LECTURE 25 11/02/22 (LECTURE 12/13 SLIDES: EKG SUPPLEMENTAL SLIDES) Flashcards
For this course what angles on Einthoven’s Triangle will be considered a left axis deviation?
What will be considered a right axis deviation?
Any angle less than 59 degrees to -90 degrees will be considered a left axis deviation.
Any angle greater than 59 degrees to 180 degrees will be considered a right axis deviation.
(10:50)
Per Dr. Schmidt, a vector pointed between what angles will be considered an extreme axis deviation?
Extreme Axis Deviation: Vector would be pointed between 180 degrees and -90 degrees (11:00)
What specific area in the heart is being depolarized?
How is the current moving in this picture?
Where is the mean axis deviation pointing?
Septum depolarization (14:12)
Current is moving from negative charge on the outside of the cell (area of depolarization) to area of positive charge on the outside of the cell (resting). (14:30)
Left Foot or Lead II’s eyeball.
If you need to look at the heart from a different angle using Einthoven’s triangle. What additional leads can you use?
What is another name for these leads?
Name the leads (full name).
Augmented Leads (16:00)
Unipolar Leads
aVR (Augmented Vector Right)
aVL (Augmented Vector Left)
aVF (Augmented Vector Foot)
For aVR, where is the positive electrode located on the body?
What about the negative electrode?
Positive electrode for aVR is stuck on the right arm (17:50)
Negative lead will be a combination of connections placed on the left leg and left arm. (18:00)
Normally, the ________ lead will be observing current going away from it resulting in a negative QRS deflection.
The ________ lead will be observing negative current coming towards it from the origin in the middle of right arm and left arm.
The ________ lead will be observing negative current coming towards it from the origin in the middle of right arm and left leg.
aVR (18:45)
aVF (20:03)
aVL
Typically, aVR is going to be witnessing current moving _______.
You would expect to see aVR’s P-wave, R-wave, and T-wave to have a ________ deflection.
Away from the positive lead (eyeball) (19:04)
Negative deflection (19:10)
A perfectly normal heart is depolarization from RIGHT to LEFT. Depolarization is moving away from the aVR lead.
For aVF, where is the positive electrode located on the body?
What about the negative electrode?
Positive electrode on left leg
Negative electrode is a combination of leads placed on the right arm and left arm. (19:45)
If a current is directly traveling towards aVF what degree of deflection is that vector?
If a current is directly traveling towards aVL what degree of deflection is that vector?
If a current is directly traveling towards aVR what degree of deflection is that vector?
+90 degree deflection
-30 degree deflection
-150 degree deflection
For aVL, where is the positive electrode located on the body?
What about the negative electrode?
Positive electrode is on the left arm.
Negative lead is a combination of the right arm and left leg. (20:20)
Which of the three augmented leads is least useful?
aVR (22:00)
How would you categorize the mean electrical axis if the current is traveling directly towards aVR?
Extreme Axis Deviation
V1 and V2 of the precordial leads are located on opposite sides of the sternum. Between which ribs are these leads placed between?
Because of V1 and V2’s proximity to the heart, they are thought of as ________________ leads.
Rib #4 and Rib #5 (4th Intercostal Space). (24:40)
Septal (25:30).
Where should V4 be placed?
Where should V3 be placed?
Because of V3 and V4’s positions on the chest, they are thought of as _________ leads.
V4 should be placed at the left mid-clavicular line between the 5th intercostal space (26:00)
V3 should be between V2 and V4
Anterior (26:25)
Where should V6 be placed?
Where should V5 be placed?
Because of V5 and V6’s positions on the body, they are thought of as _________ leads.
V6 should be placed at the lateral end of the left clavicle, 5th intercostal space on the mid-axillary line. (27:00)
V5 should be placed between V4 and V6 on anterior axillary line.
Lateral
Why do we see a negative QRS deflection in V1 and V2?
V1 and V2 are situated on top of the AV node, depolarization current will go away from these two leads. (28:09)
Which precordial lead has a biphasic QRS complex?
Which precordial lead has the tallest QRS complex?
What precordial lead will be used as an indicator for a current of injury?
V3 (biphasic)
V4 (tallest QRS complex)
V2 (current of injury)
(29:30)
What makes V2’s position unique for indicating current of injury?
