EKG Ch. 2,3,4,5
circumflex artery
30-40%, supplies blood to the SA node
right coronary artery
SA node receives its blood supply primarily from the
Lead
a pair of electrodes such as chest Lead I,II,MCL
conductivity
ability of cardiac cells to receive an electrical stimulus and then transmit it to other cardiac cells
excitability
ability of cardiac cells to respond to an electrical stimulus
automaticity
ability of cardiac pacemaker cells to generate their own electrical impulses spontaneously without external stimulation
all-or-none phenomenon
action where all cells will respond or none will respond
sodium-potassium exchange pump
active mechanism of transport where potassium and sodium ions are moved in and out of the cell through the cell membrane
electrode
adhesive pad that contains conductive gel and is designed to be attached to the patients skin
EKG paper
arrangement of a series of horizontal and vertical lines printed on graph paper that provides a printed record of cardiac electrical activity
myocardial working cells specialized pacemaker cells
basic myocardial cell groups
SA artery
branch of the right coronary artery in approximately 60-70% of the population
syncytium
cardiac muscle cell groups that are connected together and function collectively as a unit
action potential
caused by stimulation of myocardial cells which extends across the myocardium; propagated in all-or-none fashion
action potential
change in polarity; a five-phase cycle that produces changes in the cell membrane's electrical charge
excitability
characteristic shared by all cardiac cells
12-Lead EKG
commonly used in hospitals and clinics; used regularly to aid in screening patients who are potential candidates for precutaneous intervention or fibrinolytic therapy
thin layer of atria, thicker muscular layer of ventricular walls
composed of myocardial working cells
bundle of His
conduction pathway that leads out of the AV node; common bundle
QRS complex
consists of Q,R,S waves and represents the conduction of the electrical impulse from the bundle of His throughout the ventricular muscle or ventricular depolarization
bundle of His
contains pacemaker cells that have the ability to self-initiate electrical activity
internodal tracts
distribute the electrical impulse throughout the atria and transmit the impulse from the SA node to the AV node; pathways
EKG paper
divided into small square 1 mm in height and width and represents time interval of 0.04 seconds
negative
during polarized, or resting state, the inside of the cell is electrically ______________ relative to the outside of the cell
depolarization
electrical occurrence normally expected to result in myocardial infarction movement of ions across cell membranes, resulting in positive polarity inside cell membrane
leads
electrodes are connected to the monitor or EKG machine by wires called
R wave
first upward (positive) deflection of the QRS complex largest deflection seen in chest Leads I and II
T wave
follows ST segment normally seen asymmetrical, slightly rounded, positive deflection resting phase
Bachmann's bundle
group of interatrial fibers contained in the left atrium
calcium
has an important function in myocardial depolarization and myocardial contraction
bipolar leads
have one positive electrode and one negative electrode limb leads
specialized group
have the ability to create an electrical impulse without being stimulated by a nerve
nodes or bundles
heart's conduction system consists of specialized cells and fibers
Einthoven's triangle
imaginary inverted triangle formed around the heart by proper placement of bipolar leads
S wave
immediately following the R wave, there is a downward deflection
hypercalcemia
increase in calcium blood levels
hyperkalemia
increase in potassium blood levels
hypernatremia
increase in sodium blood levels
<20 BPM
intrinsic firing of Purkinje network
60-100 bpm
intrinsic firing of SA node
35-45 BPM
intrinsic firing of the AV junction is
cation
ion with a positive charge
anion
ion with negative charged cells
baseline
isoelectric line the straight line seen on an EKG strip; represents the beginning and end point of all waves
SA node
located in the upper posterior portion of the right atrial wall, near the opening of the superior vena cava fewer than 50% are actual pacemaker cells
AV node
located on the floor of the right atrium near the opening of the coronary sinus and just above the tricuspid valve; electrical activity is delayed by 0.05 seconds
electrocardiograph
machine used to record electrocardiogram
QRS complex
measured from the beginning of the Q wave to the point where S wave meets the baseline
time
measured on the horizontal line of EKG paper
amplitude or voltage
measured on the vertical line of EKG paper
Wenckebach's bundle
medium bundle of the heart's conduction system that leads to the AV node
Purkinje network
network of fibers that carries electrical impulses directly to ventricular muscles
electrocardiogram
noninvasive procedure; graphic representation of the ELECTRICAL activity of the heart
