3. ECG Flashcards
What is responsible for the P wave form?
Atrial depolarisation
What does the PR interval represent?
Delay at AV node
How long should the PR interval last?
.1 second
What does the Q wave represent?
Left bundle branch depolarising the intraventricular septum
Why is the Q wave deflected negatively?
Moves from left heart to right heart so causes negative deflection as it moves towards negative electrode
What does the QRS wave represent and why is it shown as positive?
Depolarisation of the ventricles
Left ventricle is bigger than right so mean vector is towards positive electrode
What is the S wave?
Depolarisation moves upwards and around ventricles, causing a negative deflection as they move away from positive electrode
Why is the T wave shown as a positive deflection?
Wave of negative charge moves towards the negative electrode so it appears positive
Which leads show the inferior view of the heart?
2, 3, AVF
Which leads show the anterior surface of the heart?
V1-4
Which leads show the lateral surface of the heart?
1, AVL, V5, V6
Which leads show the right atrium?
V1, AVR
Which leads show the Q wave?
3, AVR, V1, V6
How long is a normal P wave?
120-200mS
How long is a normal QRS complex?
<120mS
What is the value of 1 large box and 1 small box on the x-axis?
Large: .2 seconds
Small: .04 seconds
What is the value of 1 large box and 1 small box on the y-axis?
Large: .5
Small: .1
How do you calculate the HR using an ECG for a regular rhythm?
Count the number of boxes between 2 QRS and then divide 300 by that number
How do you calculate the HR using an ECG for an irregular rhythm?
Multiply number of QRS on rhythm strip by 6
What does no p wave mean?
Atrial fib
What does a sawtooth pattern on ECG mean?
Atrial flutter
Define 1st degree heart block
PR interval>200mS
What can 2nd degree heart block be classified into?
Mobitz type 1 and 2
Define 2nd degree mobitz type 1 heart block
Progressively prolonged PR until QRS is missing
Define 2nd degree mobitz type 2 heart block
Prolonged PR and a new ratio of PR:QRS
Define 3rd degree heart block
No relation between p and QRS
What is the axis of an ECG?
Average direction of flow of electricity through the heart
What is a normal axis?
90 to -30 degrees
What range is a left axis deviation?
-30 to -90
What range is a right axis deviation?
90 to 180
Describe how to find the axis on an ECG
Find the lead with the smallest deflections
Find the lead perpendicular to this lead; is it mostly positive or negative?
Where is this lead positive/negative?
How is bundle branch block seen on an ECG?
QRS >120mS, due to slow depolarisation through blocked branches
How can a right BBB be seen on an ECG?
QRS>120
M-shaped QRS in V1
Prominent S wave in 1 and aVL
What are the causes of right BBB?
Lung disease
PE
Atrial septal defect
How can a left BBB be seen on an ECG?
QRS >120
Broad R wave in 1, aVL, V6
ST depression leading into an inverted T wave
What are the causes of left BBB?
STEMI
Aortic stenosis
Cardiomyopathy
What are the causes of an elevated ST segment?
Acute transmural infarction
Pericarditis
Aneurysm
Brugada syndrome
What are the causes of a depressed ST segment?
NSTEMI
Digoxin
Hypo K+, Ca++, Mg++
What are the causes of a peaked T wave?
Hyperacute infaction
Hyper K+, Ca++, Mg++
What are the causes of an inverted T wave?
Infarction
Ischaemia
Hypo K+, Ca++, Mg++
What 2 indexes are used to determine the hypertrophy voltage criteria?
Sokolow-Lyon index
Cornell
What is the Sokolow-Lyon index?
S in V1 + R in V5/6 > 7 big squares
What is the Cornell index?
S in V3 + R in aVL >28mm (men) >20 (women)
What are the causes of hypertrophy?
Hypertension
Ischaemic heart disease
Cardiomyopathy
Aortic stenosis
