Intervals Flashcards
Big box
0.2s
Small box
0.04s
Paper speed
25mm/s
How long does the entire EKG take?
10s
How do you calculate the rate?
Count the QRS complexes and multiply by 6 (because entire strip is 10s)
How do you determine if there is normal sinus rhythm?
If there is a P before every QRS and the P wave is upright in lead II and biphasic in lead V1
How do you know if the axis is normal?
If the QRS is upright in leads I and aVF
How do you know if the axis is left-deviated?
If the QRS is upright in lead I and downward in lead aVF
How do you know if the axis is right-deviated?
If the QRS is downward in lead I and upright in lead aVF
If the action potential is originating from the SA node, what should the P wave in lead II look like?
Upright
Which direction does aVR point?
Right arm
Which direction does aVL point?
Left arm
Which direction does aVF point?
Downward
What plane are the augmented leads in?
Coronal
What plane are the V1-V6 in?
Transverse
What does aV stand for?
Augmented vector
Where does lead I point?
From R arm to L arm
Where does lead II point?
From R arm to middle foot
Where does lead III point?
From L arm to middle leg
What does the PR interval represent?
Time from start of atrial contraction to ventricular contraction
What does the QRS interval represent?
Ventricular depolarization
Why is the T wave positive even though it’s ventricular repolarization?
Because the vector is negative charge even though it’s going back up
What does the ST segment represent?
An isoelectric pause before ventricular repolarization
What’s the normal time of the PR interval?
0.12-0.20s
3-5 boxes
What are 2 causes of prolonged PR interval?
- Atrial ectopic focus
2. First degree AV block
What’s the normal time of the QRS complex?
<0.10s
2.5 boxes
What’s the normal time of the QT interval?
<440ms (men)
<460ms (women)
Which interval represents ventricular systole?
QT
“My sys is a cutie”
When do you need to use Bazett’s formula to calculate the QTc?
When the rate isn’t close to 60bmp
What are causes of prolonged QT interval?
- Medications (amiodarone, SSRI)
2. Inherited
What can QT prolongation turn into?
Torsades de pointes
What is a cause of R or L axis deviation?
Hypertrophy
What enlargement causes a tall P wave in leads II & V1?
R atrial enlargement
What enlargement causes a biphasic P wave in V1 and a double-humped P wave in lead II?
L atrial enlargement
What enlargement causes a tall R wave in V1 and a deep S wave in V5?
R ventricular hypertrophy
What enlargement causes a deep S wave in V1 and a tall R wave in V5 & V6?
L ventricular hypertrophy
