EKG Tutorial & PSW 1 - Introduction to EKG Flashcards
By convention, how can we conceive of the electrical waves traveling in the heart?
As waves of positive electrical charges moving through space
What does an upright wave on the EKG mean?
Means that a positive wave moves toward a positive electrode
Is an upright EKG wave positive or negative?
Positive
How fast are both ventricles depolarized normally?
Very rapidly, in less than 120 ms
What does the QRS represent on the EKG?
Ventricular depolarization
What does an downright wave on the EKG mean?
Means that a negative wave moves toward a positive electrode
What is the Q wave on the EKG?
Initial negative deflection of the QRS complex
What is the R wave on the EKG?
Any positive deflection of the QRS complex
What is the S wave on the EKG?
Any negative deflection following a positive deflection
Do all QRS complexes have a S wave?
NOPE => QR wave
Do all QRS complexes have a Q wave?
NOPE => RS wave
How do you call a negative deflection by its own?
Q wave
Describe the waves of a cardiac cycle on an EKG, including the 2 segments.
- P wave: atrial depolarization
- PR segment: AV node conduction (including delay)
- QRS complex: ventricular depolarization (phase 0)
- ST segment: plateau phase of ventricular repolarization (phase 2)
- T wave: phase 3 of ventricular repolarization
What does the direction of the T wave follow?
The overall direction of the QRS complex because they are opposite sign waves moving in opposite directions => concordant direction on an EKG
Is repolarization a positive or a negative wave?
Negative
Why doesn’t atrial repolarization appear on an EKG?
Because they represent such a small volume of cells in the heart and is included somewhere in the QRS complex which overwhelms that small electrical activity
Unit of EKG axes?
- x: time
- y: voltage
Dimensions of EKG squares?
- Small ones: 1 mm x 1mm
- Large ones: 5 mm x 5 mm
Speed of EKG paper? 3 ways of saying it.
- 25 mm/s
- 0.2 s/5mm = 200 ms/5mm
- 0.04 s/1mm
Duration of P wave + PR interval?
0.16 s
Duration of QRS complex?
0.08 s
Where are electrodes for normal limb leads on the body of the patient? Describe the polarity of the electrodes placed.
- Right arm: (-) and (-)
- Left arm: (+) and (-)
- Left leg: (+) and (+)
What do the bipolar limb leads form?
Frontal plane
Define lead I
- Negative electrode on right arm
- Positive electrode on left arm
Define lead II
- Negative electrode on right arm
- Positive electrode on left leg
Define lead III
- Negative electrode on left arm
- Positive electrode on left leg
Define lead AVF
- Negative electrodes on right and left arms
- Positive electrode on left leg
Define lead AVR
- Negative electrodes on left arm and left leg
- Positive electrode on right arm
Define lead AVL
- Negative electrodes on right arm and left leg
- Positive electrode on left arm
Do you need to move the electrodes around as you obtain different leads?
No the EKG can change the polarity of the electrodes
What are the 6 limb leads of the standard EKG?
I, II, II, AVL, AVR, AVF
In what direction do we say a limb lead looks toward?
Toward the (+) electrodes
What are the 3 augmented limb leads?
AVL, AVR, AVF
What are the 2 lateral limb leads?
AVL, I
What are the 3 inferior limb leads?
II, III, AVF
What are the 6 chest leads? Positive or negative?
V1-V6
All positive
What are the 2 types of leads necessary to record an EKG?
- Limb leads
2. Chest leads
How do the chest leads QRS complexes change from V1 to V6?
- R wave gets larger
- S wave gets smaller
What are the 2 right chest leads? Where exactly?
V1, V2
RV
What are the 2 left chest leads? Where exactly?
V5, V6
LV
Where are V3 and V4 located? What part of the heart do they transmit info on?
Between the R and L chest leads
Interior more medial walls of the ventricles
Where to start reading HR?
R wave
What are the 2 triplets to read HR on an EKG?
300, 150, 100
75, 60, 50
How to calculate a more precise HR without using the triplets?
Divide 1500 by number of small boxes between 2 R waves
How to find HR using the 6 s strips (3 lines on top total)?
Count number of cardiac cycles and multiply by 10 = HR
How to read an EKG strip with all leads on it?
Everything in a straight line is happening at the same time and straight longitudinal lines separate lead readings
What does the first mark of each horizontal reading on an EKG mean? What does it look like?
Calibration mark: tells you the EKG is well calibrated
Looks like upright rectangle
Other name for chest leads? Why?
Precordial leads: they are on the precordium
Purpose of having multiple leads?
Each lead shows the electrical activity of the heart from a different angle, so gives us a 3D image of its electrical activity
Which EKG lead points away from all others?
AVR
What angle does lead I point in?
0 degrees
At what point of the heart do all EKG leads meet?
Point where AV bundle divides into R and L bundle branches = Wilson central terminal
What angle does lead II point in?
+ 60 degrees
What angle does lead III point in?
+ 120 degrees
What angle does lead AVF point in?
+90 degrees
What angle does lead AVR point in?
-150 degrees
What angle does lead AVL point in?
-30 degrees
What is a positive angle and what is a negative one when talking about lead directions?
Positive: below the horizontal place
Negative: above the horizontal plane
Towards what parts of the heart do most EKG leads point? What is the exception?
R and L ventricles
Exception: AVR points toward the RA
How will a current that is going away from a lead appear on the EKG?
As a negative/downward wave
What is the precordium?
Area of the anterior chest wall over the heart
What information do chest leads V1, V2 and V3 provide?
