Download Title: The Cardiac Conduction System

Title: The Cardiac Conduction System
1- Introduction: The inherent and rhythmical electrical activity in the heart is
responsible for its continuous beating. The source of this beating is a group of
highly specialized cells called the autorhythmic cells.
a- These cells are self-excitable
b- They repeatedly generate action potentials that trigger heart contractions
c- These cells will continue to beat even when removed from the body – this
makes heart transplants possible – even after all nerves have been cut!
d- Less than 1% of the heart cells set the rhythm
e- Cells that are not autorhythmic (do not set the pace) are contractile fibers,
which cause the heart to contract
f- The autorhythmic cells act as the hearts pacemaker. They set the
contraction for the entire heart. They form the conduction system.
1- The conduction system is the route that delivers the action potentials
throughout the entire heart muscle. The conduction system ensures that
the chambers of the heart are stimulated and contract in a coordinated
manner.
II- The conduction System
A- SA Node
B- AV Node
C- AV Bundle
D- R/L Bundle Branches
E- Purkinje Fibers
F- Diagram
G- The SA Node initiates action potentials about 100 times per minute (faster
than the autorhythmic fibers) For this reason the SA node is considered the pacemaker of
the heart and sets the rate at which it beats.
1- Impulses from the autonomic nervous system and various hormones
modify the strength and timing of the beats but do not change the
rhythm.
III – Electrocardiography – Transmission of action potentials through the conduction
system generates an electric current. This current can be detected by electrodes placed on
the outside of the body. This recording is called an electrocardiogram or EKG
1-The EKG is a series of up and down waves produced by the cardiac
muscle fibers during each beat
2- We are used to seeing what is called a Single Lead II (righty arm to
left)
3- Diagram
A- P wave
B- QRS Complex
C- T-Wave
4- Variation in the size and duration of these waves can be used to
diagnose a variety of cardiac muscle and conduction system
abnormalities
5- Correlation of EKG waves with heart activity
a- Systole
b- Diastole
6- Cardiac output