R wave doesn't follow Q wave


myocardial hypertrophy shows itself on ECG, how?

extra-large R wave


Ischaemia shows itself on ECG. How?

ST segment depression in V3- V6: know which part of heart is affected, which artery supplies it


What is STEMI vs NSTEMI?
ST-elevation myocardial infarction

STEMI= sudden complete (100 percent) blockage of a heart artery (coronary artery)

NSTEMI= a severely narrowed artery but the artery is usually not completely blocked.

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