|General Concepts in EKG
As both ventricles are depolarized, from inner to outer surface, the electrical current produces what tracing on the EKG.
What is the resting state of the heart muscle called?
The polarized state
What is meant by polarization of a cell?
The resting cell has excess potassium inside and excess sodium outside, creating an ion imbalance. Selective
permeability of the membrane allows these ions to move back and forth when energy is available.
What is meant by saying that there is a potential difference across the cardiac cell membrane?
The potential difference across the cardiac cell membrane occurs when there are more electrons on one side of the
membrane than on the other, with a resulting tendency for the electrons on the crowded side to flow across the
membrane into the side with the fewer electrons.
What is the name of the heart's muscle cells?.
What is meant by depolarization of the heart?
Depolarization of the heart is the orderly passage of electrical current sequentially through the heart muscle, changing it,
cell by cell, from the resting polarized state to the depolarized state until the entire heart is depolarized.
What is meant by repolarization of the heart muscle?
Repolarization of the heart is the orderly return of each cell to its polarized state, cell by cell, until all are polarized again.
When you see an upward wave on an EKG, it represents a depolarization wave moving which way.
Toward a positive electrode.
The ability of the heart to generate a pacemaking stimuli is know as:
automaticity or autorhythmic
What are two functions of the EKG machine?
The determination of direction and magnitude of the electrical current produced by the heart.
What anatomical regions of the heart insulate the atria from the ventricles?
The mital and tricuspid valves
If ventricular systole represents the contraction of the ventricles, what does asystole mean?
This is a condition where the heart is no longer beating. You do not see any complexes or waves on the EKG.
What is more important in EKG interpretation: direction or magnitude?
The direction of the hearts current.
During depolarization, how many different directions will current be flowing through the heart?
In a multitude of directions.
If the current if flowing in a multitude of directions, how can the EKG machine draw a single line?
The stylus of the writing arm of an EKG averages all the currents at a particular lead, thus giving the mean current flow.
This average force is referred to as the resultant force. Class, remember the example of the bull and the strong man
pulling the cart from different angles. That produced a resultant force for the cart which was an average of the bulls
force and the mans force.
Does the EKG average hundreds of forces to determine the actual resultant force?
What do we call the junction between the QRS and the ST segment.
What is a dipole?
A dipole is the potential force caused by a negative and positive electrical charge in close proximity.
How does a dipole relate to a vector?
The dipole can produce a vector.
How does the hearts current relate to the dipole concept?
The production of current by the heart is really the production of a sequence of dipoles. As each myocardial cell is
depolarized, it produces a dipole.
Why is it important to be able to describe the direction of an EKG vector?
Most EKG diagnoses are based on directions.
What is meant by right and left in EKG terminology?
From the point of view of the patient.
What is meant by a bipolar limb lead?
This lead has a positive and negative electrode placed on any two limbs.
If you make an equilateral triangle from the three bipolar leads, what is it called?
Why can the three sides of Einthovens triangle be shifted so that they appear to radiate from the center of the heart?
Because the limb leads are measuring current in specific directions relative to the heart. The chest cavity is like a tub of
electrons allowing current to flow between any two points.
Why is it important to determine the direction of the QRS complex?
Because all conduction abnormalities are manifested in the QRS complex.
What is meant by the direction of the QRS?
This is the average or mean direction of the current.
So, if the QRS is going mostly toward lead 1, what will the QRS look like in lead 1?
Mostly upward because a positive current towards a positive lead will result in a positive deflection.
In EKG, how do we say the QRS is towards a certain lead?
The mean QRS vector is traveling towards the particular lead.
If for half of the depolarization the vector is traveling toward the lead and the other half of the depolarization it is
traveling away from the lead, what will the QRS look like?
If the mean vector is equiphasic, what direction is it going in reference to that lead?
What is meant when we say the vector is perpendicular to the lead?
That it is running at 90 degrees (or a right angle) to the lead.
An EKG complex that has as much area above as below the baseline is best called?
If the mean QRS is perpendicular to lead 2, what does the QRS look like in lead 2?
In what direction would you expect the QRS vector to point in the frontal plane? Why
Inferior and to the left. Because this is the direction of the main segment of the left ventricle!
What is the difference in the AV node and AV junction?
The AV juction is the portion of the AV node that has foci of automaticity.
We use the term ideo with several rhythms. What does it mean?
Idio is a preflex of Greek origin meaning ones own.
The terms sino and sinus refer to what?
When the SA Node generates pacing impulses at a constant unvarying rate, with cycles of equal length, the rhythm
is said to be.
Does the proximal end of the AV Node have automaticity foci?
No, however, the remainder of the AV Node, known as the AV Junction does.
What does arrhythmia mean?