Whether the electrical signal is going toward the anterior or posterior side of the heart
What information do chest leads V4, V5, and V6 provide?
Whether the electrical signal is going toward the left or right side of the heart
What are the 2 lateral chest leads?
V5 and V6
What are the 2 anterior chest leads?
V3 and V4
What are the 2 septal chest leads?
V1 and V2
What are the 4 lateral EKG leads?
I, AVL, V5, V6
Through what structure does the conduction from the RA to the LA happen?
Bachman’s bundle
At what HR would a heart beat in a petri dish?
100 bpm
Do all muscle cells conduct electricity?
Yes, but conduction fibers do so at a much faster rate allowing for proper contraction of the heart
What is the amplitude of each EKG wave dependent on?
- Number of cells sending the electrical signal
2. Amplitude of the electrical signal
Which ventricle is depolarizing during the QRS complex?
BOTH
Do we always call the QRS complex by its name even if it doesn’t have all 3 waves?
YUP
How many mV in one large square? What is this called?
0.5 mV
I signal
Are the rates of atrial and ventricular depolarizations the same?
Yes, unless there is a pathology
What are the 3 EKG intervals during 1 cardiac cycle? What does each correspond to?
- PR interval = how long it takes for the electrical signal to get from the SA node and start ventricular depolarization
- QRS interval = how long it takes the electrical signals to go through the ventricles
- QT interval = how long ventricular depolarization AND repolarization takes
Normal PR interval?
< 0.2 s (= 1 big square)
How does the QRS complex change for all EKG leads?
I: mostly positive II: mostly positive III: half positive/half negative AVR: mostly negative AVL: mostly positive AVF: mostly positive V1: mostly negative V2: mostly negative V3: mostly negative V4: mostly positive V5: mostly positive V6: mostly positive
What does a PR interval longer than 0.2 seconds indicate?
1st degree AV block
Normal QRS interval?
< 0.12 s (=3 small boxes)
What 2 conditions cause abnormal aka lengthened QRS intervals? How to differentiate between the 2?
- Right bundle branch block (RBBB)
- Left bundle branch block (LBBB)
To differentiate: look at V1
- If V1 is positive = RBBB
- If negative = LBBB
What particular QRS pattern can an RBBB cause? What is it due to?
Rabbit ears: R-S-R’ wave pattern
Due to the fact that the LV is receiving signals BEFORE the RV
Which leads point toward the LV?
AVL, I, II, V3-V6
Which leads point toward the RV?
AVF, III, V1, V2
Is a PR interval below 0.2 seconds pathological?
NOPE
Normal QT interval?
< 450 ms
What is long QT? What does it indicate?
QT interval is longer than normal
Indicates there is an issue with ventricular repolarization (if the QRS complex is normal)
Quick cheat to find long QT?
IN NORMAL HEART RATES: if it takes more than half way between 2 R waves for the T wave to end => long QT
How do we call the triangle that is made up of the 3 limb leads?
Einthoven’s triangle
What parts of the lead clock are considered normal axis? How to check for this? What does it mean?
AVL to AVF:
- I is positive
- AVF is positive
- IF AVF is negative: check II - if it’s positive you’re good
=> QRS is somewhere in this zone, which is considered normal
What parts of the lead clock are considered left axis? How to check for this? What does it mean?
Lead AVL to -90 degrees
- Lead I is positive
- AVF is negative
- Lead II is negative
=> left axis deviation due to extra muscle = LV hypertrophy
What parts of the lead clock are considered right axis? How to check for this? What does it mean?
AVF to +180 degrees
- AVF is positive
- Lead I is negative
=> right axis deviation due to extra muscle = RV hypertrophy
What does it mean when the QRS complex is isoeletric?
It is as negative as it is positive
How is RA hypertrophy seen on an EKG?
P wave amplitude > 2.5 mm in lead II
How is LA hypertrophy seen on an EKG?
- P wave duration > 0.12 s in frontal plane (aka in limb leads)
- Notched P wave in limb lead II
- Terminal P wave in V1 is biphasic (positive and then negative), lasts over 0.04 s and is over 1 mm high
How is RV hypertrophy seen on an EKG?
- Right axis deviation
- Tall positive R waves in V1
- Incomplete RBBB
- RAE = right atrium enlargement
How is LV hypertrophy seen on an EKG?
- Increased QRS amplitude
- Widened QRS
- Leftward axis shift
- LAE = left atrium enlargement
Why does the QRS widen when there is hypertrophy of the left ventricle?
Because there are more cells to depolarize in the ventricle, so it takes longer
What disease in LV hypertrophy seen with?
HT
What is coronary artery disease?
Myocardial infarction and ischemia
How is coronary artery disease (aka MI) seen on an EKG? Explain.
- ST segment elevation (no S wave) => means acute or recent because there is less time between depolarization and repolarization (less cells to do this to) and so the QRS complex and T wave basically merge
- Pathological Q waves
How can we tell if a Q wave is pathological or not? What does the pathological one mean?
- NORMAL = Q wave narrower than 1 small box and smaller in amplitude than 1/3 of the QRS complex
- PATHOLOGICAL = large amplitude Q wave => patient has had an MI (dead muscle) but no idea when
What does a non-pathological Q wave represent?
As the impulse goes down the septum in the His-Purjinke system, electrical signals go through the septum itself - very small signals
What does the EKG horizontal plane correspond to?
Plane of chest leads
How would a anterior coronary infarction appear on an EKG?
Large amplitude Q wave in V1-V4
How would a circumflex coronary infarction appear on an EKG?
Large amplitude Q wave in leads I and AVL
