ECG Flashcards
What does the P wave represent?
Atrial depolarisation
When does the PR interval start?
Begins at start of P wave and ends at beginning of Q wave
What does the PR interval show?
Represents time taken for electrical activity to move between atria and ventricles
What does the QRS complex represent?
Depolarisation of ventricles
When does the ST segment start?
Starts at end of S wave and ends at beginning of T wave
What is the ST segment?
An isoelectric line that represents the time between depolarisation and depolarisation of the ventricles (i.e. ventricular contraction)
What does the T wave represent?
Ventricular repolarisation
Where does the RR interval begin and end?
begins at peak of one R wave and ends at the peak of the next R wave
What does the RR interval represent?
time between two qrs complexes
Where does the QT interval begin and end?
Begins at start of the QRS complex and finishes t the end of the T wave
What does the QT interval represent?
Time taken for ventricles to depolarise and then depolarise
What is a 12 lead ECG?
records 12 leads (imaginary line) producing 12 separate graphs on piece of ECG paper
How many physical electrodes are attached to the patient to generate 12 leads?
10
Where is V1?
4th intercostal space - right sternal angle
Where is V2?
4th intercostal space - left sternal angle
Where is V3?
midway between V2 and V4
Where is V4?
5th intercostal space - midclavicular line
Where is V5?
left anterior axillary line - small horizontal level as V4
Where is V6?
left mid-axillary line - same horizontal level as V4 and V5
Where are the limb electrodes placed?
LA - left arm
RA- right arm
LL- left leg
RL- right leg neutral not used in measurements
What is the chest lead V1?
septal view of heart
What is the chest lead V2?
septal view of heart
What is the chest lead V3?
anterior view of heart
What is the chest lead V4?
anterior view of heart
What is the chest lead V5?
lateral view of heat
What is the chest lead V6?
lateral view of heart
What is lead I?
Lateral view (RA-LA)
What is lead II?
Inferior view (RA-LL)
What is lead III?
Inferior view (RA-LL)
What is lead aVR?
Lateral view (LA+LL-RA)
What is lead aVL?
lateral view (RA+LL - LA)
What is lead aVF?
(RA+LA -LL)
When do you get positive deflection?
travels towards hear
When do you get negative direction?
travels away from heart
What does the higher deflection show?
greater amount of electrical activity flowing towards lead
What does it mean if R wave is greater than S wave?
depolarisation moving towards that lead
What does it mean if S wave is greater than R wave?
depolarisation moving away from that lead
What does it mean if R and S waves are of equal size?
depolarisation is travelling exactly 90 degrees tot hat lead
Which leads show inferior view of heart?
II, III, aVF
Which leads show lateral view of the heart?
I, aVL, V5, V6
Which leads show anterior view of heart?
V3, V4
Which leads show septal view of heart?
V1, V2
Where would the axis lie in healthy individuals?
between -30 and +90 degrees
Where is the overall direction of electrical activity towards?
Lead I II and III (positive deflection in these lead with most in lead II)
Where would the most negative deflection be?
aVR
What is right axis deviation?
direction of depolarisation distorted to right (between +90 and +180degrees)
What is the most common cause of RAD?
-Right ventricular hypertrophy e.g. in pulmonary hypertension and can be normal finding in very tall individuals
What does RAD mean for deflections?
In lead I become negative and in lead aVF / III to become more positive
What is left axis depolarisation?
Direction of depolarisation distorted to the left (between -30 and -90 degrees)
What deflection for LAD result in?
defection of lead III becoming negative (only significant in deflection of lead II becomes negative)
What is LAD usually caused by?
conduction abnormalities
