Transcript Heart Function – Cardiac Cycle and the Electrocardiogram (ECG)

Heart Function – Cardiac Cycle and the
Electrocardiogram (ECG)
R. Atrium
Pulmonary Artery
R. Ventricle
TCV
PSLV
Vena Cava
Lungs
Aorta
ASLV
L. Ventricle
BCV
L. Atrium
Pulmonary Vein
Pathway of Blood – Pulmonary and Systemic
Circuits
Cardiac Cycle
All the changes that occur during one heartbeat – one cycle of
contraction/ relaxation (systole/diastole)
Measurable changes include:
• Pressure
• Volume
• Heart sounds
• Electrical impulses
Blood flows through the heart based on pressure differences
• Pressure differences caused by changes in volume
• Changes in volume caused by heart contractions
• Heart contractions caused by depolarization of muscle cells
Cardiac Cycle
Electrical
Changes
•Cause
Contraction
Contraction
•Decreases
Volume
Volume
Change
•Increases
Pressure
Pressure
Change
•Opens Valve
Blood
Moves
•High to
Low
Pressure
Cardiac Cycle
Atrial contraction/ventricular relaxation  ventricular contraction
(“Lubb”) /atrial relaxation  atrial and ventricular relaxation
(“Dupp”)

Atrial Systole = atrial contraction
 atrial pressure > ventricular pressure
 Bicuspid and tricuspid valves open

Ventricular Systole = ventricular contraction
 ventricular pressure > atrial pressure
 semi-lunar valves open
 Bicuspid and tricuspid valves close (“Lubb”)

Atrial and Ventricular Diastole = atrial and ventricular relaxation
 Arteries pressure and atrial pressure > ventricular pressure
 Semi-lunar valves close (“Dupp”)
Cardiac Cycle
Cardiac Cycle
Click here for video clip of Cardiac Cycle
Click here for a video clip of a normal heart beat
Heart Conduction System
Intrinsic Conduction (conduction from within)
 Heart contractions occur independently of the nervous system.
 Cardiac muscle fibers connected in 2 networks: 1) in atrial
walls, 2) in ventricular walls. When any part of a network is
stimulated, all fibers in it contract as a unit.
 Electrical stimulation begins in the SA node, the ‘pacemaker’.
SA node AV node Right and Left Bundle Branches
Purkinje Fibers
Heart Conduction System
Electrical Pathway:
SA node (atria contract together)  AV node AV bundle
(ventricles contract together)  Purkinje Fibers
Heart Conduction System
Click here for video clip of Heart Conduction System
Electrical stimulation causes muscles to contract
Polarization in muscle cell is due to distribution of
Sodium and Potassium ions
 Electrical stimulation  voltage sensitive proteins
rearrange Sodium and Potassium ions  Calcium ions
are released  bind to troponin  opens myosin
binding sites on actin  muscle contraction
Heart Conduction System
How an Impulse is Conducted-The Action Potential
1. Heart Muscle Cell--Polarized
++++++++
------------------------++++++++
2. Heart Muscle Cell--Depolarized
*caused by movement of ions
3.
Heart Muscle Cell –-(Re)polarized
+-+-+-+--+-+-+-+
-+--+--++-+-+-+-
++++++++
------------------------++++++++
Outside cell
Inside cell
Outside cell
*When cells
depolarize, they
contract.
*When many cells
depolarize, the
heart contracts.
The Electrocardiogram (ECG)
 Measures electrical conduction throughout the cardiac cycle
 Works by measuring electrical changes of de- and re-polarization
 Sequence:
• SA node triggers Atrial depolarization (P-wave, contraction,
blood to ventricles)
• Atrial repolarization (QRS waves, relaxation)
• AV node triggers Ventricles depolarization (QRS waves,
contraction, blood to arteries)
• Ventricles repolarization (T wave, relaxation)
The Electrocardiogram (ECG)
Abnormal ECG’s
Figure 13.15
ECG and Cardiac Cycle
Click here for a video clip of a normal heart beat
Click here for a video clip of an abnormal heart
beat – ventricular fibrillation