Basics Flashcards
Contractility
Conversion of an electrical signal to mechanical action
Excitability
Ability of cardiac muscle to respond to stimuli and generate action potential
Conductivity
Transfer of action potential from cell to cell- originating in SA node
Automaticity
Ability of cardiac cell to spontaneously generate electrical impose without innervation
Fast response action potential
- Initiated at SA node
- Na+ channels
Slow response action potential
- Initiated at AV node
- Ca++ channels
Overdrive suppression
- Inhibitory effect of faster pacemakers on slower pacemakers
SA node- Intrinsic rate
60 - 100 BPM
Atrial pacemaker- Intrinsic rate
60 - 75 BPM
AV Junction- Intrinsic rate
40 - 60 BPM
Ventricular pacemaker- Intrinsic rate
30-45 BPM
Horizontal axis- 1 small square (sec)
0.04 sec
Horizontal axis- 1 large square (sec)
0.2 sec
Vertical axis- 1 small square (mV)
0.1 mV
Vertical axis- 1 large square (mV)
0.5 mV
PR Interval- expected measurement
- 0.12 - 0.20 sec
- 3 - 5 small squares
- Beginning of P to beginning of Q
QRS Interval - expected measurement
- <0.12 sec
- 3 small squares
QT Interval - expected measurement
- 0.30 - 0.44 sec
- < 1/2 R-R intervale
Sinus bradycardia
< 60 BPM
Sinus tachycardia
> 100 BPM
P -wave
Atrial depolarization
QRS Interval
Ventricular depolarization
T wave
Ventricular repolarization
Sinus arrhythmia
Small change in rate during inspiration/ expiration
- Inspire = increase rate
- Expire = decrease rate
Systematic Interpretation
- Calculate Rate
- Identify rhythm
- Determine axis
- Check for hypertrophy
- Consider ischemia/ injury/ infarction
Normal sinus rhythm
- Rate 60-100 BPM
- Rhythm- regularly regular
- P: QRS = 1:1
- PR Interval 0.12 - 0.2 sec
- QRS < 0.12 sec
- QT 0.3 - 0.44 or <1/2 R-R
