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Cardiac Conduction System
• SA node - (pacemaker) sinoatrial
• AV node – atrioventricular
• AV bundle
Initiate and distribute impulses
throughout the myocardium
SA node - (pacemaker) sinoatrial
Initiates impulses
that contract the
heart without
brain or nerve
Located at the
right atrium
Impulse travels to
left atrium and
contracts it.
AV node - atrioventricular
• Impulse
slowly moves
through this
node in right
AV bundle
Located in
End in purkinje
fibers - in both
Ventricles are
stimulated to
• Normal average 70-75
• Emotions, exercise, hormones,
pain, anxiety, fear, and anger
can affect this.
Electrocardiogram (ECG)
• Graphic record of the heart’s
action currents.
Electrocardiogram (ECG)
• An ECG is printed on paper
covered with a grid of
squares. Notice that five
small squares on the paper
form a larger square. The
width of a single small
square on ECG paper
represents 0.04 seconds.
To successfully interpret
ECGs, you must have this
value committed to
Electrocardiogram (ECG)
• If each small square represents 0.04
seconds, then a second will be 25 small
squares across. If you print out a minute's
worth of your heart's electrical activity,
the paper would be 1500 small squares
wide. If something on an ECG is, let's say,
12 small squares in width, that means that
it lasted 12 x 0.04, or almost half a second.
A common length of an ECG printout is 6
seconds; this is known as a "six second
Electrocardiogram Waves
– Depolarization
(contraction) of atria.
• QRS-wave
– Depolarization
(contraction) of
• T-wave
– Repolarization
(relaxation) of
Cardiac cycle
Atrial systole - contracting atria
forces blood into ventricle. P-wave
of ECG
Isovolumetric contraction - blood
volume in ventricles remains
constant. QRS-wave of ECG (1st
heart sound)
Ejection - blood ejected into
pulmonary artery and aorta. T-wave
Cardiac cycle continued
Isovolumetric relaxation - relaxation of
ventricles (second heart sound)
• Rapid ventricular filling - return of venous
– Increases atrial pressure until av valves
(tricuspid and bicuspid) open and blood
rushes into ventricles.
• Reduced ventricular filling - increase in
ventricular pressure and volume will slow
blood filling.
Blood Pressure
Sphygmomanometer measures air pressure
= to blood pressure
Blood Pressure
• Systolic pressure - 1st sound
– blood pushing against artery walls
when ventricles contract.
• Diastolic pressure - 2nd sound
– closing of valves, short sharp sound
Directions for Taking Blood
• Pump pressure until no pulse is
• Release air until a spurt of blood
is heard coming through.
• Continue until sound stops
Video Clip
Congestive Heart Failure
Heart Attack