Week 8- ECGs Flashcards
What are the 5 letters used to represent the different sections during one heartbeat on an ECG?
P, Q, R, S, T
What does the P wave respresent?
Atrial depolarisation
What does the QRS complex represent?
Ventricular depolarisation
What does the T wave represent?
Ventricular repolarisation
During what stage of the ECG does atrial repolarisation occur? Does it show up?
During the QRS complex, it doesnt show up as its to small and overpowered by ventricular depolarisation
Which way does a normal P wave lie?
Upwards
Which way does a normal Q wave lie?
Downwards
Which way does a normal R wave lie?
Upwards
Which way does a normal S wave lie?
Downwards
Which way does a normal T wave lie?
Upwards
How long does a normal P wave last?
0.1 secs
How long does a normal PR interval last?
0.2 secs
How long does a normal QRS complex last?
0.08 secs
How long does a normal T wave last?
0.16 secs
How long does a normal QT interval last?
0.4 secs
What is a PR interval?
From the start of the P wave to before the start of the QRS complex
What is a PR segment?
From the end of the P wave to before the start of the QRS complex
What is a QT interval?
From the start of the Q wave to before the start of the T wave
What is a ST interval?
From the start of the S wave to before the start of the T wave
What is a ST segment?
From the end of an S wave to before the start of a T wave
What is visible on an ECG when heart rate increases?
Shorter distance between 2 adjacent R waves mainly due to the TP interval shortening
How are ECG signals measured?
Via pairs of electrodes, each pair is known as a lead
How many leads can be measured in and ECG?
12
How many electrodes are used during an ECG? Where are they found?
10- 6 on the chest and 4 on each limb (ankles and wrists)
If a wave of depolarisation travels towards a positive electrode, what will show up on an ECG trace?
A positive wave
If a wave of repolarisation travels towards a positive electrode, what will show up on an ECG trace?
A negative wave
What does lead I connect?
Right arm (negative) to left arm (positive)
What does lead II connect?
Right arm (negative) to left foot (positive)
What does lead III connect
Left arm (negative) to left foot (positive)
Which lead has the largest R wave and why?
Lead II as its most similar to the direction of ventricular depolarisation
What is a standard limb lead?
A bipolar lead formed by connecting the electrocardiograph between 2 corners of the triangle (left arm, right arm and left leg)
What are the 3 augmented limb leads?
aVf, aVr and aVl
Which direction does aVr flow?
Bottom left of torso (negative) to right of torso (positive)
Which direction does aVf flow?
From top middle of torso (negative) to left foot (positive)
Which direction does aVl flow?
From bottom right of torso (negative) to left arm (positive)
What is an augmented limb lead?
A composite lead formed by comparing a single positive electrode with a combination of the 2 other electrodes
How is aVr calculated?
RA-(LA+LF)
How is aVf calculated?
LF-(RA+LA)
How is aVl calculated?
LA-(RA+LF)
Are augmented limb leads bi or unipolar?
Unipolar
What does ‘augmented’ in augmented limb lead represent?
ECG is greater in magnitude
Which leads have a prominent R wave and a positive P and T wave?
I, III, aVf
Which lead has a negative QRS complex, P and T wave and why?
aVr as all electrical activity flows away from the lead
Where is V1 placed?
4th intercostal space, right side of the sternum
Where is V2 placed?
4th intercostal space, left side of sternum
Where is V3 placed?
5th rib, slightly lower than V2
Where is V4 placed?
5th intercostal space mid clavicular line
Where is V5 placed?
6th intercostal space anterior axillary line
Where is V6 placed?
7th rib, anterior axillary line
What part of the heart do leads V1 and V2 face?
Wall of the right ventricle
What part of the heart do leads V3 and V4 face?
Intraventricular septum
What part of the heart do leads V5 and V6 face?
The left ventricle ( at a distance)
Why do leads viewing the heart from the right side have large negative S waves?
Left ventricular muscle mass of the heart is a lot higher than the right ventricular muscle mass
Why may leads V3 and V4 have more prominent R and S waves?
They are close to the intraventricular septum
What direction are P waves in leads V1 and V2?
Positive or bisphasic
What direction are P waves in leads V4 and V6?
Always positive
What direction are T waves in leads V1 and V2?
May be inverted
What direction are T waves in leads V3 and V6?
Always positive
In what plane do the limb lead view the heart?
Coronal
In what plane do chest leads view the heart?
Transverse
Are chest leads uni or bi polar?
Unipolar- they are single positive recording electrodes
On a 12 lead ECG recording, what leads appear on the first row (go from left to right)?
aVR, V1 then V4
On a 12 lead ECG recording, what leads appear on the second row (go from left to right)?
aVL, V2 then V5
On a 12 lead ECG recording, what leads appear on the third row (go from left to right)?
aVF, V3 then V6
