Chapter 12/13 Flashcards
ECG/ EKG abbreviation
ElectroCardioGram
EKG
A recording of the electrical currents of the heart
How many EKG leads
12 because they are more detailed and accurate. 3-5 for continuous monitoring of rhythm
Value of EKG
To detect damaged heart disease, from direct heart disease or other organ failure affecting the heart, serial ECGs are valuable in checking response to treatment, does not defects in the pumping ability of the heart
When to order ECG
Signs and symptoms of acute cardiac disorder, Pre-op screening, Hx of heart disease, Hx of Cardiac surgery, physical exam findings that would indicate the need for ECG
ECG leads
View from several different angles, electrical activity of heart at different angles. Has + and - components (12 leads- 6 limb leads, 6 chest leads, 10 wires- one on each limb, 6 on chest)
Chest leads (precordial leads)
Looking at specific areas of the heart
Primary electrolytes responsible for electrical difference across the RMP are
potassium, sodium, and calcium
Which has the greatest concentration inside the cardiac cell
potassium about 151 meq/l inside cell, 4 outside
Concentration of K outside the cardiac cell is
4 meq/l
Concentration of k inside the cardiac cell is
151 meq/l
Na outside the cardiac cell is
144 meq/l
Na inside the cardiac cell is
7 meq.l
Concentration of Ca is about what outside the cell
5 meq/l
Concentration of Ca inside cell
less than 1 meq/l
When the cardiac cell is in its resting or polarized state, the inside of the cell is ___Charged with what cation
Negatively charged with K cation
When the cardiac cell is in its resting or polarized state the outside of the cell is ___ charged with what cation
Positively charged with Na cation
Na+/K+ pump establishes
- an increased Na+ concentration outside the cell 2. an increased K concentration inside of the cell. both ions then diffuse along their concentration gradients. K diffuses out, Na diffuses in at the same time.
For every 50 to 75 K ion that diffuse out of the cell only
1 Na diffuses into the cell, exchange ration results in a deficiency of positive cations inside the cell
RMP of the mycardial cells is about
-90 mV
Cornerstone to the understanding of the electrophysiology of the heart is the five electrophysiologic phases of the action potential
ECG
ECG
is used to record the five phases of the action potential
Phase 0 name
Rapid Depolarization (early phase)
Depolarization
trigger for myocardial contraction
Rapid Depolarization (early phase) activate
ventricle muscle fibers initiated by the SA node
ventricular muscle fibers are activated between
60-100 times/min by an electrical impulse initiated by the SA node
This action changes the RMP and allows a rapid inward flow of Na into the cell through specific Na channels
Phase 0: Rapid Depolarization, causing the cell to become positively charged
The voltage inside the cell at the end of depolarization is about
+30 mV, producing a rapid up stroke in the action potential
Repolarization
process by which the cells of the heart return to their resting state
Other name for Phase 1
Initial Repolarization
Immediately after Phase 0
Phase 1: Initial Repolarization
Initial Repolarization
The channels for K open and permit K to flow out of the cell, an action that produces an early but incomplete repolarization
Illustrated as a short downward stroke in the action potential curve just before the plateau
Phase 1: Repolarization
Name for Phase 2
Plateau state
Plateau state
Slow inward flow of Ca which in turn significantly slows the outward flow of K
Prolongs the contraction of the myocardial cells
phase 2 : Plateau state
Name for Phase 3
Final Rapid Repolarization
Final Rapid Repolarization
Inward flow of Ca stops, the outward flow of K is again accelerated and the rate of repolarization accelerates
Phase 4 name
Resting or polarized state
Resting or polarized state
the voltage sensitive ion channels return to their pre-depolarization permeability. the excess Na inside the cell and the loss of K are returned to normal by the Na and K ion pumps. an Additional Na and Ca pump removes the excess Ca from the cell
The heart is composed of how many cardiac cells
2
the 2 cardiac cells are
Contractile muscle fibers, and specialized “pacemaker cells” called autorythmic cells
Myocardial contractile fiber cells make up
the bulk of the musculature of the myocardium and are responsible for the pumping activity of the heart.
Approx how much of the heart is composed of the autorhythmic cells
1 %, majority of which are located in the SA node
SA Node
Have the unique ability to initiate an action potential spontaneously, which in turn triggers the myocardial fibers to contract.
Automaticity
ability of the cells in the SA node (pace maker cells) to generate an action potential without being stimulated.
Excitability (irritability)
is the ability of a cell to reach its threshold potential and respond to a stimulus or irritation
The lower the stimulus needed to activate a cell, the more
excitable the cell
Conductivity
is the unique ability of the heart cells to transmit electrical current from cell to cell throughout the entire conductive system
Contractility
the ability of cardiac muscle fibers to shorten and contract in response to an electrical stimulus
additional properties of the myocardial contractile fibers and autorythmic cells are
refractory periods
Refractory periods entail
- the ionic composition of the cells during different phases of the action potential and 2. the ability of the cells to accept a stimulus
Absolute Refractory Period
is the time in which the cells cannot respond to a stimulus. The ionic composition of the cells isnt in place to receive a stimulus.
Phases 0,1,2, and about half of phase 3 represent the
absolute refractory period
Relative refractory period
is the time in which repolarization is almost complete and where a strong stimulus may cause depolariation of some of the cells. Some cells may respond normally, some in abnormal way, and some not at all.
The second half of phase 3 represents
the relative refractory period of the action potential
the Nonrefractory period
occurs when all the cells are in their resting or polarized state. The cells are ready to respond to a stimulus in a normal fashion
Phase 4 represents what period
Nonrefractory period
Duration of each refractory period may vary in response to use of
medications or recreational drugs, presence of disease, electrolyte imbalance, myocardial ischemia, or myocardial injury
components of the conductive system include
Sinoatrial node (sa node), atrioventricular junction (AV node), bundle of His, the right and left budle branches, and the purkinje fibers.
SA node
initiates the cardiac contraction by producing an electrical impulse that travels through the right and left atria.
In the right atrium, the electrical impulse that travels through the
anterior internodal tract, middle internodal tract, and posterior internodal tract
All three internodal pathways become one at the
AV junction
Bachmanns bundle
Conducts electrical impulses by the SA node directly to the left atrium
The electrical impulse generated by the SA node cause the right and left atria to
Contract simultaneously, in turn causing the blood in the atria to move into the ventricles
Where is the AV junction located
just behind the tricuspid in the lower portion of the right interatrial septum
AV junction
relays the electrical impulse from the atria to the ventricles via the bundle of his
Bundle of His location
enters the intraventricular septum and divides into the left and right bundle branches