Transcript Co-ordination of the Cardiac Cycle

01 April 2016
Co-ordination of the Cardiac Cycle
Aims
•Describe how heart action is coordinated with
reference to the sinoatrial node (SAN), the
atrioventricular node (AVN) and the Purkyne tissue
•Be able to interpret and explain electrocardiogram
(ECG) traces, with reference to normal and
abnormal heart activity
• The heart is made of cardiac muscle.
• When the cells receive an electrical
impulse they contract - causing a
heartbeat.
• Cardiac muscle is myogenic - it can
contract on its own, without needing nerve
impulses.
Sinoatrial node (SA node)
• This specialized node is found on the upper
inside wall of the right atrium.
• The SA node is known as the pacemaker of the
heart and initiates a heartbeat every 0.85
seconds.
• This signal travels across the atria causing them
to contract and load the ventricles with blood.
• Ventricles are electrically insulated from atria so they don’t contract yet.
Atrio-ventricular node (AV node)
• The AV node is located on the bottom surface of
the right atria and is responsible for initiating the
contraction of the ventricles.
• Electrical impulse passes to ventricles via AV
node and the Bundle of His. They pass the
impulse to the base of the ventricles (~ 0.1 s
delay).
• The bundle of His is a group of fibres that
conduct impulses to Purkyne fibres which carry
impulses to left & right ventricles.
• Ventricles then contract from the bottom
upwards.
No impulse
• Cardiac muscle relaxes = diastole
Electrocardiograph
P = atrial systole
QRS = ventricular systole
T = ventricular diastole
• Records electrical activity of heart to
monitor heart function.
• Pacemaker generates electrical currents in
body fluids around the heart - detected by
electrodes to produce ECG
• Heart muscle:
depolarises (loses electrical charge) when
it contracts
repolarises (regains charge) when it
relaxes
Ventricular fibrillation is an abnormal heart
rhythm that is disorganized and irregular.
Ventricular tachycardia is a rapid, regular
heart rhythm that originates in the lower
chambers of the heart.
Heart block refers to a delay in the normal
flow of electrical impulses that cause the
heart to beat.
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