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163 Cards in this Set

  • Front
  • Back
Two functions of cardiac cells
Contractile, Electrical
Myocardial cells are
Pacemaker cells are
Myocardial cell characteristics
contractile filaments that slide together when stimulated causing contraction
Atria/Ventricle walls are made of
Myocardial cells
What is released when a nerve is stimulated
Neurotransmitters cross between the end of
a nerve and muscle (neuromuscular junction)
Ability of cardiac cells to create an electrical impulse w/out stimulation
Hearts normal pacemaker site
Sinoatrial node (SA)
Important ions in maintaining automaticity
Na+ K+ Ca++
Decreases automaticity
Increase in Na+ K+ Ca++
Increases automaticity
Decrease in K+ Ca++
Why is cardiac muscle electrically irritable
due to ionic imbalance across cell membranes
Ability of cardiac muscle to respond to outside stimulus
Excitability (Irratibility)
3 types of stimulas to heart
mechanical, electrical, chemical
Ability of cardiac muscle to recieve electrical impulse and conduct it to adjoining cells
Affects speed of impulse in conductivity
sympathetic, parasympathetic NS and medication
Ability of myocardial cells to shorten in response to an impulse
Meds that strengthen contractibility
Digitalis, Dopamine
Energy travels from
Negative to Positive
Flow of electrical charge from one point to another
Seperate electrical charges of opposite polarity contain
Potential energy
Measurement of potential energy
In a normal heart, electrical activity occurs due to what
Ionic changes within cells
Charged particles
Elements that turn into ions
Main cardiac electrolytes
Na+ Sodium K+ Potassium Ca++ Calcium Cl- Chloride
Five phase cycle that reflects difference in concentration of electrolytes across cell membrane
Action Potential
Exists due to imbalance of charged particles
Potential energy (voltage)
How electrolytes cross cell membranes
pores or channels
When a cell is at rest, what ion leaks out
Proteins and phosphates inside cell carry what type charge
When inside of cell is more negative it is called
Difference in electrical charges across cell membrane is called
Membrane potential
Electrolytes are moved from one side of cell to another via
Pumps require _______
Energy to pumps come from
Energy expended by cells to move electrolytes across cell create
flow of current
This flow of current is called
For a pacemaker cell to fire, what must exist?
a flow of electrolytes across cell membrane
When a cell is stimulated, cell membrane changes and becomes permeable to
Na+ and K+
Major extracellular ion
Na+ Sodium
Major intracellular ion
K+ Potassium
When cellular channels open ______ rushes in
Na+ causes the cell to become more
What happens on ECG when cell becomes more positive
waveform is recorded
Name for cell when it becomes more positive
Threshold Potential
When movement of electrolytes cause cell to become more positive what is generated
Impulses cause a chain reaction to
next cell membrane
Movement of impulses causing cells to become more positive is called
Eventually this impulse spreads from pacemaker cells to
Myocardial cells
Impulse spreads through myocardial layers in what order
Endocardium to epicardium (inside-out)
Expected response from depolarization
When the atria contract what is recorded on ECG
P wave
P wave represents
Atrial depolarization
When the ventricles contract what is recorded on ECG
QRS Complex
QRS Complex represents
Ventricular depolarization
Depolarization is an _______ event
Contraction is a ________ event
What happens after the cell is depolarized
quickly startes to recover and restore electrical charge back to -
Restoring cell back to - charge is called
In repolarization the cell stops the flow of _____ into cell and allows ____ to leave
Na+, K+
Cell returns to _______ in repolarization
In repolarization, the contractile proteins do what
seperate and relax
Repolarization occurs within layers of heart from ______ to ________
epicardium (out) to endocardium (in)
On the EKG, what represents ventricular repolarization
ST segment and T Wave

Five phases of Action Potential
What do these phases reflect
sequence of voltage across cell
Phases 1,2,3 are called
electrical systole
Phase 4 is called
Electrical diastole
Phase 0 represents
Phase 0 on EKG is represented by what
QRS complex
Cells of atria, ventricle and purkinje fibers contain many ______ channels
SA and AV nodes have ____ Na+ channels
If Na+ channels are blocked or slowed, what happens with heart
decresed HR and conductivity
4 Phases of cardiac action potential
Early repolarization, Plateau Phase, Final Rapid Repolarization, resting Membrane Potential
Na+ channels partiall close, Cl- enters, K+ leaves resulting in decrease electrical charge within cell
Early Repolarization
Ca++ enters cell, more K+ leaves allowing sustained contraction
Plateau Phase
Plateau Phase represented by what on EKG
ST segment
ST segment reflects
early part of repolarization of L/R ventricles
What can shorten ST segment
K+ leaves cell quickly, Na+ and ca++ channels close and cell becomes more neg
Final Rapid Repolarization Phase 3
Phase 3 is represented by what on EKG
T Wave
What could cause a longer action potential in Phase 3
Blocked K+ channels
Excess Na+ inside cell, excess K+ outside cell...pump activated to send Na out and K in
Resting Membrane Potential Phase 4
Period of recovery that cells need after being discharged before they can respond again
Refractory period
The refractory period in the heart lasts longer than the
In what period will the cell not respond at all to stimulus
Absolute refractory period
On the EKG, the absolute refractory period is during
Onset of QRS to peak of T wave
Period when cells have repolarized to threshold and can be stimulated to respond to stronger than normal stimulus
relative refractory period
Relative refractory period corresponds with what on EKG
Downslope of T wave
When cells can be stimulated by weaker than normal stimulus
Supernormal Period
Supernormal period on EKG
end of T wave
What period do arrythymias usually develop
Supernormal period
3 Refractory periods
Absolute, Relative, Supernormal

