ECGs Flashcards
What electrodes make up aVL?
LA positive to RA and LL negative
What causes the R wave?
ventricular walls depolarise
What electrodes make up lead I?
RA negative to left arm positive
Where is V1 located?
fourth intercostal space right sternal edge
What electrodes make up lead III?
left arm negative to left leg positive
What happens to the S wave from V1 to V6?
decreases
Which limb is earthed for the standard limb leads?
right leg
What does the PR interval represent?
time for the SA node impulse to reach the ventricles
What does one large box represent?
0.2s and 5mm amplitude
What does the QRS complex consist of in the chest leads?
an R wave followed by an S wave
How do you calculate HR from an ECG with an irregular rhythm?
number of R-R intervals in 6s x 10
How do you tell if there is left axis deviation?
I = positive and aVF = negative
What is the position of the reference electrode in the augmented limb leads?
centre of the heart
Which limb leads view the heart from the left?
I and aVL
What electrodes make up aVR?
RA positive to LA and LL negative
What is the normal duration of the QT interval?
0.44s in males and 0.46s in females (when adjusted for HR)
What direction does lead II see the heart from?
anterior
What does the P wave represent?
time for completion of atrial depolarisation
What causes the T wave?
ventricular repolarisation spreads away from the recording electrode
What electrode is always negative in the standard limb leads?
right arm
Where is V4 located?
fifth intercostal space mid clavicular line
How do you calculate HR from an ECG in sinus rhythm?
300/number of large squares between beats or number of large squares in R-R interval
What electrodes make up aVF?
LL positive to RA and LA negative
What is the duration of a normal PR interval?
0.12 - 0.2 s 3-5small squares
How would you pick up stable angina?
exercise ECG - ST changes during and after exercise
Which chest leads look at the interventricular septum from the right?
V1 and V2
Where is V6 located?
same horizontal level as V4 mid-axillary line
What causes the S wave?
ventricles at base of heart depolarise
What does one small box represent?
0.04s and 1mm amplitude
What electrodes make up lead II?
right arm negative to left leg positive
What does the ST segment represent?
systole
What electrode is always positive in the standard limb leads?
left leg
What view of the heart do the chest leads provide?
horizontal
How do you analyse an ECG?
- verify patient details 2. check time and date ECG was taken 3. check calibration of the ECG paper 4. determine the axis if possible 5. workout rhythm 6. look at individual leads for voltage criteria changes or any ST or T wave changes
Where is V2 located?
fourth intercostal space left sternal edge
How do you tell if there is right axis deviation?
I = negative and aVF = positive
Where is the reference electrode for the chest leads located?
centre of the heart
Where is V3 located?
mid way between V2 and V4
How would you pick up intermittent rhythm disturbances?
ambulatory ECG for 24 hrs or 7 days
Where is V5 located?
same horizontal level as V4 anterior axillary line
What is the PR interval?
start of the P wave to the start of the QRS
What causes the Q wave?
ventricular depolarisation starts in the interventricular septum and spreads from left to right
What causes an upward deflection on the ECG?
depolarisation moving towards the positive/recording electrode
In which augmented limb leads are the waves negative?
aVR
Which chest leads look at the anterior of the heart?
V3 and V4
What does the TP segment represent?
diastole
What is the normal QRS duration?
≤0.1s <3 small squares
What lead is often used as the rhythm strip?
lead II
What is the normal length of time for a P wave?
≤0.12s
What causes a negative deflection on the ECG?
depolarisation moving away from the recording electrode
What is the ST segment?
end of QRS to the start of the T wave
Which limb leads view the heart from an inferior direction?
II, III and aVF
What is the QT interval?
start of QRS to end of T wave
What conditions can present with a normal ECG?
NSTEMI, intermittent rhythm disturbances, stable angina
What provides the reference electrode for the chest leads?
standard limb leads linked together
What causes the P wave?
atrial depolarisation spreads from SA node towards the recording electrode
What does prolongation of the QT interval cause?
predisposition to arrhythmias
Where are the electrodes positioned for the standard limb leads?
right arm, left arm and left leg
Which chest leads look at the lateral aspect/left ventricle of the heart?
V5 and V6
What happens to the R wave form V1 to V6?
increases
How do you tell if there is extreme axis deviation?
I and aVF are both negative
How do you tell if the axis is normal?
I and aVF are both positive
Why is atrial repolarisation not visible on the ECG?
It occurs during the QRS complex so is masked
