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NR 340-Exam 2 Study Guide-Critical Care (Version 1), Verified And Correct Study Guide, Latest
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Exam 2 Study Guide-Critical CareExam 2 Study Guide-Critical Care
Basic Dysrhythmia Interpretation & Mgmt-Ch 7
Blood Flow Review
Basic Electrophysiology
Automaticity-The ability for the heart muscle to generate it's own electrical activity
o Pacemaker Cells arise naturally from the SA Node
o Electrolytes involved are K+, Na+, & Ca+
Cardiac Action Potentials
Depolarization-occurs when charge is more (+)
o P wave=atrial depolarization
o QRS complex=ventricular depolarization
o contraction
o Systole
Repolarization-recharging period when charge is more (-)
o T wave=ventricular repolarization
o filling
o Diastole
Electrical + Mechanical=Cardiac Contraction
, Action Potential Curve
o See Below-Sodium, Potassium, & Calcium flow in & out of the cell at different times allowing
for charge changes and contraction of heart muscle tissue.
o 4 Phases
Early Repolarization
sodium channels close
Phase 2-Plateau Phase
potassium leaves cell
Phase 3-Rapid Repolarization
calcium channels close
potassium returns into cell quickly
Phase 4-Resting Phase (polarized state)
active transport through the Na-K pump begins restoring K to inside the cell &
sodium to the outside of the cell
cell membranes become impermeable to sodium
Potassium may move in & out of the cell
Intrinsic Rates of Conduction Pathway
SA Node
o natural pacemaker
o 60-100 bpm
AV Node
o takes over as pacemaker if SA node can't do the job
, o 40-60 bpm
Purkinje Fibers
o last resort to pace heart if both SA & AV nodes fail
o 20-40 bpm
Cardiac Monitoring
12 lead ECG
o only 10 electrodes used to monitor, but gives 12 overall electrical pictures
4 limb leads
6 trunk leads
o shows change or damage to heart muscle
ischemia, infarct, enlarged cardiac chambers, electrolyte imbalances or drug toxicity
Calculating Heart Rate from a 6 Second Strip
Graph Paper
o Vertical boxes measure voltage or amplitude
o Horizontal boxes measure time (in seconds)
1 small box=0.04 seconds
1 large box=0.20 seconds
5 large boxes=1 second
a six-second strip will be 30 large boxes
To calculate rate on a 6 second strip, count R-to-R and multiply by 10
Cardiac Waveforms & Determining Rhythm
P Wave
atrial depolarization
0.04-0.10 seconds in duration
Are they present?
are they regularly occurring?
is there a P for each QRS?
are the P waves smooth, rounded, & upright?
do all P waves look similar?
QRS Complex
ventricular depolarization
0.06-0.10 seconds in duration
is the complex > 0.12 seconds (wide)?
can indicate ventricular origin
is the complex < 0.12 seconds (narrow)?
most likely supraventricular in origin (SA/AV nodes)
do the complexes have a similar appearance across the tracing?
QT Interval
, 0.38-0.42 seconds
begins at the QRS Complex to the end of the T wave
varies with heart rate
Pathological Q waves
0.04 seconds in width & more than 1/4 R wave amplitude
indication of MI or myocardial tissue death
ST Segment
Elevation
myocardial injury or hyperkalemia
STEMI
looks like a tombstone
Depression
myocardial ischemia or digoxin use
T Wave
ventricular repolarization
follows QRS Complex
U Wave
can sometimes bee seen after the T wave
can be normal or indicate hypokalemia
PR Interval
0.12-0.20 seconds in duration
is the interval > 0.20 seconds?
is the interval < 0.12 seconds?
is the interval constant across the tracing?
Cardiac Dysrhythmias
Normal Sinus
Rate 60-100
Rhythm regular
P waves before QRS & upright
PR interval 0.12-0.20 seconds
QRS complexes <0.12 seconds & look alike
Sinus tachycardia
Causes
stress, exercise, fever, anemia, hypoxemia, CHF, pain
Effects on body
faster rate decreases CO
S&S
pounding heart, dizziness, anxiety, weak pulses
decreased BP, UO
Treatment
treat underlying cause
give O2
if CHF, give Digoxin
Rate 100-160
Rhythm regular
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