Download Intrinsic Cardiac Conduction System

AP2 Lab 2
Cardiac Conduction System, ECG/EKG,
Pacemakers, and Cardiac Output
J. James
Video: Heart beats outside of body
Intrinsic Conduction System
Fig 18.13
Autorhythmic fibers of the intrinsic conducting
system
• Not the same as contractile fibers
• Are muscle cells but act like neurons
• Coordinate the sequence of contraction
among the contractile fibers
• Components
1. SA Node (sinoatrial)
2. AV Node (atrioventricular )
3. Bundle of His (AV bundle)
4. L&R bundle branches
5. Purkinje fibers
• All have autorhythmicity…
• Why?
1. Always ‘leaks’ Na+ and Ca++
inward
2. Become progressively
impermeable to K+ leaking
outward
• The normal sequence …
• The advantage …
Autorhythmicity / Automaticity
Fig 18.12
Pacemakers
Single chamber
Electrocardiogram = ECG = EKG
Fig 18.16
Video: Sinus rhythms
4 min
Normal Sinus Rhythm
Sinus Bradycardia
Sinus Tachycardia
ECG Tracings: one ‘normal,’ three dysrhythmias / arrhythmias
Fig 18.18
Normal sinus rhythm, NSR
Junctional rhythm
2nd degree heart block
Ventricular fibrillation
Asystole
Implantable Cardioverter Defibrillators, ICDs
Cardiac Output
CO def…
Formula: CO = HR x SV
HR…
SV…
Avg. 70 ml/beat
Formula: SV = EDV-ESV
SV/EDV = “ejection fraction”
- usually 60-90% of EDV
CO can increase 7X (700%)
-
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