Intro to ECG Part 2: 12 Lead ECG Flashcards
The 2 leads that show normal P waves the best are :
The 2 leads that show normal P waves the best are lead II (downward and to the left) and V1 (anterior):
When there are more P waves:
When there are more QRS’s:
When there are more P waves:
some P waves are not getting conducted to the ventricles due to conduction block in the AV node (AV node cant get the SA node signal)
When there are more QRS’s:
a QRS is being generated but no P wave is being generated
this occurs when the AV node or the ventricles generate the QRS
what might be happening?
Crazy, all those P waves! Did you count 16? And only 4 QRS’s so there is a conduction block (in the AV node).
Whats going on with the P:QRS ratio?
The first and 3rd P waves are the same. All others are different. Therefore, there are multiple origins for the P waves.
One detail that might be helpful for you: P waves almost always will have a regular rhythm if they are from the same source. Therefore, an early beat among many regular beats is most likely (> 99% of the time), arising from a different location and as such, will likely have a different size and shape.
Super important causes of slow conduction (wide QRS):
=conduction from ventricular myocyte to myocyte is much slower compared to the purkinje fibers. This happens when an electrical signal STARTS in the ventricle muscle.
= diseased conducting fibers, typically called conduction delay, aberrancy, or bundle branch block.
what is a bundle branch block?
In brief, with bundle branch block one of the bundle branches is not conducting. Therefore, the electrical signal moves quickly down from the AV node through one bundle branch, but to get to the other side of the heart, the signal must be conducted from myocyte to myocyte, which is slow conduction. This requires extra time and causes the QRS to be wide.
normal axis is indicated by a postive lead in ___ and ___
lead I and II
which precordial lead measures RV? which one measures LV?
V1-V3 more likely to measure RV because RV is more anterior. V6 likely to measure LV because it’s more lateral.
In LBBB what would the precordial leads look like
V1= small and fast initial upward signal (this is the RV monitor so it’s not super affected)
V6 = wide and slow because there’s a block in LV.
if there is an LBB, the T waves will be ___ from the QRS
it will be discordant from the QRS. Going in opposite directions.
T/F; when you have LBBB, the ST segment is
not useful for ischemia diagnosis
true. In LBB, the QRS and T complexes are abnormal (wide, discordant) Because all aspects are abnomrla, the ST segment is also abnormal and it will be difficult to know if the ST change is due to LBBB or ischemia.
in RBBB, there is early and fast depolarization of the ____. but slow and wide ____ depolarization.
in RBBB, there is early and fast depolarization of the SEPTUM. but slow and wide VENTRICLE depolarization.
common causes of left ventricular hypertrophy
hypertension and aortic valve stenosis. these cause increased afterload and the LV gets larger.
findings on ecg that indicate left ventricular hypertrophy
wider and taller QRS.
abnormal depolarization = abnormal repolarization therefor also have abnoraml ST segment and T wave.
in left ventricular hypertrophy, which precordial lead will be most affected?
V6 will have tall upgoing V6 signals.
V1 and V2 will have deep downgoing signals but won’t be as “tall” as V6
Sokolow and Lyons Criteria for Left Ventricular Hypertrophy
take deepest in V1 or V2 and tallest in V5 or V6, it should be more than 35 mm
outline the Avl criteria for left ventricular hypertrophy
AvL should be over 11mm
The following characteristics are typical of LEFT VENTRICULAR HEART FAILURE
repolarization abnormalities:
– ST segment ___ if QRS is downgoing
– ST segment ____ if QRS is upgoing
– Magnitude of elevation/depression is proportional
to the size of the QRS
– ST is “scooped” concave up with elevation
– ST is scooped concave down with depression
The following characteristics are typical of LVH
repolarization abnormalities:
– ST segment elevation if QRS is downgoing
– ST segment depression if QRS is upgoing
– Magnitude of elevation/depression is proportional
to the size of the QRS
– ST is “scooped” concave up with elevation
– ST is scooped concave down with depression
Infarct/Ischemia
Changes seen:
- Peaked or __ T waves
- ST __ (ischemia)
- ST __ (infarction)
- Deep __ waves (late or old infarct)
- Poor R wave progression
- Peaked or inverted T waves
- ST depression (ischemia)
- ST elevation (infarction)
- Deep Q waves (late or old infarct)
- Poor R wave progression
what is the j point on an ECG
the point where the QRS and ST segment joint.
