The Electrical Conduction System of the Heart Cardiac cells
have four properties: Excitability: allows response to electrical
impulse Conductivity: ability to pass on electrical impulses
Automaticity: can generate own electrical impulses Contractility:
ability to contract
Slide 3
The Electrical Conduction System of the Heart Specialized
conduction tissue propagates electrical impulses to the muscular
tissue. Pacemaker: area where electrical activity arises
Slide 4
The Electrical Conduction System of the Heart Sinoatrial node
Located in right atrium Receives blood from the RCA Fastest
pacemaker Impulses are spread through internodal pathways, causing
depolarization. Adapted from 12-Lead ECG: The Art of
Interpretation, courtesy of Tomas B. Garcia, MD.
Slide 5
The Electrical Conduction System of the Heart Sinoatrial node
(contd): Electrical impulses move from SA node to the
atrioventricular (AV) node Impulse conduction is delayed so the
atria will empty into the ventricles.
Slide 6
The Electrical Conduction System of the Heart Sinoatrial node
(contd): Normally pass: Into bundle of His Into right and left
bundle branches Into Purkinje fibers A dromotropic agent is one
which affects the conduction speed in the AV node, and subsequently
the rate of electrical impulses in the heart.
Slide 7
Resting stateBoth sodium & potassium channels are closed
& membrane is in resting state Depolarization phase Activation
gates of sodium channels open, but potassium channels remain closed
& so sodium ions rush into the cells leading to more +ve charge
inside the cells
Slide 8
Repolarization phaseInactivation gates close the sodium
channels, but potassium channels open allowing potassium ions to
leave the cells ---- leading to decrease in +ve charge inside the
cell Back to resting state
Slide 9
The Electrical Conduction System of the Heart Depolarization:
muscle fibers are stimulated to contract Occurs through changes in
concentration of electrolytes across cell membranes Myocardial
cells bathed in electrolyte solution Chemical pumps maintain ion
concentrations.
Slide 10
The Electrical Conduction System of the Heart Depolarization
(contd) Cell receives stimulus from conduction Permeability of the
cell wall changes to allow sodium ions in Calcium ions also enter.
Depolarization spreads, causing a mechanical contraction.
Slide 11
The Electrical Conduction System of the Heart Repolarization
begins with the closing of sodium and calcium channels and opening
of potassium channels.
Slide 12
The Electrical Conduction System of the Heart Myocardial cells
must be fully polarized to respond normally to electrical stimulus.
Refractory period: cell is depolarized or in the process of
repolarizing Absolute refractory period: completely depolarized
Relative refractory period: partially repolarized
Slide 13
The Electrical Conduction System of the Heart Secondary
pacemakers Any conduction system component can act as a secondary
pacemaker if the SA node is damaged. The farther removed from the
SA node, the slower the intrinsic rate of firing.
Slide 14
The Electrical Conduction System of the Heart Measuring the
hearts electrical conduction activity Show as a series of waves and
complexes on ECG Adapted from 12-Lead ECG: The Art of
Interpretation, courtesy of Tomas B. Garcia, MD.