NR 340-Exam 2 Study Guide-Critical Care graded A
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
,NR 340-Exam 2 Study Guide-Critical Care graded A
• 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
,NR 340-Exam 2 Study Guide-Critical Care graded A
o natural pacemaker
o 60-100 bpm
• AV Node
, NR 340-Exam 2 Study Guide-Critical Care graded A
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
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
,NR 340-Exam 2 Study Guide-Critical Care graded A
• 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
,NR 340-Exam 2 Study Guide-Critical Care graded A
o natural pacemaker
o 60-100 bpm
• AV Node
, NR 340-Exam 2 Study Guide-Critical Care graded A
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