V2 can see current coming towards it from the posterior side of the heart or away from V2, if the current originates in the anterior side of the heart. (30:00)
What is a current of injury?
Damaged cardiac tissue that remains partially, or totally depolarized because the myocytes are unable to reset/repolarize themselves after depolarization. (32:03)
How does the heart reset after an action potential:
-Name what will transport Ca2+ out into the ECF
-What about the ICF calcium used for depolarization?
-What about the sodium?
NCX (15%) and PMCA (plasma membrane calcium ATPase(5%)
**75% of the TOTAL ECF calcium is removed through the NCX
**25 % of the TOTAL ECF calcium is removed through the PMCA
SERCA Pump (80%)
Sodium Potassium ATPase
(30:55)
(Exam 3 Recall)
What are causes of current of injury (3)?
- Local ischemia or infarction
- Mechanical Trauma
- Infection
Where would ischemia most likely occur in the heart?
Endocardium (34:30)
Endocardium sees the highest pumping pressures and higher energy consumption than the epicardial tissue.
Describe the electrical movement of a heart that has tissue ischemia?
Area of the heart that has ischemia remains depolarized, so there will be electrical movement from area of ischemia to parts of the heart that are in repolarized or resting state. (35:00)
Describe the TP interval.
What is the expected electrical activity during a TP interval?
What happens to the TP interval when there is a current of injury?
Period of time when the ventricles are completely reset and resting. This segment is from end of the T-wave to the beginning of the P-wave. (35:30)
There should be zero electrical activity during the TP interval.
There will be electrical activity during the TP interval with a current of injury. (36:40)
What determines the magnitude of the current of injury?
Depends on how much real estate is ischemic and difficulty of the trying to repolarize itself. (37:31)
If there is a current of injury in the heart, at what point will there be no conductance?
What is this point called?
There will be no current when all the cells have depolarized.
This is known as the J-point.
Identify whether the deflections will be positive or negative in figure 5:
Lead I:
Lead II:
Lead III:
Figure 5
Lead I: 0
Lead II: 0
Lead III: 0
At figure 5, the ventricles are are totally depolarized. There will be no current. In this example, this is where you get your J-point or isoelectric point.
Identify whether the deflections will be positive or negative in figure 1:
Lead I:
Lead II:
Lead III:
Figure 1
Lead I: negative deflection
Lead II: positive deflection
Lead III: positive deflection
Identify whether the deflections will be positive or negative in figure 2:
Lead I:
Lead II:
Lead III:
Figure 2
Lead I: 0
Lead II: Positive deflection
Lead lll: Positive deflection
Lead l is zero because the current is directly perpendicular to lead l’s eyeball (positive electrode).
Identify whether the deflections will be positive or negative in figure 3:
Lead I:
Lead II:
Lead III:
Figure 3
Lead l: Negative deflection (barely)
Lead ll: Positive deflection
Lead lll: Positive deflection
Identify whether the deflections will be positive or negative in figure 4:
Lead I:
Lead II:
Lead III:
Figure 4
Lead l: Negative deflection
Lead ll: Negative deflection
Lead lll: Positive deflection (almost zero)
The current of injury will be pointed __________ damaged area.
away from (47:50)
How do we define the current of injury using the J-point? (48:34)
Everything will need to be zeroed to the J-point to help define our current of injury.
The J-point is then used to look at where our TP interval is at.
Is the TP interval above or below the zero axis of the J-point?
If TP interval is above, then we have a positive current of injury.
If TP interval is below, then we have a negative current of Injury.
How do you find your J-point?
Look at the area immediately after the QRS. That should be your J-point.
Define the current of Injury. (48:34)
Negative Current of Injury
Define the current of Injury. (48:34)
Positive Current of Injury
Plot the mean electrical axis of this current of injury.
Where is the direction is the current of injury going? (approximate degrees).
Where is the source of the current of injury, what part of the heart is most likely ischemic?
Approximately -30 degrees, pointing to the left shoulder.
Current is originating somewhere in the right ventricle.
(50:00)
A _________ current of injury in V2 will indicate an anterior wall infarct.
A __________ current of injury in V2 will indicate a posterior wall infarct
Negative
An anterior wall infarction will result in current moving from the front to the back, which will result in a negative current of injury in V2. (55:43)
Postive
A posterior wall infarct will result in current moving from the back to the front which will result in a positive current of injury in V2.
