L12 Electrocardiogram Flashcards
(38 cards)
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?
- Depolarisation moving towards exploring electrode (in direction from which the electrode views the heart)
- Repolarisation moving away from the electrode
What 2 events give Negative deflection?
- 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?
in the VERTICAL 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 VF= LEFT LEG
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
