Lecture 3: Normal ECG Part I and II Flashcards
Important things to consider when interpreting ECG
1. Rate
2. Rhythm
3. Axis
- PR duration
- QRS duration
- QRS height
- ST segment
- T wave
- U wave
- QT interval
Conduction of the heart
SA node–> AV node–> pause –> common bundle of His–> L/R bundle branch–> purkinje fibers
Is SA node fails, what happens?
AV node can be our back up
What happens in AV node fails?
Ventricular muscles can be backup
P wave
What does it represent?
When is it: upright, inverted, variable?
P wave:
- Atrial depolarization
- Normally upright in: 1, 2, V4, V5, V6 and AVF
- Inverted in: AVR
- Variable- everything else
PR interval
When does it occur?
What does it represent?
Duration?
PR Interval–> from begining of the P wave to the begining of the QRS complex.
It is the time from the SA node–> ventricular muscle fibers
Time: .12-.20 seconds
QRS complex
What does it represent?
Duration?
What should the Q waves look like?
- QRS complex–> ventricular depolarization
- Duration: .05- .10 seconds
- The Q wave should not be more that .03 seconds in width; thus, they should be narrow and small.
- In 1, AVL, AVF, V5 and V6, 1-2 mm is normal.
A QRS complex > .12 seconds means what?
bundle branch block
or
hypertrophy
How do we examine the ST segment?
The ST segment should be compared to the isoelectric line (where it should be). Thus, look to see if its elevated or depressed and the shape.
- Normally not elevate more than 1 mm in standard leads (1, 2, 3, aVL, aVF and aVR) and no more than 2mm in chest leads
- Normally not depressed more than 1/2mm
If we had a ST depression, what would that represent?
subendocardial infarction
If we had a ST elevation, what would that signify?
Subepicardial/transmural ischemia
What is the T wave and how do we examine it?
Upright-
Inverted-
Variable-
T wave–> ventricular repolarization.
- Upright- 1, 2, V3, V4, V5, V6.
- Inverted- aVR
- Variable in the rest
It is slightly rounded and assymetrical height.
Not greater than 5mm in standard leads and not greater than 10mm in precordial leads.
QT duration--> length of _____________. Thus, what can it tell us?
Ventricular systole.
Thus, it can tell us abnormalities in
- Myocardial ischemia
- Myocardial injury
- Myocardial infarction
Ischemic patterns are assx with what kind of T waves?
Inverted.
What can be indicative of patterns of necrosis or infarction?
A QRS complex >.1 seconds.
What wave can be indicative of hyperkalemia?
T waves.
African americans and athletes may have an exaggerated _______
T wave
and elevated ST segment
A short PR interval can be indivative of what?
Junctional/nodal rhythms
Short PR intervals can be indicative of what?
- Hypertensive patients
- AV junctional and low atrial rhythms
- Wolf-Parkinson White syndrome
- Lown Ganong levine syndrome
- Glycogen storing dz
Prolonged PR intervals can be indicative of what?
- AV block due to coronary dz
- Hyperthyroidism
What are the rules of thumbs for the determining Q R and S in the QRS complex?
Q wave- first deflection downwards
R wave- first upright deflection, whether or not it is preceded by Q
S wave- first negative deflection after R wave
T/F: Look at all 12 leads to make a diagnosis for T waves because they will all be varient.
True
LO: How do we determine normal sinus rhythm?
- Is there a P wave before every QRS complex and vice versa?
- P-R <.2 seconds? If yes, no AV block
- QRS complex <0.12 seconds. If yes, no bundle branch block!
What leads are the best for reading P waves?
Lead II and V1
What is the first and second half of the P wave?
What is the PR interval?
PR segment?
1st half of the P wave–> R atria depolarization
2nd half of the P wave–> L atria depolarization
PR interval–> how long it takes to go from the SA–> AV node (atrial myocardium to the ventricular myocardium)
PR segment--> how long it takes to travel from AV node–> ventricles
What is considered tachycardia?
A HR>100.
What is considered bradycardia?
HR<60mV
How do we determine the rate?
- Find the heart rate by finding a R-wave that falls on a black line and count until the next R wave.
300-150-100-75-60
Anything else below is 60 bradycardia.
OR: 300/number of large boxes
What is rhythm?
- P wave precedes QRS.
- P:QRS ratio is 1.
Are there other sinus rhythms? If yes, name them?
1. Ectopic atrial rhythm
2. Multifocial atrial tachycardia (MAT)
3. Wandering atrial pacemaker
In what situations what a P wave occur AFTER a QRS?
-Present is side of the pacemaker is changed
Seen in a SVT (AV nodal re-entry tachycardia)
and junctional rhythm
In what situations do we see no P waves? (5)
A-fib
Atrial flutter
Junctional or ventricular escape rhythms
Junctional tachycardia
VT
What is axis?
Normal axis?
How do we determine?
The direction the vector is taking during depolarization.
A normal axis will be in between 0-90.
To determine, we look at the NET QRS VOLTAGE (upward- downward QRS deflection)
How do we create the 6 intersecting leads that lie in the frontal plane of the patients chest?
Combine the bipolar limb leads with the augmented limb leads.
What is a normal axis ?
Positive defelction in leads I and aVF.
Left axis deviation
+ deflection in lead 1
- deflection in aVF
Right axis deviation
- deflection in lead 1
+ deflection in aVF