A j point can be elevated, depressed, slurred or notched.
is J point elevated or depressed?
elevated
characterize the J point
depressed
characterize the J point
J point is notched
outline these QRS waves
in an infarction, the R wave gets driven down to the point it becomes a “pathological Q wave”
What changes in V1 would you expect in left atrial enlargement?
with LAE, the P wave in V1 will be initially upgoing for the first portion (red arrow below) and then downgoing in the terminal portion (blue arrow). This is called biphasic. The green arrow points to the QRS. The T wave is not seen in this image.
what changes in lead II would you see in left atrial enlargement?
When the LA enlarges, wave of depolarization measured in lead II behaves like 2 separate waves. The first one is the right atrium and the second one is the left atrium. The 2 waves partly overlap each other, so it creates an M shaped P wave in lead II. This is also called a notched P wave. In the diagram below, there is an extra blue and red fuzzy line to show the 2 different atrial waves:
overall diagnostic criteria for left atrial enlargement
think about lead placement and think about how many more cells are in the atria if it’s enlarged, therefore it would take longer for the signal to get through.
Summary of Diagnostic Criteria for LAE:
wide P wave > 120 ms
M shaped P wave in lead II
biphasic P wave in lead V1 (initally upward, terminal portion downward)
terminal portion of V1 is at least 1 little square wide
Best leads to see right atrial enlargements
leads II and V1. also good leads to see left atrial enlargement. it’s cause it shows the P waves th ebest
diagnostic finding of RAE
when the right atrium enlarges, the electrical signal becomes stronger in the direction of the axis of lead II.
- as a result, the P wave in lead II is taller. A P wave that is >2.5 mm in lead II is diagnostic of RAE.
The enlarged RA will also create a stronger electrical signal toward__as seen in the diagram. This will result in a taller P wave in___, but only for the first half of the P wave.
The enlarged RA will also create a stronger electrical signal toward V1 as seen in the diagram. This will result in a taller P wave in V1, but only for the first half of the P wave.
compare P wave duration between LAE and RAE
In contrast to LEFT atrial enlargment, the P wave duration is normal (< 120 ms or 3 little squares) with RAE. Check the ECG above to see that even though there is a biphasic P wave in V1 (suggesting LAE), the P wave width is < 120
overall diagnostic criteria for RAE
P wave taller than 2.5 mm in lead II
P wave is usually pointy
(P wave taller than 1.5 mm in lead V1)
(P wave duration < 120 ms)
Note about left VENTRICLE hypertrophy:
To simplify, all criteria measure the height or depth of the QRS and if these values are big, then LVH is diagnosed. The differences between all the different diagnostic criteria are the selection of ECG leads and the value that is selected.
The electrical vector for the LV (yellow arrows) travels mostly AWAY from V1,2 and mostly TOWARD V5,6:
Remember that depolarization away from a lead will cause a negative deflection (__ wave) and toward a lead will cause a positive deflection (__ wave).
Remember that depolarization away from a lead will cause a negative deflection (S wave) and toward a lead will cause a positive deflection (R wave).
In LVH, the___ waves in V1/2 and___ waves in V5/6 are amplified. We measure them to see exactly how amplified they are
In LVH, the S waves in V1/2 and R waves in V5/6 are amplified. We measure them to see exactly how amplified they are. Here are examples of a deep S wave in V2 and a tall R wave in V6:
sokolow and lyos criteria for left ventricular hypertrophy
cornell criteria for LVH
aVL criteria for left ventricular hypertrophy.
3 features of St-T wave abnormalities that are secondary to left ventricular hypertrophy
- the ST segment depression/elevation will typically be in the opposite direction to the qrs.
- the magnitude of ST changes will be proportional to the size of the QRS. Really tall or deep QRS’s will be associated with greater amounts of ST segment depression or elevation.
- the ST segment will be concave away from the QRS.
ST changes in LVH vs Ischemia or infarction.
With myocardial ischemia or infarction:
ST segments will be flat(ter) and not concave
ST elevation or depression is not related to the direction of the QRS– ex/ a positive QRS may elicit a positive st elevation in ischemia. but a positive QRS would elicit an ST depression in left ventricular hypertrophy.
ST elevation or depression magnitude is not proportional to the magnitidue of the QRS- a small QRS might still have a huge ST elevation following it.
Summary of diagnostic criteria that SUGGEST the presence of RVH:
tall upgoing R wave in V1 > 6 mm
R:S ratio > 1 in V1
R:S ratio < 1 in V6
right axis deviation (RAD)
right atrial enlargement (RAE)
