Transcript Electrical conduction in the Heart

Electrical Conduction in the Heart
SA Node (the Pacemaker)
• The SinoAtrial, or SA,
node is the heart's natural
pacemaker.
• The SA node is located in the
upper part of the right atrium.
• Autonomic electrical impulses
there set the rate of the
heartbeat.
• The SA node is also called
the sinus node.
• The signal is sent from the SA
node to AV node via the
Internodal Pathway
• The AtrioVentricular, or AV node is the
electrical relay station between the upper
and lower chambers of the heart.
• Electrical signals from the atria must
pass through the AV node to reach the
ventricles.
• The AV node serves as an electrical
relay station, slowing the electrical
current sent by the SA node before the
signal is permitted to pass down through
to the ventricles. This delay ensures that
the atria have an opportunity to fully
contract before the ventricles are
stimulated.
• Once this delay has passed, the AV
node then sends the electrical impulse
along special fibers embedded in the
walls of the lower part of the heart.
AV Node
Bundle of His
• From the AV node the electrical
impulse moves into fibers
known as the Bundle of His, or
AtrioVentricular bundle.
• The bundle passes from the AV
node into the wall of the septum
between the ventricles.
• A short way down the septum
the bundle divides into left and
right bundle branches.
• These fibers continue
downward to the apex where
they divide into many small
Purkinje Fibers that spread
outward among the contractile
cells.
Purkinje Fibers
• Purkinje fibers are
located in the
atrioventricular, or AV,
bundle of the heart.
• Their function is to
send nerve impulses to
the cells in the
ventricles of the heart
and cause them to
contract.
Electrocardiogram (ECG)
• Composite of all electrical impulse
(action potentials) detected, amplified
and recorded by electrodes on arms,
legs and chest
• P wave
Reading an ECG
– SA node fires, atrial depolarization
– Atrial systole
• QRS complex
– Atrial repolarization and atrial diastole
– AV node fires, ventricular depolarization
– Ventricular systole
• T wave
– ventricular repolarization
Electrical Activity of Myocardium
1)Atria begin to
depolarize
2) Atria depolarize
3)Ventricles begin to
depolarize at apex;
atria repolarize
4)Ventricles depolarize
5) Ventricles begin to
repolarize at apex
6) Ventricles repolarize
ECGs, Normal & Abnormal
No P waves
ECGs, Abnormal
Arrhythmia: conduction failure at AV node
No pumping action occurs
Diastole vs Systole
• Diastole - the time during which cardiac muscle
relaxes.
• Systole - the time in which cardiac muscle is
contracting.
The Heart at Rest : Atrial and Ventricular
Diastole
– While both atria and ventricles are relaxing, the atria
begin filing with blood from the veins while the
ventricles have just completed a contraction.
– As the ventricles relax the AV valves between the
atria and ventricles open, and blood flows from the
atria to the ventricles.