NR 340-Exam 2 Study Guide-Critical Care (Version 1), Chamberlain College of Nursing

Exam 2 Study Guide-Critical Care



Exam 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