Basic ECG (Reading) Flashcards
Why is it necessary to do multiple ECGs?
Takes only one picture in time
Need to do multiple to compare
What other lead ECGs can be done?
3 and 5
What is the baseline?
Isoelectric line
What is the ECG paper speed?
25 mm/sec
What is the paper square size?
Small square = 0.04 sec
Large square = 0.2 sec
Small square = 0.1 mV
2 large squares = 1 mV
What is happening in the heart if the line is flat at any time in the ECG?
No electrical activity at that particular moment
What does the direction in which the waves point indicate?
Whether electricity is moving towards or away from a particular lead
What are the six chest leads and where are they attached?
V1, V2, V3, V4, V5, V6
Attached across patients chest
What are the three limb leads and where are they attached?
aVR = right arm aVL = left arm aVF = left leg
What is the lead that is attached to the right leg?
Earth, not active lead
What are the three bipolar leads?
Lead I, lead II, lead III
What is Einthoven’s Triangle?
Triangle, or line of sight created by the three limb leads
These form leads I, II, and III
Leads run negative to positive
What forms lead I?
aVR (-) to aVL (+)
What forms lead II?
aVR (-) to aVF (+)
What forms lead III?
aVL (-) to aVF (+)
What is the universal monitoring lead?
Lead II
How do you measure the rate with a regular rhythm?
Number of large squares between 2 R waves/300
How do you measure the rate with an irregular rhythm?
Number of QRS complexes in 6 second strip x10 OR
Number of QRS complexes on an ECG page x6
What does the P wave represent?
Atrial depolarisation
SA node firing
What is the intrinsic rate of the SA node?
60-100 bpm
What should the P wave be?
Rounded and upright in all leads, except aVR
Less than 0.12 sec (3 small squares)
1:1 with QRS complex
What does a peaked P wave mean?
Right atrial enlargement
What does a bifid or prolonged P wave mean?
Left atrial enlargement
What does the PR interval represent?
SA node to AV node
What should the PR interval be?
0.12-0.20 sec (3-5 small squares)
What is the intrinsic rate of the AV node?
40-60 bpm
What does a shortened PR interval mean?
Pre-excitation or alternate accessory pathway exists
What does a prolonged PR interval mean?
AV block
What does the Q wave represent?
First negative deflection
Depolarisation of bundle of His (septum)
When is the Q wave abnormal and pathological?
If >2 mm in depth or >1/3 of R wave height
What does an abnormal Q wave indicate?
Previous myocardial infarct
What does the QRS complex represent?
Ventricular depolarisation
What should the duration of the QRS complex be?
Less than <0.12 sec (3 small squares)
What does a prolonged QRS complex mean?
Conduction delay or if impulse generated in ventricles
What can vary the QT interval?
Gender
Time of day
Heart rate
What is the normal QT interval?
Less than 0.44 sec (11 small squares)
Less than half of RR interval
What does a prolonged QT interval indicate?
Delayed repolarisation due to many causes:
- Congenital
- Low electrolyte levels
- Drugs; eg: tricyclic antidepressants
How does the R wave change from V1 to V6?
Becomes more upright
V3 often biphasic
What should the ST segment be?
Isoelectric
What change in the ST segment is indicative of a myocardial infarction?
ST elevation >2 mm in chest leads or >1 mm in limb leads
What can an ST depression indicate?
Ischaemia
Reciprocal changes
What does the T wave represent?
Depolarisation of ventricles
What should the T wave look like?
Upright
Rounded
Larger than P wave
What can a T wave inversion indicate?
Myocardial ischaemia
What does a peaked T wave indicate?
Hyperkalaemia
When is the U wave most obvious?
Hypokalaemia
Which leads represent the lateral surface of the heart?
Low lateral = V5, V6
High lateral = I, aVL
Which leads represent the anterior surface of the heart?
V3, V4
Which leads represent the septal surface of the heart?
V1, V2
Which leads represent the inferior surface of the heart?
II, III, aVF
What does the S wave represent?
Second negative deflection
Depolarisation of Purkinje fibres
How do you determine the rhythm?
Is there a P wave?
Where is the rhythm being generated?
Map out R - R regularity
What indicates left atrial enlargement?
Bifid P wave
Terminal negative P wave deflection >1 mm deep and 0.04 (1 small square) long in V1
What indicates right atrial enlargement?
Peaked P waves in V1 and V2 >1.5 mm tall
What indicates left ventricular hypertrophy?
Add largest R wave of V5 or V6 to largest S wave of V1 or V2
Total >35 mm (7 large boxes)
R wave in aVL >9mm in females or >11 mm in males
What indicates right ventricular hypertrophy?
R wave in V1 >7 mm
S wave in V5 or V6 >7 mm
What indicates ischaemia or infarction?
In contiguous leads
- ST segment changes
- T wave inversion
- Pathological Q waves
