1. Conduction System of the Heart & Electrocardiography
Exercise 31
Conduction System of the Heart
&
Electrocardiography

2. Objectives Parts of the intrinsic conduction system of the heart
P, QRS, T waves on an ECG
Tachycardia, bradycardia, fibrillation

3. Intrinsic Conduction System
Intrinsic = heart beats without nervous system sending impulses to initiate contractions
Heartbeat is partially regulated by autonomic nervous system (ANS) (↑↓ heartbeat), and partially by this intrinsic conduction system

4. Intrinsic Conduction System
Nodal system
Makes sure heart muscle beats as a coordinated unit and in orderly fashion (atria to ventricles)
As the signal passes through chambers of the heart, causes contraction…once it’s passed, chamber relaxes

5. SA Node (SinoAtrial) In right atrium
Just below superior vena cava entrance
Provides stimulus for contraction, sets rate for heart as a whole
“pacemaker”
Fig

6. AV Node (AtrioVentricular)
In lower atrial septum
At atria/ventricle junction
Fig

7. Atrioventricular (AV) bundle
(Bundle of His)
Within the interventricular septum
Fig

8. Bundle Branches Right and left Also within the interventricular septum
Fig

9. Purkinje Fibers Within ventricular walls
More dense in left ventricle (larger chamber)
Fig

10. Intrinsic Conduction System: Impulse Propagation
Signal to Atria (R, L; pushes blood into ventricles)
AV node (bridge); pause to allow ventricles to fill
SA Node
Ventricular contraction pushes blood out of the heart
Right bundle branch
AV bundle/Bundle of His
Purkinje fibers
Left bundle branch

11. Fig

12. Electrocardiography (ECG)
Electrical currents eventually spread throughout whole body
Detected by ECG on body’s surface
3 recognizable waves

13. Electrocardiography (ECG)
3 recognizable waves
P wave
Atrial depolarization (change in charge across cell membrane…action potential…)
Atrial contraction
QRS complex
Ventricular depolarization & contraction
T wave
Ventricular repolarization & relaxation

14. Fig

15. Electrocardiography (ECG)
Tachycardia
Heart rate >100 bpm (beats per minute)
Fibrillation
From prolonged tachycardia
Rapid uncoordinated heart contractions
Makes the heart useless as a pump
Bradycardia
Heart rate <60 bpm
Athletes—good thing—more efficient