Cardiac Conduction

System

(1) Conduction System of Heart

• Conduction System = Heart Beat & Pumping

• Cardiac Contractions = Unconscious– Autonomic Nervous System decrease or

increase heart rate depending on circumstance

(2) Depolarization of the Heart

• Generate Action Potential & Depolarization:– Atria Ventricles

• Depolarization Path:1. SA Node AV Node

2. Atria Contract

3. (Delay) AV Bundle

4. Ventricles Contract

(Blood ejected out of arteries, leaving heart)

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter22/animation__conducting_system_of_the_heart.html

(3) Nodes & Bundles• Sinoatrial Node (SA Node)

– Right atrium– Starts each heart beat & sets rate– “Pacemaker”

• Atrioventricular Node (AV Node) = Left atrium

• AV Bundle = – Bundle Branches (along septum) – Purkinje Fibers (along entire muscular wall of heart)

(4) Cardiac Cycle• Diastole = Relax

– Blood passively filling atria

• Systole = Contract– Ventricles contract– Blood Ejected out of heart

(5) Diastole1. Ventricles relax

2. Semilunar valves closed

3. Ventricular Presure < Atrial Pressure– AV valves open– Ventricles fill with blood

4. Atria contract and force blood remaining in chambers into ventricles

(6) Systole1. Pressure increases in ventricles

- Filled with blood

2. AV valves close

3. Pressure in ventricles > Arteries leaving heart- Semilunar valves open- Blood rushes out of ventricles

4. Atria are relaxed and begin to fill back up

(7) Heart Beat• You hear something like “lub” “dup”

– “lub” = closing of AV valves• During ventricular systole

– “dup” = closing of semilunar valves• During early diastole

• You should NOT hear blood flow– You’ll hear it if flow is interrupted by blockage

http://www.csulb.edu/org/college/bme/respiratory_sounds/heart.wav

(8) Cardiac Output• Cardiac Output

– Amount of blood pumped out by each ventricle / 1 minute

– Cardiac Output = Heart Rate x Stroke Volume– CO = (HR)(SV)

• Stroke Volume– Volume of blood pumped out by ventricle – Increase of SV = Increase of ventricular force +

contraction

• Average Stroke Volume = 0.2L• Average Cardiac Output = 15L/min

(9) Starling’s Law• Starling’s Law of the Heart:

– Degree of cardiac muscle extension before contraction

– Increase Extension = Stronger Contraction– Degree of Extension result of percent filling of

ventricles