Electrocardiology (ECG): Recording electrical current Flashcards
Define ECG.
Which comes first electrical impulses or mechanical contractions?
So is ECG a direct indicator of muscle contraction?
What 3 characteristics are used to diagnose ECG abnormalities?
ECG: measurement of the electrical activation of the heart
Electrical before mechanical
SO ECG’s are not a direct indicator of muscle contraction
ECG abnormalities
- Direction of waves and segments
- Amplitude of waves and segments
- Duration of intervals
What two characteristics impact wave amplitude?
How will the amplitude of the waves in children be different than adults?
What determines shape and direction of waves?
Wave amplitude
- Mass of the tissue (ventricular wall, septum, etc.)
- distance between recording electrode and dipole
Children will have greater amplitude due to decreased distance
Shape and direction is based on electrode conventions - where you place the leads
What is occurring in the heart during P wave?
During the atrial T wave?
Why is the atrial T wave not seen on ECG?
P wave = atrial depolarization
Atrial T wave = repolarization of the atrium
Not seen on ECGs typically due to obscuring of the signal
Define each point of a QRS complex.
What is it called when there is an abnormal second upward pattern?
What is it called when there is an abnormal second negative deflection?
Q: first downward deflection (not always present)
R: any positive deflection
S: negative deflection following an R wave (must actually go below zero)
R’: abnormal second upward pattern
S’: abnormal second negative deflection
What is occurring during…
T wave
U wave
When are you more likely to see a U wave?
What is the J point?
T wave: repolarization of the ventricles
U wave: additional repolarization of the ventricles (likely papillary muscles)
More likely to see U wave in very slow heart rates, like athletes
The J point: the isoelectric point
(the zero, baseline, of the graph)
What is the P-P interval and the R-R interval?
Distance between adjacent P waves and R waves
measure heart rate
should be about equal
Label this image.
Some sources use capital and lower case letters to indicate amplitude of waves. This will not be a standard in this class, but is used in this diagram.
A 12 lead ECG tells how many stories from how many views?
Tells the exact same story from the same time, but from 12 different views
Same event from different perspectives provides means for better interpretation
By convention how many electrodes are there?
How many leads?
What are the two conventions?
Which electrode dictates the polarity of the recording?
10 electrodes
12 leads
2 conventions
Positive and negative (indifferent) electrodes
Positive electrode dictates polarity
What are the 3 divisions of the 12-lead electrocardiogram?
Which leads belong to which division?
- Frontal plane leads
- standard limb leads (bipolar)
- I, II, III
- Augmented limb leads (unipolar)
- aVF, aVL, aVR
- same electrodes as bipolar with different convention
- standard limb leads (bipolar)
- Horizontal plane leads
- precordial/chest leads (unipolar)
- V1-V6
- precordial/chest leads (unipolar)
- Supplemental leads
- VR4
- V7-V9
Describe the placement of each lead (positive and negative) for the standard (bipolar) limb leads.
Lead I: +left arm, -right arm
Lead II: +left leg, -right arm
Lead III: +left leg, -left arm
What direction of P, Q, and T waves would you expect from each standard limb lead?
What does Einthoven’s Law tell you about the amplitudes of these three leads?
You would expect P, Q, and T to be positive.
You would expect the amplitudes of I and III to add together to equal II
Where are the leads for the augmented limb leads?
How do they form the indifferent electrode?
Which one is negative and explain why.
When you add the amplitude of all three augmented limb leads what does this equal?
aVR: +right arm
aVL: +left arm
aVF: +left leg
Indifferent electrode is formed by the connection of two other leads.
aVR will give negative amplitudes - this is because the heart typically depolarizers toward the left leg, with the lead pointing to the right arm this is opposite leading to negative amplitude
Every augmented lead added together should equal 0
Label this image of the frontal plane leads
Label each of these precordial/chest leads in the horizontal plane
What region of the heart does each horizontal lead examine?
Leads V1 and V2, right ventricle
V3 and V4 septum
V5 and V6 the left ventricle
Label this standard 12 lead EKG
Define magnitude and direction as it pertains to representing current flow in vectors.
Dipole is separation of charges
Magnitude (amplitude)
distance between charges
Direction (net polarity)
negative to positive
How would you expect the depolarizing event to be recorded for each of these varying electrode placements
How would the waves describing these electrical currents change in amplitude and direction relative to the reference point?
How does the angle of the current to the reference affect the magnitude of the resultant vector?
When is the magnitude greatest?
When does the magnitude equal zero?
The more parallel the greater the magnitude, as the current angles away from the reference magnitude is lost
Magnitude is greatest when the current is parallel to the reference
Magnitude is zero when the current is perpendicular to the reference.
How would each of these instantaneous resultant vectors be recorded on an ECG?
What will each of the instantaneous resultant vectors look like for this
What would the ECG lines look like for the mean vector for atrial depolarization?
How do the ECGs appear for each standard limb lead after depolarization of the atrium?
What would the ECG look like given repolarization of the atrium in the standard limb leads?
What ECG recording would you expect from the standard limb leads after complete repolarization?
What ECG findings would you expect in the standard limb leads during ventricular septal depolarization?
Describe the sequence of ventricular activation from septal activation to complete depolarization.
Describe this in the mean vector as well as the expected ECG findings from the standard limb leads.
Between endocardium and epicardium in which order do they depolarize and depolarize?
Which has the shorter duration of action potential?
What force causes delayed repolarization?
Endocardium depolarizers first and repolarizes last
epicardium shorter duration of AP
Delayed repolarization of the endocardium due to surround pressure
