EKG book..basics of reading an EKG Flashcards
What is the charge of the inside of a cardiac cell at rest?
Negative
polarity maintained by membrane pumps
This is the fundamental electrical event of the heart
*this happens spontaneously in pacemaker cells
DEPOLARIZATION
In non pacemaker cells, this occurs by the arrival of an electrical impulse that causes positively charged ions to cross the membrane..this continues until the whole heart is in this state
DEPOLARIZATION
All waves on an EKG are manifestations of _______ and _______
Depolarization and repolarization
3 types of cells in heart
Pacemaker
Electrical conducting
Myocardial (contractile machinery)
The rate of depolarization in pacemaker cells is determined by _________ and _________
- Electrical characteristics of cell
2. External neurohormonal input
A pacemaker cell does NOT have a true..
Resting potential
What is the dominant pacemaker of the heart?
Sinoatrial (SA) node
*located high up in RIGHT atrium
What is the typical firing rate of SA node cells?
60-100
Vagal stimulation does what to the SA node firing rate
Slows it down!
Long, thin cells that carry current rapidly to distant regions of heart
Electrical conducting cells
Conducting fibers at the top of the intra-atrial septum
- allows for rapid activation of the L atrium from the R atrium
Bachman’s bundle
Largest part of the heart tissue!
Responsible for the heavy labor or repeatedly contracting and relaxing, thereby delivering blood to the body
Myocardial cells
Myocardial cells contain lots of ______ and______
Actin and myosin
When a wave of depolarization reaches a myocardial cell, calcium is released in the cell, causing the cell to contract
Excitation-contraction Coupling
A wave of depolarization, upon reaching myocardial cells, will spread HOW across the entire myocardium?
SLOWLY!
Duration
Amplitude
Configuration
3 characteristics of EKG waves
Unit of measure for duration on EKG
fraction of a second
Unit of measure for amplitude on EKG
milivolts (mV)
Horizontal axis on an EKG measures…
Time! (in fraction of a second)
Distance across 1 small square (horizontally) represents..
0.04 seconds
Distance across 1 large square (horizontally) represents..
0.2 seconds (5x greater than a small square)
The vertical axis on an EKG measures…
Voltage (in milivolts, mV)
Distance of 1 small square vertically represents..
0.1 mV
Distance of 1 large square vertically represents..
0.5 mV
SA cells spontaneously depolarize, wave of depolarization spreads outwards into atrial myocardium. Depolarization of atrial myocardial cells results in..
Atrial contraction!
During the atrial depolarization and contraction, electrodes record which wave?
P wave
A recording of the spread of depolarization through atrial myocardium start to finish
P wave
Because the SA node is in the R atrium…
The R atrium contracts before the L atrium
The first part of the p wave represents ?
The second part of the p wave represents?
First part…R atrial depolarization
Second part..L atrial depolarization
What must the electrical conduction be funneled through to get fro the atria to the ventricles?
Interventricular septum (this slow it down)
When does the electrical conduction slow down?
When it reaches the AV node (for a fraction of a second)
The conduction delay between the atria and ventricles allow for what?
The atria to finish contracting (and empty their blood volume) before the ventricles start
Like the SA node, the AV node is also under what control?
Autonomic nervous system
On an EKG, where is the delay of the AV node seen?
The flat line right after the p wave
Bundle of His
R and L Bundle branches
Terminal Purkinje fibers
ventricular conducting system
Emerges from AV node and almost immediately divides into R and L bundle branches
Bundle of His
Brings current to the R side of inter ventricular septum all the way to apex of the R ventricle
R bundle branch
Divides into:
- septal fascicle
- anterior fascicle
- posterior fascicle
L bundle branch
Termination of R and L bundle branches is..
Purkinje Fibers
Purkinje fibers deliver electrical current into the…
Ventricular myocardium
Ventricular myocardial depolarization causes..
Ventricular contraction
The amplitude of the QRS complex is much greater than the p wave because the…
ventricles have MUCH MORE MUSCLE MASS than the atria
The QRS complex is much more variable in shape than the P wave, reflecting greater ______ of the pathways of depolarization
Intricacy
If the first deflection is downwards, it is a..
Q wave
The first upward deflection is a…
R wave
If there is a second upward deflection, it is a..
R-prime
The first downward deflection following an upward deflection…
S wave
A downward deflection can ONLY be a Q wave if..
It is the first wave of a complex
any other downward wave is an S wave
The earliest part of the QRS complex represents depolarization of..
Interventricular septum (by septal fascicle of the L bundle branch)
The R and L ventricles depolarize about the same time but what do we mostly see represented on the EKG?
Left ventricular activation
because L ventricle about 3x more muscle mass than R ventricle
After myocardial cells depolarize, there is a brief..
refractory period (unable to be stimulated at this point)
Ventricular REPOLARIZATION is represented by which wave?
T wave
Ventricular repolarization is much ______ than ventricular depolarization
slower
T wave is more _____ than the QRS complex
broad (bc ventricular repol is slower than ventricular depol)
Segment
straight line
Interval
at least 1 wave plus connecting straight line
P wave plus straight line connecting to QRS complex
PR interval
Straight line running from end of P wave to start of QRS complex
PR segment
Measures the time from the start of atrial depolarization to the start of ventricular depolarization
PR interval
Measures time from end of atrial depolarization to start of ventricular depolarization
PR segment
Straight line connecting end of QRS complex to beginning of T wave
ST segment
Measures time from end of ventricular depolarization to start of ventricular repolarization
ST segment
Includes QRS complex, ST segment and T wave
QT interval
Measures time from beginning of ventricular depolarization to end of ventricular repolarization
QT interval
Describes duration of QRS complex alone, without any connecting segments
QRS interval
Measures duration of ventricular depolarization
QRS interval