Identify the J-points on Lead I, Lead III , and V2.
Identify the deflections on Lead I, Lead III, and V2.
Determine the mean axis deviation and approximate the source of the current.
Is this an Anterior or Posterior Wall Infarction?
Identify the J-points on Lead II, Lead III , and V2.
Identify the deflections on Lead II, Lead III, and V2.
Determine the mean axis deviation and approximate the source of the current.
Is this an Anterior or Posterior Wall Infarction?
_________ to the lower left ventricle will result in a positive current of injury in Lead II.
__________ to the lower left ventricle will result in a negative current of injury in Lead II.
Ischemia
Infarction
(77:47)
What would be an example of an extreme axis of deviation?
Infarction of the lower left ventricle will cause current to move towards aVR would be an example of extreme axis of deviation.
(90:00)
Scar tissues on the heart after an infarction can result in ________ voltage EKG. Why?
Lower Voltage, because scar tissue tends to be a very bad conductor. (94:00)
What is a way to increase voltage in an EKG if you have mild scarring in the heart tissue?
Heart can repair itself and compensate by growing larger muscles. (93:36)
Per lecture, what is considered a low voltage EKG?
Low Voltage, per lecture, was defined as being less than 2 big boxes (1.0 mV) for QRS. (94:00)
Per lecture, what things can cause abnormal T-waves?
- Digoxin Toxicity
- Hyperkalemia
- Fast Na+ Channel Blockers
- Energy Deficiency/ Ischemia/ MI
- Basically, anything that affects the normal depolarization and repolarization of the heart.
***Potential Select all that apply candidate? **
(95:07) (104:24) (105:40)
Define a biphasic T- wave.
Per lecture, what can cause a biphasic T-wave?
Part of the wave has a positive deflection and part of it has a negative deflection. It can happen in either order.
(95:20)
If we screw up the resetting process or if we have a T-wave with a negative deflection (95:55).
What does it mean if we have a negative deflection for the T-wave?
We are repolarizing from the endocardium to the epicardium.
Typically, the problem is somewhere in between. Not the same order, not completely reversed, which gives us a biphasic T-wave (96:42)
What sets up the concentration gradient for the NCX?
What kind of transporter is NCX? What are the Ions transported?
What transporter helps maintain the cell at resting levels between action potentials.
Sodium Potassium ATPase (97:00)
Secondary Active Transporter (Exam I and Exam III recall).
NCX: 3 Na+ in for 1 Ca2+ out
Our Favorite: Sodium Potassium ATPase (97:00)
How does Digoxin work?
How does this affect the NCX?
How does this affect the heart?
Dig works by blocking the activity of the myocardial Na+/K+ ATPase.
NCX is slowed down which slows down Ca2+ removal.
Because there is now more Ca2+ in the myocytes, there will be an increase strength of cardiac contraction.
(98:30)
What does Digoxin do to the repolarization process of the heart?
Digoxin blocks Na+/K+ pump activity which is involved in the resetting process of the cell resulting in a biphasic T-wave.
**Heart will take longer to reset, resulting in bradycardia. (100:00)
Which one is impacted less by caine derivatives? (Endocardial Tissues or Epicardial Tissues).
How does this mess with the T-wave?
Endocardial Tissues.
Epicardial Tissues are impacted more by caine derivatives because their tissue is more reactive to fast sodium channel blockers because a large portion of their depolarization depends on Na+ influx where as for the Endocardium, their sustained depolarization is due to more Ca2+ influx. (100:30)
Anything that you do that interferes with the process that kicks the action potential off in ventricular myocytes will affect the repolarization order resulting in a screwy (biphasic) T-wave (103:50).
How does Early/Mid Hyperkalemia affect the T-wave?
The myocytes will open more KDR channels to attempt to increase K+ permeability. The increase in repolarization will result in peak T-waves.
What can happen to the NCX if there is enough build-up of intracellular Na+?
What drug can cause this effect?
NCX can reverse and remove 3 Na+ ions and bring in one Ca2+.
Digoxin (107:00)
For the precordial leads what are considered the positive electrodes?
What makes up the negative lead in the precordial system?
The 6 chest leads (V1 through V6) are their own positive leads.
The negative leads for the precordial lead system is a combination of connections at the right arm, left arm, and left leg.
(110:00)