Primary pacemaker site in heart
SA node
SA Node rate
60-100 bpm
SA node artery originates from
R Coronary artery 60% people
Circumflex 40%
Path of impulse from SA node
r atria, interatrial septum, l atria
Impulse spreads to AV node via
3 Internodal pathways
Bachmans Bundle - anterior
Wenkenbachs Bundle-middle
Thorels Pathway-posterior
Conduction through AV node begins before/after atrial depolarization is complete
Pathway that conducts impulse to L atria
Bachmans Bundle
AV Junction consists of
AV node and non branching portion of Bundle of His
Conduction Pathway
SA Node, Internodal pathways, AV Junction, Bundle of His, R/L Bundle Branches, Purkinje Fibers
AV junction Rate
40-60 bpm
Ventricular Rate (purkinje)
20-40 bpm
Speed of conduction impulse is fastest in
Bundle of His and Purkinje Fibers
Speed of conduction impulse is slowest in
AV and SA nodes
Primary delay in spread of impuls from atria to ventricles occurs in
atrionodal and nodal areas of AV node
Arrythmias (abnormal rhythms) are caused by what 3 things
increased automaticity, triggered activity or re-entry
When non-pacemaker cells begin to depolarize or pacemaker site other than SA increases firing rate
Enhanced automaticity
Enhanced automaticity rhythms
atrial flutter, afib, SVT, V tach, V fib, junctional tachycardia
Causes of enhanced automaticity
Epi, Atropine, Digitalis toxicity, Electrolyte disturbances
Abnormal electrical impulses when cells are normally quiet
Triggered Activity
Triggered activity requires
a stimulus
Causes of triggered activity
Medications, decreased Magnesium, hypoxia
Beat originating outside SA node is called
Spread of impulse through cell already stimulated
REeentry requires what 3 things to happen
potential conduction circuit (accessory pathway), block in circuit and a delayed conduction through remainder of circuit
Cause of Reentry
An AV block is a rhythm disturbance associate with a
conduction disturbance
Standard Limb Leads
Lead I Positive Electrode is on ______arm, Neg electrode on ____arm
Left arm, right arm
Lead I views ________surface of heart
Lead II Pos Electrode is on _____ and Neg is on _____
Left Leg and Right arm
Lead II views ______ surface of heart
Lead III Pos electrode is on _____ and Neg is on ______
Left Leg, Left arm
Lead III views _____ surface of heart
Augemented Limb Leads
aVR, aVL and aVF
All augmented leads are _____ electrodes
Placement of augmented leads
aVR - right arm
aVL - left arm
aVF - left leg (foot)
Chest Leads
All chest leads place are _____ electrodes
The _______ is the neg electrode for chest leads
V1 and V2 placement
V1 right side of sternum
V2 left side of sternum
fourth intercostal space
V1 and V2 view _______ surfaceof heart
Septum (down the middle)
V3 and V4 placement
V3-betweeen V2 and V4
V4-midclavicular line-5th intercostal space
V3 and V4 view _______ surface of heart
V5 V6 placement
left anterior and left midaxillary 5 intercostal space
V5 and V6 view the ______ surface of heart
Lateral (low side view)
Bipolar leads consist of
a neg lead and a positive lead
Unipolar leads consist of
a positive lead and a reference lead
In bipolar leads the right arm electrode is always _____ and the left leg electrode is always
ECG paper: small box =
.04 sec
Large box =
.20 sec
1 small box is ____mm high
1 large box is ____mm high
P wave represents
atrial depolarization
Straightline recorded when electrical activity is not detected
Baseline (isoelectric line)
Movement away from the baseline in either pos/neg direction
line between waveforms
waveform and segment
several waveforms
Normal characteristics of P Wave
Smooth, rounded upright 1:1 to qrs
QRS complex represents
Ventricular depolarization
Normal characteristics of QRS complex
R always pos S always neg less than .10 sec
T Wave represents
Ventricular repolarization
Normal characteristics of T wave
slightly asymetric, less than 5mm tall
Neg T waves suggest
Myocardial ischemia
Tall, pointed T waves suggest
low amplitude T waves suggest
hypokalemia, hypomagnesia
Deep inverted T waves suggest
subarachnoid hemorrage
Tall broad spiked t waves suggest