7.7 EKG Flashcards
(38 cards)
Firing Rates:
SA
AV
Bundle of His
SA: 60-100 action potentials per minute
AV: 40-60 beats per minute
20-40 per minute
Where do you see the SA node electrical activity on EKG?
You don’t! It’s very small.
P Wave
Depolarization, contraction of both atria
Ventricular Depolarization
QRS Complex
Ventricular Contraction on an EKG
Begins with the QRS, ends with the T
Spans depolarization and repolarization
What does a long QT interval indicate?
Warns that the patient is vulnerable to irregular rhythms
Normal intervals of:
- PR
- QRS
- QT
PR: <0.4 seconds
What is the purpose of limb leads?
Record the activity in the coronal or frontal plane of the body
How do limb leads work? What type of configuration?
- Bipolar configurations
- One positive pole electrode and one negative pole electrode such as leads I, II and III.
- Energy moves from the negative electrode toward the positive electrode.
What is the purpose of chest leads?
Record activity in the axial (horizontal) plane of the body
Where are chest leads placed?
V1&2: 4th ICS, either side of sternum V4: 5th ICS MCL V3: Between V2 and V4 V6: 5th ICS: Mitral area V5: 5th ICS between V4 and V6
Meaning of positively deflected v negatively deflected
- Electrical activity moving from negative electrode to positive electrode = positively deflected
- Electrical activity moving away from positive electrode = negatively deflected
ECG paper: How fast does it roll out?
25mm or 1” per second
How large is each small square on ECG graph paper? How much time does this represent?
1mm, 0.04 seconds
On ECG paper, each large box is made up of how many small boxes? Each large box represents how much time?
five small boxes, representing 0.20 seconds.
Regular heart rate
Bradycardia
Tachycardia
Regular: 60-100
Bradycardia 100
How do you calculate rate?
What numbers do you need to know to do this (6)?
Count R-R interval and large boxes.
300 - 150 - 100 - 75 - 60 - 50
What is heart rhythm?
- The quality of timing as one heart beat is compared to the next, regardless of rate
- Determined by comparing the length of several adjacent R-R intervals
If all R-R intervals are of equal length, you would say that the rhythm is _____
REGULAR
If R-R intervals are of different lengths but there’s an overall pattern pressent
Regularly irregular
If there is no overall R-R pattern
Irregularly Irregular
What causes a premature atrial beat?
Atrial focci becomes irritable.
- Due to sympathetic stimulation (adrenergic substances like adrenaline)
- Beta 1 receptor stimulants (Caffeine, cocaine, amphetamines, excess digitalis, hyperthyroidism
Two things to note about the ECG when observing a premature atrial beat.
- The pause following the PAC is longer than the normal P-P interval, but shorter than twice the normal P-P interval.
- Note the different shape of the P-P wave.
What happens during atrial flutter? (2)
In atrial flutter, a single strong ectopic focus in an atria start to beat fast (240-360 beats per minute)
**The AV node acts as the gatekeeper, blocking some of the impulses to the ventricles.