3-5 small squares, 0.12 to 0.20 seconds in length
normal Pr interval is measured as
SA node, internodal pathways, AV node, bundle of His, bundle branches, Purkinje fibers
normal conduction of the heart follows the sequence
contractility
one of the primary cardiac cell characteristics considered a mechanical function of the heart
potassium
performs a major function in cardiac depolarization
relative refractory period
period when the repolarization is almost complete, and the cardiac cell can be stimulated to contract prematurely if the stimulus is much stronger than normal
sodium
plays a vital part in depolarization of myocardium
Thorel's pathway
posterior internodal tract bundle of muscle fibers in the human heart connecting the SA and AV nodes
hypokalemia
potassium deficit
automaticity, excitability, conductivity
primary cardiac cell characteristics considered electrical functions of the heart
automaticity excitability conductivity contractility
primary cardiac cells characteristics
generation and conduction of electrical impulses
primary function of the specialized myocardial pacemakers
contraction and relaxation
primary functions of myocardial working cells
SA node
primary pacemaker of the heart because it normally depolarizes more rapidly than any other part of the conduction system
repolarization
process whereby the depolarized cell is polarized and positive charge are again on the outside and negative charge on the inside; a return to the resting state
internodal tracts
receive the electrical impulse as it leaves the SA node
contractility
referred to as rhythmicity the ability of cardiac cells to shorten and cause cardiac muscle contraction in response to an electrical stimulus
threshold
refers to the point at which a stimulus will produce a cell response
AV junction
region where the AV node joins the bundle of His contains fibers that can depolarize spontaneously, forming electrical impulse that can spread to the heart chambers
P wave
represents depolarization of the left and right atria
PR interval
represents the distance from the beginning of the P wave to the beginning of the QRS complex
T wave
represents ventricular depolarization
specialized pacemaker cells
responsible for controlling the rate and rhythm of the heart by coordinating regular depolarization
myocardial working cells
responsible for generating the physical contraction of the heart muscle
heart's pacing or conduction
responsible for the electrical activity that controls each heartbeat
polarized state
resting state of a cardiac cell, wherein the inside of the cell is electrically negative than the outside of the cell
Q wave
seen as the first downward deflection following the PRI
repolarization
slower process than depolarization
hyponatremia
sodium deficit
Bachmann's bundle
specialized group of cardiac fibers conducting electrical activity from SA node to the left atrium
automaticity
specific to pacemaker cell cites of electrical conduction system ei. SA node, AV node, Purkinje network fibers
absolute refractory period
stage of cell activity in which the cardiac cell cannot spontaneously depolarize
resting membrane potential
state of cardiac cell in which the inside of the cell membrane is negative compared to the outside of the cell membrane
Bachmann's bundle
subdivision of the anterior internodal tract, conducts electrical activity from the SA node to the left atrium
electrolytes
substance or compound whose molecules dissociate into charged components, or ions, when placed in water producing positively or negatively charged ions
3-Lead EKG
sufficient for detecting life-threatening dysrhythmias or abnormal heart rhythms
permeability
the ability of the cell membrane to change to allow the movement of ions
rhythm strip or EKG strip
the printed record of the electrical activity of the heart
ST segment
the time interval which the ventricles are depolarized and ventricular repolarization begins isoelectric or consistent with baseline
specialized pacemaker cells
these cells are found in the electrical conduction system of the heart
conductivity
this characteristic is shared by all cardiac cells because these cells are connected together to form a syncytium
contractility
thought of as the coordination of contractions of cardiac muscles to produce a regular heartbeat
potassium (K), sodium (Na), and calcium (Ca)
three major cations that affect cardiac functions
PR interval
time interval necessary for the impulse to travel from the SA node through the internodal pathways in the atria and downward to the ventricles
bundle branches
two main branches, right and left conduct electrical activity from the bundle of His down to the Purkinje network
EKG waveforms
wave or waveform recorded on an EKG strip refers to movement away from the baseline and is represented as a positive deflection(above) or a negative deflection (below baseline)
dominance
where the fastest pacemaker assumes control of the rate of depolarization of the atrium and ventricles
AV tissue or Purkinje network fiber
will assume duties of pacemaker if dominant pacemaker fails
